Very often the Earthworks Contractor is confronted with a clear set of specifications from the Design Engineer outlining specified compaction density, moisture content and governing standards. In most instances, the contractor innocently and faithfully tries to carry out the procedure in the field without a clear understanding of what is really required and without a fundamental understanding of the Soil Mechanics principles entailed in such a “simple” task as Earthwork construction. This ignorance and oversimplification often produces disastrous results, delays in the project and financial loss to the contractor. Unfortunately, it is sometimes not only the contractor but also the Design Engineer who is ignorant of these principles, thus confounding the problem which could again further cause delays in the project. What is also dishearthening is the realization that all too often this “failure” on the part of the contractor results in countless litigation or delays because the real problem could not be identified.
The statement “problem identification is Eighty Percent of the solution” is nowhere very applicable as in this problem.
Let us consider several cases which highlight what we mean:
1.1 Runway Construction Project
A very large runway project inside a U.S. Base required a minimum of 95% of Maximum Dry Density based on ASTM D-1557 (Modified Proctor) on the subgrade which consisted of Clean Coarse Grained Materials (Granular Sand).
The contractor proceeded to do the compaction utilizing about 20 units of large Vibratory Rollers and Two (2) Water Trucks.
We were hired as the Independent Q.C. Laboratory to monitor Field Compaction. The contractor almost consistently had very large number of Field Density Test “Failures” despite numerous passes (about 10 to 12) per lane.
We were asked to look into the problem as substantial delays have been incured without significant progress. After conducting compaction trials on a 100 meter strip for half a day, we were able to achieve adequate compaction in just 3 passes!
The procedure we used in the compaction trials was immediately implemented which resulted in almost halving the vibratory compactor fleet (rented) but increased the number of water trucks to 4 at tremendous savings to the prime contractor. This also enabled the contractor to accelerate subgrade preparation by at least two (2) months.
What happened was not black magic but just the sound application of Soil Mechanics principles as we shall see later on.
1.2 Housing Project at Subic
In a housing project inside the Subic Naval Base, an American Contractor was required by the contract specifications to compact the soil to 95% of Maximum Dry Density again based on ASTM D-1557. After several rectangular slabs for the duplex housing were poured and after a heavy downpour, two of the recently poured slabs broke neatly into two at the center.
We were called in to do consulting work to solve the problem and we found out that it was a swelling soil problem.
After the study and a long protracted fight with the U.S. Navy Engineers out of Honolulu, the Navy adopted our recommendation on the basis of a “no-cost change order.”
Surprisingly, what we recommended was to bring down the compaction levels to 90% of Maximum Dry Density Based on ASTM D-698 instead of the more stringent ASTM D-1557 (Modified Proctor) (The latter having the effect of increasing the energy input or compactive effort by 4.58 times!) and to compact the soil Wet of Optimum.
Clearly this was an “Inferior” substitute that was accepted without a reduction in the contract amount.
Why was the change possible?
1.3 Lahar Project
We were again involved to do preliminary consulting work involving Lahar as a Construction Material for a significant Lahar Protection Structure.
The initial specifications called for Proctor Densities and Specified the Optimum Moisture Content required.
Since the structure would be constructed during the dry season, water was a big problem that could hamper the construction of the structure in time for the next onslaught of Lahar.
We have done preliminary work on Lahar on our own as a matter of professional interest and we knew that Lahar behaved as a clean granular soil.
Therefore, we recommended that the Lahar ought to be even compacted in a very very dry state. After a lengthy explanation and initial disbelief, everybody agreed to do so and thus eliminated an unnecessary requirement which could have even hindered the construction progress or even resulted in the specifications not being attainable in the field.
Again, a timely intervention applying sound Soil Mechanics principles saved the day for the project.
1.4 Stalled Vehicle Wheel
A hypothetical but common case which involves a car wheel stuck in a hole on loose beach sand.
As we know, accelerating only digs the wheel deeper into the ground in both cases.
Saturating the sand with sea water somehow makes the sand firm enough to hold the weight of the wheel and soon enough the vehicle is freed.
This is a commonplace solution that is done almost without the thought that Soil Mechanics principles are involved.
The solution to the foregoing case studies all have something in common, and that is a clear undestanding of the behavior and physical characteristics of the soil and application of Soil Mechanics to the solution of “simple” Earthwork Problems.
As is often the case, problems such as these have occured in the field countless times without being correctly identified and thus have resulted in significant losses to the contractor, delays in the projects and substandard quality of compacted earthfill.
Again, it must be qualified that it is not only the contractor who is to blame but also the Consulting Engineer in most instances for this state of things. Our only consolation is that the problem is not only unique to our country but also even in more advanced Western Countries.
A vigorous search of various Soil Mechanics and Foundation Engineering Books yielded only fleeting or sporadic references to these common problems we encounter in day to day Earthwork Construction where soil mechanics principles are applied.
It is the intention of this paper to unify and integrate references to these in various literature on this topic to provide a more “concentrated” understanding of Fundamental Soil Mechanics Principles as applied to Earth Compaction and Earthworks in General.
2.0 THE MECHANICS OF SOILS
In order to successfully apply Soil Mechanics to the solution of our Earth Compaction problems, it would be necessary to have a clear understanding of the fundamental principles.
However, for this paper we shall only limit ourselves to a clear understanding of Particulate Mechanics or the behavior of soils as discrete particles when acted upon by various forces such as gravity, vibration or impact, water and seepage or combinations of these forces.
We shall strive to make the problem as simple as possible even to the layman in order for him to have a fundamental grasp. We however would recommend review of various literature on the subject for those who wish to have a deeper understanding of the problem at hand.
3.0 SOIL AS A PARTICULATE MATERIAL
Under a very powerful electron Microscope, even a piece of seemingly solid mass of clay appears as an assemblage of particles with some orientation. This orientation surprisingly can be altered by reworking of the clay, addition of or removal of moisture or by altering the chemical make-up of the porewater.
Under normal conditions it would also be noted that the assemblage includes water and air. The water is either captured or adsorbed water or free water.
The process of compaction is nothing but the expulsion of air (reduction of voids in the soil). Thus, our attention is directed as to how this could be most efficiently done.
However, as we know, this assemblage that we just saw in the Electron Microscope is only but one of two major assemblages that soil can assume depending on its granulometry or Grain Size.
Soil can either be:
Coarse Grained (Sand) or Cohesionless
Fine Grained (clay) or Cohesive
The clear distinction between the two are somewhat obscured by their combinations that could be found in nature. In their unadulterated states, the differences become readily apparent or clearly distinguishable.
4.0 SOIL SHEAR STRENGTH
Particulate materials derive their strength from friction or intergranular contact and/or from bonding forces or cohesion as we know it. These bounding forces and friction prevent the particles from sliding.
The most important soil strength property that we have to deal with is the soils’ Shear Strength since most of the loading that the soil is subjected to causes the individual soil particles to slide or “shear” one against the other because of their particulate character.
Depending on the granulometry of the soil, the shear strength is either derived from electrical and chemical forces of attraction (cohesion) and repulsion as in clays or by simple grain to grain contact and friction as in Pure Granular Materials. Since shear strength depends on the integrity of the sliding resistance of the individual soil particles, it only follows that the more compact the soil becomes, the higher the shear strength and vice versa. The only way to cause this increase in strength is to lessen the interparticle distances by the expulsion of air and/or water by cementing it which is sometimes resorted as in soil cement if good materials are not readily available.
This leads us to one of the Fundamental Principle in Earth Compaction:
“Increasing Density (Strength) is achieved by decreasing the soil interparticle distance through the expulsion of air or water or both.”
As we shall see later on, reduction of interparticle distances would sometimes require addition of more water into the soil in order to dislodge more water. This statement appears to be confussing but its proof reiterates the importance of the understanding soil particulate behavior in the solution of Earthwork Problems.
5.0 MICROSTRUCTURE
5.1 Clay Microstructure
Let us now peer again at our microscope to look at a sample of cohesive or fine grained clay soil.
As we can see, the clay is composed of submicroscopic platelets surrounded by Electrical charges, a closely held layer of adsorbed water and an outer layer of loosely held water. The interparticle distances, measured in Angstroms are governed not only by the particle orientation but also by the Electrical forces of attraction as well as the thickness of the adsorbed and free water. It would take a very high input of energy in order to dislodged or remove the adsorbed layer. However, the loosely held water can be removed in the field by sample air drying or windrowing. Once the free water is removed, compaction can be attained. The particle orientation as we shall see in the succeeding table also affects some other physical performance characteristics of the soil.
5.2 Sand Particles
Obviously we do not need even a conventional microscope to be able to see the granular structure of sandy soils. In fact this can be done with the naked eye.
A very dry sand in the hand can not be squeezed into shape whereas a semi moist sand when squeezed could hold some shape until it dries out and crumbles. Surprisingly, addition of more water to saturate the sand collapses the sand as in the very dry state.
When grains of dry sand are gently deposited in a container, they fall into place in a precarious grain to grain contact. A jarring motion imparted on the container causes the grains of sand to assume a denser packing. Slight addition of water causes the sand to swell or increase in bulk while saturation with just enough water that is somehow allowed to drain causes the sand to be compacted into a dense state. This has been known to us since time immemorial as Hydrocompaction. Perhaps only the mechanism behind it is not well understood.
5.3 Microstructure of Fine Grained Soils
Fine Grained Soils, because of their sub microscopic size are influenced by Electrical and Chemical forces of attraction and repulsion This is due to the fact that the ratio of specific surface area to their volume is so large that surface electrical activity greatly influences the behavior of fine grained soils.
In nature, fine grained soils assume a flocculated or dispersed configuration as shown below depending on the manner of deposition and environmental influences that it has been subjected to.
A flocculated structure assumes a random tip to side orientation much like a “house of cards” whereas a dispersed structure have the platelets more or less aligned to each other.
The arrangement of these platelets alone have an influence on the performance and behavior characteristics of the soil.
The table above therefore suggests that we can alter the performance and behavior characteristics of the soil to suit our specific needs if only we know how.
As an example, an experiment with a clay material was made to determine the effects of compaction water on permeability. It can be noticed that although compaction density is the same left and right of optimum, the permeability values are not the same for this specific type of soil.
6.0 MOISTURE DENSITY RELATIONSHIPS
We begin with the all too familiar moisture density relationship known as the “Laboratory Proctor Test” for a clay soil.
Out total familiarity with this simple bell shaped curve and its universal acceptance as the “characteristic” compaction curve has caused most of the problems we encounter today in Earthworks compaction. Too often, it has not been realized that this is not the only shape a laboratory Proctor curve can assume and that grain size and moisture play a great part in influencing the shape of the compaction curve.
This bell shaped curve as, we shall see later on, is only applicable for fine grained soils or soils with significant plasticity as to make it perform as a clay like soil.
As we can see, at the start of the test when the soil is relatively dry, the soil assumes a flocculated structure “A” additional mechanical reworking and increasing amounts of water and subsequent expulsion of air and closing of the voids tend to produce a semi flocculated structure “B” with increasing density until a peak is attained. This peak is the maximum density that could be attained by that type of soil in the laboratory. This is expressed in terms of “Relative Compaction” which a percentage of the maximum dry density obtained in the laboratory test.
The moisture content corresponding to this maximum density is known as the Optimum Moisture Content “OMC”. Further compaction and aditional water beyond this point results in decrease in density with increasing amounts of water. The soil platelets begin to be oriented and aligned and the interparticle distances tend to widen as more and more water is captured.
We now look at the Moisture Density relationship curve for a coarse grained sand with very little or no fines.
Since the individual grains are relatively very very large compared to the clay platelets, we know that surface forces play very little influence on the behavior except at a certain moisture content range.
We see right away that the Moisture Density curve indicates two density Peaks “P1” and “P2” where density is high. The first Peak P1 occurs when the soil is very very dry (MC ‘ O) and the other Peak P2 at almost saturation conditions. We also see that between these two Peaks is a valley where density is lowest.
The reduction in density in this valley as defined by a moisture content range is known as the “Bulking Range” for this particular sand.
This reduced density is caused by surface tension forces of the water surrounding the individual grains which tend to drive the adjacent grains farther apart, causing loss of interparticle contact and collapse in the density from the previous high.
However, progressive addition of water beyond the bulking range collapses the surface tension and the additional hammer impacts increases the density again to the second Peak “P2”. The laboratory curve shows a downhill movement in density with increasing moisture content beyond saturation levels.
The real field curve shown by the dotted line suggests otherwise. The reason behind this is that in the laboratory compaction procedure, the water can not drain within the steel compaction mold and thus the soil becomes a soupy mush. However, in the field, additional water is continually drained and the Peak density is maintained.
This curve clearly shows the fallacy of specifying Proctor Compaction Procedures and an OMC for clean coarse grained soils, because definitely, the soils are insensitive to moisture content except at the very dry and very saturated conditions. Unlike clay soils which follow a typical bell shaped curve, clean coarse grained soils exhibit a typical “S” shaped curve with the Peaks P1 & P2 clearly distinguishable.
Peaks P1 & P2 may sometimes be equal but this is more of an exception than the rule and their relative maximum values could shift either way depending on the type of soil.
This soil behavior has been recognized by ASTM and standardized into two standards ASTM D-4253 “Max. Index Density of Soils using a Vibratory Table” ASTM D-4254 “Min. Index Density of Soils and Calculation of Relative Density” to arrive at a minimum and maximum density. These values are then used to compute the Relative Density DR once the Field Density is obtained.
Compaction is specified not in terms of % of MDD but rather as Relative Density DRand their relationship to each other is shown in Scalar Fashion.
Recognition of the two characteristic compaction curves (The “Bell” and the “S”) leads us to the realization that clays and sands behave very much differently when compacted and require different approaches and solutions.
We also know now that the behavior of soils can be tempered to suit our requirements as shown in the foregoing table particularly for a clayey soil.
Thus, we are led to the following conclusions:
There is not one but two General characteristic curves for soils depending on their granulometry.
The concept of Optimum Moisture Content generally does not apply to Clean Granular Soils and therefore the Proctor Standard is inappropriate or could lead to problems in the Field. Clean sands either have to be compacted very very dry or very very wet in order to achieve the maximum density.
The microstructure of the soil needs to be considered in the selection of the right compaction equipment.
For Fine Grained Soils, although density is the same for corresponding points left and right of the OMC, the performance and behavior of the soil are different due to the alteration in the microstructure arrangement.
Beyond the maximum density, additional compaction energy would be detrimental to both clays and sands as breakdown can occur causing a decrease in density. Therefore, use no more than what is necessary to attain good compaction.
For intermediate soils, it would be necessary to determine in the laboratory the characteristic behavior from zero MC to saturation levels.
In case the laboratory curve is not clearly defined or when there are doubts as to the behavior in the field, a field compaction trial would be required.
6.0 COMPACTION EQUIPMENT
Having recognized the behavioral characteristics of soils (Particulare Material) we now look at the means to achieve compaction in the Field.
However, try to remember the fundamental response of the two general types of soils to compactive effort:
Loose Clean Granular Soils because of their precarious grain to grain contact are best compacted by causing a jarring motion such as what a vibratory roller would impart.
Fine Grained Soils on the other hand respond better to a kneading type of compactive effort such as that imparted by sheepsfoot rollers and pneumatic type rollers as these tend to reorient the platelets.
We now look at the Chart below to determine the range of applicability of various compaction equipment:
We can therefore see the effective range for various compaction equipment under differing soil conditions and we recognize right away that this has something to do with the grain size (clay to rock).
At first glance, it could be said that this is a very familiar and well accepted practice.
However, it would be shocking to know that in a big project inside a U.S. Base, the Earthworks subcontractor was unable to compact the highly plastic soil despite repeated passes. Several weeks of reworks have passed before we realized that the contractor was using a Vibratory Roller on a clay soil. Over vibration of the clay soils had in fact caused the formation of Shear Cracks causing weakening of the soil! When the compactor was changed, the problems of the contractor vanished.
7.0 APPLICATIONS OF KNOWLEDGE GAINED
However, it is not only enough to know how to select the proper compactor for the job. It is also important to use this in conjunction with our knowledge of Soil Mechanics principles which we now apply:
7.1 Sands and Clean Coarse Grained Soils
Vibratory compaction works best. However, we should aid this by liberal application of water immediately ahead of the vibratory compactor. Remember, coarse grained soils compact best at the very very wet condition “P2” or at very very dry condition “P1”. Water serves as a lubricator but its total absence also prevents capillary forces from impeding the rearrangement of soil grains into a denser packing. Speed of the vibratory compactor is also important and needs to be controlled to about 2 to 4 KPH. Vibratory frequency is also essential and should nearly approach the natural frequency of the soils. Standard frequencies are in the range of 30 to 40 cps.
The static weight of the vibratory roller is also important since the dynamic force exerted on the soil is a function of the static weight. The wheels of the roller are either ballasted by water, sand or even slag in order to increase the static mass.
Because the vibratory roller causes an “advancing wave” on the top of the lift being compacted, Field Density Testing in order to be fair has to be done below this disturbed layer. It will normally be required to scrape the top 50 cms before seating the Field Density Plate in order to be able to test the actual condition of the specific lift.
Field Density testing using the Sand Cone Method (ASTM D-1556) requires extra care since the means to measure the volume is calibrated clean sand. Any jarring motion results in increased sand intake of the test hole resulting in bigger hole volume computed than the actual resulting in low compacted densities. This condition can also be caused by compaction equipment being allowed to operate very near a Field Density test in progress.
In one project, a bull headed contractor’s foreman could not be prevailed upon to stop his operations while tests were being performed nearby. He only relented when a series of “Failing” FDT results made him realize his mistake.
Back to the subject of moisture content, for clean coarse grained sands, moisture is irrelevant except for the total absence of it or its presence at saturation levels.
Thus, there is no such thing as an Optimum Moisture Content and proctor criteria is entirely inapplicable in this context.
7.2 Clays and Intermediate Soils
For Fine Grained Materials and intermediate soil types possessing significant plastic fines, sheepsfoot rollers or pneumatic tired rollers are best. The kneading action allows reorientation of the grain and allows expulsion of entrapped air.
The sheepsfoot was modelled really after the shape of a sheep’s foot perhaps based on the observations of Mr. Mc Adam. The tendency of the sheepsfoot is to walk- up by progressively compacting or densifying the lowermost layers first and walking upwards. Thus we see that topmost layers are slightly less compacted and therefore need to be bypassed when conducting a Field Density Test.
In stark contrast to clean coarsed grained soils, compaction moisture content and the Proctor criteria are fully applicable and the control of moisture during compaction is a crucial factor in the attainment of proper compaction.
Static weight is also important as it increases penetration of the sheepsfoot and increases the force pressing the platelets together.
Speed is not so critical as it is the kneading action and coverage that is important.
Vibratory motion is not necessary and is in fact harmful as it can cause build up in pore pressures in the soil and also cause shear cracking.
7.3 Lahar
Since Lahar is a byword in Central Luzon and since billions will be spent in Lahar Protection Structures, using Lahar as the primary construction material, it may be worthwhile to consider this as a separate material for this paper.
Although Lahar possess some fines, the fines are non plastic and consist of very fine ash particles.
Lahar drains easily and compacts readily as proven by river crossings which become passable as soon as the flood of Lahar subsides.
From this, we can already infer that Lahar behaves like a clean coarse grained material that it is.
Thus, Lahar is most sensitive to vibratory compaction and could compact well at very very dry or very very wet condition. Moisture control is unimportant except to see to it that either we have none of it or plenty of it during vibratory compaction.
We have done several tests on Lahar as a matter of research interest and our conclusions are as follows:
Lahar behaves as a perfectly granular material.
Lahar responds well to compaction even under ordinary vehicular loading and therefore the passage of construction traffic alone could assist compaction.
Lahar possess high initial CBR value but some degradation in the CBR strength occurs if the sample is aged at saturation conditions (this is probably due to breakdown in the ash coating the individual grains).
Significant sulfate levels were present (at least during the initial discharge) which could impair the integrity of Portland cement concrete when this is used as fine aggregate.
We have noted that several tests have been performed by some agencies which show the all too typical bell shaped curve and therefore an Optimum Moisture Content. However, it would be noted right away that compaction started at moisture contents of 3% or greater and thus the Peak “P1” remained undetected leading to erroneous conclusions and the unnecessary imposition of an Optimum Field Moisture Content.
8.0 CONCLUSIONS
The purpose of this paper would have been already truly served if the construction industry would start to recognize the differences in behavior between coarse grained and fine grained materials through the use of sound Soil Mechanics principles rather than from “feel” of guess work.
Often times, these fail in the actual field situation and the simple task of Earth Compaction becomes a costly and heartbreaking exercise.
Cracking and heaving of a Single Storey R.C. Building was initially perceived as settlement. This error led to unnecessary and costly remedial measures such as Piling for the Phase II Building which further aggravated the problem. The heaving was caused by a seemingly innocent decision during the construction stage to use Slag from a steel mill as the base course material. This Slag reacted with the highly corrosive groundwater which caused heaving of the Building and discomfort and morale problems to the Building occupants. Careful engineering study and investigation resulted in a very simple solution which saved the Building from abandonment and demolition.
INTRODUCTION
A Single Storey Precast Reinforced Concrete Research and Development Building was built in Two (2) Phases starting with the Phase I in October 1975. After the construction of Phase I, severe flooding in the area occured in October 1978. Severe cracks were observed in the Precast Post Tensioned Waffle Roof Slab and supporting Beams and Walls. Cracking and extreme waviness was also observed in the Floor Slabs, making office work very difficult. This initial cracking and distress became progressive over the years and “settlement” of the Building was suspected. Extensive structural epoxy adhesive repairs were made on the cracked portions by the original contractor. In addition full scale load tests were performed on the waffle roof slab.
Because of the suspected “settlements”, it was decided by the owner to construct Phase II on Pile Foundations. Soon after construction, cracks were also observed in this Phase II portion but in contrast to the Phase I portion, more severe cracking occurred on the walls and not on the slabs.
In the meantime, cracking continued on the Phase I structural elements despite the structural repairs. This condition was puzzling to the owners and several Engineers were consulted to look at possible remedial measures. Because of the client’s concern for the safety of its employees, abandonment and demolition of the Building were contemplated. It was at this point that our services were engaged to have a critical last look at the Building and to ascertain the cause/s of the problems. We were also asked to determine whether the progressive cracking can be arrested and the building rehabilitated with the safety of occupants being the foremost consideration.
DESCRIPTION OF THE BUILDING
The Research and Development Laboratory building was originally proposed as a two storey reinforced concrete building with precast post tensioned waffle slabs but after some distress was observed early on, the plan was abandoned. The facility was built in a low lying area in the suburban town of Pasig in Metro Manila. The area is sometimes flooded when the Marikina River overtops its Banks during a 10 year flood.
A two meter Engineered Fill was placed to elevate the Building’s Finished Ground Line from the surrounding area. A half meter layer of “heavy aggregate” base course was laid and compacted to support the slab on grade. This engineered fill and base course was laid to support the Parking, Driveway and the entire Building footprint to include the future Phase II addition. The filling and compaction for the whole area to include the proposed future Phase II addition were all done at the same time.
The center was constructed in two phases as follows:
Phase 1
This phase was constructed starting October 1975 on continuous footings supporting column loads through socket pedestals loading on to the continuous footings. Founding elevation is approximately 2.8 meters below finished floor line. The columns are 0.35m x 0.35m precast concrete columns inserted into sockets in the footing. The roof consists of approximately 1.0m x 1.0m precast waffle slabs joined together by cast in place concrete packing and post tensioning. A layer of water proofing was subsequently applied. Perimeter walls consist of 150mm CHB units and plaster finished with protruding fins also of CHB. Interior walls were also of CHB resting on the slabs. The floor is a 100mm thick reinforced concrete slab on “heavy aggregate” Base Course over the imported granular fill material.
Phase II
Phase II construction was started in August 1978 or approximately three (3) years after Phase I construction. The structural configuration is the same except that the new building was now supported on Pile foundations because of the observed distress and perceived “settlements” of the Building. This new addition was constructed by another contractor. The walls were now supported on Grade Beams with Flanges acting as continuous footings. The Grade Beams are in turn supported on Pile caps. The floor slab was still connected to the walls and columns by Dowels. Columns were embedded into the Pile caps.
OBSERVED DISTRESS
Two years after construction of the Phase I Building, Flooding occurred in October 1978. The flood waters rose to about 38 centimeters above the floor line of the Building. Although, minor cracking was observed in the Building even before October 1978, extensive cracks and more regular repairs reached its peak in 1982 and became a major problem and concern for the owner as well as the Building occupants. The corridor slabs became so wavy that normal walking was difficult and passage of pushcarts of chemicals had to be done carefully to avoid spillages. As earlier discussed, there were contrasting failure patterns and observed cracking between Phase I and Phase II construction. For clarity, these are discussed in detail separately as follows:
Phase 1 Distress
Phase I was constructed in October of 1975 on continuous footings resting on well compacted Engineered Fill. Severe cracking and extreme waviness were observed in the slabs. Maximum slab displacement is 130mm (5.21 inches) at the analytical laboratory. The 3D mesh plot of the slab deformations is shown in Fig. 1. The 2D Contour Plot is also presented in Fig. 2. Cracks have been observed in the masonry walls but were not as severe as in the Phase II Walls. A noticeable separation gap was observed between the roof and the wall with the exterior walls opening outwards. The extreme waviness of the slabs has made normal office work difficult. Desks and cabinets needed to be periodically relevelled on stilts (See Fig. 3) to prevent rolling of pens and pencils from the desk top. Fulltime carpenters had to regularly realign doors and windows to allow proper closing and opening. Light Partition Walls separated from Floor Slabs (See Fig. 4) However, the most serious effect was on the morale of the workers as they were constantly in fear that the Building is going to sink or collapse on them.
Phase 2 Distress
Soon after completion, the walls of the Phase II addition experienced more severe cracking than the corresponding walls of the Phase II portion. Waviness was detected in the slabs but somehow these were lesser in magnitude as can be seen in Figs. 1 and 2. The main indication that something was still wrong was in the extent and magnitude of cracking in the walls and constant adjustments on the doors and windows (See Fig. 3). Cracks were mainly opening upwards but in addition, some cracks tended to indicate that the walls were trying to separate from the columns (See Fig. 4). Leaks in the Precast Waffle Slab occurred, indicating movement of the roof slab. The floor slabs had perceptible bulges at the center of the panels but were not as pronounced as in the
Phase I Construction. Some Engineers consulted have even ventured as far as to say that the Piles have somehow “reduced the settlements” but no explanation could be given for the more severe cracking of the walls. These two highly contrasting distress manifestations baffled the client and the occupants of the Building. However, the general conclusion still was that the building was “settling” and that all remedies have been exhausted. Abandonment and demolition of the Building was therefore being contemplated.
INVESTIGATION
In early 1984, we were contracted by the client’s Corporate Engineering Department to undertake an investigation to unravel the seemingly conflicting failure patterns in the two buildings. Explanations were needed as to why despite substantial expenditures in Piled Foundations, the Phase II portion of the Building was still “settling” and cracking with more severe cracks in the walls than were observed in Phase I.
The investigation programme consisted of the following phases:
Soil Borings along the periphery of Phase II in order to determine underlying soil properties in the area of the piled foundation.
Test pits inside and outside of the building to retrieve soil samples and determine character of fill material in the area.
Laboratory soil classification and strength tests of soil and physical characteristics.
Laboratory chemical testing on soil leachate samples and water samples in the building.
Interviews with R&D Laboratory personnel and document review of various tests conducted for the R&D Laboratory Building relevant to the investigation.
Measurements of Ground Heave inside and outside of the building and the preparation of the subsequent Heave Contour.
Recording of observed cracks and structural features including photographs and their subsequent mapping to aid in the structural rehabilitation and repair of the building.
Analyses of possible loadings imposed on the soil by the foundation elements of the building and corresponding settlement analyses.
Understanding of construction plans furnished by the client insofar as it would assist in interpreting the responses of the various building elements to the heave forces.
The findings obtained in the foregoing investigation together with the results of various tests served as bases for the correlation and understanding of the mechanisms contributing to the observed problems in the building and outside of the building. No effort was spared to investigate possible causes of the cracks in the attempt to conclusively isolate the forces that are triggering the observed distress in the building. Immediately after our commissioning, we made exhaustive investigation and conducted interviews with Building occupants to reconstruct and piece together the chain of events. Almost all the Building occupants from the scientists to the Building Manager were of the opinion that the building was “sinking ” and that nothing further could be done to save the Building. Morale was so low that some employees interviewed thought that the investigation was another delaying tactic by the management to postpone abandonment of the Building because of the vital research studies being made at the time. All of these were proved to be untrue after a very challenging investigative work which in the end tied together all the loose ends and helped us arrive at a simple solution which saved the building. Early at the start of field work and testing, it was already clear to us that the crack patterns manifested were caused by heaving and not by settlements.
What was not clear to us at the onset were:
What was causing the heaving ?
What was the explanation for the differing crack patterns in the two phases of the building ?
Potentially expansive soils were not prevalent in the general area nor was the imported fill expansive, since it was essentially silty fine sand and therefore the agent causing the heaving had to be identified and isolated.
SOIL INVESTIGATION
The initial investigation program consisted of three boreholes around the Phase II Building to a depth of 20.0m average and several test pits outside the Building footprint. The borings were done to determine underlying soil strength parameters and also to detect the presence of potentially swelling soils. Since initially we suspected that the expansive soil was not the Engineered Fill, concentration of the soil borings was focused on natural ground about two meters below. Nevertheless, regular sampling and field classification was done starting with the base course, the Engineered Fill and the natural ground. The “Base Course” material was initially and innocently classified by the Field Engineer as “gravel base course”. It was only when we dug the test pits that we learned that this was no ordinary “gravel base” course as initially identified, since these were extremely heavy and there were large chunks that were like huge flakes in the test pit. Picks cannot even indent the material and finally, Saw cutting with a carbide blade showed that it was iron. What was also surprising to us initially was the presence of dark gray fluffy cotton like materials in the heaved portions.
SLAG USED AS BASE COURSE
Further investigation revealed to us that a well meaning and cost cutting decision was made during construction to use SLAG wastes from a steel mill as the base course material since it was free for the taking and it compacted readily. This “base course” was laid to a thickness of 0.30m to 0.50m in some places and was spread in all the proposed built-up areas including the future addition and the driveway. The gray fluffy cotton like material turned out to be SLAG that has fully expanded after corrosion (See Fig. 8 & Fig. 9). The expansion potential can be gaged from the size of the cavity and magnitude of heaving that it has caused. More numerous test pits were therefore recommended to be undertaken inside the Building footprint to verify the extent of the slag. All the additional test pits showed the uniform presence of the slag base course and the degree of expansion and corrosion that has occured underneath (See Fig. 7 & Fig. 8). Most of the test pits were excavated under the heaved areas and also some in the unaffected areas. In both cases, slag was present in varying conditions of expansion and corrosion. Levelling to determine the slab contours was also done inside the Building with the vertical Benchmark made outside the affected areas. The levelling was done using liquid level hoses because of the numerous partitions rendering optical levelling next to impossible. The results are depicted in Fig. 1 and Fig. 2.
RESULTS OF CHEMICAL TESTS ON SOILS AND WATER-R&D CENTER BUILDING
In some of our interviews, complaints were heard regarding the water from the deep well that was causing stomach problems and sometimes Diarrhea. Subsequently, we made recommendations to test the water from the deepwell and also in some of the adjacent Buildings and Factories being served by similar deep wells. The results are shown in Tabular Form in Fig. 10. The results show that most of the water from the deepwells in the area have corrosive potential as indicated by their Langelier Saturation
Index (LSI) values. Chemicals tests were performed on several soil sample Leachates and water from the Deepwell of the R&D Building. The objective of the tests is to determine corrosion potential after test pits showed the presence of slag (iron) in the general area investigated. The Langelier Saturation Index (LSI) was obtained by computation from the test parameters. The soil leachates were obtained by mixing one part of soil to one part of distilled water. The mixtures were shaken for two hours at 200 oscillations per minute and allowed to set for 24 hours.
The resulting extracts were analyzed for:
pH
Conductivity
Alkalinity
Total Hardness
Sulfates (SO4)
Chloride
Acidity
Fig. 9 tabulates the values of the various chemical tests conducted on water samples in Soil Leachates at the R&D Laboratory.
Several conclusions can be inferred therefrom as follows:
Water from R&D Laboratory and surrounding areas have corrosive tendencies. Of the thirteen (13) samples whose corrosion potential were measured using the LSI, seven (7) samples exhibited corrosive tendencies.
Chloride content for R&D well water is excessively high (about 800 to 900 ppm).
Sulfate (SO4) content of the slag is very high (975 ppm).
pH values indicate slightly basic to slightly acidic values for most of the water samples tested.
POSSIBLE MECHANICS OF CORROSION
Several possibilities could trigger the corrosion of the slag and its consequent expansion during the corrosion process. The resulting expansion has been found to increase the volume of the steel or iron by as much as 10 times its original volume, in the process generating large expansive pressures when confined.
Slag
The use of slag as a fill material proved to be detrimental as the material could corrode even in ordinary tap water given the proper environment. The slag obtained from most electric arc furnaces is slightly basic in character but contains large amounts of sulfates, manganese and other impurities from the steel making process. This is borne out by the very high sulfate content obtained in sample 5-14 of Fig. 10 from Test Pit No. 1. Because of the nature of the slag formation in the mill, vesicles were formed containing entrapped air. The large particle size (gravel to cobble size) of the slag also allowed air entrapment during the compaction process. The entrapped air promotedor accelerated corrosion because of the presence of oxygen.
Groundwater
As earlier stated, the groundwater is generally corrosive (Langelier Saturation Index Negative). In addition, chloride content is high which can trigger pitting and corrosion in the slag. The foregoing primary factors alone would already indicate the highly favorable environment to initiate and sustain corrosion. Since the total corrosion decomposition of steel or iron would be a long time dependent process, its simulation in the laboratory would for the purposes of this investigation be too long. However, samples extracted from the test pits showed varying degrees of decomposition and oxidation stages when tested in the laboratory using a NaCl solution. In order to fully understand the mechanism, the following definitions are extracted from ASTM 6-15-79a “Standard Definitions of Terms Relating to Corrosion Testing”.
Corrosion – the chemical or electrochemical reaction between a material, usually metal and its environment that produces a deterioration of the material and its properties.
Graphitic Corrosion – the deterioration of metallic constituents in gray cast iron which leaves the graphitic particles intact.
The corrosion of ferrous metals is caused by the tendency of iron (Anode) to go into solution in water as ferrous Hydroxide and displaced Hydrogen, which in turn combines with dissolved oxygen to form more water. At the same time, the dissolved ferrous hydroxide is converted by more oxygen to the insoluble ferric oxide thereby allowing more iron to go into solution.
Corrosion therefore requires liquid water (as in damp air) and oxygen (which is normally dissolved in water).
Corrosion occurs only in the presence of an ionizing medium. The most universal ionizing medium is water. No corrosion will occur in the total absence of water. The rate of corrosion is affected by the amount of dissolved oxygen present.
The dissolved oxygen could react in either of two ways:
By combining with the hydrogen film to expose the surface of the metal (which the film protects).
By combining with the dissolved ferrous hydroxide to form insoluble hydrated ferric compound and thereby allow formation of more ferrous Hydroxide.
The chloride ion solution tends to dissolve the protective coating already formed and tend to prevent new coatings being laid down thus further accelerating corrosion.
Having understood the probable corrosion mechanisms, the following can be theorized:
The corrosive groundwater as it was elevated by flooding or during the rainy season immersed the metallic slag in solution causing decomposition. Sufficient dissolved oxygen is existent in the soil and trapped in the large voids present in the slag.
The R.C. slab acted as an impermeable membrane which ensured entrapment of moisture keeping the slag in at the very least a moist environment. This ensured progressive corrosion. Because of the confinement of the surrounding soil on the slab, the slag exerted an upward pressure which offered the least resistance causing the slab to heave.
In addition to the foregoing and as can be shown in the subsequent sections, possible leakages in the pipes, more specifically in the acid and waste chemical lines could have aggravated the corrosion.
Inspection of the photographs and test pit logs (See figs. 11 & 12) clearly show that the slag layers have expanded upward and heaved the concrete pavement.
OBSERVATIONS ON THE RELATIVE MAGNITUDE OF CRACKS
With reference to the slab displacement contour map (Fig. 1 and Fig. 2), it can be shown that Phase I has heaved or displaced more than the Phase II. Although the two are supported by different foundation elements (continuous footing vs. pile foundation for Phase I and Phase II respectively), this would not really explain why there is less heaving and cracks in Phase II because if heaving of the same magnitude have occured, more damage would have resulted because of the rigid restraint offered by the piles. It is only possible then that because the slag fill have been laid out all at the same time, that substantial unconfined or unrestrained heave has already occured over time in the Phase II area before construction could take place. Unlike in Phase I, where the slab offered confinement and trapped moisture as to cause progressive heave under restraint. In addition, although it could be observed that there are relatively fewer cracks in Phase II, it can also be shown that in contrast to Phase I, the walls in Phase II are more damaged compared to the floor slab where displacements are minimal. The foregoing is explained by the fact that while substantial heaving has already transpired, the residual heave after construction, though not as large as Phase II displacements, have cracked the walls because of the relatively more rigid restraint or pullout capacity of the piles. Thus the walls were affected more than the floor.
Fig. 4 which was taken along the corridor near the interface between Phase I and Phase II showed a unique but typical crack pattern in Phase II that is not manifested in Phase I.
The crack pattern shows propagation from the floor intersecting the column line diagonally on both sides. This shows that the wall is flexing but because of the rigid restraint of the walls, has failed the wall in shear instead, because of the upward pressure on the wall footings.
Several conclusions can be made on these observations:
There is less displacement for Phase II simply because the slag has already partly expanded before Phase II was constructed.
It is not true that the pile foundation had in some way contributed to reduction of cracks. On the contrary, if the Phase II portion would have been subjected to the full heave potential of the slag as in Phase I, more damage would have occured because of the more rigid restraint.
EFFECT OF WATER AND CHEMICAL LINES
Closer inspection of the displacement contour map would show that the following areas were the most affected by the heaving in descending order.
Experimental Section
R&D Office
CENLAB Office
Technical Library
These areas have one thing in common, and this is the presence of water lines and chemical lines near the heaved areas. It is suspected that the lines have leaked or burst due to corrosion from the groundwater or galvanic corrosion with the slag (dissimilar metals in contact) or have been broken by initial heaving thus contributing to acceleration of the corrosion process. Even without the foregoing, leakage of chemicals has been detected in the PVC connections of the chemical sinks in the Experimental Section. This condition probably contributed more corrosive chemicals under the slab as to cause the extensive Heaving in the Experimental Section.
RECOMMENDATIONS MADE FOR REMEDIAL ACTION
After satisfactorily proving to the owner that the Building was actually rising due to heave and not “sinking” as originally perceived, we set out to make recommendations on remedial measures that need to be undertaken. Since the Building was not on the verge of collapse nor seriously damaged by the heaving, we submitted a three staged rehabilitation program. This was necessary as critical research work is ongoing at the time and total or major disruption could not be allowed for the time being. The following were the remedial stages as recommended:
Stage I : Release of Floor Slab from wall
The floor slabs which were originally dowelled into the perimeter walls and interior walls were recommended to be saw cut using a diamond saw. This has the effect of releasing the walls from any uplift pressures acting on the slab. This will in turn reduce the cracking on the walls and other structural elements.
Stage II : Removal of Slag Base Courses
As soon as facility work load permits, the slabs that were released by diamond saw cutting shall be removed and the slab excavated and replaced by compacted clean granular Fill. All water utilities (Drainage & Sewage) as well as chemical lines shall be inspected for damage or corrosion and if need be, replaced by PVC Pipes or Compatible Plastic Pipes in the case of the chemical lines. The columns should be inspected to determine if any pullout from the socket footings has occurred so that this could be repaired. The granular Engineered Fill Subgrade shall be tested in case any residual acidity is present and this shall then be neutralized with lime milk before the granular base course is placed and compacted.
Stage III : Monitoring and Crack Repair
We recommended installation of a permanent reference Benchmark to monitor further movements in the Building after Stage I and Stage II repairs have been implemented. In case movements have ceased, epoxy repairs of all cracks should be undertaken after thorough cleaning of all cracks.
CONCLUSION
The owner has implemented Stage I and Stage II for the Phase I structure and Stage I for the Phase II structure. In the case of the latter, the freeing of the Slabs was already sufficient to arrest further cracking of the walls. Since swelling was preinduced before Phase II Construction, the resulting heave after construction was very much less than the heaving experience in Phase I Construction.
Stage III was subsequently carried out and to this time no further distress or cracking has been reported in any of the Building Elements. The paper illustrates how a seemingly innocent decision to use “good aggregate” in the form of slag as a base course nearly caused the abandonment and demolition of a building. It also illustrates how the initial but erroneous perception of movement of the structure as being downward or “settling” has caused additional but unecessary expenditures in the form of Piled foundations for Phase II Construction. The use of Piled foundations aside from adding to the cost and giving false hopes, only aggravated the problem by increasing restraints on the walls causing more serious cracking in the latter. The investigative procedures employed led to the isolation of the slag as the agent causing the heaving of the Building and the cracking of various structural elements. The resulting simple remedial measures employed, which consisted of removal of the slag and freeing of the slab connections from to the walls, saved the Building from abandonment and demolition.
Abstract: The need for reliable, fast and inexpensive soil investigation procedures has been felt in the local construction and consulting industry. The Electric Static Cone Penetrometer (CPT/CPTU) although widely used in more developed countries has seen very limited technical and commercial applications in our country due to its near total absence in commercial testing. This paper was originally prepared as a primer for our end-user units. However, it was expanded into this paper to present the State of Practice in the gathering of soil data using the Electric Cone Penetrometer (CPT/CPTU).
The various applications and limitations of the equipment and the procedures are discussed as well as findings on the results of local correlation tests conducted in the country. Directions on future applications and enhancements are also covered to fully exploit the potential of this testing method.
1.0 INTRODUCTION
1.1 General
The Cone Penetration Test (CPT) commonly known as the Static Cone Penetration Test (as opposed to the SPT, which is a Dynamic Penetration Test) or simply the Dutch Cone Penetration test, originated in the Netherlands.
It evolved out of the need to have a relatively simple and expedient test procedure that would be more economical and cost effective when compared to the SPT and yet yield meaningful data which could be useful in site characterization and the gathering of design parameters by correlation with extensive Insitu and Laboratory Testing results.
The CPT is most useful in stratigraphic interpretation where its value is unsurpassed. Because it is a continuous test of soil resistance, it can detect minute changes in stratigraphy and consistency/density and thus give a more reliable picture of the underlying soil conditions.
Due to the wealth of data accumulated in the past throughout its evolution, soil classification is relatively well defined through correlation charts using the three basic outputs of Cone Resistance qc, Friction Sleeve Resistance fs and their ratios fs/qc known as the Friction Ratio Fr. In the case of the CPTU or Piezocone, pore pressure u is also measured leading to improvements in correlations particularly for very soft clays and borderline characterizations. Invariably, correlation with local soils are necessary, particularly for borderline correlations, but for the major generic soil types, this is fairly well established.
The Chart (after Robertson, 1991) and included as Appendix “A” is recommended for initial classification by correlations. This would normally be augmented by a limited number of Boreholes to confirm or verify the local soil characteristics specifically in Borderline correlations to come out with Detailed Stratigraphic Information on the area investigated. Gathering of design parameters for Strength (Cu, ϕ ), compressibility (M & Dr) and other parameters have also been evolved by various researchers and for routine jobs, these correlations would suffice. For more important jobs, further tests using other established methods must be necessary such as laboratory tests and correlations with other test procedures such as the Vane Shear, Pressuremeter or Dilatometer.
1.2 History
The CPT originally started in 1932 in the Netherlands when P. Barentsen used a crude device which was made of a Gas pipe, inside of which a steel rod is inserted and to which a 60 deg. Cone was attached. This assembly was pushed down by hand, the cone resistance was read by a manometer.
Improvements to this crude device were made by Begemann resulting in a Mechanical Cone Penetrometer which added an “adhesion” jacket behind the cone tip. Using this new device, the Skin Friction could be measured by means of a manometer. Readings were made every 0.20m and the Rod string (Inner Rod and Outer Rod) is advanced alternately and incrementally while recording the manometers. A method for soil classification through the Cone Resistance and Friction Resistance became possible. In 1965 Begemann was also the first to propose that the Friction Ratio Fr could be used to classify soil layers in terms of soil type. 1]
The Electric Cone Penetrometer has eclipsed the use of the Mechanical Cone Penetrometers except for very limited applications where damage to the sensitive Electric Cone Tip is possible.
The Electric Cone Penetrometer was probably first developed in Germany during the war.
It was soon recognized that this was a very important development which eliminated the uncertainties and inaccuracies associated with the Mechanical Cone Penetrometer. Among its advantages relative to the Mechanical Cone Penetrometer are:
Elimination of erroneous interpretation of test results due to Friction between inner and outer rods.
A continuous testing with a continuous rate of penetration without the need for alternative movements of different parts of the penetrometer tip and no possibility for undesirable soil movements influencing cone resistance.
The simpler and more reliable electrical measurements of cone resistance with the possibility for continuous readings and easy recording of results.
Further improvements were made such as the incorporation of an inclinometer and introduction of a pore pressure (u) measuring system resulting in the CPTU or the Piezocone.
1.3 Details of the CPT
The Cone Penetration Test (CPT) is an In-situ procedure whereby a cone of Fixed Dimensions is pushed into the ground at a constant rate of 20mm/sec + 10%. The Penetrometer Tip as used in the Modern Day Electric Cone Penetrometer consist basically of four (4) major parts. The Cone, the Sleeve, the Inclinometer and the Body.
The cone has a 60 deg. Apex with a maximum diameter of 35.7mm with a height of 30.9mm and a shoulder height of 10mm. The maximum cross sectional area of the Tip Base is 1,000 mm2 corresponding to a diameter of 35.7mm and a height of the conical part of 30.9mm.
The Friction Sleeve has an outer cylindrical surface area of 15,000 mm2 + 2% which corresponds to a sleeve length of 133.7mm and is located above the tip.
The inclinometer detects and registers the inclination of the penetrometer from the vertical which is critical to prevent damage to the sensitive parts of the penetrometer or the drill string.
The body holds the three together and contains the Electrical Strain Gages to monitor the Tip and Friction Resistances and also the inclination reading in the form of electrical signals which are transmitted via connecting cable to an analog to digital converter which records the Friction and Tip Resistance and inclination versus depth and sends them to the computer. The computer then processes these data into usable output after interpretation of the signals using the prestored Penetrometer and Inclinometer Calibration Data.
The Cone is connected to a string of Push Rod which is inserted downward at a constant rate of Penetration of 20mm/sec by a thrust machine with a push capacity of at least 5 MT to 20 MT. Depth of Penetration is automatically recorded by a Linear Transducer synchronized with the other analog signals fed into the converter.
Normally, a Friction reducer is located above the penetrometer not less than 1,000mm from it. Schematically, the set up is shown below in Fig. 1.0:
1.4 Present State of Technology
Due to its reliability and popularity, the Electric Cone had undergone numerous improvements in accuracy and performance.
In addition, and due to advances in Electronics and Computer Technology, new capabilities are being added which would make possible the gathering of other parameters needed in Geotechnical Engineering and Geoenvironmental applications.
The development of more accurate and reliable strain gages has allowed the gathering of more reliable data. Multi channel capabilities, electronics miniaturization and improvements in signal processing and conversion have allowed gathering of various data concurrently or separately such as:
Cone Resistance (qc)
Friction Resistance (fs)
Inclination ()
Pore Pressure (u)
Seismic Wave Information
Shear Modulus G
Ground Water Chemical Properties
PH
Resistivity
Conductivity
Heat Flow (T)
Density (s), Moisture Content (MC) by Nuclear Probe
The Basic Electric Cone Penetrometer as we know it today, as a result of these advances, has come to be known as a rugged, reliable and relatively cost effective In-situ testing device for Geotechnical Engineering.
1.5 Test Standardization
During its early stages of Development, various sizes and configurations from various countries were in use. In order to provide reliable data through correlations, it was recognized that standardization was highly necessary as differing Penetrometer Geometry and the test procedures could produce highly differing test results. Since to some extent, soil strength is dependent on the rate of deformation (insertion of penetrometer) it was necessary to standardize this to 20mm/sec + 10%.
Several National Standards such as the Swedish Standard for Cone Testing and the US ASTM D-3441-86 have evolved.
In a bid to unify various national standards, the ISSMFE (International Society for Soil Mechanics and Foundation Engineering) came out with a reference Test Procedure which is expected to be adopted as The world standard for Cone Penetration testing. This is expected to be revised soon.
The present Swedish Standard for Cone Testing of 1993 exclusively refers only to the Electric Cone Penetrometer by specifying that measurements shall be done by Electrical means.
The mechanical cone is used less and less today because of related inacurracies and the cumbersome test procedure involved.
2.0 OFFICE & FIELD PROCEDURES
2.1 Equipment
Essentially, the Electric Cone Penetrometer set up would include the following:
Thrust Machine 20 MT Push Capacity (normally a special purpose Built Truck)
CPT Set
Cone
Friction Reducer
Push Rod String
Cable
Field Computer & Data Logger
Field Tools for Clearing and Maintenance of CPT
Office Computer
This is shown schematically in Fig. 1.0.
2.2 Office Procedure
2.2.1 Job Diskette Preparation
In order to avoid confusion in the Field, as invariably CPT Exploration would involve numerous exploration points per project and because the system is fully automated, it is necessary to prepare the exploration plan in the office.
Normally, Job Floppy diskettes would be prepared in the office which would contain the following information:
Job Number
Project Name
Location
Client Name
Cone & Inclinometer Calibration Data
2.2.2 Calibration
In addition, regular calibration at maximum 3 month intervals are carried out in the office as mandated by ISSMFE. The calibration is done to ensure that the cone & sleeve strain gages are within tolerance using a Force Transducer that is in turn calibrated to a higher standard.
2.2.3 De Airing of the CPTU
In addition to the foregoing and in the case of the CPTU (Piezocone), the Pore Pressure Filter System needs to be thoroughly deaired in order to ensure proper response of the Pore Pressure system to minute changes in Pore Pressure during the Pore pressure Dissipation test. This is done by subjecting the Filter to immersion in glycol inside a closed chamber. Vacuum is introduced to allow the air bubbles to boil out of the Filter and the Glycol solution. The Filter is shipped to the field completely immersed in Glycol using say a plastic or rubber sheath until it is inserted into the soil.
2.3 Field Procedure
2.3.1 Field Test Operations
In the field after equipment set up, the Job Diskette is loaded and the corresponding test point location is chosen.
The test is initialized by first ensuring zero (No Load) reading on the Penetrometer for qc and fs by hanging the CPT Cone in the Drill String on air. This is recorded antomatically by the software as a correction.
Normally a hole is predrilled by Auger on the Thin Dessicated Dry Crust to prevent damage to the CPT Tip before starting penetration
The verticality of the Push Rod and Thrust machine is checked in order to ensure that the thrust is vertically aligned. The deviation should not exceed 2% and the axis of the rods should coincide with the thrust direction. Normally levelling is done by Hydraulic Jacks.
The rate of penetration shall be 20mm/sec + 10% and stops are only made for Push Rod addition or when performing Pore pressure Dissipation Tests.
Readings are taken by the instrumentation and software for qc & fs at maximum 50mm (2 inches) increments averaged to within 50mm.
Depth of penetration is also recorded and measured with an accuracy of 100mm by an automatic linear transducer (Depth Gage) with a resolution of 10mm.
Most software have real Time Screen Displays of qc, fs, Fr, Inclination θ , Pore Pressure (u) and Rate of Penetration to enable the operator to control the operation and monitor critical parameters and ensure that tests are performed properly. The results are automatically stored in the hard disk of the Field Computer and the Job Floppy Diskette after the test.
2.3.2 Maintenance and Repair
In between tests, the penetrometer is visually inspected for any damage. All the seals are also inspected and any dirt inclusions are removed or cleaned to ensure proper performance during the test. If necessary, the penetrometer can be field disassembled to replace any broken seals or O-Rings and to lubricate the O-Rings.
2.4 Office Data Reduction
The data gathered in the field contained in the Job Floppy Diskette is sent to the office and is reduced and interpreted to yield the stratigraphy of the site investigated and other data which could be used for determination of Design Parameters.
Software is also available to automatically determine soil parameters but this has to be tempered with local experience.
3.0 TEST DATA GATHERING AND PRESENTATION OF RESULTS
3.1 General
The primary purpose of the CPT is to gather soil resistance data in order to effectively characterize the soil continuously with very little gaps in the stratigraphy. Through well established correlations and augmented by local experience, the site characterization is accomplished most efficiently. In stratigraphic characterization, the electric CPT is acknowledged to be the best insitu tool because it gives a continuous resistance profile of the subsurface. Because it is relatively inexpensive to perform, numerous points could be investigated to yield a more accurate horizontal characterization of the site.
Although various parameters obtained by correlation do not replace more accurate laboratory tests, the quality of data can be upgraded by local correlation. This is done by performing a limited number of boreholes and performing laboratory classification and strength tests (shear strength and compressibility) on the samples retrieved.
Essentially, stratigraphic characterization and parameters correlation (Strength, Compressibility, Dr, Gs, etc.) are obtained by the CPT through the continuous recording of the following data:
qc – Cone Resistance
fs – Sleeve Resistance Fr – Friction Ratio = fs/qc μ – Pore Pressure (for the Piezocone)
Because the CPT is standardized (As, Ap and rate of penetration) the correlation with numerous other tests performed in the past worldwide have given a wealth of data to make such correlations reliable.
These cone data are discussed individually: 2⎦
3.2 Cone Resistance (qc)
The cone resistance is the force per unit area which is obtained by the dividing the total axial force against the tip by the cross sectional area of the Tip Base (1,000 mm2).
Thus:
Alternatively:
In the special case where u = 0 or u is negligible, qc≈qt. The cone resistance is expressed in Mpa or Kpa.
3.3 Local Side or Sleeve Friction (fs)
The local side Friction is obtained by dividing the total Friction force acting axially on the Friction Sleeve by the outer surface area of the sleeve.
In the special case where the pore pressure effects are zero or negligible, fs ≈ ft. The local sleeve friction is expressed in Mpa or Kpa.
3.4 Friction Ration (Fr)
The Friction Ratio is the ratio between the local sleeve friction (fs) and the cone resistance (qc).
The ratio is expressed as a percentage. Normally, Fr for sands is seldom over 1% and for clays is normally > 4%.
3.5 Pore Pressure u and Change in Pressure (Δ u)
With the advent of the CPTU or Piezocone, which measures pore pressure and enable the performance of Pore Pressure Dissipation Tests, more detailed tests can be performed and strength parameters for very soft soils can be obtained.
The Differential Pore Pressure ratio DPRR is the ratio between the generated pore pressure and the cone resistance at the actual level.
Recent studies have shown that even with careful procedures and corrections for pore pressure effects, the measurement of sleeve friction (fs) is often less accurate than the cone resistance.
To overcome problems associated with sleeve friction measurements, several classification charts have been proposed based on qT and pore pressures (Janbu and Senesset). The chart by Janbu & Senesset use the pore pressure parameter Bq.
Experience has shown that, although the sleeve friction measurements are not as accurate as qT and u, generally more reliable soil classifications can be made using all three pieces of data (qT , fs & u). Thus, the normal correlation charts for characterization is three dimensional. 1]
3.6 Pore Pressure Dissipation Tests 3⎦
The CPTU or Piezocone has the potential of providing estimates of the in-situ coefficient of consolidation from dissipation tests. A dissipation test can be performed at any depth by interrupting the penetration at that depth. This will be discussed in later sections.
4.0 INTERPRETATION OF CPT/CPTU DATA
4.1 General
Numerous studies and data correlation have been made in the past as the CPT/CPTU evolved from a simple penetration test to what it is today. With the advent of sophisticated electronics and test standardization, correlation with various soil parameters could be made with increasing confidence. However, as in all applications in soil mechanics, such correlations need to be tempered with local experience and local soil behavior and validated by actual Laboratory Tests until the local correlations are adequately established as to be reliable. Various soil information can be gleaned from the simple CPT Tests and when augmented with pore pressure data from the CPTU, increased accuracies and reliability can be obtained.
The following correlations and soil information may be obtained with the CPT/CPTU tests:
4.2 Stratigraphy
The CPT found its most useful and valuable application in stratigraphy and site characterization. And in this aspect, this insitu test is most superior to any existing method because it provides a continuous profile of the soil and is relatively inexpensive. Thus, more numerous test locations can be done providing a closer interval for visualization of soil conditions. For routine jobs the CPT test would suffice and for more critical jobs of large magnitude, the CPT can be augmented with a limited number of Boreholes and Laboratory Tests.
The stratigraphic characterization is obtained using the Basic CPT Data qc, fs, Fr and u.
The characterization is best done using the Three Dimensional correlation chart by Robertson (1990) and included in Appendix “A”.
Using raw CPT Data or normalized data, one can determine characteristic soil descriptions of soils using this chart. Only occassionally, when borderline cases are encountered in routine jobs, is there a need to do more detailed sampling by borings.
Robertson suggested that the charts are still global in nature and should be used as a guide to define soil behavior type based on CPT and CPTU data. Factors such as change in stress history, in situ stresses, densitivity, stiffness, macrofabric, mineralogy and void ratio will also influence classification.1]
Essentially for clays and silts, Cone Penetrometer is undrained thus measurement of Pore Pressure is important since the rate of PP Dissipation is a key to classification. Cone resistance should be corrected for pore pressure effects. In addition, measured pore pressures can also be used directly for interpretation in terms of soil design parameters.
4.3 Soil Unit Weight & Relative Density Dr
4.3.1 Soil Unit Weight (s)
Larsson and Mulabdic (1991) based on tests performed in Sweden and Norway, proposed the chart in Appendix “B” for obtaining a rough estimate of soil density for clays. This is an iterative procedure since an initial estimate of γ s is necessary to compute net cone resistance and Bq.
4.3.2 Relative Density Dr
Several relationships have been evolved for determining Relative Density (Dr) of Sands. However, ageing effects tend to increase cone resistance and no interpretation procedure could take account of ageing. Thus, to some extent, the obtained Dr should be referred to us “equivalent” Dr as recommended by Robertson. 1]
The value of Dr can be obtained from the chart in Appendix “D” or in equation form based on the values below:
4.4 Strength Characteristics
Various procedures have been evolved from which direct correlations can be obtained to yield soil strength parameters out of basic CPT data (qc, fs & u).
4.4.1 Clay & Fine Grained Soils
The undrained shear strength (Su) can be determined in several ways from empirical correlations.
The empirical correlation is of the general form
Robertson recommends the following procedures for Su determination: 1]
1) For deposits where little experience is available, estimate Su using the total cone resistance (qt) and preliminary cone factor values (Nkt) from 15 to 20. For a more conservative estimate select the upper limit.
For normally and lightly overconsolidated clays, Nkt can be as low as 10 and for stiff fissured clays as high as 30.
In very soft clays, where there may be uncertainties in the accuracy in qt estimate Su from the excess pore pressure (Δ u2) using NΔ u from 7 to 10 in the CPTU.
2) If previous experience is available in the same deposits, the value suggested above should be adjusted to reflect this experience.
3) For larger projects, where high quality field and laboratory data may be available, site specific correlations should be developed based on appropriate and reliable values of Su.
4.4.2 Coarse Grained Soils
Cone penetration in coarse grained soils is generally undrained, thus, no excess pore pressures are generated. Established correlations using large laboratory calibration chamber tests have been made with this assumption.
The procedure as recommended uses the charts in Appendix “E”.
The ϕ ′ from relatively uniform uncemented clean sand is empirically estimated from Fig. 5.56 in Appendix “E”. Figure 5.55 can be used to adjust the estimated ϕ ′ to account for variations in compressibility and Ko. A reasonably conservative value of ϕ ′ should be selected based on the range obtained.
4.4.3 Intermediate Soils (Clayey Sands to Silts)
The methods for interpretation applied for clays or sands may not be totally valid for silts as penetration in this material is partially drained. In this regard clay content of the silts is important.
It is important therefore to determine the type of drainage conditions encountered during the tests. If the design problem involves undrained loading and the CPT is undrained, then the CPT data can be interpreted in a manner similar to clay and similarly for drained loading and drained CPT in sands.
The CPTU Pore Pressure Dissipation tests could give the plot of pore pressure decay over the time the test was performed. From this data, τ 50 – the time for 50% dissipation can be obtained.
Robertson proposed a chart relating τ 50 (minutes) to Kh (cm/sec) since drainage in the CPTU is essentially horizontal.
Vertical Permeability Kv can be obtained from well established field values relating Kv to Kh after Jamiolkowski 1985 and presented in chart form below:
4.5.2 Coefficient of Consolidation (Ch)
The coefficient of consolidation Ch in the horizontal direction can be approximated from the chart as proposed by Robertson (1992) from an extension of the work by Houlsby & Teh and shown in Appendix “F” relating τ 50 as defined above and Ch (cm/sec2). The relationship between Ch and Cv – the coefficient of consolidation in the vertical direction is obtained similarly from the above table relating Kh to Kv.
5.0 DIRECT APPLICATIONS OF CPT/CPTU DATA
In the foregoing section, interpretation of CPT/CPTU Data was directed towards correlation with soil strength parameters aside from other properties such as unit weight, relative density, stratigraphy, etc. These parameters in turn can be plugged into the various formulas (Theoretical or Empirical) to yield Bearing Capacity, Settlement, etc.
However, and particularly for Driven Piles, direct applications of CPT/CPTU Data could result in direct prediction of Pile capacity. The CPT procedure is a scale model of a Pile being inserted into the ground. Thus predictions of capaity are fairly more reliable. The reason being the ability to do continuous profiling of the subsurface soil response.
Superiority of the CPT method over non-CPT methods have been confirmed in other studies. 1]
Literature is replete procedures to use data gathered from the Electric CPT/CPTU Tests directly to provide solutions such as:
Pile Capacity and Settlement
Bearing Capacity of Shallow Foundations
Settlement of Shallow Foundations
Ground Improvement Quality Control
Liquefaction Assessment
In all the foregoing, reduction factors need to be applied to CPT Values. The need for such reduction factors is due to scale effects of the test, rate of loading or insertion technique. 1]
6.0 CONCLUSION AND SUMMARY
The foregoing presents the Electric CPT/CPTU its advantages and advantages in obtaining soil parameters needed in Geotechnical Engineering and Foundation Design.
Its ease of use resulting in reduction in cost of investigation without degradation of information obtained from such tests is certainly an important consideration.
It is hoped that this paper would pave the way for increased understanding and wide acceptance of the procedure as an invaluable tool in Soil Exploration.
ABOUT THE AUTHOR
Engr. Emil M. Morales Graduated from Mapua Institute of Technology where he earned his Bachelor of Science Degree in Civil Engineering. He Finished his Master of Science Degree in the same field at Carnegie Institute of Technology, Carnegie Mellon University, Pittsburgh, PA, USA.
He worked as a Project Engineer at D’Appolonia Consulting Engineers, Monroeville, PA. Where he was involved in the preparation of Software for Data Reduction for the Menard Pressuremeter.
He attended a short course in the Use of the CPT, Pressuremeter and the Dilatometer at Texas A&M University under Dr. Briaud.
He also recently trained in CPT Operations, calibration, maintenance and Software at the facilities of A. P. Van den Berg in Heerenveen, the Netherlands.
He is currently Chairman of the ASEP Geotechnical Committee and a Life Member of the same Association. He is also a member of the ASFE – Professional Firms Practicing in The Geosciences, ASCE, ACI, CRSI & ASTM.
1] Lynne and Robertson. “Cone Penetration Testing” 1st Ed., 1997. Blackie Academic Press, London, UK
2] Swedish Geotechnical Institute. “Recommended Standard for Cone Penetration Test”. Linkoping & Swedish 1992, Swedish Geotechnical Institute.
3] Briaud, J.L. “The Cone Penetrometer Test.” 1991 FHWA Office of Technology Administration, Virginia, USA
ABSTRACT: Quality in the Construction Industry and the workplace is a necessary ingredient for success. Too often, Quality is neglected sometimes with disastrous results.
As a Professional Design Engineering and Consulting Firm, we realized very early on that we needed to formalize our Quality Control procedures into a single coherent strategy in order to assure consistency and reliability of the Checking, Peer Review and Management Review processes. These activities were necessary not only to assure quality but also to safeguard our reputation and protect the general public by ensuring safe and cost effective designs.
The opportunity came when our biggest client, who was also getting into the ISO 9000 Quality System, required that downstream contractors and service providers also qualify for ISO 9000 Accreditation. We took the challenge and became the First Filipino Engineering Consulting Firm to be accredited under the ISO 9000 System.
This paper describes our quest for ISO 9000 accreditation which we would like to share with the Profession and the Construction Industry. Admittedly, as we shall soon find out, there is not “one single” Quality System for all and that Quality Systems and procedures should be attuned and tailor made to each individual organization’s needs. However, it is hoped that conscientious adherence to the ISO 9000 Quality System Guidelines and our experiences which we share in this paper will somehow help our Industry to become one of the most efficient, safest and cost effective sector in our country.
1.0 INTRODUCTION
We got introduced to the ISO System through the backdoor. Our sister Laboratory, Philippine Geoanalytics, Inc. just completed accreditation as the First Philippine Laboratory ever to be accredited under ISO Guide 25. The quality system was therefore in place in one of our sister organizations, although in this respect ISO Guide 25 is a more stringent system than ISO 9000 in that it required checking of the technical competency of the personnel to perform Laboratory Testing Procedures.
In addition, and more importantly, we were informed by our biggest client to prepare for ISO accreditation if we are to remain as a service provider for them. This client even sponsored our attendance in their in-house ISO 9000 Briefings and Seminars in order for us to fully understand the quality system and how best to synergize with them. Our client, who was actually on the verge of obtaining ISO 9000 accreditation for most of their plants was the catalyst in speeding up our process for accreditation.
This is not however to be taken as an indication of the lack of desire from within to seek ISO accreditation. For already, we were seeing the positive effects of what ISO Guide 25 was doing for our Laboratory—Morale was up, client satisfaction was at an all time high, income had increased by leaps and bounds, lost records and books have become a thing of the past and order has finally been restored in a very chaotic environment normally found in testing laboratories.
Thus, there was a very strong and compelling reason for us to qualify for ISO 9000 Accreditation.
This paper describes our preparations, documentation process and employee orientation. It is worthwhile mentioning that we undertook this assignment using exclusively our internal resources and manpower. We did not hire a pre audit service nor engaged consultants. This had the advantage that all our employees needed to participate to ensure our success. It was gratifying for us to observe teamwork in action, as our employees were highly motivated to accomplish this task.
How this happened is also discussed in this paper.
2.0 BENEFITS OF THE ISO QUALITY SYSTEM TO THE ENGINEERING ORGANIZATION
Although some of the benefits may not be readily apparent, a Quality System formalized and religiously implemented in an Engineering Organization can confer numerous advantages to it.
Oftentimes, compliance to ISO 9000 may be driven by the desire to comply based on client pressure or requirements. Sometimes it is done in the mistaken belief that ISO 9000 Quality System by itself can increase revenues or can assure quality of products or services.
But what are the true and real benefits of ISO 9000 to an Engineering Organization? In our case, the ISO 9000 Quality System had given us numerous benefits unimaginable before which are normally the least tangible benefits and these are:
Substantial improvement in internal operations.
Elimination of lost or misplaced documents and communications.
Simplified and formalized procedures for review and quality control of designs
Reduced time of document retrieval to within 5 minutes.
Increased employee awareness of the need to preserve quality and reduce errors to a minimum.
Traceability of design and drafting errors resulting in reduced error counts.
Increased employee morale because everyone knows their role in the organization and their importance in the maintenance of the Quality System and Procedures.
The foregoing may not be readily apparent to an organization seeking accreditation for the first time and it was to us a pleasant surprise that these came free with the package.
To us as Professional Designers, the foregoing are more important than the more often Touted Benefits because of the need to increase client satisfaction and also reduce our liability exposure.
There have been cases in our experience where our preservation of certain documents had saved us from costly litigation and claims. This would not have been possible without a fool proof document Archiving/Retrieval System that the ISO 9000 guidelines suggest.
The other more common benefits are of course the following:
Increased competitive advantage due to enhanced efficiency in procedures.
Customer preference for ISO 9000 companies with established Quality Systems.
Global acceptability of the ISO 9000 accredited company.
Orderly conduct of company business governed by procedures.
If we are to be asked what is the best benefit that has resulted from our seeking ISO 9000 accreditation, it is this:
We have reduced the chances for errors remaining undetected before implementation. Although errors cannot be entirely eliminated due to human factors or computer glitches, our formalized Quality Control system gave us the assurance and feeling of confidence that somehow we will find these errors before they can do some harm or cause loss of reputation.
As a matter of fact, it is not a sin in our organization to commit an error. However, it is a cardinal sin for everyone and anyone if we let an error go undetected through our various checks and counterchecks, as outlined in our Quality System. Somehow, this has given our employees High Morale.
3.0 BASIC UNDERSTANDING OF THE ISO 9000 SYSTEM
3.1 Background
The ISO 9000 standards originated from the IOS which is located in Switzerland . IOS is the acronym in French of the International Standards Organization. The ISO standards had its roots during the Second World War where methods of assessment of quality of wartime suppliers was very critical. This evolved into the MIL Standards and their Civilian Counterparts. Countries in the EU began to accept the values of a single standard for quality management systems resulting in the publication in 1987 of the ISO 9000 Series of Standards.1
3.2 What is ISO 9000?
ISO 9000 is a set of international standards for a Basic Management System of Quality Assurance. It is intended to equalize Quality Systems between companies and countries. 1
The following are the unique characteristics of the Quality System:
Flexibility – the requirements of the system are guides only and could be changed if the practices within an organization do not exactly match the requirements.
Wholistic – the standard looks at how the whole organization assures the quality of its products and services.
Focus on Quality Process – the standard do not focus on the final results but rather on the procedures for assuring quality.
Global – the standards have worldwide application and acceptability.
Broad Application – the standards can be applied to all aspects of business or operational procedures.
3.3 The ISO 9000 Family
The ISO 9000 Standards has five parts or is really a set of Five (5) Standards as defined1] below:
ISO 9000 – “Quality Management and Quality Assurance Standards – Guidelines for Selection and Use” is written to help companies determine which of the three standards to adopt or apply for registration.
ISO 9001 – “Quality Systems – Model for Quality Assurance in Design/Development Production, Installation and Servicing” is the standard for companies engaged in all aspects of manufacturing or of the development and delivery of a service.
e.g. A consulting Engineering Firm with a fully integrated Design Engineering function.
ISO 9002 – “Quality Systems – Model for Quality Assurance in Production and Installation” – is for companies that perform functions except the design and development of products and services.
e.g. A manufacturer that builds to prints and designs of a customer. A general contractor who builds based on plans supplied by the owner’s engineers.
ISO 9003 – “Quality System – Model for Quality Assurance in Final Inspection and Test” – is intended for non manufacturing companies such as distribution or warehousing entities. ISO 9003 is applied less and less and is expected to be dropped in the future.
ISO 9004 – “Quality Management and Quality System Elements –Guidelines” – is an overview of the themes and intent of the standards.
The key word in all of the foregoing titles is “Model” because the standards represent models of quality assurance rather than compulsory standards. Companies need only to match as closely and as economically, and as practically as possible the guidelines. This means that companies need not dramatically change their methods of quality assurance to meet the ISO 9000 Standards.
3.4 What It Is and What It Isn’t
The ISO 9000 Quality System is a set of Guidelines that is flexible.
It does not dictate the procedures to be practiced nor does it require a company to change its way of doing Quality Assurance if it is logical and effective. However, it provides a set of coherent guidelines to enable companies to meet minimum standards in the Global marketplace.
The ISO 9000 Standard is a requirement for a management system, not the structure of a quality department within an organization. There is not one correct Guideline and Procedure to follow. Each must be tailor made to suit the particular company’s operations and Quality Assurance procedures.
As a minimum, the standards provide a general pattern to follow. However, deviations or omission can and do occur depending on the company’s specific way of doing business which may be unique and requiring special procedures.
Common Misconception
It is sad to note that there are still lingering misconceptions about the ISO 9000 System and the quest to get there. These misconceptions should be clarified and erased before an organization can start its travel towards ISO 9000 accreditation. Some of these misconceptions are:
It is very difficult to comply with the standards.
The standards are rigid and inflexible.
It would take a long time to successfully comply.
It is very expensive to obtain and maintain.
It must be prepared by a consultant
It must be prepared and packaged by the management because employees would look at the standards with bias.
Employee compliance must be mandated from the top.
The quality system process must be management driven all the way.
It is not necessary provided you know what you are doing.
The documentation process is a waste of time and resources.
4.0 ESTABLISHING THE QUALITY COMMITTEE
Some of the major misconceptions in ISO 9000 accreditation are:
The process should be management driven.
You need a consultant to prepare the procedures and quality system.
Employees should be handed the complete procedure for their compliance.
The foregoing are quaranteed paths to failure because more than anything else, employee direct involvement is crucial to the success of any quality system. The effort should therefore be employee driven with the full logistical and moral support of top management.
We realized this very early on and we created a Total Quality Committee drawn from rank and file, tasked to prepare the company for accreditation. The Chairman of the Total Quality Committee in our case was a Lady Middle Level Engineer at that time and the following as representatives:
Management Representative – Technical Manager and Senior Partner
Engineering Representative – Junior Engineer representing Design Group And CAD Group
Admin Representative – Senior Clerk representing Admin and Non Technical Group
Q.C. Engineer – Full time Independent member of the Committee Designated as such.
The Total Quality Committee (TQC) spearheaded the company’s program for ISO 9000 Accreditation. It independently set the goals, milestones and work objectives of the company. Top management interference was unheard of and the main function of management was to keep the activities focused and monitor progress to attain a fixed deadline we have mutually agreed upon during the formation of the TQC.
The members were free to make the necessary suggestions and draft the procedures pertinent to their areas of operation. They were given blanket authority to draw upon any company resource or personnel in order to attain the objectives set by the TQC.
Directly under the TQC but not its members were two (2) Archive and Documentation Clerks. They received guidelines and instructions on the filing and records retrieval system being evolved and undergoing dynamic revision throughout the life of the TQC. These clerks were on full time assignment and were aided by our clerks and secretaries. They were not part of the mainstream operations as their job was to compile, catalog, file and debug the system. Little did we know that this decision saved us a lot of time and was partly instrumental in clinching the accreditation for the company.
As can be seen, the TQC was employee driven and this was very crucial not only to the preparation of the Quality System and Procedures but also in the subsequent implementation and maintenance of the Quality System. The procedures, having been originated by the employees themselves were widely accepted and embraced by all. In other words, the procedures were not rammed down the throat of rank and file but were prepared, polished and nurtured by them.
This to us is the single most crucial decision leading to the success of our Quest for ISO 9000 Accreditation.
5.0 PREPARING FOR ACCREDITATION
The Total Quality Committee established the necessary documentation requirements and the procedures needed to be documented. It also set out the guidelines for the archival and retrieval system.
The Quality Manual was reviewed and continually revised to contain new procedures or revised/eliminated/ outdated/superseded procedures.
Numerous working copies were reprinted for comments by employees as soon as these have undergone revisions- each revision being issued a Revision number. Thus, everyone got involved in the process of rewriting the procedures manual. The paper generated by the preparations was humongous but it was well worth the effort and time.
We also acquired several books on the ISO System which served as reference and guide for our efforts. Our books were the poor man’s substitute to a Consultant to assist in the accreditation process.
As part of our preparations and to serve as “Dry Run” to the Pre Audit and Audit activities ahead, we conducted internal audits using the checklist published in these references.
There was a compelling need to ensure that the system is thoroughly checked and debugged as external audits are expensive. In our case the Pre Auditor came from Austria and the Auditor from India. Both have to be billeted in Five (5) Star Hotels and their airfares paid for in addition to the Audit Fees charged by their company.
Thus, we can not afford failing in both audits and no room or allowance for non- compliance reaudits, and the rallying cry for the TQC is “Hit it one Time” this battle cry had a double meaning to us because HIT is our acronym for:
H – Personal Honesty
I – Integrity
T – Technical Excellence
We aimed for single pass Pre Audit and Audit and got it, saving us a lot of anxiety and plenty of hard earned money.
Dedicated as they were, the TQC members were driven by the Chairman who almost worked full time developing and coordinating the standards preparation. To add to the incentive, the Chairman was promised and got an all expenses paid trip to Hong Kong for getting accreditation in one pass. To get accredited in one audit was to us hard earned divine providence. The Internal Audits and Dry Runs were repeated until we were very satisfied that our system met ISO 9000 Standards. The personnel were in high state of morale and eager to get it over with.
We were ready!
6.0 THE DOCUMENTATION PROCESS
The main task in the ISO 9000 Accreditation Process is to ensure adequate Documentation of Procedures and Quality Systems. This also involved creating Document Filing, Archiving and Retrieval system to ensure the traceability and retrievability of all documents that need to be stored and that meant everything except junk mail.
No project document or communication was considered unimportant as not to be logged and stored in the archives.
The archived files consisted of Project Files which in our specific case involved:
⦁ Project Communications ⦁ Project Calculations ⦁ Project Plans & Drawings (Hard Copy, CD and Bernoulli Disk Files) ⦁ Project Specifications ⦁ Project Contract File ⦁ Estimates & Quantity Take Off
All these project files were interlinked and coded to assure fast retrieval and filing.
It is worthwhile to note that as a result of systematizing our document archiving and retrieval system, we can retrieve any project document within five minutes after the request for each documents is initiated. This includes travel time from the groundfloor to the third floor of our office.
In addition, lost document or lost files have become a thing of the past.
7.0 THE ISO 9000 QUALITY SYSTEM
7.1 ISO 9000 Elements
The ISO 9000 Quality System sets out Guidelines for companies to consider in the preparation of their Quality Systems and Procedures. It identifies vital elements that may comprise the system.
Note that in this definition, there are no mandatory statements such as “required” “shall” etc. Instead the words or phrases such as “consider” “may comprise” and that the provisions are “Guidelines”.
What this suggests is that the ISO 9000 is totally flexible and does not prescribe how the system should be done. It must completely suit each individual companies product or processes.
In our case, we evaluated the Guidelines element by element, and we adopted or incorporated those elements or sub elements related to our operations.
The following are the Elements for ISO 9001:
Management Responsibility
Quality System
Contract Review
Engineering Design Control
Document and Data Control
Purchasing
Control of Customer Supplied Product
Product Identification and Traceability
Process Control
Inspection and Testing
Inspection, Measurement & Test Equipment
Inspection and Test Status
Control of Non Conforming Product
Corrective and Preventive Action
Handling, Storage, Packaging, Preservation and Delivery
Control of Quality Records
Internal Quality Audits
Training
Servicing
Statistical Techniques
In our specific instance, we deemed all the twenty (20) Elements as necessary for our system but with a lot of modifications in order to suit our way of doing business and conducting our work.
It would be necessary to acquire references and guides such as the books mentioned in our references in order to have a clear and concise General Guide in preparing the Quality Manual and Procedures.
Emphasis is placed on the word “General” because the system and procedures are unique to the individual company’s operations.
The biggest temptation, is to copy some other company’s manual. This is a big mistake and a shortcut to failure due to lack of immersion and voluntary participation of rank and file.
7.2 ISO 9000 Levels of Documentation
The ISO 9000 Guidelines is relatively flexible in terms of document structure. However, it is necessary to have several levels of documentation mutually supportive of each other in order to have a fully Integrated Quality System. In our case, we adopted the Document Structure Pyramid 2 commonly used by a lot of companies as shown below:
From the above, the documentation levels or hierarchy can be easily seen as follows:
LEVEL 1 Quality Manual – the Quality Manual answers the question: why? It is a company’s statement of philosophy and approach to quality. The Quality Manual discusses in general terms how the company complies with each element of the standard, it also includes the company’s quality objectives (such as “Zero Defects”), gives an overview of the company’s processes and contains the quality philosophy of the company.
The Quality Manual is the Bible for Quality for the company.
LEVEL 2 Procedures – The procedures document the company’s Quality Plan and defines the implementation strategy. It indicates compliance to the ISO 9000 Standards, demonstrate the processes and ensures that there are no loopholes in the system.
The procedures are process oriented and covers:
⦁ The Tasks: What? ⦁ The Responsibility: Who? ⦁ The Frequency: When? ⦁ The Department: Where?
Necessarily, the procedures should be written by the people who will use them. Not by a Consultant. Because the procedures are process oriented, we decided to Flow Chart our procedures. This had the advantage of:
⦁ Making it easily understandable by anyone reading it even without prior knowledge of flow charting. ⦁ Saving a lot of manhours and pages of paper during the preparation. ⦁ Enabling in thorough checking of the process as it was Graphical and easily checked. ⦁ Expediting the audit procedures enabling us to get accredited.
We saw the need to include 12 Flow Charts defining our operations. These are:
Proposal Preparation: New Clients Procedure Flow Chart
Awarding of Contract: New Clients Procedure Flow Chart
Awarding of Contract: Old Clients Procedure Flow Chart
Control of Client Provided Info/Data Procedure Flow Chart
Isuance of Documents and Books Procedure Flow Chart
Purchasing Procedure Flow Chart
Handling of Documents Procedure Flow Chart
Internal Audit & Reviews Procedure Flow Chart
Handling Client Request Procedure Flow Chart
LEVEL 3 Work Instructions – The work instructions answer the question How? They are the step by step instructions specific to the company’s procedures. Work instructions includes direction for doing specific tasks such as Checking and Peer Review, Document Storage and Retrieval, Handling of Complaints, etc. In our case, and for the same reasons above, we have integrated these into a procedures Flow Chart indicating the process, the documents needed or generated and the persons responsible.
The Quality Documents or Forms we generated are as follows:
Transmittal Letter
Project Summary Sheet
Request Form
Confirmation of Documents Received
Checkprint Report
Internal Project Bulletin
Internal Quality Audit
Complaints Form
Purchase Order
Quality Control Checklist
Weekly Project Monitoring
Zero-Defects Score Card Form
Statistical Record of Defects
Checklist of Client Inputs Form
LEVEL 4 Quality Records – The quality records provide evidence of the company’s compliance. They are the ongoing objective evidence of the system and evolve from the company’s procedures. The standards does not specify exactly which records to keep because the individual company has to define this depending on its process. However, most elements of ISO 9000 require Quality Records.
The records that we decided we needed to keep as a minimum are as follows:
Project Files
Hardcopy Plans
Electronic Plan Files (CD Format & 3.25 Floppy Diskettes)
In the generation of documents, it is necessary to focus on the company’s actual needs and the procedures that it implements. Some procedures may overlap and therefore can be joined into one detailed procedure. The
key thing to remember is to limit documentation to what is really essential to the Quality System defined procedures. More documents mean a larger number to manage (or neglect), fewer documents may mean larger and crammed individual documents which may decrease usefulness or reduce understanding. In addition, our Quality Manual included the following:
Quality Committee Table of Organization
Company Table of Organization
Amendments Record
Official Company Quality Policy Statement
8.0 PREPARING FOR THE PRE AUDIT AND FINAL AUDIT
In order to obtain proof of compliance that the ISO 9000 System is functional and being implemented within the company, a Third Party Independent Auditor (TPA) normally ISO certified as such would need to be engaged. The TPA would need to conduct a Pre Audit Review and as many audits as necessary until you run out of money or you obtain compliance. Because Third Party Audit is expensive, it would be necessary and imperative that the Quality system and procedures are fully debugged internally prior to Audit. Otherwise, non compliances could stretch the time and be very costly and demoralizing to both rank and file.
The Pre Audit
The pre audit is an audit conducted by the TPA in order to check: ⦁ Completeness of Quality Systems and Procedures (Elements involved) ⦁ Adequacy of Documentation to cover the company’ processes ⦁ Cursory evidence of implementation of the Quality System ⦁ Archived Documents and Document Retrieval system ⦁ Top Management commitment to the Quality System
We prepared for the pre audit as though it was our final audit. This involved at least 3 months of preparations and weekly staff orientation meetings. Each individual staff was given his own copy of the Draft Quality Manual which required voluminous printing of documents. Internal audits and peer audits were required at every step of the process. The pre audit required two (2) days to complete and to our relief, only minor non compliances were observed. Management and the TQC were briefed by the TPA on the deficiencies to prepare for the final audit. To our great relief we were told that we were ready for the final audit.
The Audit
More intense preparations were made to include training and retraining of staff in the implementation of the system. The audit, aside from being more rigid, would require individual interviews of staff chosen at random by the TPA. Everyone therefore must know the system by heart. Aside from the more detailed checks on the pre audit items, the following were done:
Interview of top management to determine level of participation or involvement in the quality process.
Meeting with the TQC to gage its inner workings and level of commitment
Individual staff interviews to determine level of understanding of the Quality System
Checking of Office Procedures
Checking that Software is validated
Test of the Document Archiving and Retrieval System
In this specific instance, several projects were randomly chosen by the TPA and related Files were requested to be presented. The retrieval time was monitored.
Also, as an example: a project was chosen and the work order and minutes of coordination meeting were requested to be exhibited.
Checkprints were asked to be displayed and compared with final plans to see whether all corrections were implemented.
The audit was conducted for three (3) straight gruelling days, and all office functions were directed towards the audit. Other activities not related to the Audit ground to a halt. That was how important the audit was to us. The TPA was crucial to us.
Besides, it would be very expensive for us not to pass the audit as the TPA had to be billeted again in a 5 Star Hotel and the Airfares (from Europe or elsewhere) had to be paid in addition to his man day rates.
9.0 COMPLIANCE AT LAST
It was a combination of very hard and dedicated work and the grace of God the Almighty that we successfully handled the audit and obtained acceptance of the company’s Quality System with a few minor comments in one pass. There was a feeling of general relief and satisfaction for a job well done.
We got our accreditation on June 14, 1996.
We had a reception to honor the members of the TQC and it also gave us the opportunity to thank our clients and announce to the world that our Quality System is at par with the World’s Best.
True to our promise, the Chairman of the TQC was given a 3 day Holiday in Hong Kong.
Morale was very high and everyone had a feeling of pride and accomplishment for a job well done!
10.0 MAINTAINING AND SUSTAINING THE SYSTEM
The effort does not stop at accreditation time. Yearly audits by the TPA are mandatory to retain Accreditation and Certification.
But to us, the incentive in maintaining the system is because we have seen that the system really works for us and has given us a very competitive advantage over peer companies.
To us, at least and to potential clients, “we are more equal among equals”. Whether this is true or not, is not the question. In our minds and our hearts we know that we are because we have a formalized system that works.
In closing, we wish to state that in this difficult times, an engineering company can survive or survive better with a formalized and working Quality System and as forces realign, the ISO 9000 accredited company is better positioned to meet a more discriminating and quality conscious client.
REFERENCES
Clement, R.B. “Quality Manager’s Complete Guide to ISO 9000”. 1993 Prentice Hall Inc., NJ.
Novack, J.L. “The ISO 9000 Documentation Toolkit”. 1987 Prentice Hall Inc. N.J. pp.20
Emilio M. Morales took up his Master’s Degree in Civil Engineering at the Carnegie Institute of Technology, Carnegie-Mellon University, Pittsburgh, PA. USA in 1981. He is formerly a Senior Lecturer of the Graduate Division, College of Engineering, University of the Philippines, Diliman, Quezon City. Presently, he is the Principal of EM2A Partners & Co., Technical Manager of Philippine Geoanalytics, Inc. and Technical Director of PGA Calibration & Metrology Laboratory. Committee Member, TC-11, Bureau of Product Standards Technical Committee on Steel Products. He is currently Chairman of ASEP Geotechnical Committee.
He can be contacted at: EM2A Partners & Co., 17-C Scout de Guia corner Scout Reyes Streets, Diliman, Quezon City. Telephone Nos. 371-18-06 / 410-29-23 to 24 Telefax No. 924-98-94; E-mail: em2apart@mozcom.com
With the advances in Ground Technology and Foundation Techniques, Difficult Foundation Problems involving Ground Distress, Settlements, Difficult Construction Conditions and Unstable Slopes are finding new solutions that were unheard of particularly in our country until very recently. One of these solutions now available in the country is Jet Grouting. Jet Grouting is a process of Ground Stabilization by high pressure injection of Cement Grount into the soil. Because of the controlled insertion, rotation and withdrawal of the high pressure Jetting Pipe, a columnar element of Grouted Soil known as “Soilcrete” is produced. The diameter and strength of this solidified mass of “Soilcrete” is controlled during the installation process. Although this description appears to be overly simple, the process is more complicated than the foregoing. In order to understand this fully, we need to go back to the historical development of Jet Grouting as the evolutionary processes have contributed to the present day technology and its successful application.
HISTORICAL BACKGROUND
The procedure and idea of using high velocity Jet Streams to cut, remove and cement soils were first originated in Japan starting around 1965 by the brothers Yamakodo. In early 1970, there were already two competing forms developed nearly simultaneously. The Jet Grouting technique developed by Nakanishi utilized chemical and cement grouts injected at ultra high pressure through very small nozzles (1.2 – 2.0mm Ø) which were located at the bottom of a single rod. Because the single rod is both lifted and rotated while jetting the grout, a pile like soil cement column is formed, from where arises the name of this type of Jet Grouting: chemical churning pile or CCP Jet Grouting. Water, Air and Cement Grout. Other variations in Jet Grouting quickly followed. The most important modification being the Jumbo Special Grout (JSG) which is essentially CCP Jet Grouting with air encapsulating the Cement Grout Jet. By merely using compressed air, the JSG columns are typically 1-1/2 to 2 times larger than ordinary CCP columns constructed using similar jetting parameters.1 Following this rapid development in Japan, the technology gained acceptance in Italy, Russia, Western Europe and very much later in the United States.
WHAT IS JET GROUTING?
Having seen the evolutionary process, we are now able to define Jet Grouting in its present form as used here in our country.
Jet Grouting is a ground stabilization procedure which uses the principle of Ultra High Pressure Injection of Cement Grout into the ground. The procedure employs a bottom-up installation sequence. The Double Tube or Triple Tube Pipe is rotated at a fixed RPM and automatically raised in fixed increments. The double tube system is used in the country. Cement Injection under Ultra High Pressure is done within a protective encapsulating conical shroud of compressed air. The compressed air allows increased ground penetration (larger diameters) by preventing significant pressure drops as the Grout leaves the nozzle.
Due to the Ultra High Pressures involved, the permeability of the soil is of no critical importance as the procedure relies more on the very high erosive power of the Jets to gain lateral Penetration. The solidified column of grouted soil is termed as “Soilcrete” and the compressive strengths would depend on the parent soil material and can be controlled to some extent by the Jetting Procedure. Soilcrete columns behave as a columnar pile with load carrying capacity coming from Skin Friction and Point Bearing. Typically, diameters would range from 0.8m to 1.4m. Jet Grouting is the only soil stabilization procedure that would work equally well in plastic clays and granular materials although compressive strengths and load capacity are typically higher in the latter material.
COMPONENTS OF THE JET GROUTING SYSTEM
The schematic equipment layout shows the main components of the system.
The heart of the system is the Ultra High Pressure Pump which generates pressure in the order of 200 kg/cm2. The Ultra High Pressure Slurry or Grout is fed to the inner tube of a double Tube Jetting Pipe. Compressed air to shroud the grout during injection is fed to the outer pipe. The discharge is sidewise through a small orifice nozzle approximately 1.2mm to 1.8mm in diameter. The pipe is inserted, rotated and raised in controlled increments by a Jetting Machine which is a modified drill rig with automatic hydraulic controls and timers. The Jetting pump possess very sensitive electronic monitors and controls which senses and adjusts the pumps strokes and speed to ensure constant pressure and controlled volume of grout injection. The rest of the system is composed of support elements such as:
Water Pump and Reservoir
High Speed Mixer
Paddle Agitator
Air Compressor 600 CFM
⦁ Generator
Of critical importance in the whole procedure and one which enables increased penetration of the Grout is the encapsulating conical air shroud which prevents sudden pressure drops during injection. The figure below illustrates the system:
INSTALLATION PROCEDURE
The accompanying figure illustrates the step by step installation of Jet Grouted Piles on any type of soil.
Appendix “A” illustrates the step by step procedure. First the double tube cutting bit is inserted and jetted into a soil through a downward Jetting Nozzle until the target depth is reached. This insertion and jetting disaggregates the soil and creates an annular cavity zone to allow for jetting to start. A ball bearing is dropped to close the downward pointing nozzle and divert the slurry injection through the side discharge nozzle (approximately 1.2mm Ø to 1.8mm Ø). At the same time, compressed air is injected through the outer orifice surrounding the side discharge center nozzle. This air shroud, conical in shape envelopes the slurry Jet to prevent its sudden decrement to athmospheric pressure. In addition, the hydrostatic head of the cuttings in suspension is prevented from contaminating the Jet and also from decreasing its pressure. As grout injection is progressing, the drill string is automatically rotated at the rate of approximately 7.0 RPM and raised in increments at the rate of 2.5 cm per second. Grout pressure is maintained at approximately 3,000 psi. In case of sudden pressure loss due to increased grout flow into voids or cavities, the automatic sensors in the pump system increases the pumping rate to ensure a nearly constant pressure and volume delivered. Once the procedure is completed, reinforcement can be installed by pushing down the rebar normally at the center. Installation of reinforcement along the side is possible provided the rebar insertion points are predrilled. However, ties can not be installed for obvious reasons.
The Jet Grouted Pile normally should be terminated 1.0m to 2.0m below ground to allow for confinement of the Grout. The Grout within this space is normally weaker due to the same reasons. During the drilling, if obstructions are encountered, the jetting pipe can just core through the obstruction and later on incorporate the obstruction within the cemented mass. Grouting can also be at various levels not necessarily continuous as say to stabilize a weak layer sandwiched in between two dense layers.
UNIQUENESS OF JET GROUTING AS A SOIL STABILIZATION PROCEDURE
Jet Grouting as a soil stabilization procedure is quite unique as it overcomes some limitations inherent with other procedures such as:
⦁ Insensitivity to Low Soil Permeability
Due to the ultra high pressure injection of cement grout, highly erosive forces ensure grout penetration to the desired radius. The reduced permeability of clays does not adversely affect the grout penetration unlike unidirectional grouting procedures. Thus, the procedure is effective for both clays and granular materials.
⦁ Decreased Danger of Soil Fracturing or Heaving
Because the procedure is normally open to atmospheric pressures and because the nozzle is rotated at a constant rate, grout pressure build up which could lead to serious soil heaving or soil fracturing is eliminated. Even in cases where the hole is blocked, the increased pressure and reduced grout take is detected by the instrumentation to allow quick response of the crew and thus heaving is prevented.
⦁ Limited Headroom or Maneuver Space Requirements
The relatively small and lightweight equipment needed for installation allows Jet Grouting to be performed in very tight places for underpinning of existing Buildings or other works.
⦁ Automated Installation Process
The automated process of installation by control of rotation, raising of drill string and pressure/volume compensation by the ultra high pressure pump contribute to the highly predictable and consistent quality of the Jet Grouted Column. Thus, minimum compressive strength of the Soilcrete and the diameter of Grouted Column can be predicted with a reasonable degree of accuracy.
⦁ Ease of Installation
The procedure can be employed in difficult ground or working conditions and the Jet Grouted Pile can be installed in any angle with the vertical up to slightly less than 90 . Beyond 90 difficulty in retaining the Grout is encountered as grout flow out is possible.
⦁ Ability to Bypass Obstructions
Jet Grouting has the unique ability to bypass obstructions such as boulders and buried structures and incorporate these into the cemented columnar mass. Thus, Boulders could be embedded and incorporated into the soilcrete mass and be part of the load support system. The sketch shows this graphically.
⦁ Increased Lateral Compaction of Soil
The ultra high pressure jet other than eroding the soil also increases the lateral compaction of the soil due to high pressure pulsating jet. Thus, some degree of densification is possible particularly for granular soils. The effectiveness of lateral compaction is at least a radius away from the perimeter.
⦁ Increased Frictional Resistance
The very uneven eroded surface produces a serrated configuration or a very highly irregular cylindrical surface. This increases the skin side frictional resistance of the Jet Grouted Column.
⦁ Reduced Permeability of Soilcrete
Cementation of the soil after washing and disaggregation helps eliminates voids and zones of high permeability because a uniform soilcrete body is formed. The permeability is in the order of 10-6 cm/sec very much like heavy impermeable clays.
⦁ Control of Depth of Installation
Since this is an insitu Bottom-up Installation Procedure, the depth of installation and the installation length can be controlled to the desired depth without wastage. In addition, the Grouting can be done at selective levels and need not be continuous.
APPLICATIONS IN DIFFICULT FOUNDATION PROBLEMS
Although Jet Grouting is not a cure all for all foundation problems that confront us day to day, there are difficult problems where it becomes the primary solution candidate or the only solution available. There are myriads of problems in foundation engineering where the effectiveness of Jet Grouting becomes a crucial factor in the selection process for a solution. We therefore group these into several classes of problems as follows:
⦁ Underpinning of Structures
Structural underpinning of existing structures becomes difficult particularly due to low headroom or space restrictions. In addition, disturbance of the already distressd structure or adjacent structures becomes a critical consideration. Jet Grouting eliminates most of these problems as the Jetting Machine can crawl into very tight spaces. Disturbance is minimal and avoided if installation is not concentrated in one area as to allow localized weakening of the soil support while the grout is curing. In addition, disturbance to adjacent structures is minimal as there is no vibration or shock. The Jet Grouting procedure could also be called upon to recover from settlements with the aid of chemical jacking. In addition, very expensive connection details can be avoided with Jet Grouting as the jet Grouted Section is very much bigger than the hole through the foundation being underpinned. Only a dowel might be required in such cases.
⦁ Landslides
The large cross sectional area of the Jet Grouted Pile and the ease of installation enable the use of Jet Grouting for the control of Landslides and creep. The shear resistance of the cross section can further be enhanced with the addition of soil reinforcement. The ability of the Jetting Machine to reach inaccessible areas makes it possible to strengthen unstable slopes on impending slide or areas subject to creep movements. In addition, areas where slides have occurred can be stabilized by the use of Jet Grouting essentially to reinforce the failed mass and strengthen it.
⦁ Seepage Cut Offs
The very low permeability of the “Soilcrete” produced in the Jet Grouting Process allows it to be used as an Impermeable Barrier. Its ability to overlap in Secant Pile arrangement makes it water tight.
⦁ Foundation Piles
Particularly for very shallow applications in very tight or inaccessible areas, Jet Grouting is sometimes the only viable solution. Its large cross sectional area and highly irregular perimeter allows it to sustain large heavy loads controlled only by the strength of the Soilcrete material.
⦁ As Ground Anchors
Jet Grouted Anchors have been used in projects to provide a deadman or a large diameter anchor with appreciable pullout capacity. The use of High Tensile Strands drilled into and subsequently grouted inside the Jet Grouted Pile allows for large pullout loads and resistance against uplift. This is particularly useful for Temporary Ground Anchors on poor soils where the HTS length can be appreciably shortened or these could be used as Deadman for Anchored Sheetpiles or Bulkheads.
CONCLUSION
This paper has presented the State of Practice of Jet Grouting in the Philippines. Clearly, we have seen the versatility of Jet Grouting in the Solution of Difficult Problems in Foundation Engineering. However, it should be understood that Jet Grouting is not a cure all to foundation problems. There are some deterrents to its successful application, one of which is cost. Also, the procedure becomes non competitive to existing conventional foundation solutions where difficulty or restrictions on the use of such conventional solutions are non existent. In addition, the load carrying capacity of the Jet Grouted Pile is limited by the quality of the Soilcrete in a double tube system as the soil is not totally replaced by Cement Grout but is mixed with it. Several other examples of applications are included in the Appendix. It is hoped that a greater understanding of the system could lead to its full utilization in solving difficult ground conditions where conventional solutions are not feasible.
1 Kauschinger, et. al. “Jet Grouting: State of Practice” Vol. 1 Grouting, Soil Improvements and Geosynthetics – Geotechnical Special Publication, ASCE, NY 1992.
Of all activities in the realm of construction, nothing is as taken for granted as Earthworks. This is perhaps due to the misconception that “Soil is Soil” and that brute force alone will suffice in order to compact it. Nothing can be farther from the truth and numerous projects here and abroad have highlighted the important fact that soil can not be taken for granted as it can spell trouble in the construction site. The purpose of this paper is to focus on the special characteristics of various soils and how best to harness this knowledge for optimum construction expediency.
2. THE NATURE OF SOILS
Soil is an aggregation or assemblage of particles which are the products of weathering or decomposition or rocks. They could have been weathered in place or transported by wind or water. The manner of deposition as well as the parent material dictate how the soil behaves when subjected to loading or other environmental factors.
Soil particles are either visible to the naked eye or are submicroscopic. Being a particulate material, soil behaves differently than say a solid material. Particulate behavior can be fully understood and once this is so, the treatment of problems involving soils and soil particles becomes simpler. Soil is a structural material, but unlike other construction materials with known or predictable properties that could be specified at design stage, the engineer has to contend with what he will encounter in the field. Being a natural material, the soil will exhibit large variabilities even within the confines of a construction site. In most instances, soils must be used “as-is” and “where-is” because of its great bulk and difficulty of transporting such large volumes. Soil properties can also change with time and this must be anticipated. On the other hand, soil structure can also be altered by man in order to improve its characteristics significantly.
1) Soil Microstructure
Soil microstructure plays a very important part in the engineering behavior of soils. Soil structure can be altered or changed mechanically or chemically to produce desired characteristics for the project. Soil can either be Coarse Grained (sands and gravels) or Fine Grained (clays and silts). In addition, these soils can be adulterated say by organic materials as to effectively alter its characteristic behavior.
2) Coarse Grained Soils
Sands and gravels constitute the bulk of these soils , the individual sand grains are visible to the naked eye and are “gritty” to the trouch. Clean sands behave as particulate material. They derive their strength chiefly from contacts between the individual sand grains which results in “friction”. Although the individual grains may not be fully in contact with each other. The large concentration of stresses at the contact points produces increased resistance to sliding one past the other. Granular soil strength is essentially based on its Angle of Internal Friction “ϕ ” or its ϕ -Angle. The ϕ -Angle is not a unique value for a certain type of soil. Rather the ϕ angle is dependent on the degree of compactness of the soil and the confining pressure. The more compact and the more confined the granular soil is, the larger the ϕ -Angle. Coarse grained soils in their loose state are sensitive to vibration and are thus easily compacted by vibratory means whether very dry or in saturated state. When subjected to vibration, the loose coarse grained soils assume a denser packing and are thus compacted. A similar effect although to slightly lesser degree can be achieved by totally saturating the loose sands with water. The loose packing collapses with flooding by water and the soil assumes a denser packing.
3) Fine Grained Soils
Fine grained soils such as clays and silts are generally submicroscopic and the individual soil particles are not readily visible to the naked eye. Depending on the source or mineralogy, clays and silts may be plastic or non plastic.
Because of their very small size, the ratio of the surface area to the volume or mass is very very large and thus, surface activity due to electrochemical forces of attraction and repulsion come into play.
The shear strength or “cohesion” of these clays and silts are essentially derived from such forces and not through interparticle friction as one would suspect. The individual soil particles known as platelets are seldom in contact as they are surround by highly bounded adsorbed water due to electrical forces of attraction and further by absorbed water which is weakly bonded. Thus, the individual platelets slide one past the other because of these adsorb and absorbed layers of water. Compaction of this soil is dependent chiefly in expelling this absorbed water and any air with it to reduce the interparticle distance between clay platelets so that the forces of attraction is increased due to the reduction in distance. The resulting strength due to electrochemical attraction is known as “cohesion”.
4) Intermediate Soils
Intermediate soils are either predominantly granular or fine grained but have fractions of the other as to significantly alter its characteristic behavior in its unadulterated state. Data from tests made on sands used for molding indicate that its shear strength reaches a maximum and levels off with about 9 to 14% of clay depending on the clay mineral. If the clay content exceeds about 25% the strength degrades as the “Wedge Block” structure disappears and the individual sand or silt grain become separated and “floating” in a matrix of clay.2] When sufficient clay is present to form a matrix enclosing coarser grained soils (normally 25-30% clay), the structure of the clay dictates the structural behavior of the soil.
3. MOISTURE DENSITY RELATIONSHIP OF SOILS
1) Proctor Moisture Density Relationships
R.R. Proctor is generally regarded as the originator of principles dealing with a rational approach to soil compaction.3]
Proctor felt the need to have a laboratory compaction test to control field compaction operations. His first decision was the selection of a laboratory compaction energy that would simulate compaction energies imparted by construction equipment in the field.
He accomplished this by specifying a 5.5 lb hammer dropping at 12 inches height on soil samples confined in a 4″ diameter steel mold. This came to be known as “Proctor Density”.
Later on, as the need for bigger airplanes and wheel loads developed during the war years, it was found that the original compaction requirements for airfields and highways would need to be increased. Thus, higher compaction requirements resulted in the use of higher hammer energies in the laboratories. This came to be known as the “Modified Proctor” and the original Proctor Density became the “Standard Proctor Density”. The table below shows the comparison between the two methods:
It can be seen from the foregoing that Modified Proctor energy is 4.51 times that of Standard Proctor Energy. The two procedures came to be standardized as:
ASTM D-698 – “Laboratory Compaction Characteristic of soil using Standard Effort (12,400 ft-lb/ft3)”
ASTM D-1557 – “Laboratory Compaction Characteristic of soil using Standard Effort (56,000 ft-lb/ft3)”
There is a large difference in the compaction energy (and effort) needed in the laboratory and in the field to move from Standard to Modified Proctor Density.
Sometimes unknowingly or through ignorance, Engineers or the owner would specify the degree of relative compaction without specifying the reference as say: “to be compacted to 95% MDD” where: “to be compacted to 95% MDD based on ASTM D-698” would have been more appropriate.
4. IS THE PROCTOR MOISTURE DENSITY RELATIONSHIP APPRO-PRIATE FOR ALL SOILS?
This question does not often surface because there has been an implicit acceptance of this as the reference procedure for the compaction of all soils. In point of truth, this is not so as relatively clean coarse grained soils are insensitive to moisture content except in the extreme ranges of being very dry or highly saturated. The concept of “Optimum Moisture Content” (OMC) therefore is not applicable to clean coarse grained “Free Draining” soils such as sands and gravels.
The compaction of clean coarse grained soils are not referenced against Proctor Densities (Standard or Modified) but rather on the concept of Relative Density (DR) using ASTM D4253 “maximum Index Density and Unit Weight of Soils using a Vibratory Table” and ASTM D4254 “minimum Index Density and Unit Weight of Soils and Calculation of Relative Density” and plugging the minimum and maximum values obtained therefrom to arrive at the reference relative density DD for the material.
Thus, the Relative Density of the soil as calculated is different from the Proctor Density. Why then is Proctor Density still being specified for even clean sands? We can only guess that this is because of plain ignorance or probably the lack of test equipment for this test in the country. Although, relative compaction and Proctor maximum densities can be used, one is never sure whether the maximum density has been allowed or not. In most cases this is not attained.
1] Emilio M. Morales holds a Master’s Degree in Civil Engineering from Carnegie Mellon University, PA., USA and is currently the Chairman Geotechnical Specialty Committee. Currently, He is the Technical Director of Philippine GEOANALYTICS, Inc. Soils and Materials Testing Laboratory and can be reached through e-mail: pgamain@pgatech.com.ph www.pgatech.com.ph
2] Spangler, M. “Soil Engineering”. 4th Ed. Harper & Row Publishers. NY, NY 1982.
3] Monohan, E. “Construction of and on Compacted Fills”. Wiley & Sons, Inc. NY, NY 1986.
