Mechanically Stabilized Earth (MSE) walls and slopes are innovative solutions for ground stabilization and earth retention. At PGATECH Group, we offer cutting-edge MSE technologies designed to enhance the stability and durability of infrastructure projects. This article explores what MSE walls and slopes are, their history, purpose, advantages, applications, desirability, and the problems they address.
What are Mechanically Stabilized Earth (MSE) Walls and Slopes?
Mechanically Stabilized Earth (MSE) walls and slopes are structures that use layers of engineered materials to stabilize and retain soil. These systems typically consist of compacted backfill, reinforcing elements (such as geogrids or metal strips), and a facing material (such as concrete panels, blocks, or natural vegetation). MSE walls and slopes are designed to support heavy loads and prevent soil erosion, making them ideal for various construction projects.
History of Mechanically Stabilized Earth (MSE) Walls and Slopes
The concept of MSE dates back to ancient times when natural materials were used to stabilize embankments. In the 1960s, innovative use of steel strips and compacted soil layers revolutionized earth retention techniques. Since then, advancements in materials and engineering practices have further refined MSE systems, making them a preferred choice for many infrastructure projects worldwide.
With production of stronger and better quality geosynthetics and its increase in use in the geoconstruction industry, MSEs reinforced with geosynthetics started being referred to as Geosynthetic Reinforced Soil (GRS) or Geosynthetically Confined Soil (GCS). This modern type of MSE Walls has proven to be a better choice because of its lightweight reinforcement that provides internal stability with more reliable, closer spacing between lifts.
What is the Function/Purpose of Mechanically Stabilized Earth (MSE) Walls and Slopes?
The primary purpose of MSE walls and slopes is to provide effective soil stabilization and earth retention. Key functions include:
Supporting Loads: MSE systems can support heavy structural loads, making them ideal for retaining walls, bridge abutments, and embankments.
Preventing Erosion: The reinforced structure prevents soil erosion, maintaining the integrity of slopes and embankments.
Improving Stability: Enhances the overall stability of the soil, reducing the risk of landslides and slope failures.
Aesthetic Integration: MSE walls and slopes can be designed to blend seamlessly with the surrounding environment, providing both functional and aesthetic benefits.
What Do Mechanically Stabilized Earth (MSE) Walls and Slopes Replace?
MSE walls and slopes often replace or complement traditional earth retention methods such as:
Gravity Retaining Walls: Concrete or masonry walls that rely on their mass to resist soil pressure.
Cantilever Retaining Walls: Reinforced concrete walls that use a cantilevered design to stabilize soil.
Gabion Walls: Structures made of wire baskets filled with rocks or other materials.
Natural Slopes: Unreinforced slopes that may be susceptible to erosion and instability.
These traditional methods can be more expensive, labor-intensive, and less adaptable to various project conditions compared to MSE systems.
Advantages of Mechanically Stabilized Earth (MSE) Walls and Slopes
MSE walls and slopes offer numerous advantages, including:
Cost-Effectiveness: Lower material and labor costs compared to traditional retaining walls.
Speed of Construction: Faster installation process, reducing overall project timelines.
Flexibility: Adaptable to a wide range of soil types and site conditions.
Durability: Long-lasting performance with minimal maintenance requirements.
Environmental Benefits: Can be designed with natural vegetation, promoting ecological sustainability.
Where are Mechanically Stabilized Earth (MSE) Walls and Slopes Applicable?
MSE walls and slopes are applicable in various scenarios, such as:
Highway and Railway Embankments: Providing stable support for transportation infrastructure.
Bridge Abutments: Supporting bridge structures and connecting them to roadways.
Retaining Walls: Stabilizing soil in residential, commercial, and industrial developments.
Slope Stabilization: Reinforcing slopes to prevent landslides and erosion.
Landscaping: Creating aesthetically pleasing and functional terraced landscapes.
Flood Control: Constructing levees and floodwalls to manage water flow and prevent flooding.
What Makes Mechanically Stabilized Earth (MSE) Walls and Slopes Desirable?
The desirability of MSE walls and slopes stems from their:
Efficiency: Rapid construction and effective soil stabilization.
Economic Savings: Lower overall project costs due to reduced material and labor expenses.
Minimal Disruption: Less invasive construction methods compared to traditional retaining walls.
Versatility: Suitable for a variety of applications and environmental conditions.
Aesthetic Appeal: Can be designed to blend with natural surroundings, enhancing visual appeal.
Problems Addressed by Mechanically Stabilized Earth (MSE) Walls and Slopes
MSE walls and slopes effectively address several engineering challenges, including:
Soil Instability: Reinforces weak soils to support structural loads and prevent failure.
Erosion Control: Prevents soil erosion on slopes and embankments.
Space Constraints: Provides effective earth retention in limited space, allowing for vertical construction.
Load Support: Supports heavy loads in infrastructure projects such as highways and bridges.
Environmental Impact: Reduces the need for extensive excavation and concrete usage, promoting sustainability.
Mechanically Stabilized Earth or MSE Walls are support systems that are used in construction projects to help control and support slopes or soil on inclines. This technology combines soil reinforcement and a facing system to provide support. MSE Walls are mostly used in highway and railway embankments, bridge abutments and other projects where soil slopes require stabilization/retention. MSE Walls are favored for their cost effectiveness and versatility in construction projects. An MSE Wall has 3 main components that help fulfill its purpose.
Reinforcement
One of the three main components is the reinforcement. The reinforcement can come in various forms such as steel strips or geogrids which are embedded within the soil mass creating a stable composite body. The reinforcement aids the wall in such a way that it distributes lateral forces and improves the overall strength of the wall.
Backfill
The second component would be the backfill. To fill the space between the reinforcement layers, certain backfill types with known properties are used. This includes Granular Backfill, Cohesive Backfill, and reinforced soil
Granular Backfill
The granular backfill is the most common type of backfill used for MSE walls. It contains well graded and compacted granular materials that provides reliable interparticle friction resistance, and at the same time promotes interaction with the reinforcements.
Cohesive Backfill
This type of backfill contains cohesive soils such as clay or silt. Cohesive backfill is rarely employed in situations where granular material is scarce. The strength from this backfill mainly comes from cohesion and internal shear strength of the material.
Reinforced Soil
Reinforced soils are fill materials mixed with reinforcing elements to upscale its shear strength and tensile properties. This type of backfill is only used in some cases where design specifications require higher strength.
Facing
The last component of the MSE wall is the facing. The facing is the front and visible surface of the MSE Wall. This component shields the wall from erosion. It also provides an aesthetic surface for the structure. Common facing techniques include: (a) wrap-around system which can be used to cultivate a vegetative face after several weeks; (b) gabions that are multipurpose and can be used with surfaces that are exposed to bodies of water; and (c) concrete panels used for vertical walls applications typical for abutments and other highway constructions.
Conclusion
At PGATECH Group, we are dedicated to providing state-of-the-art Mechanically Stabilized Earth (MSE) Wall – Geosynthetic Reinforced Soil (GRS) or Geosynthetically Confined Soil (GCS) – and slope solutions that ensure the stability and durability of your construction projects. Our expertise and advanced techniques enable us to tackle even the most challenging ground stabilization tasks, delivering reliable and cost-effective results. For more information about our MSE services, please contact us today.
Geopiers, also known as Rammed Aggregate Piers (RAPs) or Rammed Aggregate Columns (RACs), are an innovative ground improvement technology used to enhance soil bearing capacity and control settlement. At PGATECH Group, we specialize in providing top-notch RAP solutions tailored to meet the specific needs of your construction projects. This article delves into the details of what RAPs are, their history, purpose, advantages, applications, desirability, and the problems they address.
What are Rammed Aggregate Piers (RAPs) / Geopiers?
Geopiers, commonly referred to as RAPs (Rammed Aggregate Piers), are ground improvement elements created by densely compacting aggregate (crushed stone) into drilled holes in the ground. These piers or stiff columns reinforce weak soils, providing a robust foundation that can support heavy structural loads and reduce settlement.
History of Rammed Aggregate Piers (RAPs) / Geopiers
The concept of using aggregate to improve soil properties dates back to the early 20th century, but the modern technique of Rammed Aggregate Piers was developed in the early 1990s. The Geopier system was introduced as an alternative to deep foundations, offering a cost-effective and efficient method for ground improvement. Over the years, the technology has evolved, with advancements in installation techniques and equipment, making RAPs a reliable choice for many construction projects.
Rammed Aggregate Piers (RAPs) / Geopiers in the Philippines
Since October of 2000, the patented Rammed Aggregate Pier System has been used to support virtually all types of structures ranging from warehouses, tanks, embankments, low-rise to mid-rise buildings, MSE Walls, GRS Walls, and more.
Our clients from various industries have retained our services in their projects across the nation. Our team of experts and skilled personnel have also worked on government projects as Rammed Aggregate Columns have been recognized as a locally proven technology to support roadways and publicly-owned buildings.
What is the Function/Purpose of Rammed Aggregate Piers (RAPs) / Geopiers?
The primary purpose of RAPs/Geopiers is to improve the load-bearing capacity and reduce settlement of weak soils. The key functions include:
Increasing Bearing Capacity: Enhances the strength of weak soils to support structural loads.
Reducing Settlement: Controls and limits both total and differential settlement of structures.
Improving Stability: Provides additional stability for foundations on problematic soils.
Enhancing Soil Performance: Facilitates better load distribution and soil reinforcement.
What Foundation Systems Can Rammed Aggregate Piers (RAPs) / Geopiers Replace?
RAPs/Geopiers often serve as an effective alternative for more traditional and sometimes more expensive foundation solutions such as:
Deep Foundations: Piles, drilled shafts, and caissons, which can be more costly and time-consuming to install.
Over-Excavation and Replacement: Removing and replacing poor soil with engineered fill, which involves extensive excavation and material handling.
Soil Stabilization Methods: Chemical grouting and soil mixing, which may not always be cost-effective or environmentally friendly.
Advantages of Rammed Aggregate Piers (RAPs) / Geopiers
RAPs/Geopiers offer several advantages, including:
Cost-Effectiveness: Generally less expensive than deep foundation systems.
Time Efficiency: Faster installation compared to traditional deep foundations.
Flexibility: Suitable for a wide range of soil types and project conditions.
Environmental Benefits: Uses natural materials (aggregate) and minimizes soil disturbance.
Performance: Provides reliable improvement of soil bearing capacity and reduction of settlement.
Where are Rammed Aggregate Piers (RAPs) / Geopiers Applicable?
RAPs/Geopiers are applicable in various scenarios, such as:
Commercial and Residential Buildings: Enhancing foundation support for buildings on weak soils.
Industrial Facilities: Supporting heavy machinery and storage areas.
Infrastructure Projects: Roads, highways, bridges, and railways.
Embankments and Slopes: Stabilizing slopes and embankments to prevent landslides.
Wind Turbines and Utility Structures: Providing a stable foundation for tall and heavy structures.
What Makes Rammed Aggregate Piers (RAPs) / Geopiers Desirable?
RAPs/Geopiers are highly desirable for several reasons:
Efficiency: Quick installation process minimizes construction delays.
Economic Savings: Lower overall project costs due to reduced material and labor requirements.
Minimal Disruption: Less invasive installation compared to traditional deep foundations.
Versatility: Adaptable to a variety of soil conditions and structural requirements.
Sustainability: Environmentally friendly approach using natural aggregates.
Problems Addressed by Rammed Aggregate Piers (RAPs) / Geopiers
RAPs/Geopiers effectively address several common soil and foundation problems, including:
Low Bearing Capacity: Enhances the ability of weak soils to support structural loads.
Excessive Settlement: Controls and reduces settlement, ensuring long-term structural integrity.
Differential Settlement: Mitigates uneven settlement, which can cause structural damage.
Construction Delays: Speeds up the foundation preparation process, allowing for timely project completion.
Conclusion
At PGATECH Group, we are committed to delivering high-quality Rammed Aggregate Pier / Geopier solutions that ensure the stability and durability of your construction projects. Our expertise and advanced techniques guarantee that even the most challenging soil conditions are effectively managed. For more information about our RAP/Geopier services, please contact us today.
Ground improvement is a crucial aspect of modern construction and civil engineering. At PGATECH Group, we specialize in delivering state-of-the-art ground improvement solutions to ensure the stability, safety, and longevity of your projects. In this comprehensive article, we will explore what ground improvement is, its history, functions, advantages, applications, desirability, and the problems it addresses.
What is Ground Improvement?
Ground improvement refers to a range of techniques used to enhance the physical properties of soil. These techniques are designed to increase the load-bearing capacity, reduce settlement, and mitigate liquefaction potential in soils. Ground improvement is essential for construction projects on sites with poor soil conditions, ensuring that structures are built on a stable and secure foundation.
History of Ground Improvement
The concept of ground improvement dates back to ancient times, where early civilizations used basic methods to stabilize and strengthen soil. Techniques such as compaction and the use of natural binders like lime and clay have evolved significantly. In the modern era, the development of advanced materials and machinery has revolutionized ground improvement practices, allowing for more efficient, effective, and flexible solutions.
What is the Function/Purpose of Ground Improvement?
The primary purpose of ground improvement is to enhance the properties of soil to meet specific engineering requirements. This includes:
Increasing load-bearing capacity
Reducing soil compressibility
Preventing soil liquefaction during seismic events
Mitigating settlement issues
Enhancing the stability of slopes and embankments
By improving these properties, ground improvement ensures the safety and durability of structures built on challenging soil conditions.
What Does Ground Improvement Replace?
Ground improvement techniques often serve as alternatives to more traditional and costly methods such as:
Deep foundations (e.g., piles, drilled shafts)
Excavation and replacement of poor soil
Massive over-excavation followed by backfill with engineered materials
These traditional methods can be time-consuming, expensive, and disruptive. Ground improvement offers a more cost-effective and less intrusive solution.
Cost-Effectiveness: Reduces the need for expensive deep foundation systems.
Speed: Techniques can be implemented quickly, reducing construction time.
Flexibility: Applicable to a wide range of soil types and project conditions.
Sustainability: Often uses environmentally friendly materials and methods.
Performance: Enhances the mechanical properties of soil, ensuring long-term stability and safety.
Where is Ground Improvement Applicable?
Ground improvement is applicable in a variety of scenarios, including:
Construction of buildings, bridges, and other infrastructure on soft or loose soils.
Road and railway embankments.
Port and harbor facilities.
Land reclamation projects.
Industrial and commercial developments.
Areas prone to seismic activity where soil liquefaction is a concern.
What Makes Ground Improvement Desirable?
Ground improvement is highly desirable due to its ability to address challenging soil conditions without the need for extensive excavation and replacement. Its benefits include:
Efficiency: Quick and effective enhancement of soil properties.
Economic Viability: Lower overall project costs compared to traditional methods.
Minimized Disruption: Less invasive techniques lead to fewer disturbances to existing structures and the environment.
Versatility: Can be tailored to specific project needs and site conditions.
Problems Addressed by Ground Improvement
Ground improvement techniques effectively address several soil-related problems, including:
Poor Load-Bearing Capacity: Enhances the soil’s ability to support structures.
Excessive Settlement: Reduces overall and differential settlement, preventing structural damage.
Soil Liquefaction: Stabilizes soils in seismic zones, reducing the risk of liquefaction.
Slope Instability: Increases the stability of slopes and embankments, preventing landslides and mass wasting.
Erosion Control: Protects natural and man-made slopes against soil erosion in sloping ground, adjacent slope faces, coastal and riverbank areas.
Types of Ground Improvement
Ensuring the safety of your project starts with the sound engineering of building foundation and stabilization of potential geohazards. Although reinforced concrete and steel structures are reliable and popular options, optimizing the benefit-cost ratio demands more flexible engineering solutions that address geotechnical issues at their core. In general, these geotechnical solutions are commonly termed as ground improvement.
A variety of ground improvement techniques have been developed to address soil and rock conditions that don’t meet project requirements. Common issues stem from poor engineering properties on-site such as insufficient soil bearing capacity, excessive settlement projections, high liquefaction potential, unstable slope/excavation, etc.
Ground improvement techniques can be categorized into the following main types according to mechanism: densification, reinforcement, drainage, chemical treatment, and others.
Densification
Surface compaction, one of the most common procedures employed on-site, is a form of densification. These methods generally increase the density of the soil thereby improving strength and deformation properties, and reducing liquefaction potential. Several methods can be conducted to densify the soil depending on the soil type and the target depth to be improved. For shallower layers, dynamic compaction can be applied which involves dropping weights on the ground surface through a specified height at predetermined locations. For intermediately deeper granular layers, vibroflotation can be conducted by inserting a probe into the ground inducing vibrations that densify the ground.
Reinforcement
A multitude of methods of ground improvement fall under the reinforcement category. Techniques vary depending on the orientation of the installation, reinforcing material, and method of installation. Slope stabilization can be carried out using soil nails or rock anchors. Soft soil or weak, loose soil can be improved by stone columns, sand compaction piles, jet grouting, micropiles, and Rammed Aggregate Piers. The construction of mechanically stabilized earth (MSE) structures also involve the use of steel or geosynthetic reinforcements to increase load bearing capacity and stability. Some techniques such as rammed aggregate piers can virtually lower liquefaction potential.
Drainage
Drainage of pore water from consolidating clayey soils can increase overall soil strength. Moreover, consolidation settlements are also accelerated to eliminate future instability problems as much as possible. By installing prefabricated vertical drains, the pore water can be expelled faster than normal. Addition of surcharge preloading or use of vacuum pressure can accelerate the consolidation process even more.
Chemical Treatment
The use of chemical admixtures to improve intrinsic strength properties of the soil and control hydraulic conductivity have also been developed for medium to large scale applications. Problems with swelling soils can also be alleviated by these methods.
Overall, ground improvement techniques have been continuously developing for several decades giving rise to an array of alternatives to choose from. However, selecting the most viable method for a project is not a simple task. Proper technical analysis coupled with expertise honed from years of experience can guarantee that the appropriate technique selected prioritizes safety without compromising financial viability. PGATech maintains a portfolio of well-developed ground improvement technologies that have been applied in different projects across the Philippines with notable success.
Conclusion
At PGATECH Group, we are committed to providing cutting-edge ground improvement solutions that ensure the success of your construction projects. Our expertise and advanced techniques enable us to tackle even the most challenging soil conditions, delivering stable, safe, and sustainable foundations. Check our services for available options or contact us for specific solutions suited to your project. For more information about our ground improvement services, please contact us today
ABSTRACT: Quench Tempered (QT) or Thermo Mechanically Treated (TMT) rebars have crept into the market replacing the Micro alloyed (MA) steel rebars almost completely without the knowledge of the Design Engineering Community as well as the end users.
The proponents of QT/TMT rebars have stated that since these rebars have comparable Physical Test Performance when subjected to Static Tension and bend tests, then it could be a viable and safe replacement to MA rebars without qualification. Herein is where the danger lies, because QT/TMT rebars behave quite differently under Cyclic loading and are also very much affected by heating, welding, bending, galvanizing and threading procedures employed in their use particularly in high rise buildings under Seismic Zone 4.
Advanced countries have warned against these dangers and we believe it is our duty to inform the public and the Profession of the dangers associated with their use in Seismic Zone 4.
In a recent ASEP dialogue with the representatives of the Rebar manufacturing sector conducted together with representatives of the Bureau of Research and Standards, claims have been made that the rebars can be welded and used in high rise buildings under Seismic Zone 4 Conditions. This claim is very far from the truth and at best could only be done so under very strict qualifications. We have asked the Industry representatives to submit proof to prove their claims. This was received 18 March 2010 but still do not offer any satisfactory explanation as to performance under cyclic loading in a severe earthquake environment.
The premature and relatively localized and very limited yield zones of QT/TMT rebars under repeated Cyclic Loadings would result in spalling of the concrete cover in Reinforced Concrete columns and failure of the affected rebars by premature buckling and eventual tension failure of the rebars.
Various studies and research in Italy 2], New Zealand and elsewhere have pointed to the Dangers posed by these rebars when used in Seismic Zone 4.
This paper is aimed at alerting the Engineering Community to the uninformed use of QT/TMT rebars in order to reduce the dangers posed by such usage.
1 INTRODUCTION
The Structural engineering practitioners are faced with problems involving material selection. But nowhere has this been more acute than in the use of reinforcing bars that do not meet design demands in Seismic Zone 4 particularly as it applies to cyclic loading under seismic excitation.
The problems particularly are related to the use of Quench Tempered (QT) or Thermomechanically Treated (TMT) Rebars and accentuated by the noticeable artificial absence of the commonly used and previously available Microalloy (MA) rebars. Thus, the engineering community is deprived of a safe choice and left with a rebar that strongly affects the structural performance and adequacy of our designs in a retrogressive way under cyclic loading.
But first let us try to define each of these processed steel types:
1.1 Quench Tempered (QT) Rebars
The QT or TMT bar is manufactured by rapid cooling of plain low Carbon steel by a fine water spray. The quenched surface is tempered by the heat of the red hot core. This results in a layered steel rebar section with a heat treated outer skin (high tensile strength of tempered martensite and a ferrite/pearlite core with slow cooling inner core. The end result is a steel bar with a higher composite yield and tensile strength than the parent material to start with.
1.2 Microalloyed (MA) Steel Rebars
The micro-alloyed steel derives its strength from alloying materials specifically vanadium and Carbon and consists of a uniform material cross section manufactured from steel billets. The alloys are added in the heat. This is the commonly used Rebar until it suddenly disappeared in the marketplace.
1.3 Comparison of QT/TMT Rebars vs. Microalloyed (MA) Rebars3]
Major research in highly advanced countries have pointed the problems associated with QT/TMT Rebars. This is clearly indicated in the publication by Bothara. 3]
Table 1. Comparison of performance between MA & QT/TMT Rebars
1.3.1 Why have MA Rebars Disappeared in the Market?
Microalloyed rebars began disappearing in the market when most major local manufacturers completely shifted to QT/TMT rebars. In the dialogue with steel Industry representatives and ASEP with BRS, the representatives claimed that Microalloyed (MA) rebars are more expensive to produce because the alloys were expensive. Thus, in the blink of an eye, the public and the engineering design profession were deprived of a “healthy” choice that will not cause endangerment to structures.
1.3.2 Why the Endangerment?
There is a clear and present danger in the use of QT/TMT rebars in Seismic Zone 4 due to the non-ductile behavior of QT/TMT rebars under conditions that are typical or common in local Construction practice.
In addition, there are critical considerations that may be difficult for QT/TMT to meet under various conditions that it will be exposed to, such as Fire exposures and retempering due to inappropriate welding, contrary to the very strict procedures imposed on the welding of QT/TMT rebars, as well as critical outer skin loss when these are threaded for mechanical couplers4.
In addition, Performance in highly critical cyclic Seismic Loading is put to question.
The premature and relatively localized and very limited yield zones of QT/TMT rebar under repeated Cyclic Loadings would result in spalling of the concrete cover in Reinforced Concrete columns and failure of the affected rebars by premature buckling.5] Various studies and research in Italy, New Zealand and elsewhere have pointed to the Dangers posed by these rebars when used in Seismic Zone 4.
This paper is aimed at alerting the Engineering Community to the uninformed use of QT/TMT rebars in order to reduce the dangers posed by such usage.
The author seeks to highlight these problems in order for the engineering community to realize the dangers associated with the use of QT/TMT rebars so that these could be better understood.
2 STATIC STRESS STRAIN DIAGRAM
The static Stress vs Strain diagram of common steels is depicted in the Diagram below. The important thing to consider here is the size of the Yield Plateau or the Ductility of the Steel which is a function of both the TS/YS ratio as well as the % Elongation.
As can be seen from the Diagram at the right, the Yield Plateau initiates upon yielding and propagates almost horizontally. This indicates that straining occurs even without a proportional increase in stress until Strain Hardening sets in and a significant stress increase occurs before reaching the ultimate tensile failure condition which is the peak of the curve. A rapid decay in the stress occurs with decreasing steel cross sectional area due to necking.
A very important consideration is the length of the Yield Plateau represented by the TS/YS Ratio and the % Elongation. PNS 49 requires a minimum TS /YS Ratio of 1.25 as most other International Codes in high Seismic Risk areas. In addition minimum elongation values required are 12 % to 16 % for Weldable Steel. In addition, a cap of 540 MPa is placed on the yield Strength of Weldable steel bar for Grade 415 W Steel.
Why is there a cap on the Yield Stress?
There is a cap of 540 MPa on the yield stress for Grade 415 steel rebar in order to ensure that yielding will occur on the steel first before the concrete. Otherwise, concrete failure which is an explosive type of failure will occur contrary to the expectations of the designer.
3 WHAT INTERNATIONAL CODES SAY
NZ Standard 3101:2006 Concrete Structures Part 1 Section 5.3.2.2 “Restrictions on in-line quenched and tempered process shall not be used where welding, hot bending, or threading of bars occurs.”
“It is important to note that any process involving heat e.g. Welding, galvanizing and hot bending adversely affect the mechanical properties of quench and tempered reinforcing bars by modification of the microstructure.
NZ Standard 3101:2006 Concrete Structures Part 2 Section C-5.8.2 In Line quenched and tempered steel bars Welding of in-line quenched and tempered bars can have detrimental effects on the strength and ductility of the bars and associated connection. AS 3600 requires designers to assume that the strength of such reinforcement has a design strength of 250 MPa when raised to the temperature associated with welding, galvanizing or hot bending. Such a requirement is considered inappropriate in a seismically active country where concentration of yielding at a weld position would be undesirable and could result in brittle failure. (Empasis by author)
4 THE PROBLEMS ASSOCIATED WITH QT/TMT BARS
4.1 Local Studies Presented by PISI 6]
In a written communication by the PISI dated February 10, 2010 7] addressed to ASEP, a report by MIRDC 8] was attached and furnished to ASEP in response to the ASEP request during the dialogue.
In the attached report, it was concluded that the QT/TMT rebar’s TS/YS ratio “is attainable” (NOT Categorically COMPLYING) as results indicate that the rebars tested are marginally lower than the minimum 1.25 Ratio required in most instances.
The abstract8] summarizes the study and which we quote verbatim as follows:
“Characterization of Locally manufactured Tempcore Steel reinforcing steel bars (rebars) produced by the QST process was undertaken to ascertain its mechanical properties in relation to established standards as well as meet requirements of structural Engineers. Different sizes of Tempcore rebars gathered from two local manufacturers were subjected to chemical analysis, tensile testing and metallography on the as- received, heat treated and welded basis. Locally produced Tempcore rebars can be manufactured to meet established domestic standards particularly on meeting a tensile to yield (TS/YS) ratio of ≥ 1.25. Yielding characteristics as required by structural engineers can be satisfied by Tempcore Rebars. Heating at temperatures up to 500 degrees C does not affect mechanical properties, although increasing this Temperature to 700 Deg C reduces the Yield and tensile Strength. Although CE values may indicate weldability, inconsistent properties may be obtained for smaller sizes of rebars. The use of AWS E 10018 produces better properties on welding of Tempcore rebars than using the more commonly available AWS 7018 Electrodes. Stress relieving after welding improves mechanical characteristics of Tempcore rebars.” (Underlining by author)
The test results and studies made on static tensile tests and do not include cyclic loading conditions.
4.2 Welding Associated Problems
“Welding of any kind to QT steel will reduce its strength and must not be attempted. The welding temperatures far exceed 700oC in most common instances leading to distempering of the rebars.
Welding of QT Grade 500E steel should not be allowed under any circumstances. This includes welding of bars to achieve electrical continuity. For such applications, it is unlikely that Grade 500E steel will be required and other more weldable steels should be chosen.4]
In summary, designers should not rely on welding of Grade 500E steel and fabricators/contractors should not allow welding of this material.9”
Welding a Quench and Tempered (QT) reinforcing bar raises the steel above the temperature it was tempered at and without the controlled quench and temper process it will cool slowly back to ambient temperature. Through this cycle it will lose the strength of its external case and revert back to steel with much lower yield strength. Micro-Alloy (MA) weldable reinforcing steel can be welded such that it maintains its ductility and its strength using ordinary E70XX Electrodes.
CONCLUSIONS IN NEW ZEALAND STUDY 9]
Q&ST Grade 500 reinforcing can not be welded without strength loss. It is recommended that a suitable warning be added to the Standard to this effect. This is covered in the amendment to NZS 3101(7)
The standard implies that lap welds are possible with Grade 500E but testing suggests that lap welding to the Standard specified requirements does not provide a sufficient margin against failure of the weld before failure of the bar(2). This is addressed in NZS 3101, however, it is recommended that appropriate amendments also be made to AS/NZS 1554.3 to warn specifiers/designers/constructors of the likely performance of this detail
The Standard implies that butt-welding of Grade 500 E reinforcing steel is possible but is silent on the performance expected. Discussion at the recent seminars on Grade 500E reinforcing steel indicated that currently there may not be a suitable welding electrode available to provide confidence that failure will always occur in the steel rather than the weld when the bars are at the higher end of the maximum tensile strength range allowable in AS/NZS 4671 and the bars containing the weld are required to yield at over strength. Although this issue is covered in the amendment to NZS 3101, it is essential that it is also addressed in AS/NZS 1554.3 as butt-welds complying with the Tables in this Standard are deemed to be pre-qualified and could be assumed to be capable of developing the strength of the bar, unless warnings are given to the contrary.
4.3 Results of the MIRDC Study
The results of the MIRDC study by Dr. Fudolig10] kindly furnished by PISI for ASEP Consideration indicates results that clearly show the mechanical performance of welded QT/TMT rebars using two Electrode types on different rebar Diameters.
Table 6 above from the MIRDC study11] shows the reduction in the Tensile strength and yield strengths and corresponding TS/YS ratio for welded joints for both AWS 10018 and AWS E 7018 Electrodes Types. What is more critical is the observable marked reduction in % Elongation for most of the rebars whether welded with the more expensive E 10018 Electrodes or the Standard E 7018 Electrodes.
The % Elongation results for the welded joints would not meet the requirements of PNS 49 2002 12for Grade 415 W Weldable Steel, which require a minimum range of 12 % to 16 % Elongation under a Static Tension test. A lack of elongation limits the straining region resulting in premature spalling and failure of the concrete cover in turn leading to premature buckling and eventual tensile failure.
4.4 But where is the Economy?
The savings obviously accrue only to the manufacturers as the cost of producing QT / TMT rebars is very much less than MA rebars. However, this does not translate to savings to the end user as the cost of welding and the required welder skills are much more stringent than ordinary MA rebars if the correct procedures are followed, even then it does not guarantee adequate performance.
We again cite a passage in the Report by Dr. Fudolig (Ref 9) as follows:
“The choice of AWS E10018 is based on D1.1-94. The use of this kind of electrodes is also recommended for Tempcore rebars. It must be noted that AWS E 10018 electrodes are not readily available in the Philippines. The more commonly used electrode for welding of rebars, particularly for conventional type of rebars, is AWS 3 7018, which are also locally produced. Furthermore, cost of ASW E 10018 in the local market is seven (7) times that of AWS E 7018.”
So where is the economy? Even if the Tempcore bars could be allowed for use, the necessary technical welding skills as well as the special electrodes required (which do not even guarantee satisfactory performance) for QT / TMT rebars would provide an insurmountable barrier for its safe usage in general construction in Seismic Zone 4.
4.5 Tack Welding
“Tack welds can be seen as almost insignificant to the site operative. They simply help to add stability to a cage, or facilitate placement. However, placement of weld material on Grade 500E steel (Microalloyed or QT) may well lead to premature failure of the rebar. The tests at Auckland University support this. Reported failures of bars include those due to application of welding and due to inadvertent damage from gas cutting equipment.3] The Department strongly recommends against any tack welding of Grade 500E steel, and urges vigilance by designers, fabricators, contractors and inspectors to avoid damage that could jeopardize the safety of the structure.” 3]
“Q&ST Grade 500 reinforcing cannot be welded without strength loss. It is recommended that a suitable warning be added to the Standard to this effect. This is covered in the amendment to NZS 3101. 4]´”
4.6 Bending problems
Bending of Grade 500 MPa rebars will require that it must be heated if it is to be straightened or re-bent. Straighthening the steel cold will result in work hardened areas reducing the bars ductility just where it needs it when an earthquake happens. To re-bend Grade 500 the steel must be heated 700-800 degrees Celsius which is above the temperature at which QT reinforcing cannot be heated without losing its strength. It is important to note re-bending steel is a specialist process and must be carried out to steel manufacturer’s specifications.
The melting Temperature of steel is over 1500 degrees Celsius well beyond the temperature at which QT starts to lose its strength. Welding of course involves heating steel up to and beyond its melting Temperature and so welding is an obvious problem for QT steel if full strength is to be maintained. 3]
It is important that a QT bar is not heated above its tempering temperature. If it is, the outer strong casing will be tempered and revert to the same properties as the internal core and the bar will be significantly weakened. The temperature that this change starts to occur is as low as 450 degrees Celsius. An MA rebar on the other hand will not change if heated to the same temperature.
The common processes that occur above tempering temperature are hot bending and of course welding.
C8.5.2 NZ Standards:
“Welding of in-line quenched and tempered bars can have detrimental effects on the strength and ductility of the bars and associated connection. AS 3600 requires designers to assume that the strength of such reinforcement has design strength of 250 MPa when raised to the temperatures associated with welding, galvanizing or hot bending. Such a requirement is considered inappropriate in a seismically active country where concentration of yielding at a weld position would be undesirable and could result in brittle failure.
4.7 Heating High-strength and Heat-treated Steels
The effect of elevated temperatures on high strength and heat-treated steels should be thoroughly investigated. For example, quenched and tempered materials will undergo radical changes in their mechanical properties as well as toughness when subjected to temperatures above 260 degrees C (500 degrees F).
Grade 500 MPa reinforcing steel must be heated if it is to be straightened or re-bent. Straightening the steel cold will result in work hardened areas reducing the bars ductility just where it needs it when an earthquake happens. To re-bend Grade 500 the steel must be heated to 700 – 800 degrees Celsius which is above the temperature at which QT reinforcing cannot be heated without it losing strength. It is important to note re-bending steel is a specialist process and must be carried out to the steel manufacturers specifications.
4.8 Use of Couplers and Threading
Cutting a thread in a MA rebar and a QT rebar will yield different results. Because the MA bar has the same strength and ductility properties across its cross section the loss in strength of the bar is proportional to the amount of steel lost in the thread cutting operation. A QT bar on the other hand gains its strength from the hard quenched casing so cutting a thread into this outer casing will mean that the loss in strength is not proportional to the amount of steel which is removed.
“Threading of quench and tempered bar removes some to all the Hardened outer layer resulting in a disproportionate loss of strength.”
4.9 Performance at Elevated Fire Temperatures
Reinforced concrete buildings are exposed to the elevated temperatures during a fire event. Most often the elevated temperatures exceed 500 Degrees Centigrade. Unfortunately this is also about the tempering temperature of QT / TMT rebars. Thus, prolong exposures to elevated temperatures could result in retempering of the outer skin resulting in reversion to the strength of the core steel which is vastly reduced.
Thus, accelerated failure of the RC Building frame during a fire is more likely for a building designed using the Yield and tensile Properties of a QT / TMT rebar whether knowingly or unknowingly.
All the foregoing considerations point to the serious problems associated with the use of QT/TMT rebars where welding, bending, heating, threading and galvanizing temperatures are involved.
What is more compelling is the degraded performance during Cyclic Loading conditions in an Earthquake.
5 SEISMIC PERFORMANCE CONSIDERATIONS
Although, the foregoing are important considerations, the main argument against the use of QT/TMT Rebars in Seismic Zone 4 is its behavior under cyclic loading. Studies in several parts of the world notably Italy, New Zealand and Australia etc have pointed to the dangers associated with the use of QT / TMT rebars under Cyclic loading particularly in Seismic Zone 4.
These do not even include the unsuitability of the same bars when welded under cyclic loading which as the MIRDC study shows, indicate a very limited elongation of the rebars when welded and subjected to static tensile tests.
In a study by Macchi [Ref. 2] a large full scale RC specimen was subjected to cyclic loading to check the ductility of Traditional Steel and TMT rebars conforming to Eurocode EC 8 Seismic detailing.
We quote the experimental results as follows:
“With only one exception, all steel A8 (A8 referring to QT/TMT rebars) specimens failed when tested according to sequences….. In fact, all steel A8 reinforcing bars failed before the end of the Test. In many cases, they failed during the first cycle at the maximum required displacement”
“On the contrary, specimens built with steel Fe (referring to Standard MA Steel rebars) behaved satisfactorily.”
“Quite different behavior in the RC Specimens was observed with the two kinds of steel: *With steel A8 (QT/TMT), plastic strains of the bars were concentrated in a very limited vertical region of the specimen. The high local curvature necessary for the required displacement at the top caused a considerable deterioration, leading to destruction of the concrete cover. The lack of concrete cover allowed the bars in compression to buckle. The bars then failed in tension under reverse action.”
*With steel Fe, the plastic deformation spread for a considerable length along the specimen because of the high strain hardening value fu / fy, local curvature was smaller, the concrete cover remained intact and the bars did not fail. The RC member therefore sustained higher top displacement”
6 CONCLUSION AND RECOMMENDATIONS
There is indeed a Clear and present Danger associated with the use of QT / TMT Rebars in Seismic Zone 4 which encompasses the majority of the Philippine Islands except Palawan.
As shown on this paper, even international Codes such as the New Zealand Code and the Australian Standards prohibit Welding, Heating, Bending, Threading and even Tack welding of QT / TMT rebars. Welding can be used but special electrodes which “cost 7 Times more 10] ” are required with the necessary corresponding welding skills, but even then a reduction in the strength is required which prevent its use in Seismic Zone 4. We again cite in its entirety the prohibitions in the New Zealand Standards as follows:
NZ Standard 3101:2006 Concrete Structures Part 2 Section C-5.8.2 In Line quenched and tempered steel bars
Welding of in-line quenched and tempered bars can have detrimental effects on the strength and ductility of the bars and associated connection. AS 3600 requires designers to assume that the strength of such reinforcement has a design strength of 250 Mpa when raised to the temperature associated with welding, Galvanizing or hot bending. Such a requirement is considered inappropriate in a seismically active country where concentration of yielding at a weld position would be undesirable and could result in brittle failure.
So where is the place of QT / TMT is rebars in our practice?
The answer is:
ONLY IN APPLICATIONS WHERE THE ABOVE PROHIBITIONS ARE NOT APPLICABLE AND CERTAINLY NOT FOR HIGH RISE BUILDINGS IN ZONE 4.
7. THE ROAD AHEAD
The structural Engineering Profession and Consultants in General can no longer postpone action on the CONTINUED USE unqualified use of QT / TMT rebars for high rise buildings in Seismic Zone 4.
We must encourage the Philippine Steel Industry through the PISI to again bring the MA rebars in the market by categorically specifying this in our design and categorically stating that QT / TMT rebars are not to be supplied as an alternative in Seismic Zone 4 Building Designs.
The weak argument is that it will increase the cost of rebars. However, the author asks: Is there a Price on Public Safety?
If we do not do this and with the Publication of this Paper and similar papers, the Engineering community is now formally informed of the dangers associated with the continued use of QT / TMT rebars in Seismic Zone 4.
REFERENCES
Macchi G. “Ductility Requirements for Reinforcement under Eurocodes.” Structural Engineering International April 1996.
New Zealand Standard NZS 3101-2006 Amendment 1 –Concrete Structures Standard The Design of Concrete Structures.
Jitendra K Bothara “Comparing Seismic® QT and Seismic® MA, High Strength Bars and Design Considerations”.
PISI Letter of Mr Wellington Tong – President to ASEP
Fudolig,A et al “Characterization of Locally-Manufactured Quenched tempered and Self Tempered Reinforcing Steel Bars” MIRDC Feb 1999.
New Zealand Department of Building and Housing “Report on Grade 500 E Reinforcement” July 2005 Wellington NZ
Bureau of Product Standards, DTI “PNS 49:2002 Steel Bars for Reinforced Concrete- Specification”
ABOUT THE AUTHOR
Emilio M. Morales CE, Principal of EM2A Partners & Co., Master of Science in Civil Engineering, Carnegie Mellon University, Pittsburgh Pa., Fellow ASCE, PICE, and ASEP and a PhD Candidate at the Asian Institute of Technology, Bangkok Thailand.
Formerly Senior Lecturer, UP Graduate Division, School of Civil Engineering, Diliman, Quezon City. He can be contacted at EM2A Partners & Co., No. 17 Scout de Guia corner Scout Reyes Streets, Diliman, Quezon City. Telephone Nos. 371-1804 & 06. E-mail address: em2apartners@gmail.com.
1] Principal EM2A Partners, MS in Civil Engineering , Carnegie Mellon University, Pittsburgh Pa., Fellow PICE, ASEP and ASCE. PhD Candidate Asian Institute of Technology, Bangkok Thailand, Formerly Senior Lecturer, UP Graduate Division, School of Civil Engineering, Diliman. 2] Macchi G. “Ductility Requirements for Reinforcement under Eurocodes.” Structural Engineering International April 1996.
3] Jitendra K Bothara “Comparing Seismic® QT and Seismic® MA, High Strength Bars and Design Considerations”.
4] New Zealand Standard NZS 3101-2006 Amendment 1 –Concrete Structures Standard The Design of Concrete Structures. 5] Macchi G., “Ductility Requirements for Reinforcement under Eurocodes.” Structural
6] Philippine Iron and Steel Institute. 7] PISI Letter of Mr Wellington Tong – President to ASEP 8] Fudolig,A et al “Characterization of Locally-Manufactured Quenched tempered and Self Tempered Reinforcing Steel Bars” MIRDC Feb 1999.
9] New Zealand Department of Building and Housing “Report on Grade 500 E Reinforcement” July 2005 Wellington NZ
10] Professional Waiver kindly granted by Dr. Fudolig of MIRDC. 11] Fudolig A. et al – “Characterization of Locally-Manufactured Quenched Tempered and Self Tempered Reinforcing Steel Bars” MIRDC Feb 1999.
12] Bureau of Product Standards, DTI “PNS 49:2002 Steel Bars for Reinforced Concrete- Specification”
ABSTRACT: Several significant failures of Civil Engineering Projects ranging from catastrophic to functional failures have been investigated involving structures or structural components.
The causes of these failures have been studied and as a result, remedial measures were implemented. The failures were caused either by design oversights, construction deficiencies and sometimes error in the computerized Analyses and Design Procedures. The cases highlight the need for a greater degree of care and vigilance in the analysis, design, checking and construction of Civil Engineering Projects.
The lessons learned could be put to good use in avoiding the recurrence of similar problems in the future.
For reasons that are obvious, names and some details about the projects have been changed. Any reference to a real person or organization is unintended and purely coincidental.
INTRODUCTION
Failure of Civil Engineering Structures could mean several things. It could be a catastrophic failure or collapse, it could be a loss in functionality or it could mean a degradation in the serviceability of the building to a level that would be uneconomic to maintain.
In the course of the practice of the Profession, Civil Engineers are often exposed to problems in Design and Construction whether done by other professionals or organizations or by the professional himself or his organization. These problems often could result in damage to person or property and involve time consuming litigation. Learning from the past or the mistakes of the past certainly could help the practicing Engineer in avoiding such problems.
It is the intention of this paper to highlight several failures investigated by the author. This paper discusses the failure, the verified causes of the failure, the remediation aspects recommended and the potential cost or damage to parties involved.
For obvious reasons, the names of the persons or organizations involved have been withheld or changed as well as the actual project names.
The intention in presenting these experiences is to aid the profession in recognizing that failures can and do occur in the real world. Experiences of the past are a reliable reference and source of knowledge in avoiding the recurrence of similar accidents.
1.0 CASE STUDY NO. 1 – ROOF FRAMING SYSTEM COLLAPSE
1.1 Background
A large area warehouse being constructed for XYZ Company had a serious accident. The Roof Trusses fell in Domino Fashion while these were being erected. The accident caused several fatalities, mostly from workmen who were painting the Trusses as these were being erected.
The cause of the accident was immediately attributed to the Erection Crane Boom hitting the front truss resulting in the “Domino” like failure. Subsequent investigation, while accepting this as the immediate “Trigger” to the failure detected several other deficiencies in construction that led to the catastrophic collapse.
It is noteworthy to mention that deficiencies in the design, although not generally contributing to the failure were noted. What is surprising is that these deficiencies were cancelled out by an error in the computer analyses. Thus, a defective design was rendered “Safe” by a compensating error. The result was a “Safe” design by accident! The general contractor was a reputable company who subcontracted the services of a steel fabricator with very limited experience in structural steel erection. Geometry of the individual trusses also contributed to the collapse as well as substandard procedures employed during the erection.
1.2 The Accident
Almost 24 Bays of the Building had received the trusses and purlins were already being installed. Due to the critical schedule, the trusses have been erected only with a primer shop coat. Final painting was being done atop the trusses by several painters as these are erected.
The bottom chords were inadequately braced by light gage “C” purlins doubled into a box section by stitch welding.
Several of the workmen painting atop the Trusses fell and were pinned down by the collapsed steel trusses resulting in several deaths.
Immediately on the day after the collapse, we were called in to investigate the cause/s of the accident.
The results of our investigation revealed very surprising details contributing to the collapse.
1.3 Investigation
We had to conduct the investigation hurriedly to prevent removal of evidence and in order to interview people involved or have knowledge of the accident. Numerous photographs were taken which served as the incontestable proof of what contributed to the accident. A full peer review of the design was also conducted.
What led to the collapse? Why did the Trusses topple like dominoes? Why was the erroneous design not contributory to the failure? Why did a similar adjacent bent not fail? These and other questions became clear when we completed the investigation.
1.4 Findings
Our findings were as follows:
⦁ Wrong erection procedures resulted in dangerous connections The Subcontractor who fabricated and erected the trusses was not a Structural Steel Fabricator or had very little experience in Structural Steel Fabrication and erection. During the process of erecting the trusses, the trusses became “short” because of Elastic Deflection as the trusses were on two or three point pick up. This resulted in the Trusses to be “bowed” down thus shortening it.
Since the anchor bolts were already cast onto the concrete corbels, the bolt holes on the bearing plates attached to the Truss ends were now out of alignment because of the shortening. In the rush to erect the Trusses, the bolt holes and slots were enlarged to allow the Trusses to be erected.
In most instances, the enlarged holes and slots were wider or larger than the Nuts! Thus, there was no restraint on the Trusses and the anchor bolts were practically useless except a very limited few.
⦁ Truss Geometry contributed to collapse too
The Trusses were designed as simply supported Trusses with a Roller-pin connection at the ends. There were two Gables or Truss bents and Bent ‘A’ was being erected while Bent ‘B’ was already erected. Inspection of the finished Bent ‘B’ showed the same deficiencies and defects.
The figure below shows the unfavorable geometry represented by a triangular shaped truss. Vertically, the system would be “Stable”. However, once there is lateral disturbance, the system failed by toppling progressively.
1. MODEL OF TRUSS SYSTEM2. SECTION AA3. ROTATIONAL MOMENT “M” CAUSED BY TILT OF TRUSS FROM VERTICAL
As can be seen, this unfavorable geometry offered very little rotational resistance when the Trusses were loaded laterally. In some of the Truss ends that did not fall, the Truss ends were restrained by the bolts but toppled on its side just the same because the ends were twisted due to lack of rotational resistance.
⦁ Substandard Horizontal “Struts”
The horizontal bracing or “Struts” for the top and bottom chords of the Trusses used substandard and poor quality construction.
The struts were assembled from two Light Gage “C” purlins which were joined by widely spaced stitch welds. The “Struts” simply buckled progressively as the Trusses Toppled. ⦁ Design made “Safe” Accidentally
There were numerous and sometimes serious design deficiencies noted during the Peer Review process. However, and as earlier stated, the design process did not contribute to the collapse because a subsequent error in the computer program caused by a “Bug” in the software tended to compensate for the underdesigned columns by over designing these!
Thus, the design was rendered safe by a computer bug. Our finding in the peer review revealed that: · The Building would have been grossly underdesigned. The gross deficiency could have resulted in a collapse under design loading conditions had it not been for a compensating error due to the software “Bug”.
The following are the deficiencies:
1. Column Design
Incorrect wind and earthquake loads were used. Wind forces applied to the roof were all positive (Downward) when in fact the governing loads were negative (suction pressures) for the roof pitch used.
The columns were designed using a popular Integrated Structural Analysis and Design Software. The “Bug” tended to overdesign compression members.
Seismic Loading and Building type classification were entirely wrong . Gross underestimate of the base shear resulted in a 60% reducting in Seismic Loading. The building was classified as an OMRSF – Ordinary Moment Resisting Space Frame which for a concrete structure is prohibited by the code in Zone 4.
2. Truss Design
The analyses considered that the Truss members were rigidly connected yet the Trusses were designed as axially loaded members only, totally neglecting the moments.
The saving grace was that for the Bottom Chord and also the Top Chord, only the maximum stress was used in the design. Similarly for the web members, only very limited stress values were used. While the analyses veered towards underdesign, the resulting over simplification in the design tended towards overdesign except for a few members.
This cancelled out the problem but resulted in a very heavy and expensive roof truss. The resulting overdesign due to simplifications and accidental errors resulted an increase in the Truss weight by 30%!
3. Height Structure
The height of the structure as used in the analyses and design was 10.0 meters. The actual height was 15.0 meters.
It can not be ascertained when and at what point was the height changed. This should have automatically triggered a redesign.
4. Concrete columns considered as purely axially loaded members
The computerized Analysis Loading Diagram clearly showed that the Truss reactions were co-axial with the column centerline.
In actual fact, the trusses were supported on 500mm corbels and hence induced bending moment on the columns.
This could have resulted in an underdesign of the columns if not for the “Bug” in the computer program.
5. Overall Roof Framing System is Inefficient
The Roof Framing System adopted consisted of two Truss Bents resting on corbels in a Roller/Pin connection detail as shown below:
Thus, the Truss Bents could not participate efficiently in carrying lateral loads and redistributing loads as these are essentially simply supported elevations. Thus, there are no redundancies in the structure nor alternative stress paths in case of overstress.
The Roof Framing System adopted consisted of two Truss Bents resting on corbels in a Roller/Pin connection detail as shown below:
Thus, the Truss Bents could not participate efficiently in carrying lateral loads and redistributing loads as these are essentially simply supported elevations. Thus, there are no redundancies in the structure nor alternative stress paths in case of overstress.
1.5 Lessons Learned
Erection is a critical operation requiring care and experience. It can not be entrusted to inexperienced contractors.
The use of torches to enlarge the anchor bolt holes should not be allowed at site without adequate technical supervision.
Use of substandard struts and purlin connections allowed the collapse to propagate to adjacent trusses.
Unstable truss geometry allowed the collapse to become a total system failure.
Although the design was not the cause of the collapse, gross oversights and deficiencies occurred such as:
Errors in loading assumptions
Computer code errors were unchecked
Wrong computer modeling
Lack of peer review checking procedures
2.0 CASE STUDY NO. 2 – ALTERNATIVE DESIGN RESULTED IN DEFECTIVE STRUCTURE
2.1 Introduction
Our firm was engaged to design a large Industrial Complex for ABC Company. Part of the Complex was a large area warehouse with a floor area of approximately 4.0 Hectares (40,000 sq.m.).
When the project was bid, the low bidder offered an alternative design build proposal which was P20M lower than their offer using our design.
Because of the potentially huge savings, the owner opted for the alternative design build proposal.
This proved to be a mistake!
2.2 Problem Detected
Six months into the construction and when 4 hectares of purlins have already been laid and all structural framing are waiting only for the roofing and cladding installation, the owner’s Project Engineers noticed deflections in the purlins and trusses based on pure deadweight alone. The owner had to engage our services again to conduct a peer review of the Contractor’s design.
Subsequently, a professional waiver was obtained from the Contractor’s Engineers for us to undertake a professional design review.
2.3 FINDINGS
A study of the design calculations and loading data revealed very startling facts.
1. Wind pressures used were very much below Code values and neglected exposure factors due to location which would have further increased the wind pressures and in some locations uplift pressures would have been doubled.
Note: The warehouse is situated along a flattened slope fronting the sea. Exposure factors for this should have been Ce=1.51 for Exposure Category D.
In some critical areas, wind load was inadvertently not considered.
2. The computational model used by the Contractor’s Engineer resulted in a collapse mechanism as all the joints for the columns were “pin” connections as well as the truss to column connections. This is statically inadmissible.
Lateral loading in the computer analyses would have already triggered or signaled a “Fail” condition but this was missed or was neglected.
Fortunately, in actual construction, the column anchorage connections indicate that it is “semi-fixed” condition as the anchor bolt details are not indicative of a pinned connection.
3. Loading assumptions used in design were 50% lower than code provisions. This would have directly resulted in a structure that would also be underdesigned by this magnitude. However, other errors contributed to a gross underdesign. Seismic loading (although not significant) was entirely neglected.
2.4 As Constructed Members Deficient
As a result of the foregoing erroneous assumptions and incorrect modeling of the structure geometry and fixity conditions, the following were our findings:
Truss members were grossly inadequate for the actual design loads.
Columns now with partial fixity assumed in the peer review were “safe”.
Purlins exceeded allowable stress limits by as much as 100% and violated deflection limitations.
Wall furrings exceeded allowable stress limits by 100%.
Truss carrier girders were designed based on unrealistic slenderness ratios resulting in underdesigned members
2.5 Software Bug Contributed to Error
In the course of our review, we noted further that the allowable stresses for compression members used by the Contractor’s Engineer were relatively high compared to our computer results.
We were using the same program but the Contractor’s Engineer used a newer version (Ver. 22) and we used an older but licensed version.
We then proceeded to calculate the allowable stresses in compression by hand and we were able to verify that our calculations were correct.
Still, the Contractor’s Engineer was insistent that their calculations were correct considering that they were using a newer version! In order to resolve the matter, we wrote an official letter of inquiry to the Software company. They immediately replied by admitting to a bug when they revised the new version! This finally laid matters to rest. We provided a copy of our findings to the Owner and Contractor’s Engineer.
2.6 “Value Engineering” Turns to Financial Disaster
As a result, 4.0 hectares of already erected purlins were totally removed and replaced. We prepared remediation measures for the trusses by providing cover plates for all overstressed members and beefed up the longitudinal bracing and carrier girders. The exercise proved to be a costly one, both for the contractor and the owner.
The owner suffered 2.5 months of delay in the project. They were also forced to hire outside storage space for sensitive electronic equipment and controls for the industrial plant.
The contractor suffered a huge financial loss. Defective purlins covering an area of 4.0 hectares were totally removed and replaced. Expensive reinforcement coverplating operations involving overhead welding work were performed on the trusses while these were on temporary supports.
We are not aware if the owner slapped penalties on the contractor.
2.7 Lessons Learned
Computer programs can not be given blind trust.
Entrusting design to inexperienced Junior Engineers could result in disaster.
Oversights in the interpretation of code prescribed loadings and exposure factors was a major contributor to the problem.
Proper in-house review could have already detected a statically inadmissible collapse mechanism but this was not detected at all until it was too late.
3.0 CASE STUDY NO. 3 – NEAR PANIC CAUSED BY WRONG DETAILING
3.1 Introduction
This failure was not as significant financially or technically as the Near Panic it raised. The remediation nevertheless proved to be costly.
The project is an ultra hygienic sanitary facility for the manufacture of infant formulation. The facility is for spray drying liquid milk to powder form.
Entry is strictly limited requiring gowns, head covers, removal of wrist watches and eye glasses, use of disposable shoe socks and alcohol hand washing.
The facilities manager was in near panic when black stains were found between the column/masonry joints. It was immediately suspected as Bird Droppings as the blackish color would indicate. Bird droppings is the most common source of the dreaded “Salmonella” bacteria. Any reported occurrence could have required a total prolonged shutdown and sterilization of the Seven Storey Spray Drier Tower.
We were called in to provide consultation. We inspected the location and true enough, we verified the presence of black stains along the vertical joints between the columns and masonry wall. This was very alarming indeed having been briefed about what would be the repercussion when “Salmonella” is detected in an otherwise ultra hygienic facility.
3.2 Instant Problem Identification
We immediately proceeded to the Engineering office of the manufacturer to look at the As-Built Plans. What we saw immediately identified the problem. The problem is explained by the sketch:
A clear study of the detail above clearly showed that the joint seal placement was reversed!
The Asphalt Impregnated Mineral Board Compressible Filler was exposed to the elements and the sealant was placed inside. Weathering and exposure to sunlight melted the asphalt and degraded the mineral fiber.
Breaks in the sealant allowed the melted asphalt diluted by water to find its way inside and was initially suspected as stains from bird droppings which equates to potential salmonella infection.
3.3 Remedial Measures
The remedial measures recommended and instituted was simple but very costly. It required removal of these numerous vertical joints throughout the Seven Storey Facility and replacement with proper jointing procedures. This was very expensive for the owner.
3.4 Lessons Learned
Even very simple and seemingly innocent mistakes in small details could cause problems if not checked by a built in checking and review process.
4.0 CASE STUDY NO. 4 – SINKING OR RISING?
4.1 Introduction
A very large specialty packaging materials printing plant was constructed partly on cut and partly on fill. Two thirds of the plant was resting on compacted fill material.
A very expensive four color offset printing equipment costing tens of millions of pesos was installed. The offset machine consisted of four presses connected by a drive rod about 35mmØ. The machine sits on a thick mat foundation integrated with the floor slab. The offset machines required very small tolerances and any misalignment horizontally or vertically would be intolerable as it would result in inexact color laying and printing.
Soon after commissioning, the printing machinery was wasting a lot of expensive rolls of materials due to misalignment. Corrections were periodically being made but the problem became worser with the passage of time until production was totally stopped for this machine. The whole production schedule was in jeopardy.
The Building footprint was surrounded on two sides with depressed areas that ponded water during heavy rains due to inadequate drains.
4.2 The Problem
The owners as well as the foreign equipment supplier immediately suspected settlement as the probable cause.
We were invited to visit the site in order to look at the problem.
What we saw was contrary to the owner’s suspicions as the machinery was actually rising and not settling!
When we informed the owner about our initial findings he could not believe what he heard. Nevertheless, he engaged our services to prove it and recommend remedial measures.
4.3 The Investigation Program
We recommended a fourpart investigation program (subsequently accepted) consisting of:
Undertaking Elevation Survey (Topographic) of the immediately affected area.
Undertaking five shallow test pits to extract soil samples.
Performance of laboratory testing to determine swelling characteristics and swell pressure of extracted soil samples.
Study of surrounding terrain and drainage areas.
The results of the investigation program were formalized in a report including our remediation procedures.
4.4 Results of the Investigation
The investigation results corroborated our initial findings. The Topo Survey confirmed that the slabs were indeed rising and dragging the equipment up.
A section through the longitudinal and transverse axes of the equipment revealed the vertical heaving of the slabs as well as the equipment foundation without a doubt.
The laboratory tests also essentially proved the swelling tendencies of the soils. Most of the Fill material underneath the slabs classified as CH/MH with LL>55 PI>25. The swell potential is from medium to high with swell indices as high as 10 in most cases.
Generated swell pressure in confined swell tests indicated a swell pressure of 744 psf (35.6 kPa). Based on calculations, this swell pressure alone would not have been sufficient to lift the heavy mat foundation. Therefore the question: why did it rise? became a priority to be answered.
Inspection of the floor slab and equipment foundation gave the answer. The floor slab was connected to the equipment foundation and were cast monolithic with rebars being continuous. This provided a connection to the slab. When a large area of the slab was heaved, the large force accumulated was sufficient to pull the machine foundation upward. The problem is illustrated below:
4.5 Mechanism of Failure due to Heaving
4.6 Remediation
4.6.1 Background
The slab distress definitely has been caused by Swelling/Heaving and it is only necessary to establish by what mechanism this has occurred in order to come out with proposals to solve the problem.
It must be understood that any solution of total removal of the swelling soils would not entirely eliminate the swell potential.
In addition, the presence of entrapped water in the form of Natural Moisture Content of the existing soils, which is relatively high based on laboratory test on test pit samples, could trigger further settlements. This is still possible even if remedial intervention.
4.6.2 Water Saturation by Ponding
The drainage of surrounding low lying areas around the plant is impeded or prevented by the absence of adequate drainage structures and outlets. Thus, surface runoff accumulates and the surrounding areas become a detention pond which saturates the area.
Water has a natural tendency to migrate from hot to cold areas. Since the plant footprint is shaded by the roof, insulated by the floor slab and is well ventilated, the underlying soils are definitely cooler inside than outside the plant footprint.
Thus, a thermal gradient is set up and water follows this gradient. The attractive forces are greater than gravity forces, and therefore water can rise up also aided by capillary action as to cause Swelling of the Highly Plastic Soils (CH/MH).
4.6.3 Mechanics of Swelling Soils
Since expansive soils are characterized by very fine granulometry and thus large surface area to mass ratio, it has a great affinity for water. Water is captured and absorbed by the water and held tightly with great attractive force.
The absorbed and adsorbed water increases with further attraction and volumetric expansion as swell occurs. Since the affinity due to powerful electrical and chemical forces of attraction is great, the expansion generates tremendous pressure when confined or restrained. This results in high swell pressures that could lift lightly loaded slabs or machine foundations.
Therefore, the key to further swelling is the presence of water. Since the swelling process is reversible in a sense, alternate wetting and drying as would occur during periods of rain and drought would cause shrink and swell, shrinkage causes collapse of the soil structure and therefore aggravates and accelerates pavement deterioration.
Based on this, it is also necessary to attain equilibrium of moisture condition to prevent seasonal and cyclical volumetric changes.
Thus, the primary direction for the solution of problems related to swelling soils, if the swelling soil can not be removed and replaced is:
Elimination of sources of water
Maintenance of moisture equilibrium within the critical area which in this case is the plant footprint.
4.7 Proposed Remedial Measures
We have divided our recommendations on the mitigation and prevention of further swell damage to most urgent and immediate.
4.7.1 Most Urgent
We have recommended the cutting or uncoupling of the accidental connection or friction joint between the slab and the machine bases.
We also recommended that the general floor slab be uncoupled or connections cut along the perimeter and interior walls. This would be necessary to release the restraint which could cause further cracking of the slab.
The cut was done by a diamond cutting wheel. The cut was then sealed by elastomeric sealant that is solvent and oil resistant.
4.7.2 Immediate Solutions
Elimination of Sources of Water
Swales and ponded areas were regraded to divert water from the plant footprint. Backfill was compacted after the subgrade has been cleaned and grubbed and also compacted to 95% MDD based on ASTM D-698.
Effective drainage away from the site was implemented to remove ponding and detention of water.
Roof drains and collectors (RCP Pipes) near the plant perimeter were decommissioned and replaced by lined ditches at least 2.0 meters away from the plant footprint. This will ensure that any leaks or breaks are clearly visible. The downspouts now drain directly into these trenches.
Footpaths along the Building perimeter have reversed slopes due to Swelling allowing water to seep into the building. These were reconstructed by additional concrete topping sloping away from the building as shown in Fig. 1.0.
4.7.3 Recommendation for Preventing Further Water Ingress and for Maintaining Moisture Equilibrium
To prevent additional water ingress underneath the Building footprint, it was necessary to provide an impermeable Barrier Wall. The Barrier Wall was constructed as near as possible to the Building perimeter and extended at least 1.5 meter vertically below Finished Floor Line.
This Barrier consisted of an HDPE Liner 2mm thick and with all joints fusion welded to ensure that there are no breaks in the impermeable barrier. The trench was backfilled by Compacted Fill and the top impermeabilized by concrete pavement.
The Schematic Sketch is shown below:
4.8 Lessons Learned
Care should be exercised in the selection and classification of Fill soils underneath structures.
Water ponding around structures should be avoided as these will eventually channel water underneath the structure.
5.0 CLOSURE
There are still other failures that needed to be presented. However, the other cases were caused by the now all too familiar reasons:
Professional Negligence
Computer Error
Inexperience
Construction Oversights and Negligence
Lack of Quality Control, etc
As Civil Engineers, we have the duty to our clients and the public in general to provide safe and functional structures free from defects and complying with regulations. A study of the past certainly is one way of avoiding similar mistakes.
1] Fellow, ASEP, PICE. Took up his masters degree at the Carnegie Institute of Technology, Carnegie-Mellon University, Pittsburgh, PA. USA in 1980. Formerly Senior Lecturer of Graduate Division, College of Engineering, University of the Philippines, Diliman, Quezon City. Presently, he is the Technical Director of PGA Calibration & Metrology Laboratory and PGA Geopier Philippines, Inc., Technical Manager of Philippine Geoanalytics, Inc. Civil Engineering Laboratory and Principal of EM²A Partners & Co. Chairman, Specialty Committee on Geotechnical Engineering. He can be contacted at Tel. Nos. 371-1804 & 06 and 410-2923. Fax No. 374-4338; E-mail address: em2apart@pgatech.com.ph.
The paper is designed to give a clearer perspective of the Liquefaction Phenomenon including the causative conditions that will trigger liquefaction as well as the soil mechanics principles involved.
An understanding of the Geotechnical environment that could be susceptible to liquefaction including the groundwater influence, granulometry including fines content, Plasticity of the fines (LL & PL) and the triggering Earthquake intensity are discussed.
Much of the work have been gleaned from state of the art papers on soil liquefaction such as the “Queen Mary Paper” by Seed et al and references from the USGS website as well as the Authors’ own experiences in evaluation of liquefiable ground conditions have been included in this paper.
Significant advances in the body of knowledge and state of practice in liquefaction evaluation have been published in numerous literature and technical papers. This paper in effect is a compilation and summary of the current State of Practice in liquefaction evaluation and mitigation.
Essentially this Paper is a Literature Review of Current knowledge about Liquefaction. The figures and entries most of the time have been copied verbatim and therefore major credit is due to the sources listed in the references and the authors acknowledge this.
1.0 Introduction 3]
Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world.
Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily move with respect to each other.
Liquefaction has been observed in earthquakes for many years. In fact, written records dating back hundreds and even thousands of years describe earthquake effects that are now known to be associated with liquefaction. Nevertheless, liquefaction has been so widespread in a number of recent earthquakes that it is often associated with them.
Because liquefaction only occurs in saturated soil, its effects are most commonly observed in low-lying areas near bodies of water such as rivers, lakes, bays, and oceans. The effects of liquefaction may include major sliding of soil toward the body slumping and of water.
Earthquake shaking often triggers an increase in water pressure, but construction related activities such as blasting and vibratory pile driving can also cause an increase in water pressure.
When liquefaction occurs, the strength of the soil decreases and, the ability of a soil deposit to support foundations for buildings and bridges are reduced as seen in the photo of the overturned apartment complex buildings in Niigata in 1964.
2.0 The Liquefaction Phenomenon
To understand liquefaction, it is important to recognize the conditions that exist in a soil deposit before an earthquake. A soil deposit consists of an assemblage of individual soil particles.
If we look closely at these particles, we can see that each particle is in contact with a number of neighboring particles. The weight of the overlying soil particles produce contact forces between the particles – these forces hold individual particles in place and give the soil its strength.
To understand liquefaction, it is important to recognize the conditions that exist in a soil deposit before an earthquake. A soil deposit consists of an assemblage of individual soil particles.
If we look closely at these particles, we can see that each particle is in contact with a number of neighboring particles. The weight of the overlying soil particles produce contact forces between the particles – these forces hold individual particles in place and give the soil its strength.
However, when ground shaking occurs, these delicate grain to grain contacts are disturbed and the soils grains are dislodged.
This causes a momentary loss of support which transfers the vertical stresses to the porewater. The pore water in turn further increases in pore pressure thus further buoying up the individual soil grains.
Since water has practically no shear strength, collapse of the support happens and thus all superimposed structures and the soil itself slumps due to gravity.
Much of the previous knowledge of liquefaction attributes this phenomenon exclusively to Clean Sands. However, current State of the art have established that even fine grained soils and coarser materials such as Gravels will liquefy given the right conditions and the right earthquake characteristics. This paper seeks to update our current understanding based on the current State of Practice as gathered from various literatures.
3.0 Types of Liquefaction Related Phenomena
There are several types of liquefaction related Phenomena as Follows (Ref 1.0)
Flow Liquefaction– Flow liquefaction can occur when the shear stress required for static equilibrium of a soil mass (the static shear stress) is greater than the shear strength of the soil when it liquefies. Once triggered, the large deformations produced by flow liquefaction are actually driven by static shear stresses. Flow liquefaction produces the most dramatic Effects.
Flow Liquefaction failures are characterized by the sudden nature of their origin, the speed with which they develop and the large distances over which the liquefied materials often move.
Cyclic Mobility– Cyclic mobility in contrast to Flow Liquefaction occurs when the static shear stress is less than the shear strength of the liquefied soil. It is basically driven by both Cyclic and static shear stresses. The deformations produced by cyclic mobility failures develop incrementally during earthquake shaking. A special case of cyclic mobility is level ground liquefaction.
Because horizontal shear stresses that could drive lateral deformations do not exist, level ground liquefaction can produce large chaotic movements, known as ground oscillation during earthquake shaking but produces little lateral soil movement.
Level Ground failures are caused by the upward flow of water when seismically induced excess pore pressures dissipate. Excessive vertical settlements and consequent flooding of low lying land and the development of sand boils are characteristic of level ground liquefaction.
4.0 Liquefaction Susceptibility 2]
Liquefaction Susceptibility is determined by the grain size, fines content (LL), the presence of groundwater, the static state of stress as well as the characteristics (amplitude and length of time of propagation) of the triggering Earthquake Magnitude that could induce adequate ground shaking.
The following are the criteria for identifying possible liquefaction susceptibility:
4.1 Historical Criteria
Soils that have liquefied in the past can liquefy and liquefaction can recur in these same soils when soil and groundwater conditions have not changed. Thus, liquefaction case histories in a particular site can be used to identify specific sites or general areas that are susceptible in future earthquakes.
4.1 Compositional Criteria
Liquefaction susceptibility is influenced by the compositional characteristics that influence volume change behavior. Compositional characteristics associated with high volume change potential tend to be associated with high liquefaction susceptibility. These characteristics include particle size, shape and gradation and % fines.
For many years, only sands were thought to liquefy. Finer grained soils were considered incapable of generating the high pore pressures commonly associated with liquefaction and coarser grained soils were considered too permeable to sustain any generated pore pressure long enough for liquefaction to develop.
However, present day experience on recent liquefaction events, suggest otherwise. More recently, the bounds on the gradation criteria for liquefaction susceptibility have broadened.
The most important work was done by a team headed by R.B. Seed (Ref 2.0) in their seminal paper delivered at the HMS Queen Mary, on April 30, 2003.
Although previous work have been done by the Chinese in 1979, the Queen Mary Paper further moved it several notches to reflect current recorded liquefaction events.
State Criteria
Even if the preceding criteria are all met, it still may or may not be susceptible to liquefaction. Liquefaction susceptibility also depends on initial state of the soil (i.e. its stress and density characteristics at the time of the earthquake).
Since the tendency to generate excess pore pressure of a particular soil is strongly influenced by density and initial stress conditions, liquefaction susceptibility depends strongly on the initial state of the soil.
5.0 Initiation of Liquefaction
Procedures to determine the initiation of liquefaction have now been updated beyond the understanding before the publication of the Queen Mary Paper.
5.1 Cyclic Stress Approach
Research on the on the advances of present day knowledge on Liquefaction was started by H.B. Seed and continued and refined by the son, R. B.
This general approach came to be known as the “Cyclic Stress Approach” as expounded by Seed, the elder.
Seed, initially leading to the determination of the loading conditions that could trigger liquefaction. This loading was described in terms of cyclic shear stresses and liquefaction potential was evaluated on the basis of the amplitude and the number of cycles of earthquake induced shear stresses.
The improvements came in a more reliable prediction of the non-linear mass participation factor rd as well as the reduction in the peak cyclic stress ratio (CSR).
This CSR has since been modified by R. B.Seed et al as follows:
Recommended NOMOGRAPH for Probabilistic SPT based Liquefaction Triggering Correlation for Clean Sands 3
6.0 Effects of Liquefaction
Liquefaction can induce landslides or collapse of structures, including horizontal infrastructures.
Sand boils can be induced when the excess pore water pressure dissipates by exiting into the ground surface bringing with it fine sand particles much like an erupting volcano.
Ground motion characteristics are also altered after liquefaction when originally stiff soils are altered by positive excess pore pressures. A liquefiable soil that is relatively stiff before may be much softer at the end of liquefaction. Thus, the amplitude and frequency of the soils may change considerably.
This can cause increase in Ground motion and can produce large displacements.
Damage to horizontal and vertical structures can occur depending on the type of liquefaction whether Cyclic Mobility or Flow liquefaction.
Dams and slopes are very vulnerable to flow liquefaction because the static stress is highly influenced by gravity forces and large lateral spreading occurs.
Cyclic mobility on the other hand occurs mostly on level ground with very little or no lateral spreading. The main effects are on vertical structures which can settle significantly or tilt and collapse when loads are imbalanced or where the soil stratification is uneven.
7.0 Liquefaction Mitigation Methods
A lot of mitigation techniques are currently available which have been used as ground improvement methods to improve strength or reduce deformations. While not covered in this paper, the methods are enumerated for Brevity as this may not be covered in this Paper.
The author’s hope that a clearer understanding of the liquefaction phenomenon has been presented to the local Engineering community. Most of the contents of this paper have been directly extracted from the listed references as well as the Author’s own experiences in the evaluation of liquefaction problems.
It is suggested that further readings by the Professional are needed in order to achieve a full understanding of the liquefaction phenomenon. This is something which cannot be achieved within the limitations of time and space for this paper.
References
Kramer, S. “Geotechnical Earthquake Engineering “Prentice Hall, New Jersey 1995.
Seed, et al. “Recent Advances in Liquefaction Engineering: A Unified and Consistent Framework” 26th annual ASCE Los Angeles Geotechnical Spring Convention.
University of Washington Liquefaction Website http://www.ce.washington.edu/~liquefaction/html/main.html
Lade et al “Physics and Mechanics of Soil Liquefaction” A.A. Balkema, Rotterdam 1998.
1 Emilio M. Morales, MSCE took his Master of Science in Civil Engineering at Carnegie-Mellon University, Pittsburgh, PA. USA in 1980. He was employed as a Project Geotechnical Engineer and Software Engineer at D’Appolonia Consulting Engineers. Currently, he is the Principal of EM²A Partners & Co. and formerly elected as President for IGS Philippines, Chairman for the PICE & ASEP Specialty Committee. He is a Fellow of ASCE, PICE & ASEP.
2 Mark K. Morales, MSc took his Master of Science in Civil Engineering Major in Earthquake Geotechnical Engineering at University of California – Berkeley, USA in 2004. He is the Technical Manager of Philippine Geoanalytics, Inc. and CEO of PGA Earth Structure Solutions Inc. (PGAESS) a specialty foundation and Geosynthetics and slope protection Organization.
3 Probabilistic Approaches taking into account various acceleration values and Fines content have been evolved in the Virginia Tech Spreadsheet implementation by Gutierrez et al.
4 In the case of Rammed Aggregate Piers ®, the drainage is greatly facilitated by prestressing and lateral compaction due to the method of installation. Thus, time to U 90 is greatly speeded up, sometimes to weeks instead of months.
