Study of Expansive Soils and Residential Foundations on Expansive Soils in Arizona

Construction on expansive soils is challenging and thus prone to some problems and litigation. The engineering community makes extensive use of local experience and empirical procedures to address these problems. Although there has been extensive study of expansive soils and foundations on expansive soils, data related to performance of residential structures are limited in general and limited in the Phoenix area, in particular. In this study, an overview of the Phoenix Valley, Arizona, geotechnical practice and foundation performance related to residential structures on expansive clays, was developed through surveys and interviews with geotechnical engineers, structural engineers, and homebuilders. Using data obtained from files of Phoenix area geotechnical firms and government agencies, the existing Natural Resource Conservation Service map showing expansive soil locations throughout the Phoenix region was updated through the use of correlation developed in this study relating expansion index to common soil index properties such as Atterberg limits and percent passing the No. 200 sieve. Files of forensic investigations linked to expansive soil regions were made available for this study by several geotechnical engineering firms, and Phoenix Valley areas where forensic investigations have been identified, were mapped for comparison to regions identified in the updated map as having expansive soils. Comparison of the forensic investigation map to the updated map of expansive clay locations revealed that most of the forensic investigations were in regions identified with clays labeled as high to moderately high expansion potential, with a few forensic investigations in regions of medium expansion potential. Finally, unsaturated flow analyses were conducted for an Arizona expansive clay profile for two very different landscaped conditions of well-irrigated turf and desert landscape. The results of the numerical analyses were consistent with the reported observations and modes of failure identified through the surveys and interviews conducted with engineering and homebuilder professionals, including the finding that site drainage was found to be extremely important to good foundation performance, regardless of the type of landscape selected.     

Damage of Reinforced Concrete Structure due to Severe Soil Expansion

In Irbid City, Jordan, foundation designs made before 1983 were based on bearing capacity criteria with a limited knowledge of high shrink/swell soil problems. The use of wide and shallow foundation systems was generally the practice rather than the exception in this area. Lack of structural rigidity and insufficient dead load pressure of the foundation systems used in the Irbid area where soils of high shrink/swell are present often cause serious problems related to the performance of constructed facilities. This paper presents a case study typical of a severely cracked one-story reinforced concrete (RC) building constructed over the expansive clay of Irbid City. The building is founded on a mat foundation (solid RC structural slab) embedded at a shallow depth and bearing directly on expansive clay. It is unfortunate that the high shrink/swell potential of the foundation soil had not been recognized properly in the design stage. Based on field and laboratory investigations, remedial construction for the damaged building was proposed. The proposed remedial construction was performed, and more than 10 months have elapsed since the remedial work was completed, with the performance of the building in perfect condition.     

Case Study of Courtyard House Damaged by Expansive Soils

This paper presents a case study of a U-shaped, courtyard house damaged by expansive soils. The field investigation revealed that the damage was caused by edge heaving as a result of water ponding in the courtyard. A back-analysis procedure using finite-element analysis is presented that is based on the measured slab surface levels. The back-analysis provides a representation of the underlying ground movement. The results of the back-analysis compared reasonably well with the actual observations in the field. It was deduced that the slab cracking could have been prevented and the distortion of the house would have been significantly reduced if a strap beam had been added in the courtyard area.     

Survey of Residential Foundation Design Practice on Expansive Soils in the San Francisco Bay Area

The San Francisco Bay Area, California has experienced significant population growth over the last 60 years. The design practices for residential foundations have evolved substantially over this period, as a result of improved geologic characterizations, better engineering understandings of foundation performance, building code changes, and project litigation. The majority of residential foundations are constructed on expansive soils and bedrock, with the primary movement as a result of swell due to wetting of materials in an arid environment. A survey of design practice of practicing geotechnical engineers in the bay area was conducted using a written questionnaire and telephone interviews to compile data regarding the most commonly used design procedures, design details, drainage recommendations, and construction monitoring practices. The results of this survey are compiled and presented in this paper. Three primary foundation systems were identified in the survey as being commonly used in the bay area—rigid footing grids, drilled piers, and mats/slabs. To illustrate problems that have occurred with each of these foundation systems, case histories are presented for recent bay area expansive soil projects for each of these three foundation types.     

Measured and Estimated Suction Indices for Swelling Potential Classification

McKeen’s expansive soil classification methodology relies on a parameter referred to as the “total suction-water content index” for describing the slope of the soil–water characteristic curve on a semilog plot. The swelling potential of expansive soils is qualitatively classified (e.g., “low” or “high”) based on the magnitude of the total suction-water content index. This study examines the validity of using a “benchmark intercept simplification” for indirectly estimating the total suction-water content index when complete soil–water characteristic measurements are not available or economical. Suction indices estimated using the benchmark intercept simplification are compared with indices measured directly using the noncontact filter paper technique for 80 undisturbed expansive shale specimens from the Colorado Front Range Corridor. The results show that the suction-water content index is consistently overestimated using the benchmark simplification by amounts ranging from negligible to 50%, and averaging 23%. For 49 of the 80 specimens (61%), the estimated indices fall in different swelling potential categories than the measured indices. In 44 of the 49 cases (90%), the estimated indices fall in higher swelling potential categories than the measured indices. These discrepancies reflect potential errors that may arise from the use of the benchmark intercept simplification in classifying expansive soils.     

Analysis of Deep Moisture Barriers in Expansive Soils. II: Water Flow Formulation and Implementation

Several alternatives have been proposed to prevent damage to civil infrastructure founded on expansive soils. For example, deep moisture barriers have been used in highways and buildings. However, in some cases, the protected lanes or structures degrade to similar levels as the unprotected ones, although at a smaller rate. In spite of these poor results, relatively few efforts have been devoted to the development of analytical methods for rational designs on expansive soils. This paper couples the constitutive model for expansive soils developed in the companion paper with flow equations in a deforming medium and a finite element code is developed. The resulting numerical tool has the capacity of computing soil suction and volumetric strain changes of expansive soils under a defined wetting–drying regime. To verify the capabilities of this computer code, a laboratory barrier model was built. The model was instrumented to measure soil suction changes and the corresponding surface displacements. The experimental and theoretical results were compared. Finally, the numerical model was applied to a design example of a deep moisture barrier.     

Analysis of Deep Moisture Barriers in Expansive Soils. I: Constitutive Model Formulation

Expansive soils cause important economical losses in many arid or semiarid countries in the world. Considering the large economic impact, relatively few efforts have been devoted to develop analytical methods that may help practitioner engineers to adequately design civil infrastructure on this type of soil. A rational design method should be able to quantify the heave or subsidence of the soil associated with the suction changes during water diffusion, as well as the contact pressures on soil-structure interfaces. Accordingly, in this and in a companion paper, the problem of volume changes due to nonpermanent water flow in expansive soils is studied and applied to the case of vertical moisture barriers. In this paper, a constitutive model for expansive soils is proposed. This model is an extension of that developed by Alonso et al. in 1990, in the sense that it can take into account the behavior of expansive soils. The advanced model is evaluated by comparing the numerical results with experimental data.     

Legal Consequences of Damages to Underground Facilities by Horizontal Directional Drilling

Horizontal directional drilling is rapidly becoming the method of choice for installing new underground systems including water, sewer, electrical, telephone, fiber-optic cables, and gas lines. Due to its minimal impact to surface activities and competitive cost, this technique is being utilized worldwide. Unfortunately, poor drilling practices by some contractors have caused utility strikes that have resulted in major legal ramifications and subsequent negative image of the technique. Just one incident alone can result in significant monetary judgments due not only to the reparation for repairing the damaged utility, but also for damages due to “loss of use.” This paper presents theories of legal liability and recoverable damages applied to incidents of damages to underground facilities by the contractor. Recommendations for preventing the repetition of these types of incidents through the discussion of prior identification of potential hazards and proper drilling practices are discussed.     

High-temperature creep and the defect structure of nickel-based superalloy single crystals after hot isostatic pressing

The influence of hot isostatic pressing on the high-temperature creep of single crystals of a nickel-based superalloy containing rhenium and ruthenium is studied. The microstructural damages caused by the development of creep have been studied. Hot isostatic pressing is found to weakly influence the life and creep of the superalloy at 1150°C. The distribution of deformation pores over the length and cross section of failed samples has been studied. A high pore concentration is shown to exist at the sites of severe plastic deformation.     

Engineer’s Legal Exposure for Facilities Built on Expansive Soils

This paper will focus on the legal liability issues facing the professional engineer engaged in the design and construction administration of facilities built on expansive soils. These legal liability issues will be discussed from the perspectives of the geotechnical, civil, and structural engineer to alert those professionals to the legal ramifications of their daily activities. By focusing on these legal aspects facing the engineers that are involved in the process of building on expansive soils, hopefully litigation can be avoided or successfully defended. Attention to the legal ramifications of engineering is mandated by today’s litigious environment in the construction industry, especially when designing and administering the construction of facilities built on expansive soils.     

Seasonally Frozen Soil Effects on the Seismic Site Response

Several large-magnitude earthquakes, including the Prince William Sound earthquake of March 1964 and the Denali earthquake of November 2002, occurred in the state of Alaska and caused considerable damages to its transportation system, including damage to several highway bridges and related infrastructure. Some of these damages are related to frozen soil effects. However, only limited research has been carried out to investigate the effects of frozen soils on seismic site responses. A systematic investigation of seasonally frozen soil effects on the seismic site response has been conducted and is presented in this paper. One bridge site in Anchorage, Alaska, was selected to represent typical sites with seasonally frozen soils. A set of input ground motions was selected from available strong-motion databases and scaled to generate an ensemble of hazard-consistent input motions. One-dimensional equivalent linear analysis was adopted to analyze the seismic site response for three seismic hazard levels, i.e., maximum considered earthquake (MCE), AASHTO design, and service design level hazards. Parametric studies were conducted to assess the sensitivity of the results to uncertainties associated with the thickness and shear-wave velocity of seasonally frozen soils. The results show that the spectral response of ground motions decreases as the thickness of seasonally frozen soil increases, and the results are insensitive to the shear-wave velocity of seasonally frozen soils. In conclusion, it is generally conservative to ignore the effects of seasonally frozen soils on seismic site response in the design of highway bridges.     

Soil-Water Characteristic Curves of Stabilized Expansive Soils

The engineering properties of expansive soils are conventionally improved through the use of additives such as fly ash, lime, and chemical additives. Such soils are often referred to as stabilized or modified or treated expansive soils. The soil-water characteristic curves (SWCC) of two expansive soils from Texas were measured both in natural and stabilized conditions using the pressure plate apparatus in the suction range of 0-1,000 kPa. The SWCC results are used to interpret the expansive soil behavior due to stabilizer treatment. In addition, relationships were developed between the basic soil and stabilizer properties such as water content, dry density, liquid limit, plastic limit, and stabilizer dosages and the model constants of the SWCC formulation of Fredlund and Xing via multiple linear regression analysis. The analysis showed that higher coefficients of correlations can be achieved by using six independent soil properties. The comparisons between the predicted and measured volumetric water contents are within ±20% for ash-treated expansive soils, and within ±15% for combined ash- and fiber-treated expansive soils. The research data and interpretation analysis presented here can be extended to understand volume change behaviors of other stabilized expansive soils using the SWCC test data.     

Not Making the Grade: Expansive Soils and Higher Education in Texas

Expansive soils are a serious geologic hazard in Texas; accordingly, one would expect Texas engineering colleges to offer a strong educational program on expansive soils at both the undergraduate and graduate levels. However, data from the geotechnical programs within the civil engineering departments of Texas engineering colleges suggest that while Texas educational programs cover the topic of expansive soils in varying degrees, the educational effort is highly skewed toward traditional geotechnical and foundation issues. In most cases, treatment of the expansive soil problem is limited and is not adequate when measured against the scope and extent of expansive soil problems in Texas.     

Influence of Gypsification on Engineering Behavior of Expansive Clay

Volume change in argillaceous sediments can take place due to either swelling of expansive clay or gypsification of anhydrous calcium sulfate. Gypsification offers a variety of serious geotechnical hazards such as high swell pressure, floor heave in tunnels, massive rock uplift in dams, and damages to light structures and pavements. Some of these phenomena have been observed in the Arabian Gulf coastal region, where the behavior of local argillaceous sediments is controlled by severe climatic and environmental conditions. Based on laboratory investigation of natural and synthetic samples, this paper studies the influence of gypsification of anhydrite on the engineering behavior of calcareous expansive clay.     

Use of Class C Fly Ashes for the Stabilizationof an Expansive Soil

Excessive heave associated with swelling of expansive soils can cause considerable distress to lightweight civil engineering structures. Several methods have been suggested to control this problem. The most commonly used method is addition of stabilizing agents, such as lime or cement to the expansive soil. In this study, high-calcium and low-calcium class C fly ashes from the Soma and Tuncbilek thermal power plants, respectively, in Turkey, were used for stabilization of an expansive soil. An evaluation of the expansive soil-lime, expansive soil-cement, and expansive soil-fly ash systems is presented. Lime and cement were added to the expansive soil at 0–8% to establish baseline values. Soma fly ash and Tuncbilek fly ash were added to the expansive soil at 0–25%. Test specimens were subjected to chemical composition, grain size distribution, consistency limits, and free swell tests. Specimens with fly ash were cured for 7 days and 28 days, after which they were subjected to oedometer free swell tests. Based on the favorable results obtained, it can be concluded that the expansive soil can be successfully stabilized by fly ashes.     

Erosion Study of New Orleans Levee Materials Subjected to Plunging Water

During Hurricane Katrina, overtopping water caused erosion and subsequent failure of several sections of I-type flood walls in New Orleans. Erosion stemmed from the kinetic energy of water falling from the top of the flood wall, unlike the typical surface erosion caused by shear flow. This study evaluated the effects of important parameters of levee soils—fines content, degree of compaction (DOC), clay mineralogy, and water content in relation to the erosion behavior of New Orleans levees subjected to the plunging water. In general, test results showed that a higher fines content contributed to greater erosion resistance. The trend became unclear when fines content exceeded 20–25%. A higher degree of compaction did not necessarily contribute to greater erosion resistance. Underwater soaked soils showed much less erosion resistance than nonsoaked soils. Soils containing expansive clay minerals showed less erosion resistance than soils containing nonexpansive clay minerals.     

Vapor Adsorption Index for Expansive Soil Classification

A laboratory index defined as gravimetric water content at ambient relative humidity of 75% (w75) is proposed for qualitatively classifying the swelling potential of clays and clayey soils (e.g., low, moderate, high). The methodology is calibrated by comparison with existing plasticity-based and suction-based classification methodologies for a series of natural clays from Missouri and Colorado and clay mixtures prepared to represent a wide range of swelling potential. Procedures are described for obtaining w75 by placing samples in the headspace of an environmental chamber maintained under controlled humidity using a saturated NaCl solution. The proposed methodology has potential advantages over existing expansive soil classification methods because a large number of samples may be tested concurrently, no specialized testing equipment is required, and testing procedures may be readily automated. Measurements may be obtained in as little as 3–5?days with coefficients of variation ranging from 5 to 25%.     

Structural, Construction, and Procedural Failures Associated with Long-Term Pyritic Soil Expansion at a Private Elementary School in Pennsylvania

This paper examines the background, history, and results of multiple investigations associated with pyrite-based expansive soils spanning almost 40 years in conjunction with a private elementary school located in western Pennsylvania. The school was initially designed in 1960. Original construction was completed in September 1961 and the first signs of distress, which were primarily related to slab heave, were reported in early 1962. One wing of the school, a 1965 classroom addition (1965 addition) with different structural and foundation systems, did not experience any expansive soil-related damages and served as a valuable comparison throughout multiple subsequent investigations. Pyritic soil material in the subgrade in conjunction with oxygen-rich groundwater was determined to be the cause of soil movement and building distress. Expansive soil-related problems at the school continued for decades despite an investigation, civil court action, and judgment in the late 1960s followed by a remediation program in the 1970s and 1980s. Following a second round of investigations and litigation in the late 1990s, all of the original classroom, office, and gymnasium building sections, with the exception of the 1965 addition, were demolished in late 2000 and early 2001 based on safety concerns and economic evaluation. Investigation and monitoring to confirm subgrade conditions continued throughout the demolition process. As a part of this paper, the history of this case dating back to one of the early identifications of pyrite as an expansive element of concern in building construction, including one of the earliest comprehensive identifications of the complete chemical-microbiological oxidation process is presented. The initial 1960s investigation and conclusions are identified as well as the series of engineering, procedural, and construction errors that took place during and after the first remediation process that led to ongoing soil expansion and structural damage, including misguided actions and misunderstandings that complicated and delayed a final resolution in this case. Today, the industry is more familiar with the potential for pyrite-related construction problems, nevertheless, the paper incorporates lessons learned for avoiding problems and in particular, the procedural failures that led to the eventual need to abandon and demolish the school facility.     

Effect of Fly Ash on Engineering Properties of Expansive Soils

This note presents a study of the efficacy of fly ash as an additive in improving the engineering characteristics of expansive soils. An experimental program has evaluated the effect of the fly ash content on the free swell index, swell potential, swelling pressure, plasticity, compaction, strength, and hydraulic conductivity characteristics of expansive soil. The plasticity, hydraulic conductivity and swelling properties of the blends decreased and the dry unit weight and strength increased with an increase in fly ash content. The resistance to penetration of the blends increased significantly with an increase in fly ash content for a given water content. Excellent correlation was obtained between the measured and predicted undrained shear strengths.     

Effects of Organic Matter on Physical, Strength, and Volume Change Properties of Compost Amended Expansive Clay

In recent years, the recycling and composting of municipal solid wastes has gained acceptance as an alternative to landfilling and incineration. Compost materials have been used as soil amendments in landscaping, erosion control, expansive soil treatment, and turf management. Compost amended soils are enriched with decomposed organic matter and hence usually exhibit different strength and compressibility in soil behaviors. An experimental investigation was carried out on compost amended soils to understand the effects of decomposed organic matter on strength and volume change properties. Two types of composts, a biosolids compost and a dairy manure compost, and a control cohesive soil were chosen as test materials. Tests conducted on these materials showed that the presence of organic matter enhanced shrinkage resistance and shear strength at low compost proportions (20–30%). At high proportions (beyond 30%), the shear strength reached plateau conditions. One-dimensional vertical swell and secondary consolidation properties increased with an increase in compost proportions. As low proportions of composts yielded better enhancements to most expansive soil properties, it was concluded that compost materials can provide engineering benefits to control soils when used in moderate proportions.