Expansive soils are extremely problematic in transportation projects, and significant research has been done into examining the effect of moisture content changes and index properties on the swelling of soils. However, little has been reported on the effect of soil structure, or fabric, on swelling. The purpose of this study is to examine the effect of the soil fabric on swelling while, at the same time, validating a new set-up for a centrifuge testing program developed over the course of the project to allow for testing of undisturbed specimens. Testing to examine fabric was performed using two methods at the same effective stress, the conventional swelling test, ASTM D4546, and a new double infiltration approach in a centrifuge, on specimens of the Cook Mountain clay which were either compacted in the testing set-up or trimmed into cutting rings from soil compacted via ASTM D698, the Standard Proctor test. Specimens were compacted either dry of optimum to create a flocculated soil structure or wet of optimum to create a dispersed soil structure. Specimens were tested at their as-compacted moisture content or at a moisture conditioned moisture content to remove the effect of the initial moisture content. The results show that soils with a dispersed structure tended to swell more, over a longer time frame, and with a higher amount of secondary swelling in relation to soils with a flocculated structure when tested using the same initial moisture content. The strong influence of the initial moisture content on swelling was also verified. Further, soil specimens prepared at a comparatively high dry density for a given fabric and initial moisture content were found to swell more than soils prepared at a comparatively low dry density. The new centrifuge set-up, involving submerged specimens, was validated and was found to produce similar swelling results as those obtained from the ASTM D4546 tests. In addition, the new centrifuge approach was found to be more expeditious and results in less secondary swelling than the conventional ASTM approach. / text

This dissertation includes the three major parts of the study: volume change, and lateral earth pressure due to suction change in expansive clay soils, and design of civil infrastructure drilled pier, retaining wall and pavement in expansive soils. The volume change model in expansive clay has been refined to reinforce realistic characteristics of swelling and shrinkage behavior of expansive clay soils. Refinements include more realistic design soil suction versus depth profiles and improved characterizations of the effects of soil cracking, overburden stress, and lateral earth pressure. The refined model also includes an algorithm of assigning suctionvolumetric water content curves and diffusivity through the soil. The typical lateral earth pressure distribution during wetting against a stationary wall is proposed. The proposed stationary retaining wall-soil system in expansive soils includes an upper movement active zone and a lower anchor zone. Mohrâ s circles and failure envelopes are used to define the effective horizontal stress and shear failure in an unsaturated soil. The prediction of the horizontal pressures due to suction change in a soil is compared with the in situ measurement of natural horizontal pressures and the measurements from the large scale tests. It is found that agreement between the measured and predicted horizontal pressures is satisfactory. Case studies of axial and bending of the pier are presented with both uniform and non-uniform wetting. The pier case study for axial behavior shows a good agreement with a heave at ground surface and uplift forces. Three case studies for bending behavior of the pier and retaining wall are presented based on suction change. Pavement design program has been refined to extend the design capabilities into both flexible and rigid pavements supported by pavement treatments. The comparative case studies using both current and new methods in pavement design show that the current method criterion of 1-inch is unnecessarily conservative. Furthermore, the current method does not provide a means of anticipating subgrade shrinkage that will result in longitudinal cracking along the edge of the pavement. The design calculations with both methods lead to the conclusion that neither the swelling movement, as in the current method, nor the total movement, as in the new method, is a reliable indicator of likely acceptable pavement performance. Instead, all of these case studies show that it is important to use the predicted history of the present serviceability index and the international roughness index as the proper design guideline for an acceptable treatment of the subgrade of an expansive soil.

Expansive soils have damage light structures due to movement of soil which was a common problem all around the world. Soils exhibiting expansive properties were common throughout Australia. The damage to light structures founded on expansive soils in Victoria occurred mainly in properties built on quaternary basaltic clays and Tertiary to Ordovician clays. A review of existing literature in the area of expansive soils showed a lack of a thorough scientific diagnostic of the damage to light structures founded on expansive soils. Very few studies had been performed on damage to light structures on expansive soils in Victoria. There were no models so far to predict damage condition to light structures. More over, most of the reports on damage to light structures on expansive soils in Victoria were poorly documented. The aim of this research project was to develop a model to predict the damage condition of light structure on expansive soils in Victoria. A hybrid Neural Network trained with Genetic Algorithm was adopted for the de-velopment of the Predictive Damage Condition model. The Neural Network and Ge-netic Algorithm toolboxes from MATLAB� version 7.1 were used. The development of a Predictive Damage Condition model was driven by the shortage of defined quanti-tative studies and methods of selecting the factors that influenced the damage to light structure on expansive soils. The data used was based on information extracted from the Building Housing Commission which was recorded by different engineering companies based only on the tenants complain and site investigation of the properties. A series of factors that were believed to be dominant in influencing damage to light structures were chosen including: structural type, foundation, the presence of vegetation, soil type, age, and climate change. The model showed that it was able to resolve the problems facing light structures on expansive soils. First and foremost, the Predictive Damage Condition model was able to predict the damage condition or damage class using different combinations of fac-tors. It was also possible to identify the factors contributing to the damage of the struc-ture and to assess their relative importance in causing damage to light structures on expansive soil. It was found that the construction footing and vegetation were the most important among all the other input parameters. Change in Thornthwaite Moisture In-dex or climate was ranked second. Construction wall and age, were ranked third and fourth respectively while both region and geology were ranked fifth. In addition, Change in Thornthwaite Moisture Index was noted to have the strongest correlation with other input parameters.

A comprehensive field and laboratory investigation at the location of the Lymon C. Reese Research Wall is presented. Soil at the site is a stiff, fissured and heavily overconsolidated clay from the Taylor Group. Index properties such as Atterberg limits and clay fractions were used with common empirical guidelines to assess the qualitative swell potential. The soil's compressibility and strength characteristics were difficult to measure in the lab, owing to the stiff soil's secondary structure. Measured values were compared to well established correlations and test results from similar soils sampled from locations near the present test site. Cyclic swell tests were to predict the soil's lateral swell potential after multiple cycles of wetting and drying. Empirical guidelines indicated the soil has a "high" to "very high" swell potential. This was validated by the swelling that was observed during consolidation and cyclic swell tests. The soil's drained and undrained strengths were both rather large, often more typical of rock than soil. The stress history was not evident from consolidation results, either due to disturbance, cementation or extreme overconsolidation. The hydraulic conductivity was particularly elusive, again due to the soil's secondary structure. / text

Lateral earth pressures (LEP) that arise due to backfill on retaining structures are typically determined by extending the principles of saturated soil mechanics. However, there is evidence in the literature to highlight the LEP on retaining structures due to the influence of soil backfill in saturated and unsaturated conditions are significantly different. Some studies are reported in the literature to interpret the variation of LEP on the retaining structures assuming that the variation of matric suction in unsaturated backfill material is hydrostatic (i.e. matric suction is assumed to decrease linearly from the surface to a value of zero at the ground water table). Such an assumption however is not reliable when the backfill behind the retaining wall is an expansive soil, which is extremely sensitive to the changes in variation of water content values. Significant volume changes occur in expansive soils due to the influence of environmental factors such as the infiltration and evaporation. In addition to the volume changes, the swelling pressure of the expansive soils also varies with changes in water content and can significantly influence the LEPs behind the retaining wall. In this thesis, a framework for estimating the LEPs of unsaturated soils is proposed considering the variation of matric suction with respect to various water flow rates (i.e. infiltration and evaporation). The proposed approach is extended for expansive and non-expansive soils in this thesis taking into account of the influence of both the cracks and the lateral swelling pressure with changes in water content. A program code LEENES (Lateral pressure estimation on retaining walls taking account of Environmental factors for Expansive and Non-Expansive Soils) in MATLAB is written to predict the LEP. The program LEENES is valuable tool for geotechnical engineers to estimate the LEPs on retaining structures for various scenarios that are conventionally encountered in geotechnical engineering practice. The studies presented in this thesis are of interest to the practitioners who routinely design retaining walls with both expansive and non-expansive soils as backfill material.

Master of Science / Department of Architectural Engineering and Construction Science / Darren D. Reynolds / Highly expansive soils can severely damage the foundations which they support. These damages create unnecessary maintenance cost to the owner and can be detrimental to the building superstructure. Post-tensioned ribbed mat foundations are commonly used in light commercial construction in areas in the United States that have highly expansive soils. Mild reinforced ribbed mat foundations are rarely used in these areas. This report investigates why post-tensioned ribbed mat foundations are more common in these areas than mild-reinforced ribbed mat foundations. The approach to this investigation is a design example which designs and compares the two foundation types. The design example is a typical 2-story office building located in Dallas, Texas, which is an area that has highly expansive soils. First, a post-tensioned ribbed mat foundation is designed for the office building. Next, a mild-reinforced ribbed mat foundation is designed for the same building. A comparison is done between the two foundations based on serviceability, strength requirements and construction costs. The findings in the comparison is that post-tensioning is a more economical and constructible method. Using mild-reinforcement requires the use of shear reinforcement in the ribs which is not typical in foundation design and construction and is less economical, and additional reinforcement in the slab is needed to resist bending stresses which is also less economical. The finding of the report is that of the two foundation types, the post-tensioned ribbed mat foundation is the better design based on the three areas of interest listed above. The use of a mild-reinforced mat foundation would require construction procedures that are not typical and would be less economical.

No description available.

A study of 12 expansive soils in four major physiographic provinces in Virginia was initiated to examine and quantify the relationship between shrink-swell potential, shrink-swell indices, and soil properties. The mineralogy classes, soil series, and (physiographic provinces, parent materials) examined include smectitic -- Jackland and Waxpool (Triassic, diabase), Iredell (Piedmont, hornblende); vermiculitic -- Kelly (Triassic, thermal shale); kaolinitic -- Cecil (Piedmont, granite gneiss), Davidson (Triassic, diabase); and mixed -- Carbo and Frederick (Valley and Ridge, limestone), Craven and Peawick (Coastal Plain, fluvial and marine sediments), and Mayodan and Creedmoor (Triassic, sandstones). Three sites in each of the 12 map units were described and major horizons sampled for physical, chemical, and mineralogical laboratory analysis. An expansive soil rating system, termed the Expansive Soil Index (ESI), was developed using the soil properties best correlated with shrink-swell potential. The sum of swelling 2:1 minerals, swell index, liquid limit, and CEC gave expansive soil potential ratings (ESI) for each soil series. The higher the ESI, the greater the shrink-swell potential. Smectite distributions within the soil profiles were investigated. Smectite concentration in the clay fraction increases with depth in soils formed from diabase and thermally altered shale. Smectite weathers to kaolinite and hydroxy-interlayered vermiculite with increasing proximity to the soil surface thus accounting for the observed decrease in smectite toward the soil surface. The highest amount of smectite from the granite gneiss, limestone, sandstones and shales, and Coastal Plain sediments were in the Bt2 horizon where maximum expression of the argillic horizon occurs. Smectite contents decrease away (upwards and downwards) from the maximum in the Bt2 horizon. A satellite study focused on locating and quantifying the variability within five map units in the Culpeper (Triassic) Basin in northern Virginia. Variability of the shrink-swell indices and related properties are high in all map units. Dissimilar inclusions could adversely affect foundations if a home is sited on both moderate and high shrink-swell soils. Although there is extreme variability in the map units, the variability occurs within the delineations of each map unit. Each delineation within an individual map unit contains similar levels of variability. / Ph. D.

abstract: In a laboratory setting, the soil volume change behavior is best represented by using various testing standards on undisturbed or remolded samples. Whenever possible, it is most precise to use undisturbed samples to assess the volume change behavior but in the absence of undisturbed specimens, remodeled samples can be used. If that is the case, the soil is compacted to in-situ density and water content (or matric suction), which should best represent the expansive profile in question. It is standard practice to subject the specimen to a wetting process at a particular net normal stress. Even though currently accepted laboratory testing standard procedures provide insight on how the profile conditions changes with time, these procedures do not assess the long term effects on the soil due to climatic changes. In this experimental study, an assessment and quantification of the effect of multiple wetting/drying cycles on the volume change behavior of two different naturally occurring soils was performed. The changes in wetting and drying cycles were extreme when comparing the swings in matric suction. During the drying cycle, the expansive soil was subjected to extreme conditions, which decreased the moisture content less than the shrinkage limit. Nevertheless, both soils were remolded at five different compacted conditions and loaded to five different net normal stresses. Each sample was subjected to six wetting and drying cycles. During the assessment, it was evident from the results that the swell/collapse strain is highly non-linear at low stress levels. The strain-net normal stress relationship cannot be defined by one single function without transforming the data. Therefore, the dataset needs to be fitted to a bi-modal logarithmic function or to a logarithmic transformation of net normal stress in order to use a third order polynomial fit. It was also determined that the moisture content changes with time are best fit by non-linear functions. For the drying cycle, the radial strain was determined to have a constant rate of change with respect to the axial strain. However, for the wetting cycle, there was not enough radial strain data to develop correlations and therefore, an assumption was made based on 55 different test measurements/observations, for the wetting cycles. In general, it was observed that after each subsequent cycle, higher swelling was exhibited for lower net normal stress values; while higher collapse potential was observed for higher net normal stress values, once the net normal stress was less than/greater than a threshold net normal stress value. Furthermore, the swelling pressure underwent a reduction in all cases. Particularly, the Anthem soil exhibited a reduction in swelling pressure by at least 20 percent after the first wetting/drying cycle; while Colorado soil exhibited a reduction of 50 percent. After about the fourth cycle, the swelling pressure seemed to stabilized to an equilibrium value at which a reduction of 46 percent was observed for the Anthem soil and 68 percent reduction for the Colorado soil. The impact of the initial compacted conditions on heave characteristics was studied. Results indicated that materials compacted at higher densities exhibited greater swell potential. When comparing specimens compacted at the same density but at different moisture content (matric suction), it was observed that specimens compacted at higher suction would exhibit higher swelling potential, when subjected to the same net normal stress. The least amount of swelling strain was observed on specimens compacted at the lowest dry density and the lowest matric suction (higher water content). The results from the laboratory testing were used to develop ultimate heave profiles for both soils. This analysis showed that even though the swell pressure for each soil decreased with cycles, the amount of heave would increase or decrease depending upon the initial compaction condition. When the specimen was compacted at 110% of optimum moisture content and 90% of maximum dry density, it resulted in an ultimate heave reduction of 92 percent for Anthem and 685 percent for Colorado soil. On the other hand, when the soils were compacted at 90% optimum moisture content and 100% of the maximum dry density, Anthem specimens heave 78% more and Colorado specimens heave was reduced by 69%. Based on the results obtained, it is evident that the current methods to estimate heave and swelling pressure do not consider the effect of wetting/drying cycles; and seem to fail capturing the free swell potential of the soil. Recommendations for improvement current methods of practice are provided. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2013

abstract: The experience base of practitioners with expansive soils is largely devoid of directly measured soil suction. This historical lack of soil suction measurement represents an impediment to adoption of modern unsaturated soil engineering to problems of expansive soils. Most notably, soil suction-based analyses are paramount to proper design of foundations in expansive soils. Naturally, the best method to obtain design suction profiles is to perform an appropriate geotechnical investigation that involves soil moisture change-appropriate drilling depths, sampling intervals, and requisite laboratory testing, including suction measurement. However, as practitioners are slow to embrace changes in methodology, specifically regarding the adoption of even relatively simple suction measurement techniques, it has become imperative to develop a method by which the routine geotechnical procedures currently employed can be used to arrive at acceptable approximations of soil suction profiles. Herein, a substitute, or surrogate, for soil suction is presented, such that the surrogate agrees with observed field soil suction patterns and provides estimates of soil suction that are acceptable for use in practice. Field investigations with extensive laboratory testing, including direct suction measurement, are used in development of the soil suction surrogate. This surrogate, a function of water content and routinely measured soil index properties, is then used in estimation of field expansive soil suction values. The suction surrogate, together with existing geotechnical engineering reports, is used to augment the limited existing database of field soil suction profiles. This augmented soil suction profile database is used in development of recommendations for design suction envelopes and design suction profiles. Using the suction surrogate, it is possible to proceed from the beginning to the end of the Suction-Oedometer soil heave/shrinkage analysis without directly measuring soil suction. The magnitude of suction surrogate-based heave estimates is essentially the same as heave estimates obtained using direct soil suction measurements. The soil suction surrogate-based approach, which uses a complete-stress-state approach, considering both net normal stress and soil suction, is an intermediate step towards the adoption of unsaturated soil engineering in expansive soils analyses, wherein direct soil suction measurements are routinely made. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2019