Expansive soils are widely distributed in arid and semi-arid regions around the world and are typically found in a state of unsaturated condition. These soils are constituted of the clay mineral montmorillonite that is highly active and contributes significantly to volume changes of soils due to variations in the natural water content conditions. The volume changes of expansive soils often cause damage to lightly loaded structures. The costs associated with the damage to lightly loaded structures constructed on expansive soils in the United States alone were estimated as $2.3 billion per year in 1973, which increased to $13 billion per year by 2009. In other words, these damages have increased more than five fold during the last four decades. Similar trends in damages were also reported in other countries (e.g., Australia, China, France, Saudi Arabia, United Kingdom, etc.). Numerous methods have been proposed in the literature over the past 50 years for the prediction of the volume change movement of expansive soils. However, the focus of these methods has been towards estimating the maximum potential heave, which occurs when soils attain the saturation condition. The results of heave estimation considering saturated soil conditions are not always useful in engineering practice. This is because most of damages due to expansive soils often occur prior to reaching the saturation condition. A reliable design of structures on expansive soils is likely if the anticipated soil movements in the field can be reliably estimated over time, taking into account the influence of environmental factors. Limited studies are reported in the literature during the past decade in this direction to estimate/predict the expansive soil movements over time. The existing methods, however, suffer from the need to run expensive and time consuming tests. In addition, verification of these studies for different natural expansive soils has been rather limited. A simple approach, which is referred to as a modulus of elasticity based method (MEBM), is proposed in this study for the prediction of the heave/shrinkage movements of natural expansive soils over time. The proposed MEBM is based on a simplified constitutive relationship used for the first time to estimate the vertical soil movements with respect to time in terms of the matric suction variations and the corresponding values of the modulus of elasticity. The finite element program VADOSE/W (Geo-Slope 2007) for simulating the soil-atmospheric interactions is used as a tool to estimate the changes in matric suction over time. A semi-empirical model that was originally proposed by Vanapalli and Oh (2010) for fine-grained soils has been investigated and extended for unsaturated expansive soils to estimate the variation of the modulus of elasticity with respect to matric suction in the constitutive relationship of the proposed method. The MEBM has been tested for its validity in five case studies from the literature for a wide variety of site and environmental conditions, from Canada, China, and the United States. For each case study, factors influencing the volume change behavior of soils, such as climate conditions, soil cracks, lawn irrigation, and cover type (pavement, vegetation), are successfully modeled over the period of each simulation. The proposed MEBM provides good predictions of soil movements with respect to time for all the case studies. The MEBM is simple and efficient for the prediction of vertical movements of natural expansive soils underlying lightly loaded structures. In addition, a new dimensionless model is also proposed, based on the dimensional analysis approach, for the estimation of the modulus of elasticity which can also be used in the constitutive relationship of the MEBM. The dimensional model is rigorous and takes into account the most significant influencing parameters such as matric suction, net confining stress, initial void ratio, and degree of saturation. This model provides a comprehensive characterization of the modulus of elasticity of expansive soils under unsaturated conditions for different scenarios of loading conditions (i.e., both lightly and heavily loaded structures). The results of the present study are encouraging for proposing guidelines based on further investigations and research studies for the rational design of pavements, shallow and deep foundations placed on/in expansive soils using the mechanics of unsaturated soils.

The one-dimensional (1-D) potential heave (or swell strain) of expansive soil is conventionally estimated using the swelling pressure and swelling index values which are determined from different types of oedometer test results. The swelling pressure of expansive soils is typically measured at saturated condition from oedometer tests. The experimental procedures of oedometer tests are cumbersome as well as time-consuming for use in conventional geotechnical engineering practice and are not capable for estimating heave under different stages of unsaturated conditions. To alleviate these limitations, semi-empirical models are proposed in this thesis to predict the variation of swelling pressure of both compacted and natural expansive soils with respect to soil suction using the soil-water characteristic curve (SWCC) as a tool. An empirical relationship is also suggested for estimating the swelling index from plasticity index values, alleviating the need for conducting oedometer tests. The predicted swelling pressure and estimated swelling index are then used to estimate the variation of 1-D heave with respect to suction for expansive soils by modifying Fredlund (1983) equation. The proposed approach is validated on six different compacted expansive soils from US, and on eight field sites from six countries; namely, Saudi Arabia, Australia, Canada, China, US, and the UK. The proposed simple techniques presented in this thesis are friendly for the practitioners for using when estimating the heave in unsaturated expansive soils.

Expansive soils, which are widely referred to as problematic soils are extensively found in many countries of the world, especially in semi-arid and arid regions. Several billions of dollars are spent annually for maintenance or for repairs to the structures constructed with and within expansive soils. The major problems of expansive soils can be attributed to the volume changes associated with the alternate wetting and drying conditions due to the influence of environmental factors. Pile foundations have been widely accepted by practicing engineers as a reasonably good solution to reduce the damages to the structures constructed on expansive soils. Typically, piles foundations are extended through the active layer of expansive soil to reach the bedrock or placed on a soil-bearing stratum of good quality. Such a design and construction approach typically facilitates pile foundations to safely carry the loads from the superstructures and reduce the settlement. However, in many scenarios, damages associated with the pile foundations are due to the expansion of the soil that is predominantly in the active zone that contributes to the pile uplift. Such a behavior can be attributed to the water infiltration into the expansive soil, which is a key factor that is associated with the soil swelling. Due to this phenomenon, expansive soil typically moves upward with respect to the pile. This generates extra positive friction on the pile because of the relative deformation. If the superstructure is light or the applied normal stress on the head of the piles is not significant, it is likely that there will be an uplift of the pile contributing to the damage of the superstructure. In conventional engineering practice, the traditional design methods that include the rigid pile method and the elastic pile method are the most acceptable in pile foundation design. These methods are typically based on a computational technique that uses simplified assumptions with respect to soil and water content profile and the stiffness and shear strength properties. In other words, the traditional design method has limitations, as they do not take account of the complex hydromechanical behavior of the in-situ expansive soils. With the recent developments, it is possible to alleviate these limitations by using numerical modeling techniques such as finite element methods. In this thesis, a three-dimensional finite element method was used to study the hydro-mechanical behavior of a single pile in expansive soils during the infiltration process. In this thesis, a coupled hydro-mechanical model for the unsaturated expansive soil is implemented into Abaqus software for analysis of the behavior of single piles in expansive soils during water infiltration. A rigorous continuum mechanics based approach in terms of two independent stress state variables; namely, net normal stress and suction are used to form two three-dimensional constitutive surfaces for describing the changes in the void ratio and water content of unsaturated expansive soils. The elasticity parameters for soil structure and water content in unsaturated soil were obtained by differentiating the mathematical equations of constitutive surfaces. The seepage and stress-deformation of expansive soil are described by the coupled hydro-mechanical model and the Darcy’s law. To develop the subroutines, the coupled hydro-mechanical model is transferred into the coupled thermal-mechanical model. Five user-material subroutines are used in this program. The user-defined field subroutine (USDFILD) in Abaqus is used to change and transfer parameters. Three subroutines including user-defined material subroutine (UMAT), user-defined thermal material subroutine (UMATHT), and user-defined thermal expansion subroutine (UEXPAN) are developed and used to calculate the stress-deformation, the hydraulic behavior, and the expansion strain, respectively. Except for the coupled hydro-mechanical model of unsaturated expansive soils, a soil-structure interface model is implemented into the user-defined friction behavior subroutine (FRIC) to calculate the friction between soil and pile. The program is verified by using an experimental study on a single pile in Regina clay. The results show that for the single pile in expansive soil under a vertical load, water infiltration can cause a reduction in the pile shaft friction. More pile head load is transferred to the pile at greater depth, which increases the pile head settlement and pile base resistance. In future, the proposed method can also be extended for verification of other case studies from the literature. In addition, complex scenarios can be investigated to understand the behavior of piles in expansive soils.

Expansive soils are a worldwide problem especially in the regions where climate is arid or semi arid. These soils swell when they are exposed to water and shrink when they dry. Cyclic swelling and shrinkage of clays and associated movements of foundations may result in cracking of structures. Several methods are used to decrease or prevent the swelling potential of such soils like prewetting, surcharge loading, chemical stabilization etc. Among these, one of the most widely used method is using chemical admixtures (chemical stabilization). Cyclic wetting and drying affects the swell &ndash / shrink behaviour of expansive soils. In this research, the effect of cyclic swell &ndash / shrink on swell percentage of a chemically stabilized expansive soil is investigated. Class C Fly Ash is used as an additive for stabilization of an expansive soil that is prepared in the laboratory environment by mixing kaolinite and bentonite. Fly ash was added to expansive soil with a predetermined percentage changing between 0 to 20 percent. Hydrated lime with percentages changing between 0 to 5 percent and sand with 5 percent were also used instead of fly ash for comparison. Firstly, consistency limits, grain size distributions and swell percentages of mixtures were determined. Then to see the effect of cyclic swell &ndash / shrink on the swelling behavior of the mixtures, swell &ndash / shrink cycles applied to samples and swell percentages were determined. Swell percentage decreased as the proportion of the fly ash increased. Cyclic swell-shrink affected the swell percentage of fly ash stabilized samples positively.

Expansive soils occurring in arid and semi-arid climate regions of the world cause serious problems on civil engineering structures. Such soils swell when given an access to water and shrink when they dry out. Several attempts are being made to control the swell-shrink behavior of these soils. Soil stabilization using chemical admixtures is the oldest and most widespread method of ground improvement. In this study, waste limestone dust and waste dolomitic marble dust, by-products of marble industry, were used for stabilization of expansive soils. The expansive soil is prepared in laboratory as a mixture of kaolinite and bentonite. Waste limestone dust and waste dolomitic marble dust were added to the expansive soil with predetermined percentage of stabilizer varying from 0 to 30 percent. Grain size distribution, consistency limits, chemical and mineralogical composition, swelling percentage, and rate of swell were determined for the samples. Swelling percentage decreased and rate of swell increased with increasing stabilizer percentage. Also, samples were cured for 7 days and 28 days before applying swell tests. Curing of samples affects swell percentages and rate of swell in positive way.

Expansive soils are one of the most serious problems which the foundation engineer faces. Several attempts are being made to control the swell-shrink behavior of these soils. One of the most effective and economical methods is to use chemical additives. Fly ash and desulphogypsum, both of which are by-products of coal burning thermal power plants, are accumulating in large quantities all over the world and pose serious environmental problems. In this study, the expansive soil was stabilized using the fly ash and desulphogypsum obtained from &Ccedil / ayirhan Thermal Power Plant. Fly ash and desulphogypsum were added to the expansive soil from 0 to 30 percent. Lime was used to see how efficient fly ash and desulphogypsum on expansive soil stabilization were, and was added to the expansive soil from 0 to 8 percent. The properties obtained were chemical composition, grain size distribution, consistency limits, swelling percentage, and rate of swell. Fly ash, desulphogypsum, and lime added samples were cured for 7 days and 28 days, after which they were subjected to free swell tests. Swelling percentage decreased and rate of swell increased with increasing stabilizer percentage. Curing resulted in further reduction in swelling percentage and further increase in rate of swell. 25 percent and 30 percent fly ash and desulphogypsum additions reduced the swelling percentage to levels comparable to lime stabilization.

Drilled shaft retaining walls are common earth retaining structures, well suited to urban environments where noise, space, and damage to adjacent structures are major considerations. The design of drilled shaft retaining walls in non-expansive soils is well established. In expansive soils, however, there is no consensus on the correct way to account for the influence of soil expansion on wall behavior. Based on the range of design assumptions currently in practice, existing walls could be substantially over- or under-designed. The goal of this research is to advance the understanding of the effects of expansive clay on drilled shaft retaining walls. The main objectives of this study are to identify the processes responsible for wall loading and deformation in expansive clay, to evaluate how these processes change with time, and to provide guidance for design practice to account for these processes and ensure adequate wall performance. The primary source of information for this research is performance data from a four-year monitoring program at the Lymon C. Reese research wall, a full-scale instrumented drilled shaft retaining wall constructed through expansive clay in Manor, Texas. The test wall was instrumented with inclinometers and fiber optic strain gauges, and performance data was recorded during construction, excavation, during natural moisture fluctuations, and during controlled inundation tests that provided the retained soil with unlimited access to water. In addition to the test wall study, a field assessment of existing TxDOT drilled shaft retaining walls was conducted. The main process influencing short-term wall deformation was found to be global response to stress relief during excavation, which causes the wall and soil to move together without the development of large earth pressures or bending stresses. Long-term wall deformations were governed by the development of drained conditions in both the retained soil and the foundation soil after approximately eight months of controlled inundation testing. To ensure adequate wall performance, the deformations and structural loads associated with short- and long-term conditions should be combined and checked against allowable values. / text

Expansive clays undergo a large swell when they are subjected to water. Thus, expansive clay is one of the most abundant problems faced in geotechnical engineering applications. It causes heavy damages in structures, especially in water conveyance canals, lined reservoirs, highways, airport runways etc., unless appropriate measures are taken. In this thesis, Granulated Blast Furnace Slag (GBFS), GBFS - Lime combinations and GBFS Cement (GBFSC) were utilized to overcome or to limit the expansion of an artificially prepared expansive soil sample (Sample A). GBFS and GBFSC were added to Sample A in proportions of 5 to 25 percent. Different GBFS-Lime combinations were added to Sample A by keeping the total addition at 15 percent. Effect of stabilizers on grain size distribution, Atterberg limits, swelling percentage and rate of swell of soil samples were determined. Effect of curing on swelling percentage and rate of swell of soil samples were also determined. Leachate analysis of GBFS, GBFSC and samples stabilized by 25 percent GBFS and GBFSC was performed. Use of stabilizers successfully decreased the amount of swell while increasing the rate of swell. Curing samples for 7 and 28 days resulted in less swell percentages and higher rate of swell.

El principal indicador para evaluar la calidad del suelo como subrasante en el diseño de pavimentos es la capacidad de soporte CBR. En muchos casos, no es posible su obtención mediante ensayos, al menos en la frecuencia requerida, y son muy costosos. Por ello, la necesidad de cuantificar este parámetro mediante modelos matemáticos que utilicen propiedades fácilmente determinables y permitan evaluar rápidamente la eficacia de una solución de estabilización. En el presente trabajo de investigación tiene como propósito desarrollar herramientas prácticas para la predicción del valor de CBR del suelo expansivo post estabilización con ceniza de cáscara de arroz (CCA) y cal. Se plantea obtener modelos matemáticos basados en la regresión lineal múltiple haciendo uso de sus propiedades índice (%F, IP) y de compactación (OCH, MDS), los cuales se generaron mediante la aplicación del software SPSS Statistics, cuya ecuación resultante fue: 〖CBR〗_f=46.116-0.526 %F+0.034 IP+0.218 OCH+5.06 MDS Esta ecuación presenta una correlación muy alta con R = 0.975 y un ajuste de bondad excelente de R2 = 0.95. Esto quiere decir que la variable de respuesta CBR es explicada en un 95% por las variables predictoras %F, IP, OCH y MDS. El modelo de regresión propuesto se aplicó a un tramo de la carretera PE-8B en la región San Martín donde se observó que el valor de CBR se incrementa en promedio 272% al estabilizarse con los agentes de estudio sugeridos. / The main indicator to evaluate the quality of the soil as a subgrade in pavement design is the California Bearing Ratio (CBR). In many cases, it is not possible to obtain them by testing, at least at the required frequency, and they are very expensive. Therefore, the need to quantify this parameter through mathematical models that use easily determinable properties and will evaluate the effectiveness of a proposed stabilization solution. The purpose of this research work is to develop practical tools for the prediction of the CBR in expansive soil post stabilization with rice husk ash and lime. It is proposed to obtain mathematical models based on multiple linear regression using their index (% F, IP) and compaction (OCH, MDS) properties, which were generated by applying the SPSS Statistics software, whose resulting equation was: 〖CBR〗_f=46.116-0.526 %F+0.034 IP+0.218 OCH+5.06 MDS, which presents a very high correlation with R = 0.975 and an excellent goodness fit of R2 = 0.95. This means that the CBR response variable is 95% explained by the predictor variables %F, IP, OCH and MDS. The proposed regression model was applied to a section of the PE-8B highway in the San Martín region where it was found that the CBR value was found on average 272% when stabilized with the suggested study materials. / Tesis