This dissertation includes the three major parts of the study: volume change, and lateralearth pressure due to suction change in expansive clay soils, and design of civilinfrastructure drilled pier, retaining wall and pavement in expansive soils.The volume change model in expansive clay has been refined to reinforcerealistic characteristics of swelling and shrinkage behavior of expansive clay soils.Refinements include more realistic design soil suction versus depth profiles andimproved characterizations of the effects of soil cracking, overburden stress, and lateralearth pressure. The refined model also includes an algorithm of assigning suctionvolumetricwater content curves and diffusivity through the soil.The typical lateral earth pressure distribution during wetting against a stationarywall is proposed. The proposed stationary retaining wall-soil system in expansive soilsincludes an upper movement active zone and a lower anchor zone. Mohr? s circles andfailure envelopes are used to define the effective horizontal stress and shear failure in anunsaturated soil. The prediction of the horizontal pressures due to suction change in asoil is compared with the in situ measurement of natural horizontal pressures and themeasurements from the large scale tests. It is found that agreement between themeasured and predicted horizontal pressures is satisfactory. Case studies of axial andbending 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 surfaceand uplift forces. Three case studies for bending behavior of the pier and retaining wallare presented based on suction change.Pavement design program has been refined to extend the design capabilities intoboth flexible and rigid pavements supported by pavement treatments. The comparativecase studies using both current and new methods in pavement design show that thecurrent method criterion of 1-inch is unnecessarily conservative. Furthermore, thecurrent method does not provide a means of anticipating subgrade shrinkage that willresult in longitudinal cracking along the edge of the pavement. The design calculationswith both methods lead to the conclusion that neither the swelling movement, as in thecurrent method, nor the total movement, as in the new method, is a reliable indicator oflikely acceptable pavement performance. Instead, all of these case studies show that it isimportant to use the predicted history of the present serviceability index and theinternational roughness index as the proper design guideline for an acceptable treatmentof the subgrade of an expansive soil.
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