Earth pressures and deformations in civil infrastructure in expansive soils

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. Mohr? 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.