Mohamed Farid Abbas

Compacted expansive soils in situ are subjected to a variety of stress, boundary, and wetting conditions as well as different states of stress history. Investigating the volume change (VC) behavior of compacted expansive soils under conditions that replicate stress states and wetting conditions prevailing in the field is therefore essential to reducing the undesirable impacts of unrealistic assessment for such parameters from both an economic and safety perspective. This study presents a comprehensive investigation of the influence of loading-induced stress history on strain and stress states, in either the axial or lateral direction, during wetting under one-dimensional loading condition. The loading-induced stress history was found to influence wetting strain and axial and lateral swell pressure. Subjecting compacted expansive soil to higher stress history resulted in an increase in swell potential and a reduction in collapse potential, but with a unique void ratio state after wetting. The compression and swell indices (C _c and C _s , respectively) were found to be independent of pre-wetting loading-induced stress history. Finally, an enlargement of yield surfaces depicted in either (σ _a –s) or (p–q) space was observed.

A sustainable design of some engineering applications, such as earth dam cores, landfill liners, clay barriers, and radioactive waste disposal systems, that utilize compacted expansive soils requires simulation for probable field conditions. This study investigated the hydraulic and volume change (H-VC) behaviors of highly expansive compacted soils in Al-Qatif city under different seasonal climatic variations for a wide range of stress conditions, aiming for more economical and rational design and practices. The extent of the effect of the start cycle condition of the cyclic wetting and drying (W/D) process on the examined properties is examined, as well. Two testing series of the cyclic W/D process, representing the probable seasonal climatic variations, were executed for varied axial stress conditions. The H-VC behaviors of expansive soils are affected by the simulated seasonal variation (i.e., cyclic W/D process), with the first cycle of W/D being the most effective cycle and an elastic state being attained by the third to fourth cycle. Swell fatigue is noted for both testing series, and this is attributed to the initial placement condition. Analysis of results recommends exposure of the compacted expansive soil layers in the field to drying after compaction to reduce their equilibrium wetting potential. As a consequence of the noted shrinkage accumulation, a reduction tendency of saturated hydraulic conductivity (k_sat) with repeated W/D cycles is reported for both series under all the stress states applied. Finally, it is recommended for clay barrier projects to be submerged once compacted to obtain barriers with the lowest values of hydraulic conductivity.

This study investigates the effect of loading path on the drained shear strength of Al-Qatif expansive clay obtained from the northeast region of Saudi Arabia. Testing was performed on statically compacted samples using strain controlled direct shear tests. Two loading paths simulating different field conditions were considered. First load path involved the inundation of test samples under target normal stress then shearing. Second load path involved inundation of test samples under low normal stress (10 kPa) followed by incremental increase in normal stress to target value before shearing. Results of the tests indicate that proposed loading path has an insignificant effect on the drained shear strength of tested samples. In addition, a unique relationship exists between drained shear strength and final water content for both load paths.