Effect of swelling on the shear strength behaviour of expansive soil

Swelling soil is predominant in the Nineveh province of Iraq, leading to severe problems for many civil structures. The present study attempts to investigate the effect of stress state on the shear strength of highly expansive soil from Mosul city. Variations of shear strength parameters, namely cohesion (c) and angle of internal friction (phi), with the swelling potential, swelling pressure, stress relief, initial normal load, and loading-unloading cycles are studied experimentally. The shear parameters (c and phi) were found to decrease with increasing swelling potential and specific percentage of stress relief, but increase with increasing swelling pressure and initial normal load. During the first cycle of loading-unloading, c shows higher reduction, after which the rate of reduction decreases; the reduction is almost insignificant after the second cycle. In contrast, phi shows continuous reduction although at a slow rate.