Effect of swelling deformation on stability of expansive soil slope

Adopting reasonable shear strength parameters, calculation results obtained from conventional limit equilibrium method and limit analysis method can not explain the reason why some expansive soil slopes failure under a fairly small dip angle. In fact, there has obvious swelling deformation when water infiltrating into the soil, so as to induce large shear stress near the border between the saturated and unsaturated regions. This effect should be considered in the stability analysis of expansive soil slope. Based on the upper bound theorem in plasticity, a new energy-work balance equation has been strictly derived including the work rate done by expansive stress. Factor of safety defined by strength reduction explicitly exists in such equation can be solved by iteration; and minimized by optimizing the slip surface. The upper bound limit analysis of the slope is numerically performed by element integration method (EIM). By means of EIM, the calculation result obtained from stress analysis can be conveniently utilized. Applying the presented method to an expansive soil slope with a gradient of 1: 4, it is demonstrated that the expansive deformation brings obvious decrease to the safety factor of the slope. When considering expansive of the soil, the critical failure pattern obtained from optimization is a small range of shallow slide, which will induce the upside soil mass into another small range of shallow slide. This agrees well with the common traction characters in the failure of expansive soil slope.