Algorithm Implementation of Equivalent Expansive Force in Strength Reduction FEM and Its Application in the Stability of Expansive Soil Slope

Loss of matric suction during rain has an important effect on the instability of expansive soil slope. A new device was designed for testing the expansive force in order to propose and determine the equivalent expansive force corresponding to the matric suction. First, the internal relation between the matric suction and the corresponding equivalent expansive force of unsaturated expansive soil was analyzed. Then, numerical algorithm implementation of the equivalent expansive force was discussed, and the equivalent expansive force was introduced into the strength reduction finite element method (FEM). Finally, the equivalent effects of the matric suction and the equivalent expansive force were compared and analyzed by evaluating the stability of an unsaturated expansive soil slope. The results show that the new testing device significantly improves the accuracy of the expansive force test and shortens the testing time. The relation between the matric suction and the equivalent expansive force with the change in initial water content is obvious. The equivalent expansive force can reflect the macro contribution of matric suction to unsaturated expansive soil, and the developed strength reduction FEM based on the equivalent expansive force can be used to evaluate the rainfall-induced instability of an expansive soil slope caused by the decrease in matric suction resulting from the rainfall infiltration.