Upper Bound Solution Analysis of the Ultimate Bearing Capacity of Two-Layered Strip Foundation Based on Improved Radial Movement Optimization

Considering the change of different soil layer parameters of a two-layered strip foundation, a planar kinematically permissible multi-block failure mechanism of a two-layered strip foundation under vertical uniform load is formulated. Based on upper-bound limit analysis theorem, the solution process of ultimate bearing capacity of a two-layered strip foundation is proposed. The improved radial movement optimization (IRMO) could search the critical slip surface of the foundation and calculate associated ultimate bearing capacity. On this basis, analyze the influence parameters. The results show that the IRMO algorithm is feasible, stable, and efficient in solving the ultimate bearing capacity. With the increase in the internal friction angle and cohesion of the two-layered strip foundation, the critical slip surface will expand more deeply, and the ultimate bearing capacity will increase. The influence of upper soil parameters on the calculation results is greater than that of lower soil. For the case with upper-hard soil, the ultimate bearing capacity of it increases gradually with the increase in the H/B ratio. For the upper-soft case, the ultimate bearing capacity of it decreases gradually with the increase in the H/B ratio. Moreover, the increase of ground overload will also cause a linear-increasing in the ultimate bearing capacity.