Abstract
The results of a series of plane strain model tests of unreinforced and reinforced sand slopes loaded with a 10 cm-wide strip footing, which was described in the companion paper in the previous issue, are analyzed by limit equilibrium methods. A statically rigorous method, namely Janbu's method, is modified in order to incorporate the reinforcement force acting on the potential failure surface and the inter-slice faces in the force equilibrium formulation. It is shown that the results of stability analysis using a composite failure surface can predict rather accurately the stability and the location of failure surface for both unreinforced and reinforced slopes, provided that all three factors that impact the mobilization of the friction angle φ along the failure surface are taken into account. These factors are the pressure level-dependency of φ, the strength anisotropy, and the progressive failure. In that case, the mobilized angle of friction along the failure surface is not constant. The degree of progressive failure increases as the effect of reinforcing increases. The comparison of some other simplified stability analysis methods currently used in the design of reinforced slopes with the modified Janbu's method showed that a less realistic assumption concerning force equilibrium leads to a more unrealistic result, and when the increase in the shear strength of soil from the tensile force in reinforcement is not taken into account, the stability could be largely under-estimated.
