Authors: Pabodha Maduranga Kannangara, Shi-Yu Xu
The Mononobe – Okabe (M-O) equation is the most widely used closed form analytical model to evaluate the seismic earth pressure in non-cohesive soil. Nevertheless, M-O is known to yield non-conservative results under passive conditions, leading to unsafe design, when the wall-soil interface frictional angle is high. Consequently, although simple and easy to implement, the M-O model is not recommended to use in design practice when assessing seismic passive earth pressures. A more advanced, recently published limit-equilibrium based model, known as the Log-Spiral-Rankine (LSR) method, on the other hand has shown improved results over existing earth pressure models including M-O. The implementation of LSR model is, however, tedious in its current form as it involves a few iterative schemes to generate the final outcome. A semianalytical equation, combining the M-O equation with a modification factor to incorporate the effects considering a curvilinear failure surface, is developed herein for evaluation of the seismic passive earth pressure in non-cohesive backfill. The proposed equation can produce much improved predictions as the LSR method, yet is as simple in mathematical form as the M-O model. The proposed equation is thus suitable for use in routine design practice.
Keywords: seismic passive earth pressure; Mononobe-Okabe model; Log-Spiral-Rankine model; curvilinear failure surface