Evaluation of active and passive seismic earth pressures considering internal friction and cohesion

• The model evaluates seismic earth-pressure force and its point of application.
• Adhesion along wall–soil interface is considered.
• Removes the equilibrium inconsistencies in previous model.
• “Exact” stress state along failure surface of mobilized c–ϕ soil mass is obtained.
• Shear stress redistribution within mobilized soil mass is captured.

The Log-Spiral-Rankine (LSR) model, which is a generalized formulation for assessing the active and passive seismic earth pressures considering the internal friction and cohesion of backfill soil, is reviewed and improved in this study. System inconsistencies in the LSR model are identified, which result from an inaccurate assumption on the vertical normal stress field (σz=γz) in a general c–ϕ soil medium, and from omitting the effect of soil cohesion when solving for the stress states along the failure surface. The remedies to the said inconsistencies are presented, and local and global iteration schemes are introduced to solve the resulting highly coupled multivariate nonlinear system of equations. The modified LSR model provides a more complete and accurate solution for earth retaining systems, including the geometry of the mobilized soil body, the stress state along the failure surface, as well as the magnitude and the point of application of the resultant earth thrust.