Formulation of seismic active earth pressure coefficient considering adhesive force on back face of retaining wall and cohesion along failure plane in backfill soil

In the seismic diagnosis and the aseismic reinforcement design of railway retaining walls, the effects of cohesion in the backfill of the retaining wall are not considered. On the other hand, aseismic design and seismic diagnosis without the consideration of backfill cohesion may lead to too conservative estimation, since the backfill of existing retaining walls sometimes exhibits a certain magnitude of cohesion. Therefore, by considering the effects of backfill cohesion, it is possible to evaluate the seismic active earth pressure more realistically. A formula evaluating the seismic active earth pressure, which considers both the effect of the cohesion along the failure plane generated in the backfill and the adhesive force between the back face of the retaining wall and the backfill, is derived. The validity of the derived equation is verified by comparison with the result of the trial wedge method and the equation derived in the relevant study. In addition, the derived equation is extended so that the derived formulas can be applied even at high seismic intensities by considering the peak and residual strength of backfill soil. Moreover, the simpler method by introducing the apparent frictional angle is also proposed.