Discussion of the Technical Note “Seismic Passive Earth Thrust on Retaining Walls with Cohesive Backfills using Pseudo-Dynamic Approach” by A.H. Shafiee, A. Eskandarinejad, M. Jahanandish: Geotechnical and Geological Engineering, DOI 10.1007/s10706-010-9327-3

Excerpt

The writers are greatly appreciated for extending the pseudo-dynamic approach to estimating the seismic passive earth pressure on a vertical retaining wall from the cohesionless soil (ϕ soil) backfills presented by Choudhury and Nimbalkar (2005) for computing the seismic passive earth pressure from cohesive soil (c-ϕ soil) backfills. These works use the concept of phase difference due to the finite shear wave propagation behind a retaining wall as presented by Steedman and Zeng (1990), and Zeng and Steedman (1993), and derive the expressions for the total seismic passive force (\( P_{pe}^{*} \)) in nondimensional form, considering the equilibrium of forces on an assumed failure wedge. The expression presented in Eq. (11) involves several parameters including the angle of inclination (α) to the horizontal of the failure plane. No attempt was made to present an expression for the critical value of α that can be used to estimate minimum total seismic passive force. Presenting expression for the critical value of α has been the most important aspect in the analysis of static/dynamic passive earth pressure since the development of classical Rankine, Coulomb, and Mononobe-Okabe expressions for the earth pressures (Okabe 1926; Mononobe 1929, Lambe and Whitman 1979; Terzaghi et al. 1996; Das and Ramana 2010). In fact, an analytical derivation for the critical value of α for a generalised case considering both cohesion c and angle of shearing resistance ϕ of the soil backfill has been a challenging problem for the researchers. For the total seismic active force on a retaining wall from the c-ϕ soil backfills, Shukla et al. (2009) presented an explicit analytical expression along with an expression for the critical value of α based on the pseudo-static analysis. Similar expressions have been derived recently by Zahid et al. (2010) for the total seismic passive force. The discusser notices that the writers have used the analytical expression for the upper limit of horizontal seismic coefficient presented by Shukla et al.; Eq. (23) from this work has been reproduced as Eq. (12) in the technical note (see Sect. 4 on page 528). The discusser is surprised to note that the reference for Shukla et al. has not been included in the list of references on page 531. It has been recommended that to obtain the minimum value of \( P_{pe}^{*} \) from Eq. (12), one should optimize Eq. (10) with respect to α and t/T. In the discusser’s opinion, this is the real expected task, which has not been explained in the note from the readers’ point of view so that the concept presented in the note can be used conveniently. …