Seismic analysis of tall anchored sheet-pile walls

Abstract

The state of practice in designing of anchored steel sheet-pile (SSP) walls for strong earthquake shaking in non-liquefiable ground is reviewed, prior to investigating the performance of a typical quay-wall with a free height of 18m, embedded into relatively dense sandy “foundation” soil. Supporting moderately dense silty sand, the SSP wall is subjected to seismic motions of various intensities with respect to the PGA at the rock-outcrop level, namely 0.15g, 0.30g, and 0.50g. The long-established simplified design methods of (i) pseudo-static limit equilibrium (pLEM) and (ii) beam-on-Winkler-foundation (BWF), in conjunction with the Mononobe-Okabe (MO) method, are shown to lead to results for bending moments that in some cases are larger than, but in other cases quite similar to, those computed with two commercially available finite element (FE) codes, ABAQUS and PLAXIS. The pLEM neglects the effect of the anchor on the distribution of earth pressures on the wall, while at the same time the predetermined MO actions and reactions do not take advantage of the arching in the backfill due to the wall flexure. In contrast, the numerical FE analyses can capture well the physical phenomena of this complex interaction problem leading to reliable results, although the computed deflection of the wall is quite sensitive to the soil constitutive model. The hydrodynamic effects on the seaward side of the wall are shown to have a small effect on the wall performance, contrary to the pseudo-statically applied Westergaard pressures which exaggerate the effect.