External stability of waterfront reinforced soil structures under seismic conditions using a pseudo-static approach

Abstract

This paper presents an analysis of the external stability of a waterfront reinforced soil retaining structure. Such structures, in addition to being subjected to normal hydrostatic pressures, are also subjected to earthquake, which gives rise to additional seismic inertia forces and hydrodynamic pressure. Simple pseudo-static approaches are adopted to calculate the seismic inertia forces on the waterfront retaining structure, and a conventional approach is used to estimate the hydrodynamic pressure. The failure wedge is considered to be confined by a planar rupture surface. The results are presented for direct sliding and overturning failure modes of the retaining structure (including results for sloped and vertical walls). By considering all combinations of forces, generalised expressions are developed for the length of geosynthetic reinforcement needed to counter these two modes of failure. The expressions are fairly simple, and can be used directly by practising engineers for the design of waterfront reinforced soil structures. The required geosynthetic length in the direct sliding mode increases from 0.56H to 5.02H when the horizontal seismic acceleration coefficient is increased from 0 to 0.3. It has also been found that, of the two modes of failure, the direct sliding mode is critical. In addition, the requirement for geosynthetic reinforcement for a slope angle of 60° to the horizontal is greater than that needed for a vertical wall (i.e. with a slope angle of 90°). A parametric study is also presented. In addition to the horizontal seismic acceleration coefficient, the downstream water height, pore pressure ratio and soil friction angle all have a significant effect on the sliding and overturning stability of the waterfront retaining structure. Comparison of the present methodology with a previously existing methodology, but for the dry case, shows a close match.