Seismic Analysis and Design of Retaining Structures

Abstract

Retaining wall is a structure designed to resist lateral pressure exerted by the backfill soil. The backfill material is retained by the wall at a slope steeper than it would actually adopt in absence of the wall. For many centuries, retaining walls has been used for stabilizing slopes. During events of an earthquake, backfill material exerts dynamic force on the wall in addition to static forces and the passive resistance offered to retaining wall by soil against sliding reduces. Increase in dynamic lateral active earth pressure and decrease in dynamic lateral passive earth pressure on retaining wall during an earthquake has caused several major damages of retaining structures in the past years. Thus, the estimation of seismic force acting on retaining wall from backfill is an important problem. For estimation of lateral earth pressure acting on the wall, various approaches i.e. Static Approach, Pseudo Static Approach and Pseudo Dynamic Approach are being used. In static approach, only static forces acting on the wall are considered, while in pseudo static approach, static as well as seismic forces acting on the wall are considered. In pseudo static approach, seismic forces are taken as equivalent inertial body forces acting on the wall. Lateral earth pressure exerted by the soil backfill on the wall is major concern in design of the retaining wall. Lateral earth pressure in active and passive case exerted on the wall, supporting cohesionless or cohesive soil backfill has been studied by various researchers under static and seismic loading conditions. In the present study, an attempt has been made to compare active and passive earth pressures given by various researchers considering static and pseudo-static approach. Effect of angle of internal friction of backfill soil, cohesion, surcharge, horizontal seismic acceleration coefficient, ratio of vertical to horizontal seismic acceleration coefficient, submerged soil backfill and angle of friction between the wall and soil backfill on lateral earth pressure has been studied. In design of the retaining wall, classical theories assumes earth pressure distribution to be varying linearly along the height of the wall. The earth pressure intensity is assumed to be minimum at the top of the wall and to be increasing linearly with towards bottom of the wall. However, many experimental and theoretical studies in the past under static loading conditions have concluded that variation of earth pressure is curvilinear in contradiction to assumed linear variation. In the present study, distribution of lateral earth pressure distribution along the height of the wall has been studied under static loading conditions. Finite element based software, ABAQUS has been used to study distribution of earth pressure behind retaining wall in static loading condition. Variation of earth pressure intensity with height has been shown in form of graph for all considered cases by carrying out a parametric study. Structural design and detailing of the retaining wall has been done as per relevant Indian Standards.