Pseudo-Dynamic AnalysisandDesignof Retaining Wall

Abstract

Retaining wall is a structure designed to resist lateral pressure exerted by the backfill soil and it is major concern in the design of the retaining wall. 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. There are mainly three, Static Approach, Pseudo-Static Approach and Pseudo-Dynamic Approach are being used for estimation of lateral earth pressure acting on the wall. In static approach, only static forces acting on the wall are considered. In pseudo static approach, static as well as dynamic forces are considered. In this approach seismic forces are taken as inertial body forces and applied permanently. In pseudo static approach, time and phase effects of seismic force is also considered in calculating lateral earth pressure. Lateral earth pressure on the wall in both active and passive case, retaining cohesionless and cohesive soil backfill has been studied by various researchers under static and seismic loading conditions. Primarily analytical solution to get lateral earth pressure is given by Rankine and Coulomb based on the basis of static earth pressure analyses and design procedures for static lateral loading on retaining structures. In seismic condition due to dynamic effect of loading earth pressure distribution becomes curvilinear and study requires that encounter nonlinear nature of earth pressure distribution in analysis. Present analytical study was undertaken to develop a better understanding and capture realistic distribution and magnitude seismic earth pressures on rigid cantilever retaining structures. Previous pseudo-dynamic analysis literature does not contain the complexity of battered wall retaining inclined C-$\phi$ backfill soil. In the present study, an attempt has been made to get lateral earth pressure in active case for battered wall retaining inclined cohesive backfill and it’s earth pressure distribution along the height of wall using pseudo-dynamic approach. Effect of angle of internal friction of backfill soil, cohesion, surcharge, horizontal and vertical seismic acceleration coefficient and angle of friction between the wall and soil backfill on lateral earth pressure has been studied. The procedure is demonstrated in the study that by removing additional parameters how developed expression can be proved identical to previous expression derived by various researchers using pseudo-dynamic analysis. Results obtained from the analytical analysis were subsequently used to get moment and deflection in STAAD and calibrate a one-dimensional, nonlinear, finite element model built on the MIDAS GTS NX shows a reasonably good agreement with the results from derived equation. Steps for the calculation of static and dynamic analysis is illustrated.