DISPLACEMENT ANALYSIS OF RETAINING WALLS UNDER STATIC CONDITION

Abstract

A displacement analysis under static condition is proposed by modelling the backfill as closely spaced independent elastic springs fixed to the back of retaining wall at different locations and the other ends of the springs are fixed to an immovable support. The spring constants are evaluated treating the retaining wall as a beam to be simply supported at the spring locations and subjected to soil reaction which depends on the type of soil and direction of wall movement. Depending upon the wall and backfill characteristics, the limitng strain for each spring is specified so that, when all springs possess limiting strain, the analysis will yield pressures as given by classical earth pressure theories. To start with, it is assumed that the springs are precompressed ,so as to create at rest condition. Now, for any displacement the spring forces are found out and these are substracted from (or added to) initial forces for displacements away from the backfill (or towards backfill). The resulting sum of spring forces gives the.pressure for the given displacement. The pressure distribution is determined from the spring forces. The model also incorporates the effect of friction between the wall and the backfill. Study has been carried out with several assumed values of limiting strains and from there, yield strain, 'that corresponds to Coulomb's earth force has been determined. Plots between yield strain and height have been given for various backfill soil conditions for two modes of wall movement (translation and rotation about bottom) in both active and passive states. Corresponding earth pressure distributions were also plotted. It is noticed from these plots that the assumption of hydrostatic pressure distribution is not correct and it will result in error, particularly that in case of active-translation, where pressure distribution is nearly parabolic, therehy causing point of application of earth pressure higher than the one third point. For limiting strain less than yield strain, pressure distribution is more close to hydrostatic. For passive case, although, the pressure distribution can not be approximated to be a parabola, it is easily noticed that the distribution is also not hydrostatic, as assumed in classic.al earth pressure theories. 3