Passive Pressure in Sands with Uniform Surcharge on Backfill

Abstract

An extensive retaining wall model testing program is described which includes a study of the shape of rupture surface and pressure distribution, and the validity of existing theories. The experimental apparatus was designed to allow three types of wall movement, translation, and rotation about the top and bottom of a rigid steel wall 45.0 cm high. Dry sand was used for backfill. The results are reported of tests which include a condition when a uniform surcharge was applied on the backfill. Figures are presented which show the observed rupture surfaces for different types of wall movement and surcharge intensity for the dense and loose sands respectively. The data indicate that the shape of failure depends on the nature of wall movement and that it is curved in all cases. The size of the passive wedge increases with sand density as predicted by theory. The rupture surface observed in the case of rotation about the top is closer to Coulomb's wedge. The stress distribution obtained for wall rotation about the bottom is shown. The values of the coefficient of passive earth pressures, Kp, obtained in all the tests where a uniform surcharge was applied are slightly less than those where no surcharge was applied. The value of Kp for dense sand is found to be greater than for loose sand, Kp is a maximum for the case of wall rotation about the bottom, and minimum for wall rotation about the top. These data reflect that the typed wall movement has an effect on the stress distribution on the wall.