Passive Earth Pressure of Overconsolidated Cohesionless Backfill

Abstract

An experimental investigation on the passive earth pressure of overconsolidated cohesionless soil on retaining walls was conducted. A prototype model of a vertical rough wall, retaining horizontal backfill, was developed in the laboratory. The model was instrumented to measure the total passive earth pressure acting on the wall, the passive earth pressure acting on selected locations on the wall, and the overconsolidation ratio (OCR) of the sand in the testing tank. In order to develop the state of passive pressure, the wall was pushed horizontally toward the backfill without any rotation. Overconsolidated sand was produced in the testing tank by placing the sand in thin layers; each was compacted mechanically for a period of time. Tests were performed on walls retaining homogeneous overconsolidated sand, and overconsolidated sand backfill overlying the deep sand layer. The method of slices developed for predicting the coefficient of passive earth pressure for normally consolidated soil was adopted for the conditions stated above. The theoretical values compared well with the experimental results of the present investigation. It is of interest to note that the OCR and the soil condition below the founding level significantly affect the value of the coefficient of passive earth pressure on these walls. Design charts and formulae are presented for practical use.