This dissertation is mainly concerned with the experimental investigation of the passive failure of an initially vertical, rough, plane wall which is rotated about its toe in to a mass of dry sand with an unloaded, horizontal surface. The sand is constrained to deform in plane strain. Measurements of the distribution of the normal and shear stresses on the wall are made for tests on loose and dense samples of Leighton Buzzard sand with walls of heights between 6" and 13". Strain fields are determined from observations by an X-ray technique of the positions of lead shot buried in the sand mass. A new method is developed for placing shot in loose samples and a full analysis of the strains for tests on loose and dense sand is given. The variation of the forces and-moments on the wall is investigated and it is found to be very different for tests on loose and dense sand. The distribution of stress on the wall changes little during a test on loose sand but changes radically in a test on dense sand. The distribution of normal stress is not linear at any stage of either test. Rupture planes are observed in dense sand well before peak moment is measured on the wall, but at peak moment, there are no rupture planes at 2 depths greater than 3 the wall height. A comparison of rupture planes and the observed trajectories of zero extension is made. Analysis of the strain data ShOHS that the angle of dilation is constant for a large range of strain in dense sand. Loose sand strains without discontinuities but there are high strains near the top of the wall. The Sokolovskii method of analysis is used to predict the stresses and the principal stress directions for two problems with boundary conditions similar to those of the experiments. Comparisons are made with the measured wall stresses and the observed principal strain directions in loose and dense sand. Stresses are predicted from the measured strains in loose and dense sand by the method of Arthur, James and Roscoe. (1964) and are compared with the measured wall stresses and the stresses predicted by the Sokolovskii analysis. A simple velocity field for rotation of a wall about its top or its toe or for wall translation is developed for an idealised mat~rial that dilates at a constant rate. Detailed comparison between the predictions of the field and the experimental data is made and approximate stress distributions at two stages of a test on dense sand are calculated. The simple field allows prediction of the rupture plane mechanisms that are observed in dense sand for wall rotation about the top or toe or for wall translation, and gives great insight into the behaviour of sand in the three problems.