Abstract: The research about spatial form of non-cohesive soil slip surface in passive failure behind the retaining wall in translation was done by the method of model tests. A model test device was designed to carry out 6 passive failure tests for soil behind the retaining wall. The spatial coordinates of the points where the fragile glass strips embedded before break were recorded, in order to determine the location where the soil slide occurred and plot the spatial form of slip surface behind the retaining wall. The test results show that: the 3D effect of the slip surface behind the retaining wall is obvious; in the width of the retaining wall, the slip surface height in longitudinal direction slowly increases in the beginning and then increases in an approximately linear pattern. The initial fracture angle is 9° and the average fracture angle is 26° while the Rankine theory fracture angle is 28°. The maximum length of longitudinal fracture surface was 1.8 times the height of the retaining wall which is generally consistent with the plane assumption of the classical soil pressure theory. The slip surface has a certain horizontal extension, and the principal plane projection extends with initial diffusion angle of about 45°. The form which is the most distant from the retaining wall is a horizontal line with 0.7 time the width of the retaining wall, and the diagonal and horizontal lines are connected with an arc with a radius equal to retaining wall width. The results provide experimental reference for analyzing the spatial form of slip surface in passive failure.

Key words: 3D slip surface, rigid retaining wall, model test, passive failure