TESTS AND CALCULATION OF ACTIVE EARTH PRESSURE FOR UNSATURATED SOIL UNDER NON-LIMIT STATE

At present,most studies on earth pressure take the soil in the limit state as the research object,assume that the soil is in the saturated or dry state,and do not consider the influence of wall displacement and soil unsaturated characteristics on the earth pressure,which has limitations in practical engineering applications.This paper carries out the indoor model test of rigid retaining wall earth pressure of sand with different water contents behind the wall under active translation mode. The matrix suction and earth pressure at different depths are measured with seepage gauge and earth pressure box. The soil displacement of different retaining wall displacements is observed with DIC image correlation technology. The test results show that when the soil behind the wall is in a non-limit state,the failure surface of the soil always passes through the heel of the wall,and its shape is close to the plane. Secondly,on this basis,combined with the development characteristics of the frictional strength of the wall-soil under the non-limit state and the unsaturated soil strength criterion,a displacement-related unsaturated soil strength model is proposed. A calculation model of the unsaturated soil active earth pressure in the non-limit state is established. The comparison with the laboratory test results verifies the rationality of this model. Finally,the influence of wall displacement and matric suction on active earth pressure is discussed. The parametric analysis results show that the active earth pressure of unsaturated soil decreases gradually with the increase of the displacement of the retaining wall,but it first decreases and then increases with the increase of the matrix suction. There is a very small earth pressure value. The Rankine earth pressure and the Fredlund's extended Rankine earth pressure values are the special values of the model when the displacement reaches the limit state under saturated and unsaturated conditions,respectively.