Abstract:

At present, the calculation methods of active earth pressure are mostly only for the soil in a saturated or dry state, ignoring the gradual process of soil from unsaturated to partially saturated, or from saturated to unsaturated, which leads to distortion of the calculation results. In this study, a series of model tests on the active earth pressure of unsaturated sand behind retaining wall is carried out to reveal the failure law of soil behind the wall. Observations show that, 1) there is an approximately vertical crack on the top of the soil behind the wall, and its development depth increases with the increase of wall surface roughness and water content;  2) the wall-soil interface friction has almost no effect on the plastic zone of the soil behind the wall, and the shape of the plastic zone  remains approximately flat during the movement of the retaining wall. On the basis of tests, the generalized effective stress principle is introduced, an analytical method for calculating active earth pressure of unsaturated soil considering the effect of suction stress is developed based on limit equilibrium analysis. The theoretical and experimental results show that the proposed method is closer to the experimental values than other methods. Finally, the main factors influencing the active earth pressure of unsaturated soil are analyzed, and it is found that the active earth pressure decreases with the increase of soil friction angle, but the interface friction angle has little influence on the distribution of active earth pressure; compared with no suction case, the active earth pressure is smaller when considering suction; with the increase of air-entry value, the contribution of the suction stress to the active earth pressure decreases and eventually tends to be constant.

Key words: retaining wall, model test, active earth pressure, matric suction, interface roughness