Experimental study on failure mode and lateral earth pressure distribution of unsaturated sand behind retaining walls under active translation mode

Under the active translation mode, a series of laboratory model tests on the active earth pressure against rigid retaining walls with different wall roughnesses and water contents of backfill are carried out, in which the matric suction and earth pressure are monitored by embedding the piezometer and earth pressure cell, respectively, and the position of the failure surface is obtained by using the DIC technique, and the effects of the matric suction and interface roughness on the earth pressure and the shape of the failure surface are discussed. The test results show that with the increase of the water content, the failure surface tends to move outward. The reason is that when the matric suction of sand is greater than its air entry value, the suction stress decreases with the increase of the matric suction, which in turn reduces the shear strength of the soil. After reaching the active limit state, the fracture surface passes the wall heel but is shallower than the Coulomb failure surface, and the difference between them increases with the decrease of the matric suction. The wall-soil interface friction has a few effects on the shape of failure surface. Furthermore, in the middle and upper parts of the wall, the active earth pressure increases approximately linearly with the increase of depth, but in the area near the heel of the wall, the earth pressure shows a slight decrease, which is mainly caused by the frictional resistance transmitted by loose sand. The measured active earth pressure is always smaller than that of Coulomb active earth pressure, and the difference increases with the increase of the water content. Compared with the influences of the friction angle, the suction stress has a more obvious effect on the earth pressure.