Calculation of loosening earth pressure in deep trapdoor tests on unsaturated sandy soils

The loosening earth pressure acting on the deep trapdoor test is of great significance for the interaction analysis between soils and structures. The traditional model for soil arching and the solutions for loosening earth pressure mainly focus on dry and fully saturated soils. The unsaturated conditions commonly encountered in engineering practice are seldom considered. Based on the ABAQUS finite element software, a series of numerical deep trapdoor tests are conducted to study the model for soil failure by considering the effects of soil saturation. Then, an analytical model for the calculation of the loosening earth pressure is established according to the influences of soil saturation. By combining the major principal arc arch theory with the shear strength theory of unsaturated soils, the analytical solutions for the height of the loose zone and the loosening earth pressure are proposed. The rationality of the proposed model is verified by comparing the results with those of unsaturated trapdoor tests, existing analytical solutions and numerical simulations. The results of parameter analysis show that with the increase of the soil saturation, the loosening earth pressure exhibits a decreasing trend first and then an increasing trend at the critical saturation point, and the value of the loosening earth pressure reaches its minimum value. With the increase of the relative depth ratio, the loosening earth pressure shows a slowly decreasing trend.