Calculation of the Loosening Earth Pressure in Deep Trapdoor Test in Unsaturated Sandy Soil

The loosening earth pressure acting on the deep trapdoor test is of great significance on the interaction analysis between soil and structures. Traditional soil arching model and the loosening soil pressure solutions mainly focus on dry and fully saturated soil. The unsaturated condition which is commonly encountered in engineering practice is seldom considered. Based on ABAQUS finite element software, a series of numerical deep trapdoor tests are conducted to study the soil failure model by considering the effect of soil saturation. Then, an analytical model for the calculation of the loosening earth pressure is established according to the influence of soil saturation. Combined the major principal arc arch theory with shear strength theory of unsaturated soil, an analytical solution for the height of the loose zone and the loosening earth pressure is proposed. The rationality of the model in this paper is verified by comparing the results with that of unsaturated trapdoor experiments, existing analytical solutions and numerical simulations. The results of parameter analysis show that with the increase of soil saturation, the loosening earth pressure shows a decreasing trend first and then an increasing trend at the critical saturation point, the value of the loosening earth pressure value gets the smallest. With the increase of relative depth ratio, the loosening earth pressure shows a slow decreasing trend.