Earth Pressure of the Trapdoor Problem Using Three-Dimensional Discrete Element Method

Abstract

Load transformation from the yielding part of the soil to the adjacent part is known as the soil arching effect, which plays an important role in the design of various geotechnical infrastructures. Terzaghi’s trapdoor test was an important milestone in the development of theories on soil arching. The research on earth pressure of the trapdoor problem is presented in this paper using the three-dimensional (3D) discrete element method (DEM). Five 3D trapdoor models with different heights are established by 3D DEM software PFC 3D. The variation of earth pressure on the trapdoor with the downward movement of the trapdoor, the distribution of vertical earth pressure along the horizontal direction, the distribution of vertical earth pressure along the vertical direction, the distribution of lateral earth pressure coefficient along the depth direction, the magnitude and direction of contact force chain are studied, respectively. Related research results show that the earth pressure on the trapdoor decreases rapidly after the downward movement of the trapdoor, and then reaches the minimum earth pressure. After that, the earth’s pressure will rise slightly, and whether this phenomenon occurs depends on the depth ratio. For the bottom soil, due to the stress transfer caused by the soil arching effect, the ratio of earth pressure in the loose area decreases, while the ratio of earth pressure in the stable area increases. With the trapdoor moving down, the vertical earth pressure along the depth in the stable zone is basically consistent with the initial state, which shows an approximate linear distribution. After the trapdoor moves down, the distribution of earth pressure along with the depth in the loose area changes, which is far less than the theoretical value of vertical earth pressure of its self-weight. Because of the compression of the soil on both sides, the lateral earth pressure coefficient of most areas on the central axis of the loose zone is close to the passive earth pressure coefficient Kp. The existence of a ‘soil arch’ can be observed intuitively from the distribution diagram of the contact force chain in the loose zone.