New analytical solutions for shallow cohesive soils overlying trench voids under various slip surfaces

Abstract

This paper investigates the effects of cover ratio and soil strength parameters (cohesion and friction angle) on the failure mechanisms of cohesive soils overlying trench voids using trapdoor technique. Adaptive finite element limit analyses (AFELA) were conducted to study the failure mechanisms of trapdoors covered with soils of different thicknesses, cohesions and friction angles. It was found that slip surfaces in the cover soil could be in the shape of vertical, trapezoid, spiral or arching, depending on the combination of soil strength parameters and cover ratio. Analytical solutions under various slip surfaces, considering major principal stress trajectories to describe load transfer paths, were further proposed to study the load transfer mechanisms in shallowly embedded trapdoors. The solutions in terms of arching ratios and lateral earth pressure coefficients were validated against the results of previously reported laboratory tests and AFELA. The results show that the modified earth pressure coefficient is greater than 1.0 due to the consideration of the major principal stress trajectory. The vertical stresses acting on trapdoors are in an inverted parabolic distribution, which are lower in the middle. The arching ratio decreases with increasing soil cohesion, friction angle and cover ratio. For cohesionless soils, the arching ratio decreases as the surcharge loading ratio increases, but for cohesive soils, the arching ratio increases with increasing surcharge loading ratios.