New Analytical Solutions for Cohesive–Frictional Soils above Deep Active Trapdoors

Abstract Even though extensive research works have been carried out to understand the trapdoor responses in frictional materials, those in cohesive–frictional materials have not yet been well studied due to the complexities involved. This paper focuses on formulating new analytical solutions for cohesive–frictional soils above deep active trapdoors. Finite-element limit analyses (FELA) were conducted to study the failure mechanisms of a deep active trapdoor considering various cover ratios, soil cohesion, and soil friction angles. Three distinct failure modes could be observed, depending on various combinations of cover ratio and soil strength parameters: internal, vertical, or external collapses. The analytical solutions, allowing the failure mechanisms and load-transfer mechanisms to be taken into account, were further proposed to calculate the modified lateral earth-pressure coefficient and vertical stresses in soils. The results from previous works and FELA solutions were compared with validate the proposed solutions. A parametric study was performed to explore the effects of cover ratios and soil-strength parameters on soil-arching ratio. The proposed solutions provide a theoretical guideline available for the initial design of geo-infrastructures spanning voids.