Active and passive arching stresses outside a deep trapdoor

The classic trapdoor configuration has been useful to examine the changes in stresses expected on buried structures. However, the primary focus of previous studies has been on investigating the loads on the surface of the trapdoor, while stresses outside the trapdoor boundaries have generally been overlooked. This paper presents and discusses results of three-dimensional laboratory model tests conducted to investigate changes in the vertical soil pressure measured at various locations within a granular soil mass surrounding a deep rectangular trapdoor acting in both active and passive modes. The study aimed at investigating stress changes within the portion of the soil mass beyond the boundaries of the trapdoor. Redistributions of soil pressure were found to occur in a large zone of the soil outside the trapdoor under both active and passive conditions. Results indicate that active conditions induced the development of an unloading region in the soil, which includes the collapsing mass above the trapdoor and a portion of the soil surrounding the trapdoor. A stable load-transfer region could be identified in farther portions of the backfill. In passive conditions, the development of a load-transfer region above the trapdoor and an unloading region extending to farther zones in the backfill was also identified. The soil relative density, soil confinement and trapdoor shape were found to affect soil pressure distributions outside the trapdoor limits.