Experimental and Theoretical Investigations on Evolution of Soil-Arching Effect in 2D Trapdoor Problem

Soil arching effect has been widely recognized as one of the most critical factors governing load-transfer mechanism in the design of various geotechnical infrastructures. However, most existing studies on soil arching effects are limited only to the state when soil arching effect is fully mobilized, while the knowledge about the evolution of soil arching effects with relative displacement remains largely unknown. In this study, a series of classical trapdoor tests are conducted to investigate the evolution of soil arching effects with the progressively developed relative displacement for the trapdoor problem. A particle image velocimetry (PIV) technique is employed to measure the progressive development of displacement and shear strain of soil mass. The development of slip surfaces as well as stress transfer in soil mass are studied. The observed evolution of slip surfaces in soil mass is then related to the load-displacement characteristics of the soil mass under various magnitude of surcharge during trapdoor tests. The test results indicate that the triangular and vertical slip surfaces correspond with the minimum and residual values of loosening earth pressure, respectively. Upon the experimental observations, analytical solutions are proposed to predict both the minimum and the residual values of loosening earth pressure acting on top of the trapdoor, where the deflection of principal stress axes is considered. Comparisons between the model predictions with test results are carried out. Good agreement is observed, which validates the proposed theoretical model.