Numerical Investigations on Evaluation of Undrained Stability of Active and Passive Strip, Circular, and Annular Trapdoors

The redistribution of stresses caused due to relative induced displacements of the soil particles and the displacement between soil and structure is termed as soil arching. The arching in the soil is generally evaluated using a trapdoor test in active and passive conditions. In the study, the undrained stability of strip, circular, and ring shape trapdoors is evaluated numerically considering the Brom’s and Bennermark stability numbers. A FEM-based program Plaxis2D is used to perform the sensitivity analysis to evaluate the effect of different undrained parameters on the stability of strip trapdoors. The undrained stability number is sensitive to the unit weight of soil, and magnitude of surcharge, whereas it is insensitive to the undrained cohesion of soil. The effect of change in shape and dimension of a trapdoor on undrained stability number is also evaluated. The undrained stability number is insensitive to the variation in the width of the circular trapdoor. A FELA-based program OptumG2 is used to evaluate the stability of active and passive movement of annular trapdoors having radii ratio (ri/ro) varying from 0 to 1 and for a normalized depth ratio H/B = 1–10. The arching effects have been noted for a certain range of radii ratio of the annular trapdoor and the corresponding failure mechanisms are also evaluated.