Undrained stability of active and passive trapdoors

The recent growth in the number of sinkhole occurrences due to human activities has highlighted the need for better understanding and prediction of the problem. This paper investigates the use of Broms and Bennermark’s original stability number for trapdoor problems in cohesive soil. The shear-strength-reduction method built in a finite-difference method software program (FLAC) is used to obtain the factor of safety (FOS) under different combinations of pressures for collapse and blowout. Unlike previous research on the use of critical pressure ratios, the FOS results are now functions of the original stability number and depth ratio. The obtained numerical results are compared and validated by using rigorous upper- and lower-bound finite-element limit analysis, as well as other existing solutions available in the literature. Surface failure extents are also examined in the paper. The dimensionless ratios employed in this study are useful for preparing design charts with a broad range of trapdoor geometries and soil parameters