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Numerical Investigation of Undrained Trapdoors in Three Dimensions


The stability of soil overlying the cavity is often a concern when it comes to the risk of sinkhole occurrences. Current sinkhole studies have been centred on the use of geophysical techniques to detect underground cavity sizes and associated depths. With the measured information, it is possible to theoretically predict the extent of a ground surface collapse. This paper studies the stability of trapdoors and the associated extent of ground surface failure. The shear strength reduction method is used to obtain factors of safety for various scenarios associated with the collapse of a three-dimensional trapdoor underlying undrained clay. Numerical solutions are verified by using the finite element limit analysis technique with upper and lower bound theorems and other published results. A number of practical examples are provided to demonstrate the use of design charts and tables, which can be used together with the application of geophysical tools to predict sinkhole occurrences.

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Author information




All authors contributed to the study conception and design. Conceptualization: JS. Methodology: JS. Formal analysis and investigation: JS and MMH Writing—original draft preparation: JS and MMH. Writing—review and editing: JS and MMH. Resources: JS. Supervision: JS.

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Correspondence to Jim Shiau.

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Shiau, J., Hassan, M.M. Numerical Investigation of Undrained Trapdoors in Three Dimensions. Int. J. of Geosynth. and Ground Eng. 7, 30 (2021).

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  • Sinkhole
  • FLAC3D
  • Strength reduction method
  • Surface failure extent