Numerical investigation on the mechanical behaviour of karst sinkholes

The mechanical behaviour of soils overlying weathered bedrock is often a concern when it comes to the risk of sinkhole occurrence. Cavities often form near the interface between cover soil and fissured bedrock and propagate upwards with internal soil erosion, ultimately resulting in surface collapse known as sinkhole. This paper presents and discusses the mechanical behaviour of sinkholes by investigating the stability associated with the size and depth of the cavity. The two failure modes considered in this study correspond to tensile failure and excessive yielding around a subsurface cavity. Numerical modelling with the finite-difference software Flac was employed to determine the stress distributions and deformations around the cavity. The results of numerical analyses were used to quantify the effects of factors affecting sinkholes such as bedrock depth, cavity size, overburden thickness and soil strength. The results also illustrate the yielding behaviour, which is related to a cover-subsidence sinkhole with a gradual depression over time but no structural collapse. The analysis result shows that the critical overburden thickness of around 25m turns the yielding condition from unstable to stable.