Undrained Stability of Residual Soil in Karst

Human activity on the karst landscape can result in subsidence or collapse, particularly when the thickness of the residual soil layer is reduced due to excavation. When collapse occurs beneath or adjacent to structures or highways, it may result in extensive damage. The stability of the residual soils that overlie solution cavities in limestone is often a concern during the construction, and a simple means to evaluate the stability of these residual soils may be valuable. In this study, the undrained stability of residual soil in karst terrain was investigated by the Finite Element Method (FEM). The results are summarized in a design chart in terms of dimensionless stability numbers and the geometry of a potential soil void above a cavity in the underlying limestone. The use of the stability chart for short-term stability is demonstrated by an example. Such stability numbers can be useful to estimate the stability of a given site based on the expected thickness of the soil overburden and the likely range of anticipated soil void diameters.