Stability Charts for the Collapse of Residual Soil in Karst

Collapse of the residual soil over bedrock cavities often occurs during construction in karst terrain, particularly when the thickness of the residuum is reduced during excavation. Even if an estimate of the strength of the residual soil is known, uncertainty with respect to the size/geometry of the subterranean voids makes a detailed analysis difficult, and straightforward methods to check the stability are needed. In this study, numerical analyses were performed to develop a stability chart expressed in terms of a dimensionless stability number and the geometry of a potential void in the residual soil. The stability charts include the effect of friction angle, and are also developed to allow the investigation of the effect of the inverted strength profile typically observed in karst terrain. Such stability numbers may 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.