Stability charts for predicting sinkholes in weakly cemented sand over karst limestone

Forty-nine physical models of sinkhole development were constructed and tested using a geotechnical centrifuge to replicate full scale sinkhole development in the small models. The soil profile studied was weakly cemented sand, overlying cavities in karst limestone with uncemented sand over the cemented sand layer in half the models. figurations with no uncemented soil overburden, the parameters critical to predicting failure were: the unit weight of the cemented sand, γc; the thickness of the cemented sand overlying the karst cavity, Hc; the true cohesion of the weakly cemented sand, c; and the diameter of the underlying karst cavity, D. Brittle collapse of the cemented soil into the underlying cavity took one of two forms depending on geometry: when Hc/D was less than or equal to 0.25, the plug of soil that fell into the cavity penetrated through the full thickness of the cemented layer leaving an open hole. When Hc/D was greater than or equal to 0.31, the plug of soil that fell into the cavity did not penetrate through the full thickness of the cemented layer, but left behind a stable arch. A dimensionless stability chart was developed based on model results relating (γcHc/c) and (Hc/D) at failure; that chart can be used to predict the onset of failure extrapolating to configurations and soil cementation strengths not specifically tested in this research. y was also made of the influence of uncemented sand overburden on hastening sinkhole development for configurations with ratios of Hc/D less than or equal to 0.25; the thickness of the uncemented overburden was varied. At the brink of sinkhole development, there was significant arching within the uncemented sand, and the influence of the overburden on hastening sinkhole failure was much less than the full geostatic overburden. The maximum uncemented overburden pressure bearing down on the breakthrough plug never exceeded the weight of a cone of sand of diameter D′, and height 1.25D′, where D′ equals the diameter of the top of that inclined plug.