Modeling of Sinkholes in Weakly Cemented Sand

Sinkhole development in a profile with a weakly cemented sand overlain by an uncemented sand and underlain by a karst limestone was studied using 51 reduced-scale stress-correct centrifuge models. The interaction between the thickness ( H c ), cohesive strength ( c ), and unit weight (γc) of the cemented sand layer; the thickness ( H s ) and unit weight (γs) of the uncemented sand overburden; and the diameter ( D ) of the cavity in the underlying karst formation was examined. Collapse of the cemented sand layer into the underlying opening was observed to occur either as a breakthrough plug with steeply inclined sides at an average angle of 61° to the horizontal or as a dome fallout that left behind a stable arch. The type of failure depended on the model geometry, described by H c /D. A dimensionless design chart was developed to predict failure, relating N γcH c/c to H c /D for configurations without uncemented sand overburden. The overburden pressure over the cavity at collapse was less than the geostatic overburden pressure. The fraction of full geostatic stress decreased with increasing overburden depth relative to the size of the cavity opening and approached an asymptotic value of about 5%.