Preliminary Screening of Residual Soil Stability in Karst Terrain

摘要

The stability of the residual soils that overlie cavitose limestone is often a concern during the siting, construction, and maintenance of facilities in karst terrain. Voids or domes often form in the residual soil above the rock cavities, and unless the thickness of the residual soil is sufficient for the development of arching, the soil may collapse and sinkholes may form. A preliminary screening method is proposed to estimate the thickness of residual soil required to provide stability for a given range of potential soil-void diameters. The method considers two modes of instability for sites with shallow (less than 25 m) overburden. Stability with respect to the first mode (cover collapse) depends on the development of arching in the residual soil and suggests a minimum allowable cover thickness for stability. Stability with respect to the second mode (cover subsidence) corresponds to the yielding and plastic flow of the soils into the soil and/or rock void and suggests a maximum cover thickness above which subsidence should be evaluated. Sites with very thick overburden (more than 25 m) are generally not considered problematic. The limiting conditions for the first stability mode are compared with estimated sinkhole dimensions reported in the literature and the application of the stability chart is demonstrated by an example.