Principles and methods for preventing and controlling the hourglass-type karst ground collapse

There are 6 limestone belts trending in nearly EW trending fold structures in the Wuhan area, where karst ground collapse occurs frequently. Such failure can be divided into three basic types, i.e. hourglass type, soil cavity type and vacuum erosion type, each has its special geological conditions and corresponding collapse mechanism. As the disaster caused by hourglass-type collapse is the most serious and most difficult to control, this paper focuses on its geological conditions, collapse mechanism, prevention principles and methods. Analysis shows that the key factor to cause the hourglass is the groundwater (karst water and pore water ) seepage, of which original power is the karst water seepage. Consequently, the fundamental measure to prevent hourglass collapse is to set up curtains to cut off karst water seepage. At last, the principles and methods of preventing and controlling the hourglass collapse of subway stations and section shield are proposed, which have attained good effects in practice.