Stability Assessment of Natural Caves Using Empirical Approaches and Rock Mass Classifications

The stability of underground voids such as caves can be assessed, in an initial approximation, by geomechanical classifications such as the Barton Q index. From a geomechanical viewpoint, the stability of 137 large span natural caves was analyzed herein. The caves were graphically represented based on existing tunnel and underground graphs, according to width and rock quality index Q. Many natural caves analyzed by a tunnel-type engineering approach could result as apparently unstable when represented in empirical existing graphics and would require reinforcements incompatible with speleothems and large chamber heights. A new graph and equation are proposed herein for the maximum span, for the exclusive case of caves, resulting in a reliable representation of large stable natural caves. The main contribution is a new stability chart for natural caves, consisting of two zones: a zone where stable caves are represented and a zone where unstable caves and collapsed caves are located.Instituto Geológico y Minero de España, Españ