Prediction of a karst collapse diameter in a coherent dispersed and hard-rock massive using the “organ pipes” mechanism: a geomechanical method and its verification

Relevance of the research. The choice of the calculation parameter of karst deformations and forecasting its size is the most important task when assessing the karst danger of territories. As a rule, a collapse is used as a calculation parameter. When predicting a collapse using the “organ pipe” mechanism, estimating its diameter presents severe difficulties. The main one is the lack of described and verified deterministic geomechanical (analytical) methods. The aim of the research is to introduce into engineering practice a verified geomechanical method for predicting the diameter of a karst failure using the “organ pipe” mechanism. Research methods: field observations of a very large number of “organ pipes”; instrumental (geodetic) measurements of the “organ pipes” sizes and their elements (rockslides under the “pipes”, karst sinkholes above the “pipes”); analysis of engineering-and-geological conditions in which the “organ pipes” were formed; generalization of the results of field observations and geodetic measurements; comparison of the predicted diameter of the failure, calculated using the proposed geomechanical method, with the actual (measured) diameter of the “organ pipe” (verification of the method). Results of the research. Generalization of the results of long-term field observations and geodetic measurements allowed us to develop a geomechanical method for predicting the diameter of a karst sinkhole using the mechanism of “organ pipes”. Dependencies were obtained that allow us to take into account the subsequent development of a sinkhole into a funnel. Verification calculations of the proposed solutions were performed using the example of the diameters of a sinkhole and a funnel formed above one of the “organ pipes”, which is located in the Kungur Ice Cave. The predicted value of the sinkhole diameter differs from the actual one by only 6,5 %, and the diameter of the funnel by 1.4 %. Based on the verification results, the possibility of using the proposed geomechanical method to solve engineering problems was confirmed.