Analogical model test and theoretical analysis on zonal disintegration based on filed monitoring in deep tunnel

Field monitoring carried out in a deep tunnel of the Dingji coal mine in China confirmed the zonal disintegration phenomenon by using the borehole TV. Based on field monitoring, an analogical model test was conducted to research the fracture shape and forming conditions of the rock mass in the Dingji mine. To perform the model test, an analogical material and optical sensor were developed independently. Through the test, the occurrence of zonal disintegration was confirmed and the forming process was monitored. The fracture pattern of zonal disintegration was determined, and the radii of the fractured zones were found to fulfil the relationship of geometric progression. The displacement laws of surrounding rocks during zonal disintegration were obtained and found to be non-monotonic. The test results are in agreement with the field-monitoring results. Through a theory analysis based on fracture mechanics, the mechanism of zonal disintegration was revealed. The fracture zones occur as circles concentric to the cavern periphery, which is the false face. Each fracture zone ruptures at the elastic-plastic boundary of surrounding rocks and then coalesces into a circle. The geometric progression ratio was determined; it is related to the mechanical parameters and ground stress of the surrounding rocks and calculated as follows: [(p(0)/c tan phi + 1)(1 - sin phi)]((1-sin phi)/2sin phi). And the mechanism of the non-monotonic displacement law is revealed; the continuous formation of the false face causes the geostress redistribution and crack opening.