In Situ Observation and Model Test on Zonal Disintegration in Deep Tunnels

The mechanical behavior of deep rock masses differs from that of shallow rock masses. Deep rock masses are classified into alternating fractured and intact zones. This unique geological phenomenon is known as zonal disintegration. It is difficult to explain the formation mechanism of such phenomenon under the framework of traditional rock mechanics. The fractured shape and forming conditions of this occurrence also remain unclear. In our present study, we conducted an exploration in deep tunnels of the Dingji coal mine in China to investigate the forming mechanism of zonal disintegration. This phenomenon was observed using a borescope TV. A geomechanical model test was then constructed based on the results of the exploration. An analogical material referred to as barites iron sand cementation analogical and optical scale multi-point displacement meters were developed independently for the model test. The model test was then used to validate zonal disintegration and monitor the formation process. The strain and displacement laws of the surrounding rocks during zonal disintegration were obtained and found to be non-monotonic. The fractured shape of zonal disintegration was determined, and the radii of the fractured zones were found to fulfill the relationship of geometric progression. The experimental results were in accordance with the in situ exploration findings. The mechanism of the zonal disintegration was revealed by theoretical analysis based on fracture mechanics. The fractured zones are reportedly circular and concentric to the cavern. Each fracture zone ruptured at the elastic plastic boundary of the surrounding rocks and then coalesced into the circular form. The geometric progression ratio was found to be related to the mechanical parameters and the ground stress of the surrounding rocks.