Evolution models of the damage to the near-field rocks surrounding the drift under the disturbance caused by extraction of the longhole stope

Abstract

Strong blasting disturbances and excavation unloading effects may result in rib spalling and roof collapse of the near-field rocks surrounding the drift during longhole stope mining. An underground gold mine in Shandong Province, China, was selected as a case study to investigate the evolution of the damage to the near-field rocks surrounding the drift through theoretical analysis and field tests, and the relationship between the convergence deformation and damage zone radius of the rock surrounding the drift was established. The results of this study revealed that the convergent deformation of the near-field rocks surrounding the drift exhibited a stepwise increase with time. At the moment of stope blasting, the maximum increment of the convergent deformation of the rock surrounding the drift reached 30.90 mm. Moreover, the convergence deformation of the rock surrounding the drift exhibited exponential decay with increasing distance from the stope boundary. The area within the vicinity of the drift and 7.32 m from the stope boundary was defined as the strongly affected zone, and the area within 7.32–21.62 m of the stope boundary was defined as the moderately affected zone. In view of the functional relationship between the convergence deformation and the damage zone radius of the rock surrounding the drift, a method of calculating the damage zone depth of the rock surrounding the drift was established by considering the effects of the deformation relief before convergence monitoring and the disturbance caused by the extraction of the longhole stope based on the unified strength theory. The error between the damage zone depth obtained using the proposed method and the actual value was less than 3.00%. It was found that the increment of the damage zone depth reached 2.07 m in the strongly affected zone and the average increment was 1.76 m. The method developed in this study can be used to assess the depth of the damage zone in the near-field rocks surrounding the drift in the longhole stope in similar mines.