Stress induced damage in tunnels in a cave mining environment in kimberlite

In any cave mining method a horizontal slice of rock is mined out at the base of the block to be caved by drilling and blasting. Once a sufficiently large area has been mined continuous caving initiates and propagates through the block. High stress levels are set up in the abutment zone around the perimeter of the caving area that can affect tunnel stability to a distance of 20 metres from the cave front. A second level must be created below the caved rock to allow mining of the overlying, caved ore. The mining sequence implemented impacts on the levels of stress to which the tunnels on the lower level are subjected. Ideally all development on the upper, undercut level should be completed and development on the lower, extraction level should be carried out in de-stressed rock. Logistical constraints often preclude this mining sequence. Alternate strategies and controls must be implemented to limit stress induced damage to the extraction level.