Innovative liner support trials in underground hardrock mines: S. Espley, C. Langille & D. McCreath, CIM Bulletin, 88(922), 1995, pp 66–74

Abstract

In 1993, trials of two innovative applications of liner support involving the replacement of bolts in the ground support system were undertaken at Inco mines. The first trial involved an evaluation of the effect of dynamic loading on mesh-reinforced boltless shotcrete in a sub-level cave mining area on 2400 level at Stobie Mine. The second trial involved an evaluation of the MIROC Mineguard spray-on liner as a replacement for bolts and screen support, or as a replacement for screen support alone, in a topsoil heading of a bulk, VRM (vertical retreat mining) stope on 3240 level at Lower Coleman Mine. In the Stobie Mine trial, an uppers retreat heading was supported using a two-pass system. Fist, shotcrete was applied 2 inches thick, following by pinning of mesh screen to the back and walls. A second pass of another 2 inches of shotcrete was then performed. For recovery of the ore zone, a vertical slot was created using a Borepak blind boring machine. The uppers rings were blasted, one or two rings at a time, starting at the slot and retreating out of the heading. During blasting of the production rings, blast monitoring was used to record the ppvs (peak particle velocities). For a serie of 5-ring blasts, the maximum ppvs were measured to be 0.4 m/s (16 in./s) with a maximum charge weight per dely of 357 kg (800 lb). Six 5-point convergence measurement stations were set up and after each blast the total rockmass convergence was measured using a tape extensometer. Although a maximum displacement of 100 (4 in.) was measured, the shotcrete still managed to provide some support function. A support damage assessment was also done to try and relate blast vibration of effectiveness of the mesh reinforced shotcrete liner. This trial demonstrated the effect that blasting has, on a support system, and it also demonstrated the necessity of having the mesh reinforcement properly placed within the shotcrete. The Lower Coleman Mine trial involved the development of an engineered design to create a dead-weight loading system to test the standard rockbolts and screen support system versus a polyurethane liner support system, with and without the installation of rock bolts. Each support was evaluated on its ability to support a dead-weight load or a slab of rock having dimensions 12 ft by 20 ft by 4 ft thick. A development and blasting scenario was designed and implemented for the creation of the dead-weight load in the topsill heading. Initially the heading was driven developed 20 ft high and 20 ft wide and then it was advanced another 100 ft using a reduced back height of 15 ft. This created a 5 ft hanging breast, support system. For each test, the brow was drilled off with closely spaced horizontl perimeter holes, each being 12 ft in length and with a 4 ft burden. Additional horizontal perimeter holes were drilled along the shoulders of the brow area to within 1 ft of the back. Further down the drift from the brow, closely spaced up-holes were drilled, each 5 ft in length, to intersect the toe-locations of the horizontal perimeter holes.