Volume 35, N. 2, May-August 2012 | PDF(4 downloads)
The main purpose of this paper is to study the effect of annulus thickness on the quality of resin mixture for fully grouted resin bolt. Pullout and mixture tests were made in underground coal mines for the following arrangements: (a) 29 mm borehole diameter, and 19 mm roof bolt diameter with steel wire around the roof bolt; (b) 29 mm borehole diameter, and 19 mm roof bolt diameter with no wire around the roof bolt; and (c) 24 mm borehole diameter, and 19 mm roof bolt diameter with no wire around the roof bolt. The mixture test in steel pipe showed that the best resin mixture is for the 24 mm borehole diameter. The arrangement (b) produced big voids around the bolt. But for the 24 mm hole, arrangement (c), the mixture showed the best results. This was corroborated with the pullout tests results where there was a difference in grout stiffness: in the 24 mm borehole diameter is was about 10 times higher than in the 29 mm borehole diameter. On the other hand, as far as the cohesive strength is concerned, the difference is not significant. Numerical models were built to simulate the pullout tests, and also to simulate the roof support at an intersection. Convergence at two underground intersections, consisting of an immediate roof with laminated sandstone, was monitored to evaluate the performance of the roof supports, using the 29 and 24 mm diameter boreholes (i.e. arrangements ‘a’ and ‘b’). The readings showed that the 24 mm borehole diameter resulted in a slightly smaller convergence.