Effect of grouting on shear behavior of rock joint

Improper ground conditions should be improved to gain higher strength suitable for construction and the grouting with cement injection is the best option. Understanding the mechanical behavior of grouted fractured rock mass is based on characterization of grouted rock fractures. A systematic comprehensive study on the effect of consolidated grouting on mechanical behavior of fractures has yet to be conducted. The present research work incorporated identical artificial fractures produced through silicon casting and dental plaster as analogs to the ones found in Chamshir dam area in Gachsaran of Iran. By using dental silicone, samples with three different surface roughnesses were molded and finally by using dental plaster that had more strength than gypseous and more faster built up than concrete, several replicates of each samples were casted. Grouts with the water-cement ratios of 1:1 and 2:1 were generated and placed into the fractures. The grouted fractures were subjected to direct shear test and cohesion of the joint and friction angle in both residual and maximum shear strength were determined for different characteristics of rock joints like roughnesses and apertures. The results show that grouting is of positive effect on shear strength. With decreasing the water-cement ratio, grout compressive strength is increased but not necessarily an increase in its shear strength. Maximum friction angle of fractures experienced a decrease by 36-48% by means of 2:1 ratio grout and fluctuated between 5% and 15% through 1:1 ratio grout which approximately equals that of a natural joint. While maximum cohesion rose by 145-282% with 2:1 ratio grout and by 59-96% with 1:1 ratio grout.