Experimental study on the mechanical properties of grouted rock bolts subjected to sulfate attack and freeze-thaw cycling

Abstract

This paper examined the effects of freeze-thaw cycling and sulfate attack on the pull-out capacity of rock bolts. The freeze-thaw cycling experiments consisted of alternating 4-hour freeze-thaw cycles in a high-low temperature environmental test system; some specimens were subjected to sulfate attack during freeze-thaw cycling. After exposure to a number of freeze-thaw cycles, the specimens were tested to failure. The displacement, strain and ultimate pull-out capacity of the rock bolts were determined. The experimental results show that the compressive and shear strength values of the specimens subjected to freeze-thaw cycles in pure water (PW) decreased with increasing freeze-thaw cycles, whereas in the early stage of freeze-thaw cycling, the compressive and shear strength values of the specimens subjected to freeze-thaw cycles in sulfate solution (SS) increased and then decreased. Both freeze-thaw cycling and sulfate attack reduced the bearing capacity and increased the deformation of rock bolts, which caused stress relaxation in the bolts. Moreover, both freeze-thaw cycling and sulfate attack can reduce the mechanical properties of rock bolts. Under the combined action of sulfate attack and freeze-thaw cycling, freeze-thaw damage played a dominant role. In this study, the effect of freeze-thaw damage was quick, whereas the effect of sulfate attack was slow. After a period of exposure to sulfate attack or freeze-thaw cycling, the damage from sulfate attack was greater than that from freeze-thaw cycling. Regression equations were given to estimate the bearing capacity of rock bolts subjected to sulfate attack and freeze-thaw cycling, thereby providing a method for evaluating the durability of rock bolts.