Experimental study on anchoring effect of brittle rock mass influenced by loading rates at low strain rate

The loading rate of external load can strongly influence the stability of surrounding rocks of roadways sup-ported by rock bolts. Currently,the anchored rocks under different loading rates are seldom studied by experiments. Surrounding rocks of anchored roadways are mostly under uniaxial loading condition,moreover,the surrounding rock pressure is mainly loaded at low strain rate. Combined with those failure characteristics of brittle surrounding rocks of roadways supported by rock bolts,the uniaxial compression experiments on sandstone with two bolt-like iron bars are performed under five kinds of loading rates at low strain rate ranging from 0. 001 mm / s to 0. 100 mm / s. The experi-mental results show that loading rates at low strain rate variously influence the mechanical properties and fracture char-acteristics of anchored and unanchored sandstone samples. The elastic modulus of anchored sandstone samples is slightly improved with the increase of loading rates at a low strain rate. Under all the loading conditions,the axial com-pressive deformations of anchored sandstone samples are mostly same as those of sandstone samples without bolts. Uni-axial compressive strengths of samples without bolt can increase with the increase of loading rates,however,high load-ing rates can result in the bad strength characteristics of anchored sandstone samples compared to those unanchored samples,its strength sensitivity to loading rate is relatively reduced which indicates that the reinforcement effect of bolts is weakened by the loading rate. The final fracture mode of all unanchored samples is the tensile-shear failure which always occurs with an initial tensile surface crack. Increasing the loading rate can make the final fracture mode of anchored samples change from tensile failure to tensile-shear failure unlike that of unanchored samples,also turns its initial tensile surface crack into the shear crack. In addition,the strength deterioration of anchored sandstone influ-enced by loading rates at low strain rate is discussed based on energy theory,the acoustic emission characteristics of anchored samples and the interaction theory of rock bolt and rock mass. Acoustic emission signals show that the an-chored specimen has large damage much early after loaded at high loading rate and its energy dissipation increases, furthermore,the high loading rate also makes the interface load transfer between the rock mass and the bolt ineffective. These results show that the load dynamics failure of rock-bolt system should be prevented especially for anchored road-ways in danger of coal bump and comprehensive rock bolts support methods need to be promoted necessarily with the relieving pressure technology.