FAILURE MODE AND CRACK PROPAGATION OF SANDSTONE WITH PRE-EXISTING FISSURES UNDER DIFFERENT ANCHORAGES BY GROUTING

Based on the uniaxial compression experimental results of fissured sandstone under different anchorages by grouting,the failure modes of fissured sandstone were investigated,and the effects of bolt number and pre-stress on failure characteristics of fissured sandstone were discussed.In the failure process of fissured sandstone with two bolts,the initiation,propagation and evolution of three-dimensional cracks were analyzed.The results show that the final microscopic failure mode of fissured sandstone becomes more complexed with the increase of bolt number.For fissured sample with a fissure angle of 30°,the failure mode of the sample indicates a transition from tension failure to tension-shear mixed failure.However for fissured sample with a fissure angle of 45°,the failure mode of the sample indicates a transition from shear failure to tension-shear mixed failure.Pre-stress restrains the expansion and propagation of tension cracks in fissured samples,which leads to a smaller crack number than that under the condition of non-prestress.Finally,taking some fissured sandstones as typical examples,we analyzed the behavior of crack propagation during the whole deformation and failure process.It is evident that the failure of fissured sandstone is asymptotic.