Mechanical responses of shotcrete specimens in direct shear tests

In this study, the direct shear tests under constant normal stress condition (CDST) and unloading normal stress condition (UDST) were conducted to investigate the shear responses of shotcrete specimens, with using a self-designed test scheme and an auxiliary device on a rock compression-shear test system in Chongqing University, China. The shotcrete specimens were of strict preparation complying with the Chinese Standards. A total of eighty five shotcrete cubic specimens (100 × 100 × 100 mm3) were tested. Results from this study show that the shear strength of shotcrete specimens (C25) is accorded with the Mohr-Coulomb criterion (M−C), with the cohesion of 5.1 MPa and the internal friction angle of 39.4° obtained. The loading path, the initial normal stress (INS) and the initial shear stress (ISS) have an influence on both displacement and shear strength of the shotcrete specimens. For instance, a higher INS or ISS leads to a higher failure normal stress and a smaller unloading amount. Compared with the results from the CDSTs, the cohesion of shotcrete specimens has a reduction of 1.746 MPa while the internal friction angle increases slightly in the UDSTs. In addition, the effects of INS and ISS on the initial micro-damage of shotcrete specimens are also investigated.