Influence of water on mechanical behavior of surrounding rock in hard-rock tunnels: An experimental simulation

To investigate the influence of water on the mechanical behavior of rock surrounding hard-rock tunnels, a series of uniaxial and true-triaxial compression tests were performed on red sandstone samples with two different water contents (natural water content (NWC) and saturated water content (SWC)). The samples taken were cubic samples containing a circular hole and cylindrical samples. During the true-triaxial tests, hole failure was monitored and recorded in real-time with in-house developed monitoring equipment. The effects of water on the stress, energy, and fracture characteristics of rock failure in hard-rock tunnel were determined. The results indicate that, after reaching the SWC state, the strength and elastic modulus of red sandstone were reduced, and the shear characteristics became more obvious. The failure mode of the NWC holes was primarily slab ejection, while the failure mode of the SWC holes was primarily slab flaking. Water changes the mesoscopic mechanism of spalling and exhibits a double effect on hard-rock tunnels. The mechanisms of water on rockburst prevention are to reduce residual elastic strain energy, avoid excessive concentration of strain energy, and increase rockburst resistance. The ratio of the far-field maximum principal stress to the uniaxial compressive strength can be used as an index to evaluate the stability of hard-rock tunnels. The results help to rethink the influence of water on underground hard rock engineering, such as the failure mechanism of surrounding rock and the analysis of tunnel (or caverns) stability in water-rich stratum, and the mechanism of water on the rockburst prevention.