Subcritical crack growth and fracture behavior of three rocks containing quartz under wet and dry conditions

•Strain and fracture process in the tensile surface of samples were successfully observed by DIC.•Transient response of rock subcritical fracture behavior to introduction of water was investigated.•Rock subcritical crack growth under air and in introduced water conditions was compared. Understanding the subcritical crack growth behavior of rocks under water-rock interaction is essential to evaluate the stability of deep resource extraction and the integrity of nuclear waste disposal or CO2 sequestration. Using the double-torsion technique, we performed relaxation tests on three rocks with different quartz contents, namely, quartz amphibolite, white sandstone and red sandstone, in air environment and in introduced water conditions to systematically investigate the effect of water on subcritical crack growth behavior of three rocks. The subcritical fracture behavior of the rock responded very rapidly to water: when water entered the crack tip, 1) the crack velocity increased with decreasing of stress intensity factor; 2) the slope of the load decay curves increased abruptly; and 3) the strain values at the bottom monitoring points extracted from three-dimensional digital image correlation increased immediately. Compared with the air environment, the subcritical crack growth indexes of quartz amphibolite, white sandstone and red sandstone in fluid conditions were reduced by 27.08 %, 80.81 % and 86.14 %, respectively, and the crack velocities were increased by one order of magnitude. The Ka values of quartz amphibolite, white sandstone and red sandstone were less sensitive to water than the subcritical crack growth indexes, decreasing by 9.43 %, 17.35 % and 37.33 %, respectively. Data from these tests reveal that the subcritical fracture properties of the three rocks were degraded despite the small amount of water flowing through the sample, proving that the long-term effects of water on actual engineering cannot be ignored.