Progressive failure characteristics and water-induced deterioration mechanism of fissured sandstone under water-rock interaction

Stability of engineered rock mass can be significantly affected by the combined action of fissures and water. In this study, uniaxial compression tests of fissured sandstone under natural state and water-chemical environments were conducted, accompanied by acoustic emission and digital image correlation to monitor the whole failure process. The results indicate that the strength and elastic modulus of fissured sandstone in the saturated state were lower than those in the natural state. The inside structural changing of dried specimen after water-chemical environments immersion had a weak influence on the strength and elastic modulus, but the peak strain and yield deformation would significantly increase. Characteristic stress determination methods were identified applicable to fissured sandstones under water-rock interactions. The sigma ci/sigma f (the ratio of crack initiation stress to peak strength) could be largely degraded by the presence of water, while the impact on sigma cd/sigma f (the ratio of crack damage stress to peak strength) was weak. The structural changing could also significantly reduce sigma ci/sigma f. However, only the sigma cd/sigma f ratio in the acid water environment exhibited the obvious reduction. The presence of water could also influence the crack initiation and failure mode of fissured sandstone. After a short period of immersion (45 d), the strength and elastic modulus degradation of fissured sandstone was mainly caused by the water-rock physical reaction, while the change in the peak strain was jointly affected by the water-rock chemical and water-rock mechanical reactions. The sigma ci/sigma f ratio was affected by the water-rock chemical and water-rock mechanical reactions, while the sigma cd/sigma f ratio was affected only by the water-rock chemical reaction. Moreover, the water-rock mechanical reaction significantly changed the initiation mode of fissured sandstone. The water-induced deterioration mechanism of fissured sandstone was lastly revealed by these results, which could provide an important reference for evaluating the stability of water-rich engineered rock mass.