Compression-shear fracture and energy evolution in rock-like materials under hydraulic-mechanical coupling effect

Natural rock masses are rich in various defects, such as microfractures, pores and joints and other macroscopic discontinuities, which not only have an vital impact on the mechanical properties of rock masses, but also seriously affect the permeability characteristics of rock masses. Hydraulic pressure penetration into the fissures will intensify the cracking, expansion and penetration of the fissures, resulting in the gradual destabilization and destruction of the fissured rock (Tang et al. 2002 ; Cao et al. 2015 ; Li et al. 2011 ). Additionally, the mechanical properties of the fissured rock will be changed, and its damage abruptness and brittleness characteristics are obviously enhanced, while reducing the internal friction angle and bond coefficient of the rock, resulting in the reduction of the effective stress on the structural surface. The change of stress field (hydraulic-mechanical coupling) is the most critical cause of destabilization damage in geotechnical engineering, which is often encountered in many projects (such as underground engineering, dam bedrock engineering, high side slope rock engineering, etc.). The mechanism of rock hydraulic—stress—damage coupling includes two aspects: on the one hand, the deformation of rock under stress and the influence of damage on hydraulic pressure change the fracture structure of rock and its permeability characteristics; on the other hand, the mechanical response of rock under hydraulic pressure, that is, hydraulic pressure induces fracture expansion and induces rock damage evolution (Liu et al. 2012a , 2013 , 2014 ). To study the mechanical mechanisms of fractured rocks under fracture hydraulic pressure, it is necessary to consider the mechanical properties of microfracture sprouting, crack initiation, extension and penetration under high hydraulic pressure, as well as the permeability evolution law and the mechanical properties of fracture surfaces, spatial spreading characteristics (Zhao et al. 2008a , 2008b ). Therefore, the hydraulic-mechanical coupling problem is getting high attention from scholars and experts in most fields.