Abstract
Hydraulic coupling often leads to progressive rock failure accidents. Mechanical tests were performed over a range of combined pore water pressure and confining pressure stress path conditions to study the progressive failure characteristics of sandstone under hydraulic-mechanical coupling and explore the crack initiation and pore water fracture mechanism. The closure stress and damage stress were determined by the axial deformation stiffness and volume deformation stiffness. The experimental results indicate that confining pressure is the main controlling factor in the crack propagation stage, and pore water pressure enhances crack evolution. With increasing effective confining pressure, the effective peak deviatoric stress strongly increases and the characteristic stress increases linearly. The initiation stress and damage stress decrease with increasing pore water pressure. The moduli in stages I, II, and III are similar to the law of the transverse and radial deformation ratio with notable differences in stage IV. The fracture trend angle was determined by the ratio of axial crack strain and radial crack strain. Compared with the experimental results, the internal cracks in the sandstone samples are mainly type-II cracks, and type-I cracks are also locally present. After stress damage, the cracks expand and extend at an angle close to the real fracture.
Highlights
Hydraulic coupling often leads to progressive rock failure accidents
Mechanical tests were performed over a range of combined pore water pressure and confining pressure stress path conditions to study the progressive failure characteristics of sandstone under hydraulic-mechanical coupling and explore the crack initiation and pore water fracture mechanism. e closure stress and damage stress were determined by the axial deformation stiffness and volume deformation stiffness. e experimental results indicate that confining pressure is the main controlling factor in the crack propagation stage, and pore water pressure enhances crack evolution
We used a ROCK600-50 triaxial rock mechanics experimental system to study the progressive failure characteristics and mechanisms of sandstone under different pore water pressure and confining pressure coupling paths. e following conclusions are obtained: (1) e closing stress σcc is determined by the boundary point of the axial stiffness change. e damage stress σcd is determined by the fluctuation of volume stiffness. e crack initiation stress σci is determined by the zero points of the volume crack strain tangent
Summary
In the triaxial pore water experiments, hydrostatic pressure was first applied at a loading rate of 6 MPa/min until reaching a predetermined value (10, 20, and 30 MPa) and held for 420 s. E pore water pressure was applied at a loading rate of 20 MPa/min until reaching the set value (5, 10, and 20) and held for 3600 s of stabilization to ensure continuous and stable water seepage at the water outlet and stability of the water flow curve. According to the crack development process, the primary microcracks and fractures closed during the initial
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