Abstract: In order to study the effect of temperature and confining pressure on rock mechanical properties and failure mode, experiments on granite under triaxial compression of different confining pressure from 0 to 40 MPa were conducted after high temperature of 25-1 000 ℃ by the MTS815.02 servo-controlled testing machine. The results show that: (1) Complete stress-strain curves of granite which heated to various temperatures under conventional triaxial compression with fixed confining pressure have experienced compaction, elasticity, yield, failure and plastic flow five stages. (2) Relationship between triaxial compressive strength of granite and confining pressure after high temperatures is nonlinear quadratic polynomial relations. When the confining pressure is 40 MPa, the triaxial compressive strength is increased 382.30% than uniaxial compressive strength; 400 ℃ is the threshold temperature of granite mechanical parameters under conventional triaxial compression conditions. (3) Elastic modulus of granite tends to increase with the confining pressure and quadratic nonlinearly decrease with the temperature, which is increased 90.26% than that at uniaxial compression when the confining pressure is 40 MPa, and when the temperature is 1 000 ℃, it is decreased 57.16% than that at 25 ℃. (4) Form of deformation and failure of rock samples is from brittle fracture transiting to plastic deformation as the temperature increases under uniaxial compression state. Instability mode is sudden instability at low temperatures, quasi- abrupt instability at medium-high temperature, and progressive failure at temperature higher than 800 ℃. Rupture type of rock samples changes from brittle tensile fracture to shear fracture gradually with the increase of confining pressure under triaxial compression. Instability mode of rock is dominated by sudden instability. In the experimental temperature and pressure range, temperature is the primary factor affecting mechanical properties of rock samples, followed by confining pressure, while the instability mode of granite depends on both confining pressure and temperature.

Key words: granite, temperature, confining pressure, mechanical characteristics, instability mode