a cylinder reaction frame, comprising a cylinder, a lower shear ring, an upper shear ring, a bottom cover, and a top cover, wherein the bottom cover and the top cover are detachably mounted at a bottom and a top inside the cylinder respectively, and an interior of the cylinder is divided to form a loading space for performing a triaxial test on a square test block; the lower shear ring is detachably embedded on an inner wall of the cylinder below the bottom cover to form a lower bearing boss for supporting the bottom cover; the upper shear ring is detachably embedded on the inner wall of the cylinder above the top cover to form an upper reaction boss for supporting the top cover;

a confining pressure reaction frame, mounted in the loading space around the square test block, the confining pressure reaction frame comprises wedge-shaped pre-press modules disposed in pairs beyond two opposed side surfaces of the square test block, each the wedge-shaped pre-press modules comprises a lower wedge-shaped block, an upper wedge-shaped block and an adjusting piece capable of adjusting and locking a relative position of the lower wedge-shaped block and the upper wedge-shaped block, the upper wedge-shaped block and the lower wedge-shaped block are overlapped between a side surface of the square test block and the inner wall of the cylinder, an outer side surface of the lower wedge-shaped block is configured as a curved surface matching the inner wall of the cylinder to disperse a reactive force, an inner side surface of the upper wedge-shaped block is configured as a plane matching the side surface of the square test block, and the upper wedge-shaped block and the lower wedge-shaped block cooperate by wedge-shaped surfaces such that when up and down relative movement between the upper wedge-shaped block and the lower wedge-shaped block occurs, a thickness is adjusted;

flexible loading mechanisms, disposed in pairs at the two opposed side surfaces of the square test block to perform triaxial loading on the square test block, wherein a top flexible loading mechanism is disposed between a top of the square test block and the top cover, a bottom flexible loading mechanism is disposed between a bottom of the square test block and the bottom cover, and surrounding flexible loading mechanisms are disposed between surroundings of the square test block and the confining pressure reaction frame, and the confining pressure reaction frame is used for uniformly transfer to an inner sidewall of the cylinder a reaction force generated by the flexible loading mechanisms during loading process;

an inner diameter of an upper part of the cylinder is greater than an inner diameter of a middle part of the cylinder, and the inner diameter of the middle part of the cylinder is greater than an inner diameter of a lower part of the cylinder such that an upper boss is formed at a connection position of the inner wall of the upper part and the inner wall of the middle part of the cylinder, a lower boss is formed at the connection position of the inner wall of the middle part and the inner wall of the lower part of the cylinder;

a first seal is disposed between a bottom of the bottom cover and the inner wall of the cylinder, a second seal is further disposed between the cylinder and the bottom cover, the second seal is disposed as O-shaped rubber ring sleeved near a middle part of the bottom cover, a sealed environment is formed by squeezing a sidewall of the bottom cover to the inner wall of the cylinder;

the top cover is covered on the upper boss, the upper part of the top cover is located inside an upper chamber of the cylinder and a lower part of the top cover is located inside the loading space of the cylinder, a third seal is disposed between a bottom of the top cover and the inner wall of the cylinder, the third seal includes a metal gasket sleeved on the top cover, a sealing ring sleeved on the top cover, an annular press plate sleeved on the top cover and a press screw for fixing the press plate at the bottom of the top cover, the metal gasket is located above the sealing ring and the press plate is located below the sealing ring, such that the metal gasket and the press plate can squeeze the sealing ring, when the top cover is covered on the upper boss, the squeezed sealing ring can achieve filling sealing on a gap between a sidewall of the top cover and the inner wall of the cylinder, a fourth seal is disposed between the top cover and the upper boss, the fourth seal is disposed as C-shaped rubber ring adhered to the top cover, when the top cover is covered on the upper boss, the C-shaped rubber ring is squeezed to achieve sealing on a gap between the top cover and the upper boss;

a supporting bracket for supporting the square test block is disposed in the loading space inside the cylinder, the supporting bracket disposed on the lower boss; and

a first oil guide hole is penetrated through the bottom cover, a second oil guide hole in communication with the first oil guide hole is penetrated through the top cover, and a hot hydraulic oil is injected cyclically into the cylinder through the first oil guide hole and the second oil guide hole to perform heating and pressurizing on the square test block.