COMPREHENSIVE STIFFNESS TECHNIQUE USED IN DEFORMATION ANALYSIS OF HARD AND BRITTLE RHYOLITE WITH FISSURES

The closure, opening and propagation of internal fissures of natural rock under compressive load can affect the mechanical properties of rock directly. Based on the classical moving point regression technique, Poisson's ratio is introduced to propose the six stage division method which is called comprehensive stiffness technique(CST).The results of uniaxial compression test under different loading paths show the following.(1) Contact strain ε₀, closure strain of cracks ε_c, elastic strain ε_e, stable crack propagation ε_i, unstable crack propagation ε_d and post-peak strain ε_f of hard and brittle rock can be achieved by the CST.(2) Under uniaxial compression test, the closure strain of cracks at 44.2% of pre-peak strain is larger than the elastic strain of rhyolite. The pre-peak crack propagation strain and post-peak strain are all small. Actually the rhyolite is significantly brittle.(3) Loading and unloading test in elastic stage shows that the contact strain can be removed by comprehensive stiffness technique and the closure strain of cracks. The comprehensive stiffness technique is more suitable to the deformation analysis of hard and brittle rock, since it can remove the contact strain and achieve more accurate strain of different stages, especially the closure strain of cracks. These strains can be the quantitative parameters of the evaluation of crack density in rock.