Experimental study of crack propagation and deformation failure of multiple-jointed rock mass

The uniaxial compression experiments of rock-like specimens with multiple intermittent joints are conducted by 10MN microcomputer-controlled electro-hydraulic servo large multi-function action force triaxial apparatus to further research mechanical behaviors of multiple-jointed rock mass with different joint dip angles. Researches on the relationship of crack characteristics, coalescence patterns, failure modes, stress-strain characteristics of multiple-jointed rock mass with joint dip angle were performed. The results show that: (1) Crack types of multiple-jointed rock mass mainly include wing crack and second coplanar crack. The propagating path of wing crack is different than that in condition of single joint. Wing cracks propagated a longer distance in the initial direction and directly coalesce with neighbouring joint or wing crack. Four patterns of crack coalescence are found (2) Three failure modes are found on specimens containing multiple joints, i.e. failure through a plane, rotation of new blocks failure and stepped failure. (3) The stress-strain curves of multiple-jointed rock mass at the strain softening stage show different characteristics of nonlinear deformation behaviors and according to that the curves are divided into four types. (4) The anisotropy of strength and deformation of multiple-jointed rock mass is highly obvious. The values of both strength and elastic modulus are maximum at joint dip angle of 90 degrees and minimum at joint dip angle of 30 degrees.