Laboratory study of dynamic mechanical characteristic of granite subjected to confining pressure and cyclic blast loading

Abstract

To investigate the deformation characteristic of deep rock under cyclic blasting, the static-dynamic loading experimental equipment was set up. The dynamic strain gauges and high-speed (HS) camera were adopted to obtain strain field and the crack propagation of rock under confining pressure of 0 MPa, 5 MPa and 10 MPa. Under the one-time loading from cylindrical charge, the cracks in crushed zone were generated by shear and tensile failure. Circumference compressive stress is formed around borehole by confining pressure, and it reduces the circumference tensile failure by blast loading. The number of radial cracks and broken radius reduce with confining pressure increase. The reflected stress wave drives the existing fissures further developing. When specimens subjected to cyclic loading from PETN Cord, the rock is controlled by elastic deformation and no damage appeared after the first loading. With the cycle-index increase, the accumulation of plastic strain is observably when the strain exceeds the elastic limit strength of rock. The cumulative damage is nonlinear increased under cyclic loadings. The existing flaws or radial cracks run through specimen when the cumulative damage exceeds the material's yield strength.

Keywords
Rock mechanics; cyclic blast loading; confining pressure; deformation characteristic; damage accumulative evolution