STUDY ON THE STRENGTH PARAMETERS OF COARSE MARBLE WITH TWO PRE-EXISTING CRACKS

Based on the experimental results of marble with two pre-existing cracks under conventional triaxial compression by the rock mechanics servo-controlled testing machine, the strength parameters of coarse marble with two pre-existing cracks are obtained by adopting the Coulomb criterion and Hoek-Brown strength criterion. The applicability of Coulomb criterion and Hoek-Brown criterion for coarse marble with pre-existing cracks is evaluated. It is indicated that the strength of intact marbles is good accorded with the Coulomb criterion or Hoek-Brown strength criterion. However, the strength of marbles with pre-existing cracks is better accorded with the Hoek-Brown strength criterion. The determined cohesion and internal friction angle of rock in accordance with Hoek-Brown strength criterion can show the mechanical property of rock material. The sensitivity of the strength of marble with pre-existing cracks on the confining pressure is higher than that of intact marble, and the obtained cohesion of marble with pre-existing cracks is distinctly lower than that of intact marble, but the internal friction angle is higher than that of intact marble. For the rock specimen with pre-existing cracks, the cohesion and internal friction angle have a complex relation with the crack angle; even more there exists a close relation with whether or not the uniaxial compressive strength is regressed on the strength analysis. In accordance with the Hoek-Brown criterion, the strength parameter (the average value by the combined regression) of coarse marble is for intact marble, and for marble with pre-existing cracks. Therefore, for the marble with the same crystal size, the strength parameter m (the extent of soft and hard) has no difference, but the parameter s (the extent of fracture) has great difference.