Abstract:Experiments were carried out to study coarse marble with discontinuous pre-existing cracks under conventional triaxial compression by the MTS815.03 rock mechanics servo-controlled testing machine. Based on the experimental results,the deformation and strength properties of coarse marble with discontinuous pre-existing cracks under different confining pressures were investigated. The results show that the deformation of intact rock specimens and marble with discontinuous pre-existing cracks after peak strength changes from strain softening into ideal plasticity. The sensitivity of peak circumferential strain to the confining pressure is higher than that of peak axial strain. The relation between strength and confining pressure can be expressed by Coulomb criterion;what¢s more,the sensitivity of residual strength to the confining pressure is higher than that of peak strength. The coarse marble has greater crystal in size of 4–6 mm. The Young¢s modulus of intact rock specimen increases with the confining pressure;and the peak strain has a positive linear relation with the confining pressure. However,the Young¢s modulus and the peak strain of rock specimen with discontinuous pre-existing cracks have more complex relations with the confining pressure and vary with the crack angles. In uniaxial compression,the peak strength of rock specimen with discontinuous pre-existing cracks has a close relation with the crack angles;and the maximal axial stress depends on the fracture modes between the inner tip of two pre-existing cracks and friction slips between crystals. Under lower confining pressure(s3≤10 MPa),the triaxial peak strength of rock specimens with discontinuous pre-existing cracks is lower than that of intact rock specimens;but for triaxial residual strength,there are no great differences between intact coarse marble and marble with discontinuous pre-existing cracks. However,under higher confining pressure(s3>10 MPa),the triaxial strengths(peak strength and residual strength) of intact rock specimen are approximately same as those of rock specimen with discontinuous pre-existing cracks,which shows that the supporting capacity of coarse marble specimen is only related to the confining pressure but no relation with the distribution of pre-existing cracks. The internal friction force determines the strength property of coarse marble.