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Abstract To study the strength and failure of rock under compression-tension stresses，hollow cylinders with 50 mm in outer diameter and 6–25 mm in inner diameters were cracked by inner hydraulic pressure under different axial loads；and ring specimens with 4.6–20.0 mm in inner diameters were tested with Brazilian split. The experimental results show that the cracking pressure for hollow cylinder is not influenced by the axial load when it is lower than 80% of the uniaxial compression strength. The cracked pressure decreases with the increase of the inner diameter；and the tangential stress at the hole wall also decreases slightly，but the average of tangential stress increases. The hollow cylinders can hold tensile stress much higher than that of the Brazilian disc. The cracking pressure for hollow cylinder with inner diameter of 25 mm is about 10 MPa；and the tangential stress is about 17 MPa on the inner surface and 7 MPa on the out surface. However，the maximum strength in 6 pieces of Brazilian disc is only 6.17 MPa. Hollow cylinders with inner diameters less than 20 mm failed for the deformation on the inner surface increasing to the limitation and cracked into two parts. Hollow cylinders with inner diameters of 25 mm failed for the tangential stress on the out surface increasing to the tensile strength，and single crack was produced. Two indices of deformation and stress are related to the failure of rock specimen suffered from nonuniform stresses.
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Received: 15 January 2010
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