Abstract: Theoretical and field experiments were carried out to reveal the relationship between the hydraulic fracturing method and the Brazilian splitting method for measuring the tensile strength of rock. Based on the classical hydraulic fracturing theory, borehole rupture pressure and tensile strength of rock were deduced under different confining pressures. The fracture mechanics theory was applied to establish the relationship between these two methods. Meanwhile, the crack initiation pressure of the hydraulic fracture was studied by using the prefabricated crack method to simulate natural crack. The results show that when the maximum principal stress was three times the minimum principal stress, its measured tensile strength was higher than that without confining pressure. The relationship between these two methods was related to three variables, including stress field, crack length and fracture toughness. The prefabricated crack experiment was performed at Wangtaipu Mine in Jincheng mine area. It was proved that the tensile strength formula established by fracture mechanics was more suitable for practical applications. The research results can provide references for the hydraulic fracturing design of prefabricated cracks in the hard and stable roof.

Key words: hydraulic fracture, tensile strength, fracture mechanics, prefabricated fracture