Experimental study on critical internal water pressure of hydraulic fracturing of fractured rock mass
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Abstract:
Many hydraulic structures are built on bedrocks, and most natural rock masses have joint fissures, which are prone to triggering hydraulic fracturing phenomenon under high water pressure. In order to study the hydraulic fracturing characteristics of fractured rock mass, we prepared specimens with pre-cast cracks using cement mortar as a substitute material of rock mass. We developed a water pressure loading system and a water sealing device, and used them to test the hydraulic fracturing of cement mortar specimens with differentinitial pre-cast crack lengths and widths. We determined the critical water pressure of pre-cast crack initiation and that of hydraulic fracturing of the specimens. The relationship between the critical water pressure of pre-cast crack initiation and that of hydraulic fracturing was analyzed, and the predictive formulas for the critical water pressures of pre-cast crack initiation and hydraulic fracturing were proposed. The test results showed that the critical water pressure of hydraulic fracturing of the specimens was 0.441 MPa-1.542 MPa. The critical water pressure of hydraulic fracturing would decrease as the initial pre-cast crack length and width increased when the other factors remained unchanged. The ratio between the critical water pressure of pre-cast crack initiation and the critical water pressure of hydraulic fracturing was 61.57%-64.17% , and it was independent of the initial crack length and width. Based on the stress intensity factor formula and the experimental results, we obtained the calculation formulas for the critical water pressure of pre-cast crack initiation and hydraulic fracturing of the specimens with consideration to the influence of the width of the pre-cast cracks.
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