裂隙岩体水力劈裂临界水压力试验研究

许多水工建筑物建于基岩上,天然岩体大多存在节理裂隙,在高水压力作用下易发生水力劈裂破坏。为研究裂隙岩体的水力劈裂特性,以水泥砂浆代替岩石、制作预制裂缝试样,研制了高压水密封装置和水压力加载系统,开展了不同缝长和缝宽的砂浆试件水力劈裂试验研究,测定了预制裂缝起裂临界水压力、水力劈裂临界水压力,分析了两者关系,提出了预测表达式。试验结果表明,试件水力劈裂临界水压力为0.441~1.542 MPa,相同条件下,试件水力劈裂临界水压力与初始缝长及缝宽呈负相关关系;预制裂缝起裂临界水压力与水力劈裂临界水压力比值为61.57%~64.17%,与预制裂缝初始缝长和缝宽无关。应用应力强度因子计算公式,综合试验结果,分析得到了考虑预制裂缝宽度影响的裂缝起裂临界水压力和试件水力劈裂临界水压力的计算表达式。

Experimental study on critical internal water pressure of hydraulic fracturing of fractured rock mass

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.