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钻孔高压压水试验是评估高水头条件下岩体渗透特性的主要手段。目前,高水压条件下岩体的渗透特性估算多借鉴基于Darcy流假定的钻孔常规压水试验行业规程推荐公式,尚缺乏成熟、有效的计算方法。基于非线性Izbash定律,建立高渗压条件下岩体渗透系数的估算公式,并将高压压水试验P-Q曲线分为线性段、非线性段和水力劈裂扩展段。提出的公式应用简便,各压水试验段岩体渗透系数的确定只需稳态下的流量和水头,并且表征水流流态的系数m可通过曲线拟合得到。通过对琼中抽水蓄能电站高岔区钻孔高压压水试验数据的研究表明,岩体的渗透特性不受水流流态的影响,在高压压水试验的线性段和非线性段基本保持一致;岩体发生水力劈裂后,岩体的渗透特性将急剧增大。建立的公式可为高渗压条件下岩体的渗透特性取值提供一种有效的途径。
High-pressure drilling water pressure test is to evaluate the high head conditions of rock mass permeability of the main means. At present, the estimation of seepage properties of rock mass under high hydraulic pressure mostly draws on the industrial formula recommendation formula based on the hypothesis of Darcy flow for conventional hydraulic test of borehole, and the mature and effective calculation methods are still lacking. Based on the nonlinear Izbash’s law, the formula of permeability coefficient of rock mass under high seepage pressure is established. The P-Q curve of high pressure water pressure test is divided into linear section, nonlinear section and hydraulic fracturing section. The proposed formula is simple and easy to apply. The determination of permeability coefficient of rock mass in each water pressure test section only needs steady flow and water head, and the coefficient m that characterizes water flow can be obtained through curve fitting. Based on the experimental data of drilling high pressure water in the Gaocha area of Qiongzhong Pumped Storage Power Station, it shows that the permeability of rock mass is not affected by the flow pattern, and the linear and nonlinear sections of high pressure water pressure test are basically the same ; After the hydraulic fracturing of rock mass, the permeability of rock mass will increase sharply. The established formula can provide an effective way for the permeability of rock mass under the condition of high seepage pressure.