基于钻孔高压压水试验非线性流模拟计算错动带渗透参数

CALCULATING THE PERMEABILITY PARAMETERS OF THE STAGGERED ZONE BASED ON THE NONLINEAR FLOW SIMULATION OF THE HIGH-PRESSURE PACKER TEST

高坝大库建设过程中,往往需要确定工程区附近岩土体在高水头作用下的渗透参数,钻孔高压压水试验是其中最常用的方法之一。与其他试验相比,高压压水试验具有很高的水头和渗流速度,很容易出现非线性渗流,这种情况下达西流公式不再适用,因此,亟需一种基于钻孔高压压水试验确定非线性参数的求解方法。本文建立了钻孔高压压水试验的非线性流数学模型,采用有限差分的方法,得到了阶梯水头变化情况下非线性流数学模型的数值解,并验证了该数值解的准确性。在此基础上讨论了非线性参数对水头和流速的影响,结合白鹤滩水电站玄武岩错动带现场高压压水试验,进一步验证了该方法的可靠性。结果表明,当非线性参数k和径向距离r保持不变时,非线性参数β越大则试验过程中的水头h和流速v都越小;当非线性参数β和径向距离r保持不变时,非线性参数k越大则试验过程中的水头h越小、流速v越大;且较大的β和k均会使得高压压水试验能更快地趋于稳定状态。如果仍按照达西流公式进行计算,将会高估透水介质中的水头,进而高估玄武岩错动带结构面抵抗渗透破坏的能力,最终对工程稳定性产生不利影响。在白鹤滩水电站进行的钻孔高压压水试验过程中地下水发生了非线性运动,求得C2错动带的非线性参数β=1.62 min·m-1,k=9.60×10^(-3)m·min^(-1),该方法对于现场确定错动带非线性参数有较好的适用性。

In the construction of high dam reservoir,it is necessary to determine the permeability parameters of the rock and soil near the engineering area under the condition of high water head,and high-pressure packer test is one of the most commonly used methods.Compared with other tests,the water head and seepage velocity are very high during the high-pressure packer test,and the nonlinear flow is prone to show up.In this case,the Darcy’s law is no longer applicable.Therefore,a method for determining nonlinear parameters based on the high-pressure packer test is urgently needed.In this paper,a nonlinear flow mathematical model of the high-pressure packer test is established.By using the finite difference method,the numerical solution of the nonlinear flow mathematical model under the condition of step head is obtained,and the accuracy of the numerical solution is verified.On this basis,the influence of nonlinear parameters on water head h and flow velocity v is discussed.Combining with the in-situ high-pressure packer test at Baihetan Hydropower Station,the nonlinear parameters are calculated to further verify the reliability of the method.The results show that when the nonlinear parameter k and the radial distance r remain unchanged,the larger the nonlinear parameterβ,the smaller the h and the v during the test.Whenβand r remain unchanged,the larger the nonlinear parameter k,the higher the h and the smaller v during the test.Furthermore,largerβand k will make the packer test reach a steady state faster.If the calculation is still carried out according to the Darcy equation,the water head in the permeable medium will be overestimated,and then the ability of the structural surface to resist seepage damage will be overestimated,which will eventually have a negative impact on the stability of the project.Non-linear movement of groundwater occurred during the field high-pressure packer test at Baihetan Hydropower Station,and the nonlinear parameters of the C2staggered zone as follows:β=1.62 min·m^(-1),k=9.60×10^(-3)m·min^(-1),this method has good applicability for determining the nonlinear parameters of the staggered zone on site.