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

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 In this case, the Darcy's law is no longer applicable.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 parameter β, the smaller the h and the v during the test. When β and r remain unchanged, the larger the nonlinear parameter k, the higher the h and the smaller v during the test. Furthermore, larger β and 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 C₂ staggered zone as follows: β=1.62 min ·m^-1, k=9.60×10^-3m ·min^-1, this method has good applicability for determining the nonlinear parameters of the staggered zone on site.