Abstract
Groundwater flow in an aquifer has frequently been found to be non-Darcian by performing in situ tests. A novel analytic model is proposed in this study for describing the unsteady non-Darcian flow in a confined aquifer by taking advantage of the observed flow rate and injection pressure during the constant head packer test. A linearization approximation of the Izbash equation is used to approximate the nonlinear term in the governing equation. This analytic model is applied to describe the non-Darcian flow in the interlayer staggered zone at the Baihetan hydropower station, China. The test results inversed by the genetic algorithm show that non-Darcian flow happened during the test under the injection pressure 0.3 MPa with the power index n is 1.278, non-Darcian hydraulic conductivity k 1 is 1.613 × 10 − 5 cm/s and the specific storage S s is 9.757 × 10 − 5 m-1, respectively. The sensitivity analysis indicated that when the power index n or the specific storage S s is larger, and the hydraulic head will increase more slowly and needs longer to stabilize, but the non-Darcian hydraulic conductivity k 1 shows the opposite trend. Moreover, the hydraulic head is more sensitive to the power index n compared to other parameters at late times. The findings of this study reveal the non-Darcian flow during the constant head packer test and provide a simple and fast way to estimate parameters for more accurate seepage field simulation.
Highlights
The permeability of rock mass is mainly determined by the development of fractures, and the packer test has been widely used to characterize the permeability of a lowpermeability aquifer
The constant injection pressure can convert to the constant head boundary condition that the water head in the radius of the water injection well is a constant value; the flow rate can be obtained by the injection system
The constant head and precise measurements of the test process gives a high requirement for test equipment
Summary
The permeability of rock mass is mainly determined by the development of fractures, and the packer test has been widely used to characterize the permeability of a lowpermeability aquifer. The constant head packer test is commonly applied for lowpermeability aquifers, and the non-Darcian flow is prone to occur with high gradient and high velocity during the test. The postlinear flow occurs in the coarse-grained and fractured medium at high velocity; the onset of turbulent flow leads to the inertial force over a viscous force which makes Darcy’s law invalid [7, 8]. The other is the Izbash equation in which the hydraulic gradient is a power function of the velocity; this equation is a fully empirical equation based on a large amount of experimental data [12,13,14,15] It lacks a physical meaning, it has been widely used for reasons
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