Study on non-Darcy seepage characteristic and model of the broken rock mass of fault zone

Non-Darcy seepage experiments of broken rock mass were carried out under high hydraulic gradient. The influence mechanism of non-Darcy flow characteristic and critical hydraulic gradient was revealed with different porosity and gradation of rock mass sample. Considering the influence of the porosity and Talbot gradation coefficient，the calculation models of the non-Darcy flow coefficient，linear and non-linear term coefficients of Forchheimer's law were established. By piecewise analyzing the relation curve of pressure gradient and flow rate with Darcy's law，the non-Darcy equivalent hydraulic conductivity was proposed，and the non-Darcy equivalent seepage model was established. The results show that the experimental data were highly compliant with Forchheimer's law. The critical hydraulic gradient was changed from 125 to 183. Because the influence of inertia force, the critical hydraulic gradient was reduced with increased porosity and the number of coarse particle of rock mass sample. The non-Darcy flow coefficient，linear and non-linear term coefficients of Forchheimer's law have negative exponential with porosity and reduced power relationship with Talbot gradation coefficient. The non-Darcy equivalent hydraulic conductivity have negative exponential relationship with hydraulic gradient and decided by the pore structure of rock mass sample. The established non-Darcy equivalent seepage model was highly agreement with Forchheimer's law. The established model possessed fewer calculation parameters and could adapt to the coexistence and interconversion between Darcy flow and non-Darcy flow. © 2023 Academia Sinica. All rights reserved.