Experimental Investigation on Non-Darcy Flow Behavior of Granular Limestone with Different Porosity

Statistics indicate that granular rock mass frequently acts as the flow channel and cause water inrush disasters under high water pressure in underground mining and tunnel engineering. The flow velocity of water inrush is so high that the flow behavior shows nonlinearity and cannot be described by Darcy's law. During the water inrush, the non-Darcy flow behavior associated with the porosity of granular rock mass is constantly changing due to seepage erosion. Therefore, this paper aims at the non-Darcy flow behavior of the granular limestone with a wide range of porosity (from 0.242 to 0.449). The non-Darcy flow properties were experimental investigated under steady-state condition by a self-designed apparatus. Based on the experimental data, an empirical hydraulic conductivity-porosity relation together with the expression of inertial coefficient was proposed. Then the non-Darcy flow regime was quantitative studied by the hydraulic conductivity-based Reynolds number. And the Forchheimer number associated with porosity was used to determine the critical flow velocity of the non-Darcy flow. From the point of view of seepage, two reasons for water inrush frequently occurred through granular rock mass with high porosity were finally discussed.