EXPERIMENTAL STUDY ON SEEPAGE PROPERTIES OF NON-DARCY FLOW IN CONFINED BROKEN ROCKS

In the underground engineering, there are two changes that will take place in the structure of the broken rock during the seepage: One is the variation in pore structure caused by water pressure; another is the breaking of the edges and corners caused by the contacting stresses between the solid grains. Thus the flow in broken rock is different from the one in rock-fills packed up naturally, and its permeating properties change greatly with the displacement or the load. In this paper, the MTS815.02 Rock Mechanics Test System together with a seepage instrument is used to test the seepage properties of non-Darcy flow in the broken sandstone, coal gangue and limestone with the grain sizes 5mm―10mm, 10mm―15mm, 15mm―20mm, 20mm―25mm and the mixed grain size by the method of steady permeating and the method of controlling the axial displacements. By the experiments, the relation curves of the pore pressure gradient and the seepage velocity corresponding to the variant axial displacement of the rock samples are obtained; furthermore the rules of the permeating properties varying with porosity are acquired. The experimental results indicate that the coefficient of deviating from Darcy-flow may be negative. Some conclusions can be drawn as follows: 1) In a general trend, the permeability declines while the absolute value of the coefficient of deviating from Darcy-flow increases with the decreasing of the porosity; 2) The permeability is related with the loading level, the present porosity, the grain size, the construction style of the grains and the initial pore structure; 3) The magnitude of the permeability for the three kinds broken rock is 10-16m2―10-12m2 and the magnitude of deviating coefficient is 1012kg/m4―1015kg/m4; 4) when the breaking of the grains is very serious, the coefficient of deviating from Darcy-flow may be negative very possibly.