Experimental study on the non-Darcy flow characteristics of soil-rock mixture

This study aims at investigating the flow characteristics of soil-rock mixtures (SRM) with different rock block percentage. A self-developed servo-controlled permeability testing system was developed and used to carry out the permeability testing. Cylindrical SRM specimens (50 mm diameter and 100 mm height) with staggered rock block proportions (20, 30, 40, 50, 60 and 70 % by mass) were produced via compaction tests with different hammer strike counts to roughly insure the same void ratio. From the test results, the non-Darcy flow characteristic of SRMs was first proposed. The relationship between hydraulic gradient and the seepage velocity obeys a power function with good correlation. The increasing trend of the seepage velocity gets much more obvious with increasing hydraulic gradient. With the increase of the rock block percentage, the average permeability coefficient decreases to a minimum at a rock block percentage of 40 %. As the rock block percentage continues to increase above 40 %, the permeability increases again. The critical hydraulic gradient decreases gradually with the increase of rock block percentage. The variation of permeability for SRM specimens is the result of soil matrix properties combined with rock blocks and rock-soil interfaces. The research results can be helpful to predict the subsurface erosion and piping hazards in soil-rock mixture stratum.