A laboratory study of the effect of confining pressure on permeable property in soil-rock mixture

Abstract

This paper aims at investigating the effect of confining pressure on fluid–solid properties in soil and rock mixture (SRM) specimens with different rock block percentage. Self-developed servo-permeable testing system was used to carry out the flow-stress coupling testing. Fifty 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 by compaction test with different count hammers to roughly insure the same void ratio of soil matrix. From the test results, the effect of loading and unloading confining pressure on permeability coefficient is discussed. Permeability coefficient of SRM presents decreasing trend with the increase of confining pressure. At confining pressure descent stage, permeability coefficient begins to increase from the minimum, but it is smaller than the confining pressure ascent stage, the decreasing rate of permeability coefficient is more rapid than increasing rate. In addition, the relationship between permeability coefficient and confining pressure follows quadratic polynomial function, and the correlation coefficients are greater than 0.98 for all studied SRM specimens. Test results also show that at different hydraulic gradients, permeability coefficient increases with time. The results show that interaction between soil matrix and rock blocks is the main reason leading to the variation of permeability coefficient.