Experimental Study on Gas Permeability of Intact Loess Under Applied Load with Constant Stress Ratio Paths

Abstract

Gas permeability tests were performed to research the effects of deviator stress and mean stress as well as water content on gas permeability coefficient of intact loess, using the refitted stress-controlled triaxial equipment for gas permeability. Decreasing gas permeability coefficient, k_a, against increasing saturation, S_r, was found to be obviously influenced by mean stress and stress ratio (deviator stress) during wetting, water content during loading, respectively. The decreasing rate during wetting was significantly less than that during loading. The unique relationship between gas permeability coefficient and saturation approximately existed whatever stress at the same water content. There was a unique relationship between relative gas permeability k_ra (the ratio of gas permeability coefficient at certain water content to that at natural water content under the applied stress) and relative saturation, S_rr (the ratio of the difference between saturation, S_r, and the saturation at natural water content under different applied stresses, S_rn, to (1-S_rn)) at different deviator stresses and mean stresses. The relationship could be well fitted by the proposed relative saturation exponential law (RSEL) model using saturation as variable. Linear relationships between logarithm of gas permeability coefficient and stress ratio were paralleled at the same mean stress, but different water contents. These relationships could be modeled by the proposed exponential law (SWEL) model using stress and water content as variable. The prediction results of gas permeability coefficient by the two models proposed were in good agreement with the test results. In comparison with the RSEL model, the SWEL model was more convenient for engineering application.