Gas permeability of intact Q₃ loess under isotropic stresses

The tests are performed to study the gas permeability of unsaturated intact Q₃ loess with various water contents under different isotropic stresses using the improved triaxial gas permeability equipment. The influences of water content, volumetric gas content and stress on coefficients of gas permeability are analyzed. Three gas permeability functions are proposed to directly and indirectly reflect the effects of change in water contents and stresses on coefficients of gas permeability. The results show that the stress remarkably affects the coefficient of gas permeability as functions of both water content and volumetric gas content. The water content and volumetric gas content slightly have higher influence on the coefficient of gas permeability during wetting than drying. The relationships between coefficient of gas permeability and volumetric gas content at the same water content but different stresses were different from that at the same stress but different water contents. The relative coefficient of gas permeability versus relative volumetric gas content, coefficient of gas permeability versus modified volumetric gas content for different stresses all can be respectively described by the unique power function. The relationships between coefficient of gas permeability and normalized stress for different water contents can be expressed by the exponential function, in which only one of parameters changes with moisture content. The proposed three functions of gas permeability can well predict the coefficient of gas permeability as water content and stress change. The exponential function of gas permeability which needs not to introduce the change in void ratio caused by hydro-mechanical coupling is more convenient for engineering application.