Wetting permeability of intact loess under triaxial stress conditions

A series of unsaturated infiltration tests on intact loess are performed using the refitted triaxial equipment for shearing and permeability measurement of unsaturated soil, whereby the suction is reduced incrementally by the direct addition of small amounts of water to the sample at constant triaxial stresses. Influences of changes in deviator stress q with constant mean net stress p, mean net stress p with constant stress ratio η and degree of saturation S_r on liquid permeability are analyzed. The results indicate that the deviator stress q, mean net stress p and degree of saturation S_r remarkably affect the coefficient of permeability, and these impacts are different. The coefficient of permeability exhibits first rapid and then slight increase in S_r with constant p and q. It decreases linearly with the increase in q with constant p or in p with constant η at the same S_r. The slope of the former is dependent on p, but irrelevant to S_r. That of the latter is dependent on S_r, but independent of η. Besides, the slope of the latter is lower than that of the former. The saturated coefficient of permeability as a function of stress ratio for different mean net stresses can be expressed by the exponential function, in which only one of parameters changes with the mean net stress. The relationship between the relative coefficient permeability and the degree of saturation can be considered as the unique at different stress states. These relationships are not described by VG-M model, but by the proposed models. The models taking the net mean stress and stress ratio as variables are more convenient for engineering application. The predicted results agree well with the test ones.