Investigation of Red Clay Internal Stress Anisotropy and Influence Factors

Permeability characterized by permeability coefficient is one of the important engineering properties of clay, and its permeation mechanism depends on the permeation process of water in clay. To clarify the characteristics and influencing factors of the anisotropy of stress in red clay, indoor variable head permeability tests were conducted to obtain the permeability coefficients of undisturbed red clay in vertical and horizontal directions under different overlying loads. The research results indicate that under the same overburden load, the vertical permeability coefficient (kV) is greater than the horizontal permeability coefficient (kH), and on semi-logarithmic coordinates, both permeability coefficients exhibit a linear negative growth relationship with the overburden load. Moreover, with a gradual increase in the overburden load, the permeability coefficient ratio kV/kH shows a decreasing trend. When the overburden load does not exceed 150 kPa, the ratio of permeability coefficients (kV/kH) shows a linear decreasing trend, and when the overburden load exceeds 150 kPa, the rate of decrease gradually slows and eventually stabilizes. It is also found that the void ratio (e) is linearly related to lgkV and lgkH, and based on this, a prediction model for the anisotropy of stress in undisturbed red clay based on permeability coefficients is established. Under increasing osmotic pressure, the permeability coefficients in both directions exhibit linear growth. Essentially, it is the osmotic pressure that alters the stress pathways of red clay, and the smaller the overburden load, the greater the effect of osmotic pressure. With the increase in the overburden load, the anisotropy of stress gradually weakens.