Figure 5. (a) Effect of permeability on friction coefficient of loess. (b) Effect of fluid viscosity on friction coefficient of loess.
The above results elucidate that the macroscopic contact and friction behavior of the geomaterials depend on the creep accumulation process of microscopic asperities in the normal and tangential directions. This is closely related to temperature and creep activation energy. However, temperature-induced changes in normal and tangential stresses and phase transitions significantly affect the changes in its frictional force. The relative creep difference in the normal and tangential directions of the asperities can cause velocity strengthening or weakening effects. It is due to the different amounts of stress reduction in the tangential and normal directions corresponding to different activation energies. In addition, the water content also significantly affects its friction coefficient, which can attribute to the lubrication effect and the role of sharing part of the pore pressure. Thus, the permeability and fluid viscosity coefficients, which affect the water flow and distribution characteristics, affect the coefficient of friction.