4. Results
4.1 Effect of temperature
The interface temperature of the geomaterial varies with the accumulation of the creep process and the sliding velocity variation. This further affects the frictional behavior of the geomaterial via changing its state. Figures 3 (a) and (b) show the friction coefficient as a function of contact temperature. The friction coefficient gradually decreases with the increase in contact temperature; meanwhile, it drops sharply when the geomaterial reaches phase transition temperature. This is because temperature affects the normal and tangential creep processes, and has a more significant impact on the tangential direction once a tangential slip occurs. Particularly, the tangential stress decreases with a faster speed than the normal stress as contact temperature increases, causing a decrease in the coefficient of friction. In addition, the geomaterials exhibit obvious flow characteristics before the phase transition temperature.
Figures 3 (c) and (d) show the relationship between the ambient temperature and friction coefficient of the loess and fault geomaterials under different sliding velocities. The influence of ambient temperature on the friction coefficient is smaller than that of the contact temperature because the maximum temperature difference between winter and summer is only tens of degrees Fahrenheit. The ambient temperature change still affects the creep stress in the normal and tangential directions of these geomaterials, thus, the friction coefficient gradually decreases with the increase in temperature.