Figure 4. (a) Effect of creep activation energy difference on friction coefficient of loess. (b) Effect of creep activation energy difference on friction coefficient of fault geomaterial.
When the creep activation energy in the normal direction of the asperities is smaller than that in the tangential direction, the friction coefficient decreases gradually with the slow increase of the sliding velocity (Figure 4). This is because normal creep is more likely to occur, and the normal stress reduction is smaller than the tangential stress reduction. As a result, the friction coefficient decreases. Similarly, when the creep activation energy in the normal direction of the asperities is greater than that in the tangential direction, the friction coefficient gradually increases with the slow increase of the sliding velocity (Figure 4). This is because tangential creep is more likely to occur and the tangential stress reduction is smaller than the normal stress reduction, causing an increase in the coefficient of friction.
The creep activation energy of geomaterials is closely related to the properties, composition, and other factors of these geomaterials. Therefore, different materials will show shear strengthening or weakening, even constant shear strength with increasing slide velocity.