Understanding the fundamental issues related with the effect of shear velocity on frictional characteristics at the interface of rock surfaces is an important issue. In this paper, strain-rate dependence on friction is investigated in relation to sliding behaviour under normal load. The phenomenon of stick-slip of granite and shaly sandstone with a tribometer at constant rate of strain under normal loads was observed.

Friction at the interface of the rock samples was developed by increasing shear strain at a constant rate by applying constant velocity using the tribometer. For shaly sandstone, state parameters (𝑎 and 𝑏) played a major role in determining the friction values and roughness of the contact surfaces as well. Higher values of 𝑏 for shaly sandstone may be attributed to the fact that its surface had a greater number of pronounced asperities. Rubbing between the surfaces does not mean that surface becomes smoother. This is because of variation of friction between surfaces.