Thanakorn Kamonphet, Supattra Khamrat and Kittitep Fuenkajorn

pp. 683 - 690

Abstract

Direct shear tests have been performed to determine the peak and residual shear strengths of fractures in sandstone,
granite and limestone under cyclic shear loading. The fractures are artificially made in the laboratory by tension inducing
and saw-cut methods. Results indicate that the cyclic shear load can significantly reduce the fracture shear strengths and
stiffness. The peak shear strengths rapidly decrease after the first cycle and tend to remain unchanged close to the residual
strengths through the tenth cycle. Degradation of the first order asperities largely occurs after the first cycle. The fracture
dilation rates gradually decrease from the first through the tenth cycles suggesting that the second order asperities
continuously degrade after the first load cycle. The residual shear strengths are lower than the peak shear strengths and
higher than those of the smooth fractures. The strength of smooth fracture tends to be independent of cyclic shear loading. 

Keywords

• shear strength
• asperity
• fracture stiffness
• dilation
• cyclic loading