Strength and deformation of frozen rocks were investigated by uniaxial compression test and cyclic loading test at -20°C. Failure processes of Shikotsu welded tuff and Bibai sandstone were considered based on their deformation behaviors. Larger deformation of wet specimen was found than that of dry specimen in both rocks due to pore ices plastic deformation. However, effect of water content on strength depends on type of rocks. UCS of wet specimens of Shikotsu welded tuff was greater than that of dry specimens. In contrast, UCS of wet specimens was smaller on Bibai sandstone. The former phenomenon can be interpreted by inclusion effect of pore ice. The latter phenomenon can be explained due to stress corrosion by unfrozen water or reduction in friction coefficient of crack planes by pore ice.
