Abstract: The fractured rock mass in cold areas is damaged and deteriorated due to crevice-water frost heaving, which seriously threatens the safety of engineering construction in cold regions. In this study, freeze-thaw cycling tests were conducted on green sandstone, red sandstone and granite samples of different porosities. The strain changing with time and temperature of saturated fracture during freeze-thaw cycling under influences of fracture length, width and lithology were analyzed. The changing rules of the characteristic values of fracture strains and the failure mechanism of fractured rock were also studied. Experimental results show that the change rule of freeze-thaw strain of fractured rock mass with different fracture geometry parameters can be divided into seven stages: the cool shrinkage stage, the frost heave stage, the frost heave stabilization stage, the thermal expansion stage, the thaw shrinkage stage, the thaw shrinkage rebound stage, and the thaw shrinkage stabilization stage. The curve of freeze-thaw strain versus temperature of saturated fractured rock mass is an unclosed hysteresis loop. The phenomenon of “freeze-thaw hysteresis” occurs, and with the increase of freeze-thaw cycles, the hysteresis loop gradually moves up, leading to a gradual increase of the residual strain. Characteristic values of freeze-thaw strain of saturated fractured rock mass include: the maximum microstrain, the residual strain, the frost heave amplitude, and the thaw shrinkage amplitude. The characteristic value of strain is related to the fracture length, the width and lithology of rock mass, and the freeze-thaw failure of fractured rock mass is caused by gradual accumulation of the residual strain.

Key words: fractured rock mass, freeze-thaw deformation, hysteresis loop, residual strain