EXPERIMENTAL STUDY ON FROST HEAVING PRESSURE EVOLUTION OF ROCK ICE CRACKS UNDER FREEZING-THAWING CYCLES

This paper explores the evolution law of frost heaving pressure in ice crack of rock mass under freezing-thawing cycles,and reveals the influence mechanism of fatigue freezing-thawing on the deterioration of rock structure. It presents a self-made 8-channel real-time frost heaving pressure monitoring system and uses it to test the frost heaving pressure under different conditions of lithology and fracture geometry. It obtains the evolution curve of frost heaving pressure in multiple freezing-thawing cycles,and analyzes the influence of lithology and fracture geometry on the evolution law of frost heaving force. The results show the following three findings. (1)The process of deterioration of rock mass structure caused by feezing-thawing cycles is the process of fatigue damage caused by frost heaving force. The evolution of frost heaving pressure during each freezing-thawing cycle goes through the stages of incubation,explosion,fall back to stability,rise again and dissipation. It is found that the phenomenon of frost heaving pressure can rise again. The peak value of initial frost heaving force can be used as the index of frost thaw damage of fractured rock mass; (2)Under the action of multiple freezing-thawing cycles,the frost heaving pressure of rock fracture continuously erupts,accumulates and releases,during which the cumulative damage of fracture drives the continuous expansion of fracture,causing further fatigue deterioration of rock mass. Under the action of fatigue freezing-thawing cycles,the change trend of the peak value of initial frost heaving pressure and the peak value of secondary frost heaving pressure can be used as the judgment basis for the damage deterioration degree of fractured rock mass affected by freezing-thawing. (3)Structural characteristics of rock mass affect the evolution law of frost heaving pressure. The micro structure of rock mass matrix affects the water migration in the process of freezing. The macro pre-set fracture geometry affects the evolution law of frost heaving pressure. The larger the expansion degree,the greater the frost heaving pressure accumulation. The research on the evolution law of frost heaving pressure under fatigue freezing-thawing can provide theoretical basis for the long-term freezing-thawing stability prediction and engineering construction of rock mass engineering in cold region.