Experimental study on rock damage frozen with liquid nitrogen under external water source

The construction of underground engineering often encounters the problems of staggered sand and soft strata with abundant groundwater. The low temperature of liquid nitrogen can make the rock and soil quickly freeze to achieve the purpose of soil stability and reinforcement. However, the rapid freezing of liquid nitrogen will also lead to the deterioration of the physical and mechanical properties of the surrounding rock and soil. Therefore, it is of great significance to explore the influence of external water source on rock deterioration under ultra-low temperature for the long-term stability and safety engineering construction. In order to study the influences of external water source on the low-temperature deterioration of rock, the ultrasonic experiment, nuclear magnetic resonance experiment and uniaxial compression experiment are carried out on rock samples under different saturated conditions after liquid nitrogen freezing treatment of liquid nigtrogen. The test results show that: (1) The rock samples still have damage in the frozen state, and the degree of damage increases further after the rock samples return to room temperature. (2) The freezing time of liquid nitrogen for about 40 minutes has the most obvious deterioration effects on the rock samples. (3) The external water environment increases the deterioration degree of the dry rock samples and decreases the deterioration degree of the saturated rock samples. (4) When there is a water source outside the rock, the long-term (> 30 minutes) freezing of liquid nitrogen will increase the strength of the rock, while the short-term (≤ 30 minutes) freezing of liquid nitrogen will deteriorate the strength of the rock.