Experimental study on frost heaving force and deformation of water saturated red sandstone fractures

Alpine and high altitude areas are affected by freeze-thaw cycles throughout the year, and frost heaves in fractured rock masses are widespread. In order to explore the evolution law of frost heaving force in fracture frost heaving deformation and reveal the frost heave damage mechanism of fractured rock, using the test system of distributed pressure film sensor, temperature sensor and strain gauge to fully monitor the freeze-thaw process of saturated cracked red sandstone samples with different crack widths in real time, then the curves of crack frost heave force, temperature and crack strain with time were obtained. The experimental results show that during the freezing and thawing process, a constant temperature platform appears at 20 mm in the water saturated red sandstone fracture, indicating that the fracture water is freezing, and the larger the fracture width is, the earlier the constant temperature platform appears; The strain of rock surface is synchronous with the inflection point of temperature, the inflection point of fracture strain lags behind the inflection point of temperature, but the change of fracture strain is synchronous with the change of maximum frost heaving force; When the constant temperature platform appears, the strain of rock surface rises rapidly, mainly caused by the joint action of the shrinkage of the rock skeleton and the frost heaving of the rock pore water; The change of temperature on the rock surface is faster than that in the fracture, which leads to the lag of frost heaving of fracture water; During the thawing process, the frost heaving force and strain both climb again, and appear the secondary peak; For cracks with a width of 2-4mm, the maximum frost heaving force increases with the increase of crack width; In the whole process of freezing and thawing, the distribution of frost heaving force is irregular, the frost heaving force increases from the four sides to the inside, and the frost heaving force around basically remains unchanged; The analysis of freeze-thaw mechanism shows that: a frozen layer is first formed around the rock mass, and then the fracture water freezes and gradually forms an ice plug. When the ice plug no longer slips and reaches a completely closed state, the fracture strain rises rapidly, the frost heaving force rises to the maximum, and the stress concentration at the fracture tip leads to microcracks. During melting, the surface of the rock melts and secondary frost heaving occurs in the fracture. and secondary frost heaving occurs in the fracture. The test preliminarily analyzes the freezing law of pore water and crack water in the fractured rock mass, which provides the basis for reasonably analyzing the frost heaving damage mechanism of fractured rock. © 2022, Science Press. All right reserved.