Experimental study on frost heaving pressure properties in fractured red sandstone

Frost heave phenomenon of fractured rock mass is widespread in the freezing engineering of water-rich rock strata. Frost heave force tends to cause stress concentration at the crack tip of rock mass to produce new micro-cracks. The propagation and penetration of micro-cracks lead to different degrees of damage of rock mass. In order to reveal the evolution mechanism of freeze-thaw damage in fractured rock mass and explore the law of fracture propagation in rock mass driven by frost heave force the frost heaving force in the connected crack of red sandstone is tested by a frost heave force testing system which consists of ultra-thin resistance pressure sensor,temperature sensor and low tempera- ture and constant temperature box under different freezing rates,fracture sizes,dip angles and boundary conditions. Then the evolution law of frost heaving pressure,the mechanism of frost heaving deterioration and the failure mode of frost heaving are analyzed. The results show that the evolution process of typical frost heaving pressure of fractured red sandstone includes initial freezing stage, rapid freezing stage, unloading stage, maintenance stage and disappearing stage. The frost heaving effect causes obvious crack propagation behavior near the tip of crack,and the samples are vertical tension destruction. The maximum frost heaving pressure increases single exponentially with the width of gap and increases linearly with temperature. During the freezing process,the boundary condition of the sample has a signifi- cant influence on the frost heaving pressure of fracture,the maximum frost heaving force is 1. 27 MPa under rigid con- fined boundary conditions. During the melting process, different boundary conditions correspond to different falling phenomena of frost heaving pressure. The characteristics of frost heaving pressure in red sandstone with penetrating fracture under low temperature is consistent with the law of AE energy change during the process of frost heave,and the damage and deterioration effect of frost heaving force on the fractured rock mass is fully verified. The research re- sults can provide a reference for the theoretical calculation and numerical analysis of frost heaving pressure in fractured rock mass,the mechanism of freezing and thawing damage,the characteristics of ice-rock coupled and the design of the frozen wall of the coal mine.