FREEZE-THAW DEGRADATION CHARACTERISTICS OF CARBONACEOUS SLATE ROCK SURROUNDING HIGH COLD TUNNEL IN XINJIANG

This paper aims to explore the degradation law and anisotropic characteristics of freeze-thaw damage of strongly weathered carbonaceous slate surrounding rock in Xinjiang's high-cold tunnel. The authors obtained three types of slate rock samples with bedding angles of 0°,45°,and 90°,and conducted 0,10,20,30,and 40 freeze-thaw cycles under open saturated conditions. After the freeze-thaw cycles,the author conducted macroscopic mechanical performance tests and fracture surface scanning electron microscopy tests. The results show that under the action of freezing and thawing cycles,the freeze-thaw damage of strongly weathered slate is mostly concentrated at the weathered joint fissures,and the main damage modes are the initiation of bedding cracks,detachment of bedding,and fracture of bedding,the natural saturated mass of slate shows a trend of slow increase followed by rapid decrease. The strength characteristics of slate with different bedding angles vary greatly and are significantly affected by weathering and freeze-thaw cycles. With the increase of freeze-thaw cycles,the compressive strength and elastic modulus of slate rock samples exhibit a nonlinear attenuation trend,and the damage variable under freeze-thaw loading gradually increases,the relationship between the resistance to freeze-thaw damage of slate with three different bedding angles is 0°>90°>45°. Scanning electron microscopy images show that the bedding fracture of the slate exhibits significant brittle characteristics,but multiple freeze-thaw cycles cause the fracture surface of the slate to exhibit certain plastic characteristics under load. Research has found that slate with a dip angle of 0°bedding structure is less affected by the freeze-thaw environment and has more stable mechanical properties. The study has revealed the deterioration laws of anisotropic freeze-thaw damage in strongly weathered directional layered slate,which can provide reference for the risk assessment of freezing damage in cold region tunnel engineering under the background of directional occurrence structure surrounding rock.