冻融作用下裂隙类砂岩断裂特征与强度损失研究

Study of fracture characteristics and strength loss of crack quasi-sandstone under freeze-thaw cycles

寒区裂隙岩体中经常发生水冰相变产生冻胀力,冻胀力的反复作用会驱动岩体裂隙扩展、贯通甚至断裂破坏。通过在类砂岩试样中预制不同倾角的单开口裂隙,分别进行预冷和不预冷饱水裂隙冻融循环试验及冻融后的单轴压缩试验,探究冻结方式和裂隙倾角对裂隙冻胀扩展过程、断裂破坏特征及单轴强度的影响机制。试验结果表明,裂隙冻胀力是驱使裂隙冻融扩展的主要动力且与裂隙水的冻结方式密切相关,采用预冷方式冻结会引起绝大部分裂隙水挤出而难以形成冻胀裂纹;在非预冷冻结方式下冻胀裂纹一般先沿着预制裂隙共面方向扩展,但由于边界效应而逐渐转向短边,共面扩展长度与裂隙倾角呈正相关;当预制裂隙倾角在60°~90°时,岩体容易沿着冻胀裂纹方向发生压缩破坏,从而引起岩体单轴抗压强度降低。研究结果可为揭示裂隙岩体冻融损伤机制及开展寒区岩体工程建设提供借鉴。

Water-ice phase transition often produces frost heaving pressure in fractured rock mass in cold regions. The repeated action of frost heaving pressure will drive crack propagation, coalescence and even fracture failure of rock mass. Through prefabrication of single open crack with different inclination angles in quasi-sandstone specimens, freeze-thaw and uniaxial compression experiments are conducted on those crack-containing specimens under precooling and non-precooling conditions, to investigate the influence of freezing mode and crack inclination angle on the process of frost propagation, rupture characteristics and uniaxial compressive strength. The experimental results show that: the frost heaving pressure is the main driving force of frost propagation, which is closely related to the freezing mode of crack water. It is hard to produce frost-heaving cracks under precooling conditions, because most of the crack water is squeezed out. Generally, the frost-heaving cracks propagate along the coplanar direction of the prefabricated cracks;and then they gradually turn to the short sides due to the boundary effect. There is a positive correlation between the length of coplanar propagation and the inclination angle of crack. When the prefabricated crack inclination angle is 60°-90°, the rock mass can easily be compressed and destroyed along the direction of frost-heaving crack, resulting in the reduction of uniaxial compressive strength of rock mass. The research results can provide reference for revealing the freeze-thaw damage mechanism of fractured rock mass and developing rock engineering in cold regions.