双裂隙类砂岩冻胀断裂特征与强度损失研究

Experimental study on fracture characteristics and strength loss of intermittent fractured quasi-sandstone under freezing and thawing

寒区裂隙岩体受冻融作用的影响经常发生断裂破坏。为了研究岩桥倾角对裂隙岩体冻胀扩展过程、断裂破坏特征以及强度损失的影响机制,利用相似材料制备含不同岩桥倾角的双裂隙类砂岩试样,并开展一系列裂隙注水、不注水的冻融循环和单轴压缩试验,得到冻胀裂纹扩展特性及对类砂岩力学特性的影响规律。研究结果表明:(1)受裂隙冻胀力的驱使,冻胀裂纹不断扩展延伸,并伴随着"枝状"微裂纹的生长;(2)冻胀裂纹的外尖端主要沿着初始裂隙方向扩展,而内尖端受应力干扰作用会朝着另一条预制裂隙外尖端发生偏转,且岩桥倾角?越大,这种偏转效应越明显;(3)试样单轴压缩破坏模式容易受到冻胀裂纹的影响,当岩桥倾角β=90°~135°时,主要沿着冻胀裂纹方向发生剪切破坏,导致试样强度明显降低;而当β=180°时,冻胀裂纹不再是试样单轴压缩破坏的主要诱因,对其强度损失和断裂特征几乎没有影响。

The fractured rock mass in cold regions is often affected by the freezing and thawing action. In order to study the influence mechanism of the dip angle of rock bridge on frost heave expansion process,fracture failure characteristics and strength loss of fractured rock mass,double-fracture sandstone samples with different dip angles of rock bridge were prepared with similar materials,and freezing and thawing cycles with and without water injection and a series of uniaxial compression tests were performed. The results indicate that,driven by the frost heaving force,the frost heaving cracks continue to expand along with the growth of dendritic microcracks,and that the outer tip of the frost heaving crack mainly propagates along the initial crack direction while the inner tip tends to deflect towards the outer tip of another prefabricated crack. The greater the dip angle of the rock bridge,the more obvious the deflection effect will be. The uniaxial compression failure mode of the sample is easily affected by the frost heaving crack. When the inclination angle of the rock bridge, β,is between 90° and 135°,shear failure occurs in the direction of the frost heaving crack,which leads to a significant decrease in the strength of the specimen. When β =180°,the frost heaving crack is no longer the main cause of uniaxial compression failure of the specimen and has little effect on the strength loss and fracture characteristics.