双轴加卸载条件下含D型孔洞方块砂岩破坏特性

Failure characteristics of cuboid sandstone with D-shaped hole under biaxial loading and unloading conditions

为了揭示深部岩体在复杂应力条件下的强度与破裂特性,构建含不同倾角的D型孔洞砂岩数值试样,并通过单轴压缩试验验证其可靠性;开展双轴加卸载条件下含D型孔洞砂岩破裂过程数值模拟研究,综合考察其力学参数特征以及裂纹扩展特性。研究结果表明:在单轴压缩下,试样峰值强度和弹性模量随孔洞倾角的增大先降低后升高然后再降低,试样最终出现由孔洞左右两侧2条裂纹不断延伸形成的斜向剪切破坏;对于同一倾角孔洞砂岩试样,试样的双轴压缩强度、双轴加卸载强度、单轴压缩强度依次递减;随孔洞倾角增大,试样双轴加卸载破坏时的侧向应力总体呈现下降趋势;D型孔洞倾角对试样的峰值强度影响较小,但对试样裂纹的起裂应力影响较明显;在双轴加卸载条件下,含D型孔洞砂岩的破坏形式较复杂多样,总体呈现出单向剪切、X形剪切和Y形剪切共3种剪切破坏模式。

Numerical specimens of sandstone having D-shaped holes with different inclination angles were constructed to investigate the strength and fracture characteristics of deep rock masses under complex stress conditions.The reliability of numerical model was verified by uniaxial compression tests.Subsequently,the numerical simulations of the fracture process of sandstone with D-shaped holes under biaxial loading and unloading conditions were carried out to comprehensively investigate the characteristics of mechanical parameters and crack extension.The results show that the peak strengths and elasticity moduli of the specimens first decrease,then increase and finally decrease with the increase of the hole inclination angles under uniaxial compression.The final failure mode of the specimen is an oblique shear fracture formed by two cracks extending from the left and right sides of the hole.The biaxial compressive strength,biaxial unloading strength and uniaxial compressive strength of sandstone specimens which have holes with the same inclination angles present a descending order.The lateral stresses at biaxial unloading-induced failures of the specimens generally show a decreasing trend as the hole inclination angle increases.The influence of the D-hole inclination angle on the peak strength of the specimen is relatively small,but the influence on crack initiation stress of the specimen is more obvious.The failure modes of sandstones containing D-shaped holes under biaxial loading and unloading conditions are more complex and variform and generally show three modes of shear fractures,i.e.,unidirectional shear,X-shaped shear and Y-shaped shear.