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岩土工程中常用的屈服准则多以压缩剪切为其破坏机制,然而硬脆性岩体的脆性破坏包括拉伸破坏、张拉剪切破坏和压缩剪切破坏3类,且随着岩体工程向深部发展,张拉剪切破坏成为了洞壁围岩的主要破坏机制。针对此问题,开展了硬脆性大理岩的室内拉剪试验,分析了大理岩拉剪破坏特征,并结合压剪试验结果,建立了考虑张拉剪切破坏机制和应力状态影响的Mohr-Coulomb准则。研究结果表明,硬脆性大理岩破裂面在拉剪应力状态和低正应力压剪应力状态下均具有张拉剪切破坏特征,高正应力压剪应力状态下则只具有压缩剪切滑移特征;拉剪应力状态下,大理岩破裂面张拉破坏特征明显,无明显剪切痕迹,剪切力固定时,剪切位移随着轴向拉力增加而增加;凝聚力和内摩擦角受应力状态影响,凝聚力随正应力增大先减小后增大,内摩擦角则随正应力的增大而减小;凝聚力、内摩擦角随正应力的变化趋势可分为4段,拉剪段、低压应力段、中压应力段和高压应力段,每段的凝聚力、内摩擦角与正应力皆可认为是线性关系,靠近抗拉强度处,内摩擦角趋近90°,凝聚力趋于无穷大;考虑张拉剪切破坏机制和应力状态影响的Mohr-Coulomb准则曲线分为两部分,可采用二次抛物线进行拟合的拉剪段和考虑凝聚力、内摩擦角随正应力演化的压剪段,由此建立的Mohr-Coulomb准则更全面、精度也更高。
Compressive shear is the most commonly used yield criterion in geotechnical engineering. However, the brittle failure of hard and brittle rock mass includes three types: tensile failure, tensile shear failure and compressive shear failure. With the rock mass engineering To the deep development, tensile shear failure has become the main damage mechanism of the wall rock. In order to solve this problem, indoor tensile shear tests of hard and brittle marble were carried out, and the failure characteristics of marble were analyzed. Combined with the results of compression shear test, the Mohr-Coulomb criterion considering the failure mechanism of tensile shear and the influence of stress state was established . The results show that the fractured surface of hard and brittle marble has tensile and shear failure characteristics under both tensile and compressive shear stresses, while compressive shear-slip characteristics under compressive and shear stress under high normal stress Under the condition of tensile shear stress, the tensile failure characteristics of marble fracture surface are obvious with no obvious cutting marks. When the shear force is fixed, the shear displacement increases with the increase of axial tension; the cohesion force and internal friction angle are affected by the stress state , The cohesion decreases first and then increases with the increase of normal stress, while the internal friction angle decreases with the increase of normal stress. The trend of cohesion and internal friction angle with normal stress can be divided into 4 sections, pull section, low pressure Stress section, medium-pressure stress section and high-pressure stress section, the cohesion force, internal friction angle and normal stress of each section can be regarded as a linear relationship. When the tensile strength is close to the internal friction angle approaching 90 °, the cohesion tends to infinity; The Mohr-Coulomb criterion curve, which is influenced by the tensile failure mechanism and the stress state, is divided into two parts. The tensile shear section can be fitted with quadratic parabola and the compression shear section with cohesion and internal friction angle evolving with normal stress. This established Mohr-Coulo mb guidelines more comprehensive, higher accuracy.