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深部岩石开挖等工况诱发的不同初始卸荷水平对其力学特征影响明显,基于对砂岩进行常规三轴压缩试验和不同初始卸荷水平的三轴卸荷试验,研究了高应力加、卸荷条件下砂岩的强度、变形及扩容特征。研究发现:在同一初始围压条件下,初始卸荷水平越高,围压降低的越小,岩样达到破坏所经历的卸围压过程越短。随着初始围压的增大,不同卸荷水平下的统一围压降参数η基本是增加的,表明在高应力状态岩样需要更大的围压卸荷量才会破坏。随初始卸荷水平的提高,凝聚力c呈指数关系增长,内摩擦角φ呈多项式关系减小。卸围压的两个阶段,侧向应变增量Δε_3都比轴向应变增量Δε_1大,表现为明显的侧向扩容。初始卸荷水平越低,其最大剪胀角越大,扩容效应越明显。扩容指标I_d与围压呈幂函数型关系,与初始卸荷水平呈二次函数关系。基于对试验数据的拟合,对不同初始卸荷水平作用的砂岩的摩尔-库仑准则表达式进行了修正。
Different initial unloading levels induced by deep rock excavation and other conditions have obvious effects on the mechanical characteristics. Based on the triaxial uniaxial compression tests of sandstone and the initial unloading levels of sandstone, the effects of high stress plus unloading Strength, deformation and expansion of sandstone under load. The results show that under the same initial confining pressure, the higher the initial unloading level, the lower the confining pressure and the shorter the unloading confining pressure experienced by the rock specimen. With the increase of initial confining pressure, the uniform confining pressure drop parameter η at different unloading levels is basically increased, which indicates that the rock sample needs more confining unloading capacity to rupture in high stress state. As the initial unloading level increases, the cohesion c increases exponentially, and the internal friction angle φ decreases in a polynomial relationship. During the two stages of unloading confining pressure, the lateral strain increment Δε_3 is larger than the axial strain increment Δε_1, showing a significant lateral expansion. The lower the initial unloading level, the larger the maximum dilatancy angle, the more obvious the dilatancy effect. Expansion index I_d and the confining pressure showed an exponential function relationship, and the initial unloading level was a quadratic function. Based on the fitting of experimental data, the Mohr-Coulomb criterion expressions of sandstone with different initial unloading levels are modified.