砂岩拉–剪力学特性试验研究

岩体工程开挖和河谷下切均将致使岩体应力沿一个或多个方向卸荷,造成岩体应力场重分布。这种卸荷常造成岩体承受拉剪应力,使得卸荷岩体的破坏呈现明显张性特征。然而由于试验技术的限制,在法向拉应力作用下岩石剪切力学行为的试验研究仍非常困难。笔者研发了拉伸–双面剪切试验装置,可直接在常规微机控制伺服直剪试验机上进行试验(将法向压应力转换成拉应力)。采用此装置,开展了砂岩的拉剪试验,结果表明:拉–剪应力作用下岩石剪应力–剪位移曲线峰前仅出现初始非线性段和线性变形两个阶段(即没有峰前的屈服段);砂岩抗剪强度和剪切刚度随法向拉应力的增大逐渐减小;Hoek-Brown准则比Mohr-Coulomb准则能更好的描述砂岩在拉剪应力下的强度特征;随着法向拉应力的增大,岩样破裂面张性特征越突出且形状更为平直。

Experimental study on tension-shear mechanical behavior of sandstone

Rock excavation and river incision result in stress unloading in one or more directions, which leads to the redistribution of stress fields of rock masses in the influenced zone. The rock masses in the unloading zone commonly bear tension-shear stress, making the failure of unloading rocks exhibit obvious tensile property. However, due to the limitation of test technology, it is still quite difficult to study the shear mechanical behavior of rock under the action of normal tensile stress. In this study, a tension double-shear test auxiliary device that can be used by conventional direct shear testing machine is designed to convert the normal compressive force to the tensile one. The direct shear tests on sandstone under tensile normal stress are carried out using this device. The results show that under the tension-shear stress, the curves of shear stress versus shear displacement before peak stress only show two deformation stages of initial nonlinear deformation and linear deformation (namely without yield stage before peak). The shear strength and shear stiffness of sandstone gradually decrease with the increase of the normal tensile stress. Compared with the Mohr-Coulomb criterion, the Hoek-Brown criterion is better in describing the strength characteristics of sandstone under tensile shear stress. Besides, as the normal tensile stress increases, the rupture surface of rock specimen has more obvious tension and is straighter in shape.