干燥和饱和状态下砂岩力学特性试验研究

Experimental study on mechanical properties of sandstones under dry and saturated conditions

为了研究岩石的基本力学特性及水对岩体的影响,利用岩石全自动三轴伺服仪,分别对干燥、饱和砂岩标准试样进行常规三轴压缩力学试验,探讨砂岩在不同荷载作用下的应力—应变曲线特征、变形、峰值强度及破坏形式等力学特性。试验结果表明,岩样从干燥状态到饱和状态,相同围压下,弹性模量平均下降了9.24%,峰值强度平均下降了12.4%。采用Hoek-Brown强度准则和Mohr-Coulomb强度准则分别对峰值强度进行模拟,模拟结果表明前者的模拟效果优于后者。干燥和饱和砂岩的应力—应变曲线均依次经历了裂纹闭合阶段、线弹性阶段、稳定裂纹扩展阶段、不稳定裂纹扩展阶段。随着围压的增加,干燥和饱和砂岩由劈裂破坏逐渐向剪切破坏过渡,并且在低围压条件下,饱和砂岩破碎程度比干燥砂岩更加明显。结合砂岩试样的破坏形式,对强度的非线性给出了合理解释。

To study the basic mechanical properties of rock and the influences of water to rock,the triaxial mechanics experiments,for both dry and saturated sandstones,were carried out by using three-axis servo instrument,to investigate mechanical properties of stress- strain curves,deformation,peak strength,and the final fracture of rocks. The experimental results show that, under the same confining pressure,the elastic modulus decreased by 9. 24% on average and the peak intensity decreased by 12. 4% on average from dry state to saturated state. The simulation results with Hoek-Brown strength criterion are better than Mohr-Coulomb criterion. Regardless of whether the sandstone is dry or saturated, the stress-strain curves have undergone the crack closure phase, the linear elastic phase, the stable crack propagation phase,and the unstable crack propagation phase. For the failure mode, with the increase of confining pressure, the sandstone gradually transitioned from splitting failure to shear failure. Under the condition of low confining pressure,the degree of frag-mentation of the saturated sandstone is more obvious than that of the dry sandstone. Combined with the failure mode of the sandstone specimen,the nonlinearity of the strength was given a reasonable explanation.