双孔洞红砂岩力学特性及孔洞周边裂纹开裂-闭合规律研究

Study on the Mechanical Characteristics of Red Sandstone with Double Holes and the Cracking-Closure Law of Crack Around Holes

为研究双孔洞红砂岩力学特性及其孔洞周边裂纹开裂-闭合机制,对含不同倾角的双孔洞红砂岩进行单轴压缩试验,采用CCD相机对孔洞周边裂纹进行监测,并基于数字图像相关方法(DIC),综合分析双孔洞红砂岩力学性能、孔洞周边裂纹开裂-闭合规律,阐述双孔洞红砂岩破坏机理。结果表明:随着双孔洞倾角的增加,红砂岩抗压强度先降低后升高,且呈良好的二次函数关系;双孔洞红砂岩周边裂纹开裂分为独立型张拉裂纹(α=30°),剪切裂纹(α=45°、60°、75°),贯通型张拉裂纹(α=90°)3种模式;双孔洞红砂岩周边裂纹闭合模式分为局部闭合模式(α=30°)、零闭合模式(α=45°、60°、75°)、完全闭合模式(α=90°);张拉裂纹主要受径向应变场影响,剪切裂纹受到径向应变场及剪应变场共同控制,若红砂岩两孔洞周边裂纹受到剪应变场影响较大,其抗压强度较低。

In order to study the mechanical properties of the red sandstone with double holes and the cracking-closure mechanism around the holes,the uniaxial compression tests were carried out on the red sandstone with double holes and dip angles.The cracks around the holes were monitored by a CCD camera.Based on the digital image correlation method(DIC),the mechanical properties of the red sandstone with double holes and the cracking-closure mechanism around the holes were analyzed.Then the failure mechanism of the red sandstone was described.The results showed that:with the increase of the dip angle of the double hole,the compressive strength of the red sandstone firstly decreased and then increased,and it showed a good quadratic function relationship.The cracking modes of crack around the two holes of the red sandstone were divided into three types,including independent tensile crack(α=30°),shear crack (α=45°,60°,75°)and through-type tensile crack (α=90°).The closure modes were also divided into three types,including partial closed mode(α=30°),zero closed mode(α=45°,60°,75°),as well as fully-closed mode(α=90°).The tensile cracks were mainly affected by the radial strain field,and the shear cracks were controlled by the radial strain field and the shear strain field.If the cracks around the two holes of the red sandstone were greatly affected by the shear stress,their strengths were relatively low.