Dynamic strength and failure modes of sandstone under biaxial compression
Dynamic strength and failure modes of sandstone under biaxial compression
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DOI：
10.1016/j.ijrmms.2020.104260
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发表时间：
2020-04
影响因子：
7.2
通讯作者：
Kai Liu;Jian Zhao;G. Wu;A. Maksimenko;A. Haque;Qianbing Zhang
中科院分区：
文献类型：
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作者：
Kai Liu;Jian Zhao;G. Wu;A. Maksimenko;A. Haque;Qianbing Zhang
岩土材料越来越多地受到准静态约束和动态载荷的影响，因此表征静态-动态载荷耦合条件下的动态行为至关重要。在这项研究中，利用三轴霍普金森杆系统、高速三维数字图像相关 (3D-DIC) 和基于同步加速器的微计算机断层扫描 (μCT) 对砂岩立方体样本进行了一系列动态双轴压缩试验。该测试装置可以确定样本在双轴静态预应力 (σ1,σ2) 条件和不同冲击速度（即 15、20 和 26 m/s）下的动态应力应变行为，对应于 80、200 和 250 s−1 的平均轴向应变率。测试中使用的σ1和σ2均在0至40 MPa之间变化，间隔为10 MPa。利用3D-DIC和基于同步加速器的μCT技术，从宏观到微观、表面到内部、2D到3D系统地表征了双轴约束岩石的动态强度和断裂行为。实验结果表明，在相同的双轴预应力下，砂岩的动双轴抗压强度随着应变速率的增加而增大，即速率依赖性。在给定的冲击速度下，动态双轴抗压强度随着冲击方向上预应力值（σ1）的增加而减小，而随着横向上中间主应力（σ2）的增加而增强，即所谓的约束依赖性。此外，在双轴压缩下观察到两种类型的岩石动态应力-应变曲线，这与峰后破裂特征有关。高速 3D-DIC 显示岩石碎片以一定的速度（包括平移和旋转）从自由表面（σ3 = 0）喷出，这类似于钻孔和爆破甚至强烈岩爆期间观察到的岩石喷出。 μCT显示双“V”形剪切断裂带在双轴压缩下对称生成。还估算了不同约束下的裂纹表面积、体积和动态断裂能，以表征受影响岩石的损伤。
Geomaterials are increasingly being subjected to the quasi-static confinements and dynamic loadings, and thus it is critical to characterise dynamic behaviour under the coupled static-dynamic loading conditions. In this study, a series of dynamic biaxial compression tests was performed on cubic specimens of sandstone by using a triaxial Hopkinson bar system, high-speed three-dimensional digital image correlation (3D-DIC) and synchrotron-based micro-computed-tomography (μCT). This testing apparatus allows for determining dynamic stress-strain behaviour of the specimen under biaxial static pre-stress (σ1,σ2) conditions and different impact velocities (i.e. 15, 20 and 26 m/s), corresponding to average axial strain rates of 80, 200 and 250 s−1. Bothσ1andσ2applied in the tests varied from 0 to 40 MPa with an interval of 10 MPa. Dynamic strength and fracture behaviours of biaxially confined rocks were systematically characterised from macroscopic to microscopic, surface to interior and 2D to 3D by using the 3D-DIC and synchrotron-based μCT techniques. Experimental results show that, under the same biaxial pre-stresses, dynamic biaxial compressive strength of sandstone increases with strain rate, i.e. rate dependence. At a given impact velocity, dynamic biaxial compressive strength decreases with increasing pre-stress values (σ1) along the impact direction, while it enhances with the increase of intermediate principal stress (σ2) in the lateral direction, which is so-called confinement dependence. Besides, two types of dynamic stress-strain curves of rocks are observed under biaxial compression, which is associated with post-peak fracturing characteristics. High-speed 3D-DIC shows that rock fragments are ejected out of the free surface (σ3= 0) with certain velocities including the translation and rotation, which resembles the rock ejection observed during drilling and blasting and even strong rockbursts. μCT reveals that the double “V” shapes of shear fractured zones are symmetrically generated under biaxial compression. The crack surface area, volume and dynamic fracture energy are also estimated under different confinements to characterise the damage of impacted rock.