动静载荷耦合作用下复合煤岩体的力学特性及破坏特征
Mechanical properties and failure characteristics of composite coal and rock mass under dynamic and static loading
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摘要: 为了弄清瓦斯爆炸与煤岩动力灾害下巷道失稳破坏的机制,利用 MTS 伺服压力机和霍普 金森压杆系统,研究了复合煤岩体在静态和动态载荷下的破坏特征,以及煤岩厚度比例、煤岩组合 角度和冲击方向对煤岩体力学性能和破坏形式的影响。 试验采用高和直径均为 50 mm 的圆柱形 试样,选取烟煤和砂岩为实验材料。 试验设置的煤岩厚度比例分别为 0 ∶ 1,1 ∶ 2,1 ∶ 1,2 ∶ 1 和 1 ∶ 0,煤岩组合角度分别为 0°,15°,30°,45°,60°和 90°。 在动态冲击试验中,分别设置冲击煤样和 冲击岩样 2 种载荷施加方向,来观察冲击方向对复合煤岩体力学性能的影响。 研究结果表明:煤岩 厚度比例越高,复合煤岩体的抗压强度和弹性模量越小;随着组合角度的增加,复合煤岩体的弹性 模量逐渐增加,弹性模量最大的组合角度为 90°,弹性模量最小的角度为 0°;抗压强度先减小后增 加,组合角度为 45°时,抗压强度最小,组合角度为 90°时,抗压强度最大。 与冲击煤样相比,冲击岩 样时复合煤岩体的抗压强度和弹性模量较大,极限应变略低。 在单轴加载下,复合试样组合角度小 于 45°时主要以劈裂破坏为主,45°时劈裂破坏和压剪破坏并存,大于 45°时为沿交界面的剪切破 坏。 在动态载荷下,45°角的应力-应变曲线由于煤岩接触面滑移没有出现回弹现象,且此时动态 抗压强度最小。Abstract: In order to understand roadway instability mechanism under gas explosions and coal and rock dynamic dis⁃ asters,the damage characteristics of composite coal and rock mass under static and dynamic loading,as well as the effect of thickness ratio, combination angle and impact direction on damage characteristics were investigated using the MTS servo press and Hopkinson pressure bar(SHPB)system. Cylindrical samples with the height and diame⁃ ter of 50 mm were adopted in the tests. Bituminous coal and sandstone were selected as experimental materials. The coal and rock thickness ratios in the tests are 0 ∶ 1,1 ∶ 2,1 ∶ 1,2 ∶ 1,and 1 ∶ 0,while the coal and rock combi⁃ nation angles are 0°, 15°, 30°, 45°, 60° and 90°. In the dynamic impact test, two loading directions were applied(strike coal sample and strike rock sample)respectively to observe the influence of impact direction on the mechanical properties of composite coal and rock mass. The results show that the higher the thickness ratio of coal to rock,the smaller the compressive strength and elastic modulus of composite coal and rock mass. The elastic modulus of the composite coal and rock mass increases gradually with the increase of the combination angle. The maximum and minimum elastic modulus is obtained under the combination angle of 90° and 0°,respectively. The compressive strength firstly decreases and then increases. When the combined angle is 45°,the compressive strength is lowest. The compressive strength is highest when the combined angle is 90°. Compared with striking coal sample,the compres⁃ sive strength and elastic modulus of the composite coal rock mass are larger when striking rock sample,while the ulti⁃ mate strain is slightly lower. Under uniaxial loading, when the combination angle of the composite specimen is less than 45°,the splitting failure occurs. The splitting failure and compression shear failure coexist when the combina⁃ tion angle is 45°. When the combination angle is greater than 45°, the shear failure occurs along the interface. Under the dynamic loading,the stress⁃strain curve at the combination angle of 45° does not show springback phenom⁃ enon due to slip on the interface of coal and rock,and the dynamic compressive strength is lowest under this condition.