深部原位应力煤岩卸荷力学特性试验研究

Experimental study on unloading mechanical properties of deep coal under in-situ stresses

为探究深部原位应力煤岩卸荷力学特性,利用MTS816岩石力学测试系统对原位应力煤岩开展不同卸荷速率的三轴加卸载试验,并与常规卸荷试验对比,通过获取全过程应力–应变曲线分析卸荷煤岩的力学性能与变形特征,结合CT三维重构技术研究煤岩的破坏特征,探讨原位应力卸荷煤岩的适用强度准则。结果表明:(1)2种方案煤岩的峰值强度与卸荷速率均成反比,但原位应力煤岩较常规煤岩的峰值强度更高,这种趋势在低速卸荷时逐渐弱化。(2)原位应力恢复过程实施后,煤岩在卸荷速率升高条件下,峰值轴向应变先减小后趋于稳定,峰值侧向应变整体不变,峰值体积应变先降低后增加。卸荷条件下原位应力煤岩的弹性模量更平稳,应变硬化模量得以增强。(3)Mogi-Coulomb强度准则能更好地反映原位卸荷煤岩的破坏强度特征;原位应力煤岩较常规煤岩的黏聚力c增加39.23%,内摩擦角φ减少11.92%,表明原位卸荷煤岩的抗破坏主控因素为黏聚力。

In order to research the mechanical properties of deep coal under in-situ unloading stresses,triaxial loading and unloading tests with different unloading rates were carried out on coal under in-situ stresses by using the MTS816 rock mechanics test system and compared with conventional unloading tests.The stress-strain curve was used to analyze the mechanical properties and deformation characteristics of unloaded coal.3D reconstruction technology by CT was applied to study the failure characteristics of coal.With this prerequisite,the applicable strength criterion of in-situ coal was discussed.The results show that:(1)The peak strengths of coal with two schemes are inversely proportional to the unloading rate.However,the peak strength of in-situ coal is higher than that of conventional coal,and this trend gradually weakens during low-speed unloading.(2)After in-situ stress recovery,as the unloading rate increases,the peak axial strain of coal first decreases and then tends to stabilize,the peak lateral strain remains unchanged,and the peak volumetric strain first decreases and then increases.Under unloading conditions,the elastic modulus of in-situ coal under unloading condition is more stable,making the strain hardening modulus enhanced.(3)The Mogi-Coulomb strength criterion can better reflect the failure strength characteristics of in-situ unloading coal.The cohesion c of in-situ coal increases 39.23%and the internal friction angle decreases 11.92%compared with conventional coal,indicating that the main control factor of failure resistance of in-situ unloading coal is cohesion.