煤岩组合体分级加卸载特性的试验研究

Experimental research on loading-unloading behavior of coal-rock combination bodies at different stress levels

通过MTS 815试验机研究了煤岩组合体分级加卸载试验。分级加卸载下煤岩组合体破坏以脆性破坏机制为主,与单轴作用相比,分级加卸载作用下煤岩组合体的破坏更为破碎,且破坏强度有所提高,但轴向和环向应变却有所降低。同一循环中的加载与卸载曲线基本不重合,且多数情况不形成闭合环路;卸载曲线与下一个循环的加载曲线通常也不重合,但会形成闭合环路。第1循环结束时残余变形较大,加卸载曲线形成了类似"牛角"状的曲线;随着循环加卸载地进行,与残余变形相比第1循环有所降低,加载和卸载曲线在逐渐靠近,并且加卸载曲线类似"竹叶"状。获得了残余变形和加卸载弹性模量随循环加卸载的变化关系,并且实验表明卸载到1 MPa附近时,卸载线是曲折波动的;但在再次加载初期,加载线几乎是直线,且随着荷载的继续增加,加载线和上一个循环的卸载线逐渐分离。循环加卸载后应变相位逐渐滞后于应力相位,内因可能是因为岩石矿物颗粒间的黏滞性以及煤岩组合体界面之间的摩擦引起的,而外因可能是循环加卸载导致了煤岩体内部损伤,并由此诱发不可恢复的残余变形。

In this paper,MTS 815 test system has been used to study the failure behavior of coal-rock combination bodies under different stress level cyclic loading-unloading.Experimental indicates that brittle failure is also the failure mechanism of coal-rock combination body under cyclic loading-unloading,but the failure under cyclic loading-unloading is more fragmentized than that under uniaxial loading.The failure strength under cyclic loading-unloading is higher than that under uniaxial loading;but the axial and circumferential strain in the contrast.The loading curves of coal-rock combination body are usually not coincidence with the unloading curves.In addition,they usually do not form a closed loop.In the first cycle,the residual deformation is large,and the loading-unloading curve forms a horn-shaped curve.The relationships of the residual deformations and the loading-unloading elastic modulus with the advancing of cyclic loading-unloading have been obtained in our tests,respectively.At the reverse position of unloading and loading,when unloading to about 1 MPa,the unloading line is fluctuant;however loading again,loading line is almost straight line in the early.In the all of cycles,some cycle loading lines are nearly coincidence with the unloading curves,some form sharp edges,or some forms cross lines.With the increasing of the loading,the loading curves separate gradually with the unloading curves.With the advancing of loading and unloading,strain phase gradually lags stress phase.The internal factors are the viscosity of rock minerals and the friction between the interface between coal and rock,and the external factors are the irreversible residual deformation under cyclic loading and unloading.