煤岩重复加载力学特性试验研究

利用MTS815.03电液伺服岩石试验系统,对运河煤矿煤岩试件在重复加载作用下的特性进行研究。研究结果表明,在重复加载作用下,煤岩强度极限较常规单轴压缩强度极限降低约23.65%;二次加载时弹性模量较初次加载时弹性模量增大约21.08%。由于煤岩含有大量原生损伤裂隙并且强度较低,在重复加载过程中,煤岩内部原生裂隙和新生裂隙的闭合与张开以及不可恢复的宏观裂纹的产生为煤岩弹性模量的增大、强度极限的降低给予较为合理的解释。在重复加载作用下,有超过1/3的能量以内部裂隙的闭合,材料的屈服、破坏、损伤、断裂以及裂隙面的滑移摩擦等形式消耗掉。煤岩的破坏过程经历了从压密、应变硬化到软化的变化过程。

Experimental Study on Mechanical Properties of Coal Under Repeated Loading

The mechanical properties of coal samples from Yunhe coal mine under repeated loading are studied through experiments of MTS 815.03 servo-controlled rock mechanical test system.The results indicate that compared with the ultimate strength under uniaxial compression test,the ultimate strength of coal samples under repeated loading decreases by 23.65%;compared with the first loading,the elastic modulus under the second loading increases by 21.08%.Because the coal samples have many initial fissures and lower intensity,the close and splay of the initial and newborn damage fissures and the non-recover macroscopic cracks offer a reasonable explanation for the increase of elastic modulus and the decrease of the ultimate strength.Under repeated loading,more than a third of the energy is consumed by the way of the close of interior fissures,the yielding,failure,breakage of the material and the sliding friction of fractures.The failure processes of coal go through pressure consolidation,strain hardening and strain softening.