真三轴条件下煤岩体冲击破坏的能量演化特征分析

Analysis of energy evolution characteristics of coal rock mass impact failure under true triaxial test condition

为进一步揭示煤岩体冲击动力学特性与能量演化之间的内在联系,采用真三轴试验系统对不同煤样厚度比例的煤岩体试样开展加卸载试验,通过积分计算求得试样在外力加卸载变形直至失稳破坏过程中所吸收的能量值,对比分析各试样在试验过程中不同阶段、不同方向的能量演化特征,并结合其失稳破坏时的强度特征与破坏裂纹特征,分析能量演化规律。结果表明:①随着煤样厚度比例的增加,试样失稳破坏时累计吸收的能量呈现先增加后降低的上凸抛物线特征,与试样破坏裂纹特征演化特征有正相关关系,说明煤岩体累计吸收能量大小与其失稳破坏所呈现的动力学特征为正相关关系;②随着煤样厚度比例的增加,试样强度逐渐下降,与试样累计吸收能量演化规律并无明显的正相关关系。因此通过能量分析并研究其调整规律相比分析破坏强度可以更好地揭示煤岩体破坏失稳本质;③在不同煤岩体介质属性条件下,原岩应力所导致的能量积聚和后期外力扰动所导致的能量增量均可以成为其冲击破坏的主导原因。进一步印证,一定条件下高静载荷和动静载荷叠加均可诱发冲击地压;④外力加载是能量吸收的本质来源,而某单一方向能量吸收还与结构面、其余方向外力卸载相关。因此抑制能量积聚的根本方法是卸载外力,同时还需考虑煤岩体结构与其他方向外力变化所引起的联动效应。研究成果对于探究煤岩体冲击力学特性具有一定的理论意义,并可为冲击地压防控提供理论及技术支撑。

In order to further reveal the internal relationship between the impact dynamic characteristics of coal and rock mass and the energy evolution,the true triaxial test system is used to carry out loading and unloading tests on coal and rock samples with different thickness ratios of coal samples.The energy absorbed by the samples in the process of external force loading and unloading deformation to instability failure is calculated through integral calculation.The energy evolution characteristics of each sample in different stages and directions in the test process are compared and analyzed,The energy evolution law is analyzed based on the strength characteristics and failure crack characteristics of the unstable failure.The results show that:①With the increase of the proportion of coal sample thickness,the cumulative energy absorbed during the instability failure of the sample showed the characteristics of an up-convex parabola that first increased and then decreased,which was positively correlated with the evolution characteristics of the failure crack characteristics of the sample,indicating that the cumulative absorption energy of the coal rock mass was positively correlated with the kinetic characteristics of its instability failure;②With the increase of thickness ratio of coal sample,the strength of sample decreases gradually,and there is no obvious positive correlation with the evolution law of cumulative absorbed energy of sample.Therefore,the essence of failure and instability of coal and rock mass can be better revealed by energy analysis and studying its regulation law than by analyzing the failure strength;③Under the condition of different medium properties of coal and rock mass,the energy accumulation caused by the original rock stress and the energy increment caused by the later external force disturbance can be the dominant cause of its impact failure.This further confirms that under certain conditions,high static load and dynamic and static load can induce rock burst;④The external force loading is the essential source of energy absorption,and the energy absorption in a single direction is also related to the external force unloading in the structural plane and other directions.Therefore,the fundamental method to restrain energy accumulation is to unload the external force,and the linkage effect caused by the change of coal and rock mass structure and external force in other directions should also be considered.The research results have certain theoretical significance for exploring the mechanical characteristics of coal rock mass impact,and can provide theoretical and technical support for the prevention and control of rock burst.