高应力状态下煤柱松弛时效性研究

With the increase of mining depth and working span, the failure of underground coal pillar differs a lot from the failure of coal pillar of shallow surface mining and traditional mining. In case of unexpected engineer disasters and mining damage, high vertical stress to ensure the long-time stability must be emphasized with higher standards. Stress relaxation is an important mechanical deformation feature which is concerned with the stability and duration of coal pillar below the mine shaft. And this feature is highly relevant to the stability and lifespan of coal pillar under high vertical stress. This project introduces the theory of stress relaxation. Based on the mechanical features of rheology and elastic-plastic of coal pillar, focusing on the failure mechanism and long-term stability of coal pillar, experiments on the properties of stress relaxation were conducted. It studies the stress evolution laws and duration and forms of the failure of coal pillar. And it establishes the model and constitutive equations of stress relaxation. Also it reveals the rule of discontinuous deformation properties in the model induced by the high vertical stress. This research explains the relationship between stress relaxation and stability of coal pillar. And it determines the conversion conditions from the stress relaxation to creep and the weight of stress relaxation and creep on the time-effectiveness. Then it analyzes the influencing factors and mechanism of stress relaxation under high vertical stress. Finally the failure criteria of stress relaxation and evaluation system on the coal pillar time-effectiveness would be established.

随着矿井开采深度及服务年限的增大，井下煤柱的失效与浅部开采及传统情况下的煤柱失效有很大区别。为避免突发性的工程灾害和开采损害，髙应力状态对煤柱的长期稳定性提出了更高要求。应力松弛是煤矿井下煤柱稳定性与时间相关的重要力学变形特性，而这一特性与髙应力状态下煤柱的稳定性和使用寿命有着非常紧密的联系。项目引入应力松弛理论，在煤柱流变、弹塑性等力学特性基础上，针对高应力状态下井下煤柱松弛失效机理及长期稳定性，进行煤柱应力松弛特性试验，研究煤柱应力场演化规律，分析煤柱松弛失效时间及失效形式，建立煤柱应力松弛模型及其本构方程，揭示高应力场演化导致的非连续形变特征在松弛模型中的显现规律。项目研究阐明煤柱应力松弛与煤柱稳定性的相互关系，确定煤柱应力松弛与蠕变之间的转化条件，并确定松弛与蠕变对煤柱时效性的权重，分析研究高应力状态下煤柱松弛的影响因素及其影响机理，给出煤柱松弛失效判据，构建煤柱时效性评价体系。

深井留设煤柱由于原岩应力数值上的绝对增加和分布状态的相对复杂，使得煤柱应力场难以在短时间内通过自身调节达到平衡，导致深井煤柱的力学行为与浅部有较大的差别。通过对深部煤柱非线性力学特点的深入研究，发现进入深部的煤岩体所属的力学系统不再是浅部煤岩体所属的线性力学系统，而是非线性力学系统，传统理论、方法与技术已经部分或相当大部分失效，深入进行深部煤岩体的应力松弛研究已势在必行。本文以此为出发点，以辽宁红阳三矿为工程背景，在许多学者的研究基础上，利用深部煤层室内实验、理论推导、数值模拟分析等方法得出主要成果如下：.（1）在三轴压缩试验中，煤样的弹性模量与围压成正比例关系，泊松比与围压成反比例关系，说明煤样的抗压强度随围压增大而增大。.（2）通过开展不同损伤程度下的煤样三轴蠕变试验，分析不同损伤程度对煤样的力学特性影响，得出蠕变量和蠕变破坏时间随损伤程度增大而减小，同时会降低蠕变破坏应力荷载强度，提高蠕变速率，此时体积应变更容易由压缩状态转变为膨胀状态。.（3）通过开展不同加载速率下的煤样三轴蠕变试验，分析不同加载速率对煤样的力学特性影响，得出随着加载速率的升高，煤样瞬时应变以V=0.01mm/s为拐点先减小后增大，且在蠕变过程中存在应力阈值，同时煤样蠕变破坏应力荷载强度呈非线性增大趋势，蠕变速率随之提高，体积扩容时加载速率与偏应力呈二次函数递增，并基于上述应力阈值建立改进的西原模型对煤样加速蠕变阶段进行更好描述。.（4）基于不同围压下煤柱松弛特性试验结果，建立煤柱体松弛模型来描述，从而进一步开展水作用下不同高宽比的煤柱松弛试验，研究应力松弛量、应力松弛度、应力松弛速率的变化规律，并以红阳三矿为工程背景开展数值模拟分析，确定基于应力松弛效应下的煤柱留设高度，为实际工程提供依据。