千米采动超限应力作用下煤体冲击响应特性试验研究

As coal mining depth is over 1000 m, an overstressed effect is commonly observed around working face which shows a higher stress than the ultimate strength of the coal mass. Under the effort of overstress effect, rock burst disasters occurred frequently. In this research, field investigation and laboratory testing will be used to study burst triggering criterion and acoustic emission (AE) response of coal mass under overstressed loading-unloading condition, aiming to reveal the types, characteristics and burst-triggering mechanism of coal mass in deep coal mining. Based on true-triaxial loading-unloading and dynamic-static experiments monitored by AE, the triggering condition of rock burst will be determined by testing the critical loads of coal mass under static-dynamic coupled stresses. Velocity models will also be constructed based on passive computed tomography (CT), which will be used to study the relationship of the velocity field, fracture field and energy field with macro- and micro-fractures of coal mass. The rock burst criterion of coal mass under overstressed loading and unloading will be established, and the result can provide a reference to monitoring, pre-warning and control of rock burst in deep coal mining.

煤矿开采深度进入千米以后，采掘工作面普遍出现围岩应力超过煤岩体自身极限抗压强度的超限应力现象。煤体在超限应力作用下，冲击地压动力灾害频发。本项目采用现场调研和物理力学试验等手段，通过研究超限应力作用下煤体的冲击孕育条件、声发射响应规律等来揭示深部采掘扰动对煤层的超限应力加载方式、特性及其诱冲机理。基于声发射监测下的真三轴加卸载动静组合试验，研究超限应力作用下不同强度煤体冲击失稳的临界载荷，确定超限应力作用对煤体的冲击破坏触发条件；建立波速被动CT反演模型，研究超限应力加卸载过程中波速场、裂隙场、能量场等与煤体宏、微观破裂之间的关系，构建深部超限应力加卸载作用下受载煤体的冲击破坏失稳准则。研究成果能够为预测和弱化控制深部冲击地压的监测预警及防治提供有益参考。

煤矿采深进入千米以后，采掘工作面围岩应力普遍超过煤体单轴抗压强度，呈现围岩应力超过煤体强度的超应力现象。基于调研分析，得到煤层单轴抗压强度的分布特征以及开采深度、原岩应力与煤层单轴抗压强度之间的关系，提出了超应力集中系数的概念。采用声发射和被动CT成像技术相结合的研究方法，开展了煤样真三轴超应力卸载作用下冲击破坏试验研究，从而探究声发射波速演化与煤样宏、微观破裂的关系，揭示深地围岩对煤层的超应力加载作用及方式。试验结果表明：（1）不同的应力卸载路径下煤样冲击破坏具有显著的时间延迟效应，应力路径变化越大，其时间延迟越短；（2）三轴卸载状态下煤样的破坏形式复杂多变，多为剪切、拉伸等耦合破坏形式；总体破坏模式表现为首先沿着与轴压方向分布的主裂隙进行扩张破坏，其次在试样表面分布着许多沿轴压方向的小张拉裂隙；（3）在加载初期，煤样内部波速变化范围较小，出现少量高、低波速区；随着载荷初步增加，煤样内高波速区转移与扩展，同时波速异常区明显扩大；当载荷进一步增加，煤样内出现大面积低波速带，波速极小值不断降低，高波速区、波速异常区迅速变化转移；（4）试样宏观破裂面和波速异常丰富区、微观裂隙演化和低波速贯通区形成了较好的对应。同时，基于实验结果初步确定了超应力煤体冲击失稳的临界静载、动载和动静组合载荷。实验成果为研究深部不同开采边界条件下的超应力煤岩体冲击破坏行为及裂隙演化提供理论依据。