采空积水对煤柱蠕变特性及其力学参数影响机理研究

This project attempts to study the spatio-temporal evolution of No. 3 Coal Mining of Shanxi Qinshui Coalfield under the effect of Goaf Water by means of combining the experimental research, numerical modeling and numerical simulation method. Firstly, the coal samples were classified by microscopic CT scanning and coal strength experiment, and the classification standard of coal sample pore scale will be established to ensure the comparability of the experimental results. Secondly , the creep constitutive model of coal before and after water softening and pore water pressure mutation will be studied in 4 steps: first, combined with the single-axis creep test of coal under different water content as well as pore scale and the triaxial creep test of coal before and after the change of pore water pressure; then, the creep characteristics of coal under different pore scale, water content and pore water pressure will be compared and analyzed; after that, the effects of water softening and pore scale, pore water pressure on the creep characteristics of coal will be investigated, and last the statistics analysis method would be adopted to create the creep constitutive model of coal. Finally, the coal pillar support effect will be numerically simulated based on the creep test results, and the prediction model of creep support effect under the action of Goaf Water will be established, which will provide the basis for long-term stability prediction of coal pillar.. Through the study of the project, it is possible to make the analysis quantitatively that whether the residual coal resources are admissibility, and provide theoretical support for the determination of the surrounding rock control method. Therefore, this study will be of great significance in the promotion of quality coal resources residual coal recovery and on improving resource recovery.

本项目拟采用实验研究、数值模拟及模型建立相结合的方法，对山西省沁水煤田3号煤在采空水作用下煤柱的时空演化规律展开研究。首先，通过显微CT扫描及煤体强度实验对煤样进行分类，建立煤样孔隙尺度分类标准，保证实验结果具有可比性；其次，结合不同含水率及孔隙尺度条件下煤体单轴蠕变实验和孔隙水压突变前后煤体三轴蠕变实验，对比分析不同孔隙尺度、含水率及孔隙水压条件下煤体的蠕变特性，探究水软化作用及孔隙尺度、孔隙水压对煤体蠕变特性的影响规律，利用数理统计分析方法，构建水软化作用及孔隙水压突变前后煤体蠕变本构模型；最后，依据蠕变实验结果对煤柱支撑效应进行数值模拟研究，建立采空水作用下煤柱蠕变支撑效应预测模型，为煤柱长期稳定性预测提供依据。. 通过该项目的研究，可以定量分析残煤资源是否具有可采性，同时为复采采场围岩控制方式确定提供理论支撑，对推广我国优质煤炭资源残煤复采，提高资源回收率具有重要的推进作用。

本项目以山西沁水煤田3#无烟煤为研究对象，首先，通过对显微CT扫描后的无烟煤试件进行三维重建，根据孔隙率大小将其分为三类：即孔隙率≤8%，8%~12%，≥12%；其次，采用升级后的HSW-200R型岩石蠕变试验机对四种不同含水率和三种不同孔隙率的无烟煤试件进行单轴蠕变试验，得出：不同含水率及不同孔隙率的无烟煤试件在单轴应力状态下均由瞬时弹性应变、衰减蠕变、稳定蠕变和加速蠕变4个阶段组成；煤样的瞬时弹性应变与应力水平大致呈线性增长关系，且含水率、孔隙率越大，其瞬时弹性应变随应力水平的增长速率越快；建立的考虑含水损伤的非线性黏弹塑性模型能够较好的反映含水无烟煤的减速蠕变、稳定蠕变和加速蠕变特征。其次，运用LDHJ-III型岩石高温三轴蠕变试验机对饱水状态下的无烟煤试件进行孔隙水压突变前后的三轴蠕变试验，结果表明：不同围压条件下，无烟煤试样的轴向应变跟径向应变随应力的增加逐渐表现出时间相关的蠕变变形，部分无烟煤试件出现加速蠕变阶段；径向应变在各级应力下均小于轴向应变。在较低应力下，试样的轴向变形仅仅表现为瞬时应变，当应力达到某一特定值后，试样呈现显著的衰减蠕变和稳定蠕变特征。轴向应变与径向应变在较低轴向应力下具有变形不协调性，在较高轴向应力下具有变形协调一致性。建立的无烟煤三轴蠕变模型能够很好地描述孔隙水压作用下无烟煤的蠕变特性。最后，运用数值模拟的研究手段，模拟了不用孔隙率下无烟煤的单轴蠕变试验和不同孔隙水压条件下的三轴蠕变试验，并与实验室试验结果相比较，结论为：模拟得出的不同孔隙率及孔隙水压下的无烟煤蠕变规律与实验室得出的试验规律相吻合。同时，以关岭山煤矿3号复采煤层为地质背景，采用数值模拟的研究手段，研究了煤柱宽度、煤柱赋存时间与其稳定性之间的关系，得出：煤柱宽度为15m、20m、25m时蠕变曲线与稳定蠕变曲线相吻合，30年内该煤柱不会进入加速蠕变阶段，不会发生蠕变破坏；煤柱宽度为10m时，在20年后，煤柱会进入到加速蠕变阶段，即煤柱可能会发生失稳破坏现象。.通过该项目的研究，其结果可为残煤复采可采性评价、复采采场围岩控制、地表沉陷控制等提供一定的理论依据，对我国优质煤炭资源的安全、高效开采具有重要的推进作用。