水-气-岩相互作用下覆岩导水裂隙自修复机制研究

After the underground coal mining, the overburden rock mass was easy to react with water and air in the goaf, then the rock mechanic strength will be alleviated, some deposits or secondary mineral will be built as well. Thereout, the water conducting fracture will be gradually repaired due to the function of mining-induce stress compaction and deposits plugging. It is of great significance to study the self-repairing law and its mechanism for scientific evaluating the damage degree of the aquifer and its ecological restoration ability. So, the experiments and tests of water-air-rock interaction will be conducted in the project by combining the knowledge of mining rock seepage theory, mineralogy, water chemistry and so on. The permeability of failure rock and its variation law under the loading condition will be tested after the physical and chemical reaction with the mixture of water and air. And the self-repairing mechanism of the fracture in the failure rock will be revealed simultaneously. With the evaluation criteria of self-repairing degree which can be calculated by the ratio of permeability of failure rock after the self-repairing function and that of original rock, the influence law of the key factors on the self-repairing degree will be totally studied. The factors include chemical property of water and air, mineral composition of rock mass, fracture form, stress parameter, action time, and so on. According to the permeability distribution in the mining overburden during different self-repairing time, the dynamic evolution law of the shape of fractured water-conducting zone with the passing of repairing time will be revealed, and the critical length of self-repairing time that the water stopped losing will be fixed. On consideration of above research results, the prediction and evaluation method of the self-repairing ability of the water conducting fracture can be formed. The study will provide an important theoretical reference for implementing water preserving mining and ecological management in western mining area of China.

覆岩采动破坏后易与采空区水、气物理化学反应而发生损伤软化和沉淀物衍生，由此促使导水裂隙在采动应力压密和沉淀物封堵等作用下逐步修复愈合；研究揭示该自修复现象的产生机理与规律对于科学评价含水层受采动破坏程度及其生态恢复能力具有重要意义。本项目交叉利用采动岩体渗流理论、矿物学、水化学等学科知识，基于水-气-岩相互作用实验，研究破坏原岩与水、气反应后在承载过程中的渗透性变化规律及其裂隙自修复机理；以破坏原岩自修复后的渗透率与原岩渗透率之比作为自修复程度的评价准则，重点考察水、气化学属性、岩石矿物成分、裂隙形态、受力参数、作用时间等因素对裂隙自修复程度的影响规律。依据不同修复时间对应采动覆岩各区域的渗透性分布，揭示导水裂隙带形态随修复时间的动态演变规律，确定水源不再漏失所需的临界修复时间，最终形成覆岩导水裂隙自修复能力的预测和评价方法。项目研究将为西部矿区实施保水采煤、生态治理等提供重要理论参考。

煤炭开采引起的覆岩导水裂隙在其产生后的长期演变过程中，会因裂隙面岩石矿物与地下水、CO2等气体发生的水-气-岩相互作用以及采动地层应力的压实等作用共同影响，而出现水渗流能力逐步降低的自修复现象；研究揭示该自修复现象的产生机理与规律对于科学评价含水层受采动破坏程度、合理制定有效的生态恢复对策等都具有重要指导意义。本项目交叉利用采动岩体渗流理论、矿物学、水化学等学科知识，基于水-气-岩相互作用实验，就采动岩体裂隙自修复的发生机理及其影响规律、覆岩导水裂隙带形态随修复过程的动态演变规律、以及不同区域不同形态裂隙的自修复能力评价等问题进行了研究。研究发现，采动岩体裂隙的自修复主要源于3方面的物理或化学作用过程：第一，粘土矿物的遇水膨胀对裂隙空间的挤占，泥化、崩解的泥化物对裂隙的封堵作用；第二，地下水的溶解、溶蚀作用造成裂隙面粗糙度降低，促进裂隙面在采动地层应力的挤压作用下更紧密贴合；第三，地下水阴阳离子与铝硅酸盐、碳酸盐等岩石矿物发生离子交换的化学反应，生成的次生矿物或化学沉淀物对裂隙的充填封堵作用。由于粘土矿物的遇水膨胀作用速度较快，故裂隙自修复过程存在“先快后慢”的分区降渗特征；且无论酸性或碱性地下水条件，裂隙均具备自修复能力，但酸性水溶液条件下的自修复效果更好。通过对比不同岩性裂隙岩样在不同化学特性水溶液下的水-气-岩相互作用降渗实验，发现中性或碱性地下水条件有利于泥岩类岩石裂隙的自修复，而酸性地下水及富含CO2条件有利于砂岩类岩石裂隙的自修复。通过建立采动覆岩渗透性的空间分布模型，得到了地下水流失主通道的路径分布特征；结合裂隙自修复机理，揭示了导水裂隙带“马鞍”形态随自修复过程的演变特征；据此提出了重点针对导水主通道开展人为调节地下水、气化学环境促进裂隙修复的含水层生态恢复新思路。研究结果为我国西北部生态脆弱矿区采动破坏含水层的生态修复与地下水保护等提供了重要理论参考。