我国西北地区煤层普遍较多、较厚，近距离煤层群开采较为典型，极易造成下层工作面及临近工作面受重复采动影响，加剧覆岩破坏及裂隙发育，造成更为复杂的漏风通道。由于上层采空区底板垮落，将显著增加采空区内遗煤量，大幅提升采空区遗煤自燃风险，严重危害矿井生产。

本文以陕西某矿重复采动工作面为试验对象，首先利用程序升温实验，研究得到不同粒径及供风条件下气体产物变化规律，确定了指标气体及临界特征值，并计算得出耗氧速率及放热强度等特征参数，为煤自燃极限参数的推算提供基础。在实验分析的基础上，应用现场试验及数值模拟综合研究采空区内部漏风特性及自燃危险区域。主要研究成果如下：

根据煤岩层力学测试结果，运用3DEC软件，构建重复采动覆岩裂隙演化模型，研究了单一采动及重复采动下，覆岩破坏特征及裂隙漏风通道发育规律。随着工作面推进，单一采动下，覆岩位移变化平缓，漏风裂隙分布规律相对简单、集中，裂隙发育最大高度约86 m；重复采动下，覆岩破坏程度加剧，位移变化更为明显，不仅造成新生裂隙通道发育，还将导致上层开采后已压实的裂隙区域重新发育，致使裂隙漏风通道分布规律更为复杂，显著提升采空区漏风风险。此外，重复采动后，裂隙发育最大高度将蔓延至173 m，造成上覆、下层采空区贯通，大幅加重采空区遗煤自燃风险。

基于上述结论，利用SF₆示踪技术测定采空区实际漏风情况，发现采空区内部及上覆岩层之间存在局部漏风现象，且随着开采深入，也存在局部漏风流流动至上覆采空区。同时，计算得出工作面的总漏风量为85.16 m³/min、漏风率为5.95%。此外，利用现场监测数据及数值模拟手段判定出重复采动采空区内部氧化带范围，进风侧为72~150 m，回风侧为14~83 m；最大宽度位于进风侧，为78 m，氧化带所处范围即为煤自燃危险区域，在生产中需加强防治。

基于正常回采期间的供风条件，设计不同模拟工况（1120、1260、1540 m³/min），研究供风条件对采空区自燃“三带”分布影响。随着供风量增大，采空区内部氧化带范围加宽，且滞后；反之，则氧化带范围变窄，造成前移。最后，通过优化物理模型，模拟了单一采动下采空区自燃“三带”分布，相较于单一采动，重复采动导致采空区内部氧化带加宽，提高了采空区内部遗煤自燃危险性。研究将为不同时期及不同采动条件下矿井防灭火措施的制定提供依据。

The coal seams in northwest China are generally more numerous and thicker, and closed distance coal seams mining is the more typical. It is extremely easy to result in the lower stratified working face and the adjacent working face to be affected by repeated mining, aggravate the overburden failure and fracture development, and cause more complex air leakage channels. Due to the collapse of the floor in the upper layered goaf, the amount of residual coal in the goaf will be significantly increased, and the risk of coal spontaneous combustion (CSC) in goaf will be greatly increased, which will seriously endanger the mine production.

In the paper, the repeated mining working face in a mine in Shaanxi Province is taken as the test object. Firstly, the temperature programmed experiment was applied to study the variation law of gas products under different particle sizes and air supply conditions, and the index gas and critical characteristic values were determined. Then, the characteristic parameters such as oxygen consumption rate and heat release intensity were determined by calculation, which provides a basis for the calculation of CSC limit parameters. On the basis of experimental analysis, field measurements and numerical simulations were used to comprehensively investigate the air leakage characteristics and spontaneous combustion danger zone inside the goaf. The main research results are as follows:

According to the mechanical test results of coal and rock strata, the evolution model of overburden fractures under repeated mining is constructed by 3DEC software, and destruction characteristics of overlying rock and the development law of fracture air leakage channel under single mining and repeated mining were studied. As the working face advances, under single mining, the displacement of overlying strata changes gently, the distribution law of air leakage fractures is relatively simple and concentrated, and the maximum height of fracture developing is about 86 m. Under repeated mining, the damage degree of overlying strata is more violent and the displacement change is more obvious, which not only causes the development of new fracture channels, but also leads to the redevelopment of compacted fracture areas after upper mining, resulting in more complex distribution of fracture air leakage channels and further improving the risk of air leakage in goaf. In addition, after repeated mining, the maximum height of fracture developing will spread to 173 m, resulting in the penetration of overlying and lower goafs, which significantly increases the risk of CSC in the goaf.

Based on the above conclusions, the SF₆ tracer technique is utilized to determine the actual air leakage in the goaf. It was found that there was a local air leakage phenomenon inside the goaf and between the overlying strata, and with the deepening of mining, there was also a local air leakage flow to the overlying goaf. At the same time, the total air leakage of the working face is calculated to be 85.16 m³/min and the air leakage rate is 5.95 %. In addition, the field monitoring data and numerical simulation method are used to determine the internal oxidation zone range of the repeated mining goaf. The inlet side is 72 ~ 150 m, and the return side is 14 ~ 83 m, the maximum width is located on the inlet side, which is 78 m. The area where the oxidation zone is located is the dangerous zone of CSC, and prevention and control should be strengthened in production.

Based on the air supply conditions during working face mining, different simulation conditions (1120, 1260, 1540 m³/min) were designed to study the influence of air supply conditions on the distribution of spontaneous combustion ' three zones ' in goaf. As the air supply increases, the range of the oxidation zone in goaf is widened and lagged behind. On the contrary, the range of the oxidation zone becomes narrow, resulting in forward movement. Finally, by optimizing the physical model, the distribution of spontaneous combustion ' three zones ' in goaf under single mining is also simulated. Compared with single mining, repeated mining leads to the widening of the oxidation zone in the goaf and increases the risk of spontaneous combustion of residual coal in the goaf. The research will provide a basis for the formulation of mine fire prevention and extinguishing measures in different periods and under different mining conditions.

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