煤自燃是矿井主要灾害之一，不仅造成大量煤炭资源损失，还严重影响煤矿的安全生产。许多矿井在开采特厚煤层时采用分层综放开采技术。上分层综放工作面回采结束，下分层工作面采用沿空留巷综放开采，使用这种开采方式很大程度上可以节约煤炭资源及提高煤炭回采率。但是由于下分层沿空留巷综放工作面巷道顶板向上分层采空区漏风，使得上分层采空区遗煤容易发生自燃，影响下分层沿空留巷综放面安全开采。下分层工作面回采时，采空区与上分层采空区沟通形成复合采空区，上分层采空区遗煤会掉落到下分层采空区有可能引燃下分层工作面采空区遗煤。同时下分层沿空留巷综放面复合采空区遗煤因水平漏风影响也会发生自燃。因此，判定下分层沿空留巷综放面复合采空区遗煤自燃危险区域尤为重要。本文以陈家沟煤矿8521工作面为研究对象，采用理论分析、现场测试和数值模拟相结合的方法对其复合采空区进行危险区域研究。

首先，结合煤自燃理论与现场调研相结合的方法分析了下分层沿空留巷综放面煤自燃影响因素，漏风供氧是采空区遗煤自燃主要影响因素。其漏风通道分布广泛，加之复合采空区内遗煤量大使得采空区煤自燃危险性突出。同时通过自然发火实验得到了煤自燃极限参数，为自燃预测预报奠定基础。

其次，运用SF₆示踪气体法进行了上分层采空区垂直漏风测试，得到了不同测点的漏风速率及漏风通道位置，同时数值模拟了上分层采空区漏风流场及气体浓度分布特征，得到了风流通过下分层沿空留巷综放面巷道顶部上覆煤层1～3号、4～5号、6～8号、9～10号及11～13号薄煤区进入上分层采空区，在采空区下部形成较密集漏风流场。此外对下分层沿空留巷综放面复合采空区进行了水平漏风现场测试，得到了漏风速率以及主要漏风通道位置，并数值模拟得到了下分层沿空留巷综放面复合采空区的漏风流场特征及气体浓度分布特征。

最后，根据上分层采空区及下分层沿空留巷综放面复合采空区氧气浓度场的分布特征。得到了上分层采空区煤柱及进风顺槽遗煤危险区域范围为：靠近进风顺槽侧沿走向方向49m～175m，回风顺槽遗煤危险区域靠近回风侧沿走向方向201m～224m区域。中部遗煤危险区域为：靠近进风侧沿走向方向49m～175m区域，靠近回风侧沿走向方向201m～224m区域。得到了复合采空区主要危险区域为进风顺槽遗煤区及中部区。进风顺槽遗煤危险区域为：沿进风侧一段的采空区深处到工作面距离23m～38m，沿倾向方向距离柔模墙0～121m区域；中部遗煤危险区域为进风侧采空区深处到工作面距离0m～23m区域，回风侧采空区到工作面距离23m～75m区域。研究成果将对陈家沟煤矿8521工作面及相似条件工作面的煤自燃防治工作提供理论指导。

Coal spontaneous combustion is one of the main disasters in mines, which not only causes significant loss of coal resources, but also seriously affects the safety production of coal mines. Many mines adopt layered fully mechanized mining technology when mining thick coal seams. The upper layer fully mechanized top coal caving face has completed mining, while the lower layer working face adopts goaf retaining roadway fully mechanized top coal caving mining. This mining method can greatly save coal resources and improve coal recovery rate. However, due to air leakage from the roof of the roadway along the goaf in the lower layer to the goaf in the upper layer, the remaining coal in the goaf in the upper layer is prone to spontaneous combustion, which affects the safe mining of the lower layer along the goaf in the fully mechanized mining face. When the lower layer working face is mined, the goaf communicates with the upper layer goaf to form a composite goaf. The remaining coal from the upper layer goaf may fall into the lower layer goaf, which may ignite the remaining coal from the lower layer working face goaf. At the same time, the residual coal in the composite goaf of the lower layered goaf with goaf retaining roadway will also undergo spontaneous combustion due to the influence of horizontal air leakage. Therefore, it is particularly important to determine the risk area of spontaneous combustion of residual coal in the composite goaf of the lower layered goaf retaining roadway in the fully mechanized mining face. This article takes the 8521 working face of Chenjiagou Coal Mine as the research object, and uses a combination of theoretical analysis, on-site testing, and numerical simulation to study the hazardous areas of its composite goaf.

Firstly, the combined method of coal spontaneous combustion theory and on-site investigation was used to analyze the influencing factors of coal spontaneous combustion in the fully mechanized top coal caving face along the goaf in the lower layer. Air leakage and oxygen supply were the main influencing factors of coal spontaneous combustion in the goaf. Its air leakage channels are widely distributed, and the amount of residual coal in the composite goaf makes the risk of coal spontaneous combustion in the goaf prominent. At the same time, the limit parameters of coal spontaneous combustion were obtained through natural ignition experiments, laying the foundation for predicting and predicting spontaneous combustion.

Secondly, the SF6 tracer gas method was used to conduct vertical air leakage tests in the upper layer goaf, and the air leakage rates and positions of the air leakage channels at different measurement points were obtained. At the same time, numerical simulations were conducted on the air leakage flow field and gas concentration distribution characteristics in the upper layer goaf. The air flow was obtained by passing through the overlying coal seams 1-3, 4-5, 6-8, 9-10, and 11-13 at the top of the lower layer goaf along the goaf, forming a dense air leakage field in the lower part of the goaf. In addition, horizontal air leakage field tests were conducted on the composite goaf of the lower layer goaf retaining roadway in the fully mechanized mining face, and the air leakage rate and main air leakage channel positions were obtained. Numerical simulations were conducted to obtain the characteristics of the air leakage flow field and gas concentration distribution in the composite goaf of the lower layer goaf retaining roadway in the fully mechanized mining face.

Finally, based on the distribution characteristics of oxygen concentration field in the composite goaf of the upper layer goaf and the lower layer along the goaf roadway in the fully mechanized mining face. The range of coal pillars in the upper layer goaf and the hazardous area of residual coal in the intake channel is obtained as follows: 49m to 175m near the direction of the intake channel, and 201m to 224m near the direction of the return channel. The hazardous area for coal residue in the middle is: an area 49m to 175m along the direction near the intake side, and an area 201m to 224m along the direction near the return side. The main hazardous areas in the composite goaf were identified as the coal residue area in the intake channel and the central area. The hazardous area for coal residue in the intake channel is: the distance from the deep goaf along the intake side to the working face is 23m to 38m, and the distance from the flexible formwork wall in the inclined direction is 0-121m; The central coal risk area is an area with a distance of 0m to 23m from the deep goaf on the intake side to the working face, and an area with a distance of 23m to 75m from the goaf on the return side to the working face. The research results will provide theoretical guidance for the prevention and control of coal spontaneous combustion in the 8521 working face and similar working faces of Chenjiagou Coal Mine.

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