关闭矿井次生沉陷监测、预测与稳定性评价研究进展和展望

Research progress and prospect of secondary subsidence monitoring,predictionand stability evaluation in closed underground mines

近年来由于部分矿区煤炭资源枯竭和国家去产能政策的出台,大量矿井被关闭。矿井关闭后,采动破裂岩体在应力、地下水等多种因素的作用下发生风化劣化、强度降低,将改变废弃采空区内破裂岩体的应力和承载能力,导致地表发生二次形变或多次形变,这种由非直接采动引起的覆岩及地表沉陷,称为次生沉陷,将对地表工程建设和人民生命财产安全造成巨大的潜在威胁。在回顾关闭矿井发展历史的基础上,首先阐述了关闭矿井的地理分布,之后分别对关闭矿井次生沉陷监测、预测方法和煤柱稳定性评价方法等方面展开综述,最后对关闭矿井次生沉陷灾害研究存在的问题和研究热点进行了展望。研究结果表明:(1)目前我国关闭矿井数量众多,仅在2016—2020年间就退出5 243处,退出产能87 538万t。(2)常规的关闭矿井沉陷监测方法虽然精度高,但存在工作量大、费用高、难以获取面域信息等缺陷,而基于InSAR技术的地表沉陷监测不仅可以获取高精度、大范围当下时间序列形变信息,还可以对已发生形变进行溯源监测,基于时域反射计和微震监测仪的地下岩层移动变形监测可以实时、高密度获取岩层移动形变信息。(3)对于复杂地质采矿条件,数值模拟法预测的关闭矿井地表次生沉陷可靠性较高,但其建模过程复杂、参数选取困难;对于简单地质采矿条件,解析法求解精度和效率更高。(4)柱式开采煤柱应力与采空区尺寸有关,当采空区尺寸与采深比在3~4时,可用从属面积理论计算煤柱应力,否则需要考虑压力拱。剥离破坏模型考虑了矿柱尺寸随时间的变化,并且其在理论上解释了矿柱宽高比对矿柱长期稳定性的影响,同时矿柱剥离破坏模型能够较好地区分稳定和失稳煤柱。(5)关闭矿井次生沉陷灾害问题的研究仍面临沉陷规律及其机理、煤柱长期强度变化规律和煤岩体风化劣化机理不明确等关键科学问题。

In recent years,many mines have been closed due to the exhaustion of coal resources in some mining areas and the release of the national overcapacity policy.After a coal mine is closed,the coal rock mass could undergo weathering deterioration and strength reduction due to some factors such as stress and groundwater,which in turn changes the stress and bearing capacity of the fractured rock mass in the abandoned goaf,leading to some secondary or multiple surface deformations over the goaf.This kind of overburden and surface subsidence caused by indirect mining,called secondary subsidence,will pose a huge potential threat to surface infrastructure construction and the safety of people’s lives and properties.On the basis of reviewing the development history of closed mines,the geographical distribution of closed mines is firstly analyzed,and then the monitoring methods,prediction methods and goaf stability evaluation methods of closed mines are reviewed respectively,and finally the existing problems and research hotspots on the secondary subsidence disaster of closed mines are prospected.The research results show that:①At present,there are many closed mines in China.From^(2)016 to 2020,5243 mines have been closed,with an exit production capacity of 875.38 million tonnes.②Although the conventional monitoring methods of closed mine subsidence have high accuracy,it has disadvantages such as large workload,high cost,small coverage,and sparse measurement points.The ground subsidence monitoring based on InSAR technology can not only obtain the current time series deformation information with high precision and a large range,but also can trace the origin of the deformation that has occurred.At present,the monitoring of underground rock movement and deformation based on time domain reflectometer and microseismic monitor can obtain real-time and high-density rock movement and deformation information.③For some complex geological mining conditions,the prediction results of secondary surface subsidence of the closed mine using the numerical simulation method are highly reliable,but the modeling process is complicated and corresponding parameters selection is difficult.For some simple geological mining conditions,analytical method has higher accuracy and efficiency.④The coal pillar stress in pillar mining is related to the goaf size.When the ratio of the goaf size to the mining depth is between 3 and 4,the coal pillar stress can be calculated using the tributary area theory,otherwise,the pressure arch needs to be considered.In terms of coal pillar strength calculation,the stripping failure model considers the change of the pillar size with time,and it theoretically explains the influence of the aspect ratio of the pillar on the long-term stability of the pillar,and the pillar stripping failure model can better distinguish stable and unstable coal.⑤The research on the secondary subsidence disaster of closed mines still faces some key scientific problems such as the indecipherable of subsidence law and its mechanism,the long-term strength variation law of coal pillar,and the unclear mechanism of coal and rock mass weathering and deterioration.