厚松散层底含直覆薄基岩开采地表沉陷预计及特征研究

Study on prediction and characteristics of surface subsidence in mining when the bottom aquifer of thick loose layer directly covers thin bedrock

针对厚松散层底含直覆薄基岩条件下开采地表沉陷机理与特征问题,采用开采沉陷理论、土体固结理论和随机介质理论,分析了厚松散层底含疏水固结过程中的水土耦合受力变形机制,根据叠加原理建立了厚松散层薄基岩煤层开采与底含疏降水共同作用下地表沉陷预计模型,讨论了该类条件开采地表沉陷特征及其主要影响因素。研究表明:提出的厚松散层底含直覆薄基岩开采沉陷预计模型,考虑了煤层开采与厚松散层底含疏水固结沉降共同作用,并得到工程验证;厚松散层底含疏水固结沉降作用,加大了地表沉陷盆地沉降量,减缓了盆地边缘收敛速度,大幅增加了地表下沉和水平移动范围,出现下沉系数大于1,且地表下沉10 mm边界点明显向采区外侧延伸现象,其地表沉陷曲线呈“中间小开口深盆地,两侧大开口浅盆地”复合型特征;采煤和底含疏降水共同作用地表沉陷范围与底含疏降水引起的地表沉陷范围相近,地表移动盆地边界角δ随厚松散层厚度Hls增大而减小;最大水头下降Δh_(m)与地表最大下沉量呈正相关,但对沉陷范围影响较小;底含疏水影响半径Rw主要影响地表沉陷范围;底含厚度M主要影响地表沉陷程度。研究结果可为科学留设类似条件工广立井井筒与建筑(构)物保护煤柱,以及开采沉陷区环境影响评价提供理论依据。

In view of the mechanism and characteristics of surface subsidence in mining with the bottom aquifer of thick loose layer directly covering thin bedrock, the water-soil coupling stress and deformation mechanism in the process of hydrophobic consolidation of the bottom aquifer of thick loose layer are analyzed by using mining subsidence theory, soil consolidation theory and random medium theory. According to the superposition principle, the prediction model of surface subsidence under the combined action of coal seam mining and bottom aquifer dewatering under the geological condition of thick loose layer and thin bedrock is established, and the characteristics and main influencing factors of surface subsidence under such conditions are discussed. The research shows that the proposed mining subsidence prediction model with the bottom aquifer of thick loose layer directly covering thin bedrock considers the combined action of coal seam mining and the bottom aquifer hydrophobic consolidation settlement of thick loose bed, which has been verified by engineering application.The hydrophobic consolidation settlement of the bottom aquifer of the thick loose layer increases the settlement of the surface subsidence basin, slows down the convergence speed at the edge of the basin, and greatly increases the surface subsidence and horizontal movement range.This results in the phenomenon that the subsidence coefficient is greater than 1 and the boundary point with a surface subsidence of 10 mm obviously extends to the outside of the mining area, the surface subsidence curve shows the compound characteristics of “small opening deep basin in the middle and large opening shallow basin on both sides”.The surface subsidence range under the combined actions of coal mining and dewatering of bottom aquifer is similar to that caused by dewatering of single bottom aquifer.The boundary angle δ of surface movement basin decreases with the increase of thick loose layer thickness Hls.The maximum waterhead drop value Δh_(m) is positively correlated with the maximum surface subsidence, but has little effect on the subsidence range.The influence radius Rwof bottom aquifer drainage mainly affects the range of surface subsidence.The bottom aquifer thickness M mainly affects the degree of surface subsidence. The research results can provide a theoretical basis for scientifically setting up the protection coal pillars for shaft and building(structure)at the industrial square under similar conditions, as well as the environmental impact assessment of mining subsidence area.