Study on the impact of microscopic characteristics of loess at different depths on mining subsidence
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摘要:
为了探究厚黄土层下开采黄土微观特性对地表移动变形的影响，以山西某矿为例，采用物理实验与数值模拟相结合的方法，分析了不同深度黄土颗粒组成及微观结构特征，建立了厚黄土层分层模型，研究了不同黄土层厚度下的地表变形特征，揭示了黄土微观结构变化对地表移动变形的影响。研究表明：随着黄土深度增加，粉粒含量不断减少，黏粒及胶粒含量升高，微观结构由似柱状堆砌到似球状镶嵌最后形成胶结凝块结构，孔隙空间由贯穿可压缩孔隙到镶嵌孔隙最后形成微孔隙空间；该矿150 m厚黄土层下开采，地表最大下沉及水平移动值分别为4.112、1.327，20 m黄土层移动变形低于地表黄土，黄土压缩量约占地表最大下沉值的12.4%且主要表现在地表浅层处；随着土岩比不断增大，地表下沉量及水平移动呈先增大后减小特征，两者分别于土岩比1.33、1.67达到转折点；黄土层随着深度的增加，其微观结构变化对于地表宏观沉陷具有缓冲作用。
Abstract:In order to investigate the impact of loess micro characteristics on surface movement and deformation during the mining of thick loess layers, a case study was conducted in a mine in Shanxi Province. A combined approach of physical experiment and numerical simulation was used to analyze the particle composition and microstructural characteristics of loess at different depth conditions. A layered model of thick loess layers was established to study the deformation characteristics of the surface under different loess layer thickness conditions. The research revealed the influence of variations in loess microstructure on surface movement and deformation. Research has shown that: with the increase of loess depth, the content of silt particles decreases continuously, while the content of clay and colloidal particles increases. The microstructure changes from a columnar-like arrangement to a spherical-like embedding, ultimately forming a cemented agglomerate structure. The pore space transitions from interconnected compressible pores to embedded pores, eventually forming micropore spaces; the mining of the 150-meter thick loess layer in the mine resulted in a maximum surface subsidence of 4.112 m and a maximum horizontal displacement of 1.327 m. The movement and deformation of the 20 m loess layer were lower than those of the surface loess. The compression of the loess accounted for approximately 12.4% of the maximum surface subsidence, mainly occurring in shallow layers of the surface; as the soil-rock ratio increases, the surface subsidence and horizontal displacement exhibit a first-increase-then-decrease trend. The turning points occur at soil-rock ratios of 1.33 and 1.67, respectively. The variation of loess microstructure with depth has a buffering effect on the macroscopic subsidence of the surface.
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图 1 不同深度黄土粒度组成含量变化曲线
Figure 1. Variation curves of particle size composition content in different depths of loess
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图 4 150 m厚黄土层条件下覆岩移动变形曲线
Figure 4. Deformation curves of overlying rock movement under the condition of 150 m thick loess layer
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图 6 不同厚度黄土层水平移动曲线
Figure 6. Horizontal displacement curves of loess layers with different thickness
表 1 黄土理化性质参数
Table 1 Physicochemical parameters of loess
深度/
m含水率/
%密度/
(g·cm−3)干密度/
(g·cm−3)孔隙率/
%液限/
%塑限/
%饱和度/
%压缩
系数1 10.60 1.528 1.382 41.3 31.62 20.71 33.70 0.328 2 11.80 1.500 1.342 41.9 31.21 19.67 36.30 0.325 3 12.20 1.529 1.351 40.3 29.98 19.70 39.20 0.349 4 12.70 1.587 1.380 38.6 31.63 19.28 39.80 0.311 5 12.60 1.593 1.365 34.2 29.95 19.73 40.50 0.291 10 11.10 1.711 1.412 29.8 27.42 19.03 41.00 0.274 20 9.90 2.013 1.424 12.8 26.77 18.72 42.10 0.189 
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表 2 黄土粒度组成
Table 2 Grain size composition of loess
深度/m 粗粉粒/% 细粉粒/% 黏粒/% 胶粒/% 平均粒径/μm 1 13.22 49.75 13.01 5.53 3.95 2 12.03 46.32 13.19 4.88 4.13 3 9.47 43.89 13.45 5.64 3.12 4 13.13 47.81 18.59 7.13 2.57 5 9.77 43.31 16.21 6.94 2.67 10 11.72 48.79 14.89 6.75 2.73 20 6.80 58.21 20.04 7.78 2.13
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表 3 数值模拟岩层物理及节理参数
Table 3 Numerical simulation of rock physics and joint parameters
岩层 岩层厚度/m 弹性模量/GPa 泊松比 内摩擦角/（°） 黏聚力/MPa 抗拉强度/MPa 密度/(t·m−3) 法向刚度/（GPa·m−1） 切向刚度/（GPa·m−1） 浅部黄土 20.0 0.015 0.15 15.00 0.115 0.013 1.300 1 1 深部黄土 130.0 1.000 0.20 24.00 0.650 0.300 1.630 2 1 细粒砂岩 32.0 9.000 0.26 35.50 3.000 1.900 2.250 6 6 泥岩 28.0 6.400 0.23 35.84 0.870 1.240 2.400 3 2 煤层 6.5 2.400 0.29 34.18 0.660 0.940 1.500 2 1 粉砂岩 33.5 5.000 0.23 38.00 1.200 2.120 2.300 7 7
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表 4 不同厚度黄土层地表下沉与水平移动参数
Table 4 Different thickness loess layer surface subsidence movement deformation parameters
模拟
编号黄土层
厚度/m基岩
厚度/m黄土基
岩比下沉值/
m下沉
系数
q水平
移动/
m水平
移动
系数bTY-1 60 60 1.00 5.102 0.785 1.949 0.382 TY-2 80 60 1.33 5.221 0.803 2.068 0.396 TY-3 100 60 1.67 4.757 0.732 1.941 0.408 TY-4 120 60 2.00 4.471 0.688 1.659 0.371 TY-5 150 60 2.50 4.122 0.634 1.327 0.322
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