陕北黄土沟壑区采煤沉陷对黄土坡面形态的影响及土壤侵蚀效应

Effect of coal mining subsidence on loess slope morphology and soil erosion in loess gully region of Northern Shaanxi

如何破解煤炭开采与水土保持之间的矛盾是实现黄河中游生态环境保护与高质量发展的关键科学问题。以陕北黄土沟壑采煤沉陷区为研究对象,针对主采煤层典型地质赋存特征,以地下采厚(9、7、5 m)、地表黄土自然坡面坡形(直线坡、凹形坡、凸形坡、复合坡)及坡度(5°、15°、25°、35°、45°)为变量,共构建了60个数值模型,基于FLAC3D数值模拟软件,研究了黄土自然坡面形态及采厚耦合作用下坡面形态演变过程与规律,基于中国水土流失方程(CSLE模型)和经验模型,计算与分析了沉陷坡面土壤侵蚀效应。研究结果表明:(1)采煤沉陷会导致地表黄土坡面的坡度增大,且采厚越大,坡度增幅越大,大采厚对采煤沉陷导致地表黄土坡面坡度的增大会产生明显的放大效应。凹形坡普遍对沉陷坡面坡度的影响显著,特别是在“采厚5 m、自然坡度>5°”“采厚7 m、任意自然坡度”“采厚9 m、自然坡度≤35°”条件下。无论在何种采厚及自然坡形情况下,≤5°的自然坡度对沉陷坡面坡度增幅的影响均最大。(2)采煤沉陷会导致“年侵蚀降雨”尺度下地表黄土坡面的土壤侵蚀模数M_(1)增大,且采厚越大,M1增幅越大;当采厚从5 m增大到9 m时,M_(1)增幅增大了1倍左右;4种坡形中凹形坡对沉陷坡面M1的增幅影响最大;≤15°自然坡度对沉陷坡面的M1增幅影响较大,在“采厚9 m,凹形坡”条件下超过了20%。(3)采煤沉陷会导致“典型场次侵蚀降雨”尺度下地表黄土坡面的土壤侵蚀模数M_(2)增大,且采厚越大,M_(2)增幅越大;当采厚从5 m增大到9 m时,M2增幅增大了1倍左右;4种坡形中凹形坡对沉陷坡面M2的增幅影响最大;≤15°自然坡度对沉陷坡面的M2增幅影响较大,在“采厚9 m,凹形坡”条件下超过了17%。该结果可为陕北矿区乃至黄河流域中游的水土流失精准防控与高质量发展提供科学依据。

How to solve the contradiction between coal mining and soil and water conservation is the key scientific problem to realize the ecological environment protection and high-quality development in the middle reaches of the Yellow River.In this paper,taking the coal mining subsidence area in loess gully of northern Shaanxi as the research object,aiming at the typical geological occurrence characteristics of the main coal seam,and taking the underground mining thickness(9,7,5 m),the natural slope shape(straight slope,concave slope,convex slope,compound slope)and slope(5°,15°,25°,35°,45°)of the surface loess as variables,a total of 60 numerical models are con-structed.In this paper,based on FLAC3D numerical simulation software,the evolution process and law of slope morphology under the coupling effect of loess natural slope morphology and mining thickness are studied.Then,based on China soil erosion equation(CSLE model)and empirical model,the soil erosion effect of subsidence slope is calculated and analyzed.The results show that:①Coal mining subsidence will lead to the increase of the slope of the surface loess slope,and the greater the mining thickness,the greater the slope in-crease.Significant Amplification Effect of Large Mining Thickness on Slope Gradient Increase of Surface Loess Caused by Coal Mining Subsidence.The concave slope generally has a significant effect on the slope of the subsidence slope,especially under the conditions of“mining thickness 5 m,natural slope>5°”,“mining thickness 7 m,arbitrary natural slope”,“mining thickness 9 m,natural slope≤35°”.No matter what kind of mining thickness and natural slope shape,the natural slope of≤5°has the greatest influence on the in-crease of subsidence slope.②Coal mining subsidence will lead to the increase of M1 on the surface loess slope under the scale of“annual erosion rainfall”,and the greater the mining thickness,the greater the increase of M_(1).When the mining thickness increases from 5 m to 9 m,M_(1) increases by about 1 time.The concave slope of four slope shapes has the greatest influence on the increase of M1 on the subsidence slope.The natural slope of≤15°has a great influence on the increase of M1,which is more than 20%under the condition of“mining thickness 9 m,concave slope”.③Coal mining subsidence will lead to the increase of M2 of surface loess slope under the scale of“typic-al erosion rainfall”,and the greater the mining thickness,the greater the increase of M_(2);when the mining thickness increases from 5 m to 9 m,the increase of M2 increases by about 1 times.The concave slope of the four slope shapes has the greatest influence on the increase of M2 on the subsidence slope.The natural slope of≤15°has a great influence on the increase of M_(2),which is more than 17%under the condition of“mining thickness 9 m,concave slope”.The results can provide scientific basis for accurate prevention and control of soil erosion and high-quality development in the mining area of northern Shaanxi and even the middle reaches of the Yellow River Basin.