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

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 constructed. In this paper, based on FLAC^3D 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: ① Coal 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 increase. 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 increase of subsidence slope. ② Coal 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 M₁. When the mining thickness increases from 5 m to 9 m, M₁ 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 ”. ③ Coal mining subsidence will lead to the increase of M₂ of surface loess slope under the scale of “ typical erosion rainfall ”, and the greater the mining thickness, the greater the increase of M₂ ; 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 M₂, 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.