Study On The Effect Of Underground Coal Mining On Surface Soil Erosion And Vegetation

Soil erosion is listed as a main environmental problem in the world and a main type of geological hazard in China. The Loess Plateau is one of the most serious soil erosion areas, and nearly half of the coal mines in Shaanxi, Shanxi and Gansu are distributed in the area. Soil erosion as the main environmental geological issue in coal mining area has posed a serious restrict for the sustainable development of coal mine in the area. In this paper, Binchang mining area in the gully region of the Loess Plateau in the northern Xianyang of Shaanxi, which is the main mining area of Huanglong Coal Base, is regarded as a study area, the gray correlation analysis method is adopted to design the framework of the numerical model including design of the surface slope form and overburden structure of coal seams on the basis of the surface slope morphology and underground mining characteristics through investigation into the geology, mining, soil erosion, soil and plants, and the collection and analysis of the soil and plant samples in the main nine coal mines. Mining thickness, mining depth, surface of the slopes and slope length are regarded as change factors to build the two series with a total of 45 numerical models. FLAC3 D is taken as an experimental platform to simulate each numerical model and extract the subsidence and horizontal movement data through the programming. The coal seam thickness of mining(mining thickness) and the depth of mining(mining depth) are selected as the key factors affecting soil erosion on the surface.Influencing law of the mining thickness and mining depth on the morphology and soil erosion of the surface slope is studied. And combined with the plant community characteristics survey of the representative samples, the affect of the coal mining activities on plants in the abandoned slag field and the subsidence area is studied and the main conclusions are drawn as follows:(1) With the increase of mining thickness, the surface slope presents the change trend of increase, with the greater natural slope, the more obvious trend of the change. The change trend varies with the different natural slope. The length of the surface slope presents the change trend of decrease with the increase of the mining thickness, totally showing the smaller the natural slope, the more obvious trend of the change. The average decrease rate of the surface slope length is different with the increase of the mining thickness due to the different natural slope.(2) With the increase of the mining depth, the increase of the surface slope presents a decreasing trend, with the larger natural slope, the more obvious trend of the change. The change trend varies with the different natural slope. The length of the surface slope presents the change trend of decrease with the increase of the mining thickness, totally showing the smaller the natural slope, the more obvious trend of the change. The average decrease rate of the surface slope length is different with the increase of the mining thickness due to the different natural slope.(3) Increasing of the mining thickness leads to the increase of the surface slope and the decrease of the slope length, resulting in the increase of the erosion modulus and soil erosion.(4) Increasing of the mining depth leads to the increase of the surface slope and the smaller decrease of the slope length, which result in the decrease of the erosion modulus increase-scale of the slope surface.(5) According to the slope and the ratio of depth and thickness, the subsidence basin of the continuous failure morphology after coal mining is divided into gently-inclined continuous failure morphology, inclined continuous failure morphology, steep continuous failure morphology, and rapid steep continuous failure morphology, and the determining conditions for each subsidence basin are given.(6) The change of the soil nutrients and water for the mining subsidence area and non-subsidence area is insignificant when the slope is less than 15°, and they are decreased when the slope is more than 15°, and when the depth is greater than 2 m, the soil has a drying phenomenon. When the slope is less than 15°, the influence of the subsidence on the community species composition and species diversity is smaller, but when the slope is more than 15°, the proportion of trees and community biomass decreases.Based on the results of the study, control of the mining thickness, and adopting of the slice mining and artificial intervention are put forward to improve the physical and chemical properties of the mining subsidence area. According to the community succession law, guide the vegetation restoration to enhance the community’s positive succession speed and control the soil erosion of the mining subsidence area.