岩溶区煤矿工程堆积体边坡细沟发育及其水沙关系研究

Development of Rills on Slopes of Mine-Engineering Dumps and Its Relationship with Water and Sediment in Karst Area

重力作用对坡面径流泥沙和细沟发育具有重要影响。以煤矿工程堆积体为研究对象,采用野外实地放水冲刷法研究不同坡度条件下,重力作用对工程堆积体边坡产流产沙细沟发育形态的影响。结果表明:(1)工程堆积体坡面侵蚀过程分为面蚀(产流3 min内)和细沟侵蚀阶段,其中细沟侵蚀存在扩张(产流3~24 min)、过渡(产流24~30 min)和稳定(产流30 min后)3个发展过程,细沟最快出现为4s、最慢为97s,二者出现时间约相差24倍。(2)重力作用是影响工程堆积体边坡产流产沙及其波动性变化的重要原因,对工程堆积体边坡总产沙量贡献在17.41%以上,最高可达99.60%;初步判定,重力作用对边坡细沟发育影响作用明显的临界径流条件为20 L·min^-1,临界坡度条件为35°。(3)重力作用造成工程堆积体边坡细沟由短向长、由浅向深、由窄向宽发展,坡面细沟沟宽在7.89~19.73 cm之间,沟深在2.17~6.73 cm之间,宽深比在2.12~4.36之间,细沟密度在1.35~3.00m·m^-2之间;径流作用主导细沟深度发育,而重力作用主导细沟宽度发育;边坡细沟密度随放水流量及坡度增加呈先增大后减小的趋势。研究结果对于正确认识煤矿工程堆积体边坡产流产沙特征、影响因素及土壤侵蚀量测算具有重要参考意义。

【Objective】Gravity is an important factor affecting development of runoff sediment and rills on slopes. Large piles of soil, rock and slag generated as waste and formed during the processes of coal mine construction are liable to have inductive geological disasters such as collapse, landslides and debris flow, occur under the action of water and gravity, causing serious impact or even damage to surrounding water resources, land resources, vegetation resources, hydrological cycle and ecological environment quality.【Method】A few of such piles in a coal mining site of a karst zone were selected as object of the study. Field scouring experiments were conducted on slopes different in condition with varying flow to explore how erosion occurs and proceeds, and how gravity affects development of runoff and sediment and morphology of the rills formed. Field investigations found that the piles in the coal-mining areas of Chongqing varied in slope in the range between 25.5°and 38°. To objectively reflect characteristics of erosions on such piles different in stacking condition, the experiments were carried out on slopes different in gradient, i.e. 25°、30°、35°and 40°, and had five flow rates, i.e. 10, 15, 20, 25 and 30 L·min^-1 designed according to the characteristics of the per-unit width discharge caused by local rainstorms relative to duration and frequency and each round of the scouring experiment lasted 60 min. 【Result】Results show:(1) The erosion on the slopes of the piles could be divided into two phases, sheet erosion(within the initial 3 min after runoff started) and rill erosion which could be further divided into three stages, i.e.rill expansion(3~24 min after runoff started), rill transition(24~30 min after runoff started) and rill stabilization(30 min after runoff started);the time of rill appearance on the slope was negatively related to the discharge flow rate and the slope;rills appeared the fastest in 4 s and the slowest in 97 s, and the latter appeared about 24 times later than the former.(2) Gravity was an important factor affecting runoff-sediment yield and its fluctuations on the slopes of the piles. During slope erosion, runoff rate varied in the range between 7.77% and 374.25% in variation coefficient, while sediment yield did in the range of 1.75% ~1021%. Gravity could explain more than 17.41% or even up to 99.60% of the total sediment yield during slope erosion. It was tentatively concluded that gravity started to act on development of rills, when runoff and slope reached their respective critical value of 20 L·min^-1 and 35°. And(3) Runoff mainly caused rills to develop in depth, while gravity mainly did in width. The two leading functions were quite similar in degree of their effects on development of rills. Gravity turned short, shallow and narrow rills on slopes of loose deposit into long, deep and wide ones, which ranged between 7.89 and 19.73 cm in width between2.17 and 7.73 cm in depth, between 2.12 and 4.36, in width/depth ratio and between 1.35~3.00 m·m^-2 in groove density. Mean depth and width of the rills increased with increasing flow rate and with increasing slope gradient, too. Under the same runoff conditions, the sediment yield increased with increasing density of the rills. However, density of the rills first increased and then decreased with increasing flow and slope gradient.【Conclusion】All the findings in this experiment are of important scientific significance to understanding correctly how runoff and sediment occurs and their influencing factors, to establishing models to predict soil erosion on slopes of the mine-engineering waste piles, and to elucidating. scientifically the roles of gravity in inducing collapse and landslide and maintaining slope stability of mine-engineering waste piles.