陕北露天矿排土场平台-边坡系统沟蚀演化与启动机制

North Shaanxi is one of energy-chemical industry base in China, in where coal mine mostly adopt the open mining. In the open pit, the runoff from the platform is large discharge and rapid afflux, which often results in serious gully erosion of dump slope. Because of the lag behind of gully erosion process of the platform-slope system, the ecological restoration and water and soil conservation design of dump were critically influenced. This project choose the platform-slope system as the research object, adopted research method of simulate rainfall and scouring experiment combined the 3D laser scanning technology and GIS system. Three different runoff patterns were set up in the rainfall and scouring experiment, which embody rainfall experiment (60 mm/min), scouring experiment (4 different level inflow) and superimposed experiment of rainfall and inflow. The objectives of this study are analyzing the special and temporal distribution of runoff -sediment characteristics, hydrodynamic parameters, and gully morphological characteristics, then comparing their differences among the three runoff patterns. At the same time, it will construct the visualization and digitalization system of erosion gully evolution. Then the relationship among gully morphological characteristics, runoff-sediment characteristics and hydrodynamic parameters under three runoff patterns and the hydrodynamic critical conditions of gully erosion can be achieved. Furthermore, the effect of gully morphological evolution on runoff-sediment relationship and the response of gully morphological evolution to hydrodynamic parameters will be elucidated. Finally，the hydrodynamics mechanism of the gully morphological evolution and gully erosion starting will be revealed. This research provides scientific basis for optimization design and ecological environment construction of open pit mine in arid and semi-arid area, which is of great scientific value.

陕北是我国重要的能源化工基地，区内煤矿主要为露天开采，产生的排土场平台径流汇集量大且急促，常导致边坡发生强烈沟蚀，严重时致边坡损毁或坍塌。但排土场平台-边坡系统在极端来水条件下沟蚀过程研究仍十分薄弱，严重制约矿区生态恢复与水保设计。以典型排土场平台-边坡系统为对象，采用野外模拟降雨、放水冲刷、降雨+放水冲刷试验、三维激光扫描和GIS技术分析相结合的方法。分析不同侵蚀动力下系统内水沙过程、水动力学参数、侵蚀沟形态演化的时空规律并比较其差异性特征，实现边坡侵蚀沟形态演化过程的图像化和数字化。建立不同侵蚀动力条件下侵蚀沟形态参数、水沙参数、水动力参数间关系，确定沟蚀发生的水动力临界条件，阐明不同侵蚀动力下侵蚀沟形态演化过程对水沙过程的影响和对水动力参数的响应，揭示平台汇水条件下平台-边坡系统沟蚀演化和启动的水动力机制。为我国露天矿排土场优化设计和生态环境建设提供科学依据，具有重要的科学意义。

排土场是露天开采矿的主要泥沙策源地，其独特的平台-边坡系统具有大面积径流汇聚和高强度泥沙剥蚀与输移的地形特点，目前针对排土场平台-边坡系统的侵蚀演变过程与机制的研究尚十分薄弱。本研究基于野外调查，采用野外放水冲刷试验、降雨+放水试验，厘清了排土场平台-边坡系统沟蚀演变的阶段性特征，探讨了排土场平台-边坡系统侵蚀过程的径流、产沙和水动力参数的阶段性变化，揭示了放水和降雨+放水两种不同侵蚀动力对沟蚀演变的影响机制，建立了产沙参数与侵蚀沟形态参数和水动力参数的关系，确立了沟蚀发生的临界水动力条件，最终揭示了平台-边坡系统沟蚀演化与启动机制。项目取得的重要结果如下：两种不同侵蚀动力和覆土条件下，平台侵蚀沟均经历3个不同特征的发展阶段，覆土边坡侵蚀沟的发展分为A层下切、A层拓宽、B层下切和沟蚀减缓4个阶段，无覆土边坡侵蚀沟的发展分为迅速发育、沟壁拓宽和沟蚀减缓3个阶段。边坡总产沙量是平台的5.39~9.86倍，是平台-边坡系统主要的泥沙来源。覆土边坡84.50~97.08%的产沙量产自前三阶段，无覆土边坡有49.33%~89.28%的产自前两阶段。边坡径流流速、弗汝德数和阻力系数等的变化主要发生在侵蚀沟剧烈发育的阶段，截至试验结束，流速和弗汝德数较初始值减小26.53%~60.87%和72.07%~88.58%，阻力系数增大2.48~29.87倍。在不同试验条件下的不同侵蚀阶段，产沙率与沟深和水流剪切力与水流功率间均存在显著线性相关，但产沙率和沟深对水动力参数的响应敏感性存在阶段性转变，在下切侵蚀为主导的阶段，产沙率与沟深和水流剪切力的关系均优于水流功率，在沟壁拓宽为主导和沟蚀减缓的阶段，产沙率和沟深对水流功率的响应更积极。平台汇聚径流是下切侵蚀的主要动力，降雨加强了沟壁拓宽过程（沟宽较无降雨的增大12.76%~45.07%），增大了沟壁拓宽阶段的产沙量（16.32~45.65%），增大覆土边坡A层下切（2.29~3.00倍）和A层拓展阶段（0.6~2.16倍）和无覆土边坡沟蚀减缓阶段（0.04~0.87）和沟壁拓展阶段（0.96~1.35）的土壤可蚀性参数。研究结果可为露天矿排土场土壤侵蚀控制与水土保持措施配置提供科学依据。