模拟降雨条件下角砾和圆砾对陡峭路堑边坡产流产沙的影响

目的]研究角砾和圆砾对陡峭工程边坡入渗、产流、产沙以及水动力学特征，为青藏高原地区工程边坡土壤侵蚀预测模型与水土保持工作提供一定的理论支撑。方法]基于青藏高原地区派墨农村公路沿线气候特征及其土质路堑边坡形态和物质组成特征，通过室内人工降雨模拟试验，研究了在强降雨(120 mm/h),大坡度(50°),3种砾石含量(30%,40%,50%)条件下圆砾和角砾坡面宏观侵蚀特征和产流产沙规律。结果]圆砾坡面平均入渗率高于角砾坡面，平均产流率低于角砾坡面，初始产流时间明显晚于角砾坡面；圆砾和角砾坡面水流流态均属于层流，流型均为急流，圆砾坡面的径流剪切力、径流功率、雷诺数略小于角砾坡面，但弗劳德数远大于角砾坡面，流速大于角砾坡面，阻力系数小于角砾坡面，径流挟沙能力更强；圆砾坡面稳定产沙率约为角砾坡面的2倍，总产沙量比角砾坡面高出约20%。结论]卵砾石表面光滑，与土壤间贴合不够紧密，形状更容易引起局部湍流，在强降雨条件下，陡峻冲洪积路堑边坡坡面易发育以卵砾石为中心，遍布坡面的环形小细沟，细沟发育数量和产沙量都将大于以棱角状碎块石组成的崩坡积路堑边坡。

Effects of Breccias and Round Gravels on Steep Cut Slope Runoff and Sediment Yield Under Simulated Rainfall

Objective] The effects of breccias and round gravels on steep cut slope infiltration, runoff, sediment yield, and hydrodynamic characteristics were analyzed in order to provide a theoretical basis for a soil erosion prediction model and soil conservation on a steep cut slope on the Qinghai-Tibet Plateau.Methods] Based on the shape and material composition of a steep cut slope and on climatic characteristics along the Pai-Mo road, the cut slope runoff and sediment yield process was observed by using indoor simulated rainfall experiments. The experimental conditions were 50° slope, 120 mm/h rainfall intensity, different gravel contents (30%, 40%, 50%), and different gravel roundness (pebble, breccia).Results] The average infiltration rate for the pebble slope was higher than for the breccia slope. The average runoff rate for the pebble slope was lower than for the breccia slope. The initial runoff time for the pebble slope was significantly later than for the breccia slope. The water flow state and pattern for both slopes were laminar and jet, respectively. Although the runoff shear force and Reynolds number for the pebble slope was slightly smaller than for the breccia slope, the Froude number and the average flow velocity for the pebble slope were larger than for the breccia slope. Therefore, the ability of runoff to carry sediment was greater for the pebble slope. The sediment yield rate for the pebble slope was double the rate observed for the breccia slope, and the total sediment yield for the pebble slope was about 20% higher than for the breccia slope.Conclusion] Because pebbles do not fit closely together in the soil, they are more likely to cause turbulence under heavy rainfall, causing small annular rills to form centered on the pebbles scattered all over the pebble slope. The rill density and total sediment yield will be greater for a steep cut slope underlain by alluvial deposits than for a steep cut slope underlain by colluvial deposits.