黄土区薄厚层浮土土质道路降雨侵蚀过程差异

土质道路经长期碾压产生了大量浮土,加剧了道路侵蚀。本文通过人工模拟降雨试验,研究不同雨强及坡度条件下薄层1.0 cm和厚层4.0 cm浮土土质道路的产流产沙特征。根据侵蚀物质的差异,将浮土道路侵蚀过程分为单独浮土侵蚀阶段和浮土、道路混合侵蚀阶段。结果表明:(1)浮土侵蚀阶段、混合侵蚀阶段薄层浮土平均径流率为厚层浮土的1.01倍~1.52倍、1.26倍~2.44倍。2.5 mm·min^–1雨强时3个坡度下的平均次降雨产流量为43.44 L,较1.0~2.0 mm·min^-1雨强提高37.36%~82.05%;(2)混合侵蚀阶段16°坡面平均含沙量均值为227.30 g·L^-1,为4°和8°的2.14倍和1.37倍。小雨强(1.0、1.5 mm·min^-1)时厚层浮土次降雨产沙量为薄层浮土的1.39倍~2.14倍;大雨强(2.0、2.5 mm·min^-1)时薄层浮土次降雨产沙量为厚层浮土的1.14倍~1.67倍。1.0 mm·min^-1雨强时3个坡度下的平均次降雨产沙量为2.08 kg,占1.5~2.5 mm·min^-1雨强的23.57%~68.59%;(3)混合侵蚀阶段及次降雨过程薄层浮土含沙量与径流率相关性较厚层浮土均增强。结果可为黄土区浮土道路侵蚀防治工作的开展提供科学依据。

Rainfall Erosion Process on Earth Road as Affected by Thickness of The Surface Regolith Layer in Loess Region

Objective] Having long been used for transportation and traffic, earth roads have a regolith layer formed on their surface, which aggravates erosion of the roads. Up to now, very little knowledge is available about how erosion proceeds on the earth roads with a surface regolith layer and how the regolith layer affects erosion of the earth roads.Method] An indoor artificially simulated rainfall experiment was used to investigate characteristics of the runoff and sediment production on roads with a surface regolith layer varying in thickness (thin layer=1.0 cm, and thick layer=4.0 cm). In the experiment a movable hydraulic slope-changeable steel trough, 2m in length, 0.5m in width and 0.55m in height, was used and packed with loess soil to simulate a earth road with a surface regolith layer. The trough was packed first with a layer of loess soil as road, 1.68 g·cm^-3 in bulk density, and then with a layer of regolith, 1.20 g·cm^-3 in bulk density. The experiment was designed to have 3 levels of slope, 4°, 8° and 16° and 4 levels of intensity, 1.0, 1.5, 2.0 and 2.5 mm·min^-1. Before each test, a white nylon thread was placed between the road and the regolith layer at the bottom end of the trough, and used to determine sources of the erosive materials by the degree of its exposure. And then the erosion process of the regolith covered road was divided into two stages:1) mere regolith erosion and 2) regolith and road soil mixed erosion.Result] Results show:(1) The mean runoff rate of regolith on the road with a thin layer of regolith was 1.01-1.52 times at the first stage and 1.26-2.44 times at the second stage that on the road with a thick layer of regolith. When the artificial rainfall was set at 2.5 mm·min^-1 in intensity, the average runoff yield per rainfall event was 43.44 L from the road regardless of slope degree, and 37.36%-82.05% higher than that when the rainfall was 1.0-2.0 mm·min^-1 in intensity; (2) During the second stage erosion, the average sediment concentration was 227.30 g·L^-1 on the road 16° in slope, and about 2.14 times and 1.37 times that on the road 4° in slope and 8° in slope, respectively. Under rainfalls low in intensity (1.0 and 1.5 mm·min^-1), sediment yield per rainfall event was high on the road with a thick regolith layer, being about 1.39-2.14 times that on the road with a thin regolith layer; whereas under rainfalls high in intensity (2.0, 2.5 mm·min^-1), it was high on the road with a thin regolith layer, being about 1.14-1.67 times that on the road with a thick regolith layer. And under rainfalls 1.0 mm·min^-1 in intensity, the average sediment yield per rainfall event on roads regardless of slope degree was 2.08 kg, which equaled to 23.57%-68.59% of that under rainfalls 1.5-2.5 mm·min^-1 in intensity; (3) During the second stage erosion and the entire course of a rainfall event, sediment concentration in the runoff was more closely related to runoff rate on the road with a thin regolith layer than on the one with a thick regolith layer.Conclusion] All the findings in this study may serve as a scientific basis for prevention and control of erosion on regolith-covered earth road erosion in the Loess areas.