崩岗堆积土体渗透特性及剖面水分特征——以广东省五华县莲塘岗崩岗为例

目的]崩岗内部堆积土体是侵蚀的主要物质来源。通过对其渗透过程进行研究,揭示其中的规律性,探索崩岗的侵蚀机理。方法]采用自制双环渗水试验装置,结合PR2/6土壤剖面水分测定仪,在广东省五华县莲塘岗崩岗野外现场进行渗水试验。结果](1)崩积锥稳渗率在0.58~2.41mm/min之间,3个试验点平均稳渗率为1.37mm/min,沟道土体平均稳渗率高达5.58mm/min,渗透过程以重力流为主,土体结构稳定;(2)入渗速率与时间成负指数幂函数关系,符合Kositakov模型;(3)初始含水率越高,湿润锋移动速度越快,影响范围越深,稳渗时湿润锋深度在600~1 000mm及以上;(4)土体剖面含水率分布受土体非均质性的影响,自上而下呈波动式下降。结论]崩岗堆积土体最大失稳深度至少为600~1 000mm,甚至可以达到1 000mm以上,崩积锥的非均质性具有阻渗作用,易形成滞水层并发生潜蚀,对崩岗侵蚀过程产生影响,是渗透研究的重点。

Permeability and Sectional Moisture Characteristics of Deposits in Collapse Hill -An Example of Liantanggang Collapse Hill in Wuhua County of Guangdong Province

Objective] The internal deposits of collapse hill is the main material source of erosion. This paper aimed to reveal the infiltration regularity in that hill, and to explore the erosion mechanism on collapse hill by studing the infiltration process.Methods] Field experiments of infiltration were conducted in site of Liantanggang collapse hill in Wuhua County of Guangdong Province using a self-made double circle infiltration device and soil moisture were measured with PR2/6 profile probe.Results] (1) Soil steady infiltration rate of colluvial cone was between 0.58~2.41 mm/min with an average value of 1.37 mm/min.The average infiltration rate of channel soil was up to 5.58 mm/min. The infiltration process was dominated by gravity flow and soil structure was stability. (2) The infiltration rate showed a negative exponential power function relationship with infiltration time as the dependent variable, which conformed to Kositakov model. (3) The higher initial moisture content, the faster wetting front moved, meanwhile, the deeper of affected region, and its depth went down to 600~1 000 mm or even more when infiltration rate attained steady state. (4) The sectional moisture content showed a varied decline from profile top to bottom as affected by the heterogeneity of the soil.Conclusion] The maximum depth of instable deposits in collapse vulnerable mount is at least 600~1 000 mm or even over 1 000 mm. Heterogeneity of colluvial cone soil can resist infiltration and form a stagnant water layer, which can potentially lead to subsurface erosion and hence has a great impact on erosion process of collapse hill. Therefore, the colluvial cone of that hill should be the focus of permeability study.