【作者】 蒋芳市；

【导师】 黄炎和；

【作者基本信息】 福建农林大学 ， 生态学， 2013， 博士

【摘要】 崩积体是崩岗的重要组成部分，土质疏松，粗颗粒含量高，坡度大，易侵蚀，其侵蚀直接影响崩壁及坡面物质的再分配，进而影响崩岗的危害程度，但目前对其土体易侵蚀的特性及侵蚀机理的研究还处于空白。本研究以福建省安溪县龙门镇洋坑村花岗岩发育的崩岗崩积体为研究对象，针对散落形崩积体的侵蚀机理开展研究。通过野外调查对崩积体的类型进行了初步分类；利用室内理化分析和岩土工程实验方法对崩积体的土壤特性进行了分析；在野外调查的基础上，利用土槽冲刷试验分析了不同流量(1.1，2.2，3.3，4.4，5.5L·min^-1)和坡度（20，25，30，35，40°）条件下坡面水流特性及与散落型崩积体土壤分离的关系；利用人工模拟降雨试验，对不同雨强(1.00，1.33，1.67，2.00，2.33mm·min^-1)和坡度（20，25，30，35，40°）、不同结皮程度（未结皮，5min结皮，10min结皮）、多场次降雨条件(1.00，1.67，2.33mm·min^-1分别降三场雨)下散落型崩积体坡面的产流产沙特征，侵蚀沟特征，侵蚀泥沙的颗粒特性，侵蚀的水动力学机制进行了分析，以阐明崩积体坡面侵蚀的机理。主要结论如下：（1）崩积体的类型与形态特征。野外调查发现，根据崩积体的产生方式，崩积体可分为散落型和滑动型两类，以散落型为主。滑动型崩积体的坡度大，可达40-70°，而散落型崩积体的坡度在20-40°之间，主要分布在30°附近；崩积体侵蚀严重，侵蚀沟分布密集。（2）崩积体的土壤特性。崩积体有机质含量极低，颗粒主要为砾石、砂粒和粉粒，粘粒含量低，土壤颗粒分形维数较小；崩积体土质疏松，造成其土壤的抗剪强度和硬度低，土壤的抗冲抗蚀性能弱，入渗性能强，但疏松的土体，更易造成土体的崩解。（3）陡坡坡面水流的水力学参数特征及与土壤分离的关系。水流的流速、水深及阻力系数主要受流量的控制；阻力系数随雷诺数及弗罗德数的增加呈幂函数减小。可通过流量和坡度、水深和坡度对土壤分离速率进行模拟；崩积体土壤分离速率与流速及剪切力呈指数函数关系，而崩岗集水坡面土壤分离速率与二者呈幂函数关系，说明崩积体比自然土体更易被水流分离；可首选分离速率与剪切力的指数函数方程作为水流分离崩积体能力方程。（4）不同条件下人工降雨试验崩积体的产流产沙过程。不同雨强和坡度条件下：入渗过程符合Ir=aT-n+If方程，径流过程符合Rr=-bT-m+Rf方程；产沙率和含沙量的变化过程有单峰型和多峰型两种类型；入渗量、径流量及产沙量均随雨强的增大而增大；入渗量随坡度的增大呈线性减小；径流量随坡度变化存在临界值，在30°附近；泥沙侵蚀存在临界坡度，且是一个变化值（25°以上）；产沙率和含沙量随着径流量的增大而增加，含沙量与产沙量呈线性函数关系（Sr=aSc+b）；可利用雨强和坡度对崩积体的入渗、径流、产沙量及含沙量进行预测。结皮条件下产流产沙特征：结皮的存在可以减缓侵蚀发生，而随着结皮程度的增加，径流对地表冲刷能力更强，造成侵蚀量增大。多场次降雨条件下产流产沙特征：坡面地形及侵蚀方式的变化，引起不同雨强下不同降雨场次泥沙侵蚀量的差别，1.00和1.67mm·min^-1雨强条件下三次降雨的侵蚀量差异不显著，但2.33mm·min^-1雨强下，随着降雨场次的增加，泥沙侵蚀愈加剧烈。（5）不同条件下人工降雨试验的细沟侵蚀特征。不同坡度和雨强下的细沟侵蚀特征：发生细沟的时间随着坡度和雨强的增大而缩短；随着雨强和坡度的增大，侵蚀沟密度增加，沟宽扩大；随着坡度的增大，宽深比减小；随着雨强和坡度的增大，侵蚀方式从片蚀为主逐渐转变至细沟侵蚀为主。不同结皮条件下的细沟侵蚀特征：结皮的出现使坡面出现细沟的时间延迟；结皮坡面的细沟侵蚀密度、侵蚀宽度、侵蚀深度均比未结皮的低；结皮坡面由细沟侵蚀引起的侵蚀量降低；结皮程度高的坡面细沟侵蚀程度大于结皮程度低的，说明结皮减缓侵蚀仅在一定程度上起作用。多场次降雨条件下的细沟侵蚀特征：由于侵蚀方式的差异，1.00和1.67mm·min^-1随着降雨场次的增加，宽深比呈减小的趋势，而2.33mm·min^-1雨强下却是相反；随着降雨场次的增加，侵蚀沟侵蚀程度愈严重。（6）崩积体侵蚀泥沙颗粒的分选特性及搬运机制。不同雨强和坡度条件下侵蚀泥沙颗粒特征：随着雨强和坡度的增大，泥沙粗颗粒含量及粗颗粒的富集率均增加，泥沙的流失呈粗颗粒化趋势；侵蚀泥沙颗粒随着坡面细沟间侵蚀-细沟侵蚀的过程逐渐变粗，最后趋于与供试土壤颗粒组成一致，表现出细沟侵蚀与泥沙的“整体搬运”相匹配的特性；崩积体侵蚀泥沙跃移质粒级较大，均大于0.537mm；在细沟间侵蚀阶段，悬移质+跃移质含量在71.26-97.64%之间，出现细沟侵蚀后，床移质的比列增加，达到了10.93-41.74%。不同结皮条件下侵蚀泥沙颗粒特征：结皮坡面表现出搬运较小颗粒的特征，但进入侵蚀后期，径流对泥沙颗粒的搬运也选择粗颗粒，且结皮程度高的10min结皮坡面对粗颗粒的选择搬运比5min结皮的早。多场次降雨条件下侵蚀泥沙颗粒特征：各雨强下三次降雨产生的泥沙不同粒级含量均表现出粗颗粒含量比例增加，细颗粒含量减少；在小雨强下，随着降雨场次的增加，径流搬运逐渐选择粗颗粒，但大雨强下各场次均表现出对供试土壤的“整体搬运”的特征。（7）降雨条件下崩积体侵蚀的动力学机制。细沟流速、水深、雷诺数、弗罗德数及动力学参数比细沟间水流大，而阻力系数和粗度系数则比细沟间水流小。细沟间输沙率与流速、粗度系数和阻力系数呈幂函数关系；细沟输沙率仅与流速呈线性函数关系；整个坡面平均输沙率与流速、阻力系数和粗度系数呈幂函数关系，与水深、雷诺数和弗罗德数呈线性函数关系。输沙率与5个动力学参数均呈线性函数关系，可首选单位水流功率、单宽能耗及断面单位能量作为崩积体降雨输沙的动力学参数。更多还原

【Abstract】 In the tropical and subtropical South China, Benggang is widely distributed. Benggangmainly consists of colluvial deposits with high erosivity. The erosion of colluvial deposits caninfluence the redistribution of the materials from clasping walls and slope surfaces, and thusfurther affect the degree of erosion damage in Benggang. Through the field survey on thegranite colluvial deposits in Yang Keng Village of Longmen town in Anxi County, FujianProvince, the types and morphological characteristics of colluvial deposits are categorized;Though laboratory experiments, the soil characteristics of colluvial deposits are analyzed. Therelationships between the overland flow hydraulic, dynamic parameters and soil detachmentof scattered colluvial deposits are analyzed on the conditions of the flow discharge (1.1,2.2,3.3,4.4,5.5L·min^-1) and slope gradient （20,25,30,35,40°）. The erosion mechanisms ofscattered colluvial deposits are stutied via the artificial rainfall tests under various conditionswhich includ different rainfall intensities (1.00,1.33,1.67,2.00,2.33mm·min^-1) and slopes（20,25,30,35,40°）, different crusts degree （uncrust,5min curst,10min crust）, and repetitiverainfalls (1.00,1.67,2.33mm·min^-1three times respectively). The main conclusions are asfollows:（1） The types and morphological characteristics. Colluvial deposits are divided intoscattered and slide types, and dominated by the scattered type. The slide type has steep slope,up to40-70°, while the slope of the scattered type is between20°and40°, and mainly in thevicinity of30°.（2） The soil characteristics. There is very low organic matter content in colluvial deposits.The soil particles are mainly gravel, sand and sediment, and the clay content is low; colluvialdeposits have loose soil which results in low soil shear strength and soil hardness, weakerosion corrosion resistance, but strong infiltration. However, loose soil can easily cause soildisintegration.（3） The relationship between the characteristics of overland flow hydraulic parameters andsoil detachment. Flow velocity, water depth and the resistance coefficient are mainly affectedby the flow control; Resistance coefficient shows a power function decrease with the increaseof Reynolds and Frode number. It is feasible to simulate the soil detachment rate throughtraffic and slope, depth and slope. The soil detachment rate of colluvial deposits and the flow velocity/shear stress exit an exponential function relationship, but the soil detachment rate ofcatchment slope （nature soil） performs a power function relationship with them. Therefore,the colluvial deposits is more easily separated by water currents than natural soil. Theexponential equation of detachment rate and shear stress is the preferred equation to analyzethe flow detachment on colluvial deposits.（4） The runoff and sediment characteristics of colluvial deposits under different conditionsby artificial rainfall experiments. The erosion characteristics under different rainfall intensityand slop conditions: The infiltration processes are fitted by the model: Ir=aT-n+If, and therunoff processes are fitted by the model: Rr=-bT-m+Rf. There are two types of changes in theyield and sediment content: single peak and multiple peak models. The infiltration, runoff andsediment yield increase with increasing rainfall intensity with a liner, exponential, powerfunction respectively; The infiltration decreases with increasing slope gradient with a linerfunction; the runoff and sediment erosion have a critical slope gradient of erosion:³0°and>25°respectively; The sediment concentration increases with increasing rainfall intensity,while the sediment content of different rainfall intensities varies according to the slopegradient. The average rate of runoff exhibit an exponential function relationship with theaverage yield and a power function with the sediment concentration, and the average sedimentconcentration has a linear function relationship with the average sediment yield. Theinfiltration, runoff, sediment yield and sediment content of colluvial deposits can be wellforecasted by using rainfall intensity and slope. The runoff and sediment shows thesecharacteristics under different crust conditions: The presence of crusts can slow erosion, butwith the increase of the crust, the ability of surface runoff erosion grows, which results inincreased erosion. The runoff and sediment appears the characteristics under repetitiverainfalls: the diversification of slope terrain and erosion patterns lead to different sedimenterosion of various rainfall intensities. Under three times of rainfalls whose intensities are1.00and1.67mm·min^-1, there is no significant difference, but under2.33mm·min^-1rainfallintensity, the sediment erosion increasingly intensifies with the rainfall time increase.（5） The characteristics of rill erosion under different conditions. Under the conditions ofdifferent slops and different rainfalls, the time that the erosion happens is shorten as the slopand rainfall intensity increases; when the slop and rainfall intensity increase, the rill density and width increase; when the slop increases, the width-depth ratio decreases; and when theslop and rainfall intensity increases, the main erosion pattern changes from sheet erosion torill erosion. Under the conditions of different crusts, crust delays the happening of rill erosion;the rill density as well as the rill width of crust slop is less than those of the uncrust slop; andthe crust rill is deeper than uncrust. The amount of the erosion generated by crust slop is lessthan uncrust slop. The more crusts are on the surface of the slop, the more serious the rillerosion is. This indicates that the crust to some extent retards the rill erosion. The rill showsmany characteristics under the conditions of different rainfalls: when the rainfall intensityreaches1.00and1.67mm·min^-1because of the different ways of erosion, the width-depthratio has decreasing trends with the increasing rainfall times, but it turns out opposite resultwhen the rainfall intensity reaches2.33mm·min^-1. Moreover, the rill erosion will be muchserious when the rainfall time increases.（6） The sorting characteristics and transport mechanism of sediment particle in colluvialdeposits. The sediment particle under different rainfall density and gradient shows manycharacteristics: When the rainfall density and slope increase, both the content and enrichmentratios of coarse particle in sediment increase, and the losing of sediment tends to be coarseparticleing. The sediment particle gradually changes to coarse in the course of the interrillerosion-rill erosion and finally keeps in accordance with the tested soil’s particlecomposition. The saltation plasmid level of sediment particle is high:>0.537mm. During theinterrill erosion, the contents of suspention load and saltation load are between71.26%and97.64%, after the rill erosion occurs, the proportions of bed load rise up to10.93-41.74%. Thesediment particle under different surface crusting shows some characteristics: The crustingslope has the feature of transporting small particles. Runoff transportation of sediment particlealso chooses the coarse particle in the late period of erosion. Moreover, the selectiontransportation of the10min high-degree crusting slope is earlier than that of the5min one.Under the light rainfall density, the transportation of runoff tends to choose coarse particlegradually as the number of precipitation increases, but in strong rainfall density allprecipitation shows the “overall-transportation” feature of the test soil.（7） The dynamic mechanism of colluvial deposits under the rainfall conditions. The flowvelocity, the flow depth, the Reynolds number, the Froude number and other dynamic parameters are smaller between rills than those of colluvial deposits, but the resistancecoefficient and the roughness coefficient have the opposite results. The relationships amongthe rate of sediment and flow velocity, rough coefficient and resistance coefficient represent apower function between rills. Only the interrill rate of sediment and the flow velocity have alinear relationship. The mean rate of sediment with flow velocity, resistance coefficient androughness coefficient have a power relationship, but the mean rate of sediment with flowdepth, Reynolds number and Froude number are shown by a linear relationship. The sedimentrate has linear relationships with five dynamic parameters. The unit stream power，energyconsumption per unit width and specific energy in sections can be the primary choices to bethe dynamic parameters of colluvial deposits’ sediment transportation under rainfallconditions.更多还原