Mechanisms of root-soil reinforcement in bioembankments of sloping farmland in the purple hilly area,China

Bio-embankment is an important soil and water conservation measure in the purple hilly area in China,which can effectively improve the ability of cultivated soil layers to resist rainfall erosion and runoff scour.In contrast,the ecological effect of bioembankment depends on the stability of the earth bank.Taking the natural grass bank as a control(CK),the root distribution,root tensile properties and shear resistance of root-soil composites for 3 typical soil and water conservation bio-embankments,namely,Morus alba Linn(Morns),Zanthoxylum bungeanum Maxim(Zanthoxylum)and Medicago sativa(Medicago)were analysed.The results included the following:(1)The root system of the bio-embankments generally decreased in extent with the soil depth;fine roots in the o-io cm depth were most prevalent and significantly higher than those at the other depths,and coarse roots were mainly distributed in the o-30cm layer.(2)The stress-strain curves of the roots of each bio-embankment were single-peak curves without clear strain softening phenomena.The smaller the root diameters were,the smoother the stress-strain curves,and the lower the capability of the earth bank to resist collapse.The larger the root diameters were,the lower the tensile strength.The average root tensile force was highest for Zanthoxylum(73.91 N),followed by Medicago(68.07N)and Morus(61.88 N),and the average root tensile strength showed the same trend,16.52 MPa for Zanthoxylum,16.08 MPa for Medicago and 13.02MPa for Morus.(3)The bio-embankment measures significantly improved the soil shear resistance,especially under vertical loads of 1oo kPa and 200kPa.The soil internal friction angle showed a significant log-positive correlation with root morphological parameters of root length density(RLD),root surface area density(RSAD) and rootweight density(RWD),while the soil cohesion force showed a positive linear correlation with these parameters.The results provide effective parameters supporting for the design of bio-embankments and promoting the use of soil reinforcement with suitable species selection in protective earth banks for stability in the purple hilly area.

模拟降雨条件下砾石含量对塿土工程堆积体坡面产流产沙的影响

为探究砾石含量对塿土堆积体坡面产流产沙的影响,采用室内人工模拟降雨试验,以土质坡面为对照,研究5种砾石含量(10%、20%、30%、40%、50%)堆积体坡面在不同降雨强度(1.0、1.5、2.0、2.5 mm·min^(-1))下的产流产沙特征。结果表明:不同试验条件下的平均径流率在2.18~13.07 L·min^(-1),不同雨强条件下平均径流率均在砾石含量10%(或20%)和50%时分别达到最大值与最小值;平均流速在0.06~0.22 m·s^(-1),流速变化复杂,砾石含量越小,流速变幅越大,变异系数也越大,砾石含量10%时平均流速最大。砾石的存在可有效抑制产沙,最大减沙效益可达84.2%,雨强相较于砾石含量对平均产沙率的影响更大。偏相关分析表明,平均径流率、流速、产沙率均与砾石含量呈极显著负相关;平均产沙率与平均径流率、平均流速以及二者交互项均呈极显著线性函数关系,其中,与平均径流率的相关性最强。本研究可为塿土区工程堆积体水土流失治理和侵蚀模型的建立提供参考。

黄土高塬沟壑区草地沟头立壁土壤抗冲性特征

黄土高原植被恢复使沟头立璧土壤侵蚀过程发生显著变化。为明确黄土高塬沟壑区草地沟头立壁土壤抗冲性特征及其影响因素,以裸地为对照,利用室内原状土槽冲刷试验研究了草地沟头立壁0~1 m不同土层(0~10、10~20、20~40、40~60、60~80、80~100 cm)土壤理化性质和抗冲性特征。结果表明:草地和裸地沟头土壤水稳性团聚体含量和粘聚力随土层加深均呈减小趋势。裸地沟头土壤有机质含量、土壤抗冲系数随土层深度的增加呈减小趋势,而草地沟头土壤有机质含量、土壤抗冲系数随土层加深先增加后减小,且均在10~20 cm土层达到最大值(24.30 g·kg^(-1)和58.86 L·g^(-1)),草地各土层土壤抗冲系数是裸地的1.7~9.3倍。沟头土壤抗冲性与土壤有机质含量、水稳性团聚体含量、黏聚力和植物根长密度呈极显著相关,其中与土壤有机质含量(r=0.98)的关系最密切。该研究可为黄土高塬沟壑区沟头溯源侵蚀机理的研究提供基础数据,并为有效防治该区域水土流失提供科学依据。