紫色土埂坎根-土复合体土水特性与抗剪强度

Soil-water Characteristics and Shear Strength of Root-soil Composites from Purple-soiled Bunds

研究根-土复合体土-水特征曲线与抗剪强度的关系,可为紫色土埂坎根-土复合体强化机理的揭示与埂坎稳定性的维持提供科学依据。选取三峡库区典型紫色土坡耕地埂坎草本植物根—土复合体为研究对象,结合Hyprop2土壤水分特征曲线测量仪、滤纸法与直剪试验,拟合土-水特征曲线,揭示基质吸力对根-土复合体抗剪强度的影响。结果表明:(1)根-土复合体土-水特征曲线明显分为边界效应区、过渡区与非饱和残余区,3种常用模型(B-C、VG、F-X)中F-X模型拟合该曲线效果最好,根-土复合体饱和含水率、进气吸力、残余区含水率以及相同体积含水率下的基质吸力均高于素土。(2)随着体积含水率降低,根-土复合体黏聚力先增大后减小,试验范围内黏聚力最大值51.25 kPa出现在体积含水率约23%时,内摩擦角则线性增大。相同体积含水率下,根-土复合体黏聚力较素土最大增加50%,内摩擦角提升不大。(3)基质吸力对根-土复合体抗剪强度的增强作用具有阶段性特征,各阶段临界吸力值与土-水特征曲线一致,过渡区(基质吸力为3~500 kPa)土体抗剪强度提高明显,进入非饱和残余区后(基质吸力>500 kPa)由于黏聚力下降,土体抗剪强度增速减慢,根-土复合体抗剪强度随基质吸力增大而提升的幅度大于素土。通过建立埂坎根-土复合体土-水特征曲线和抗剪强度的关系,可估测实际工况下的埂坎土体抗剪强度,进而为坡耕地埂坎的建设、维护管理以及坡耕地侵蚀阻控提供理论依据。

Investigating the relationship between soil-water characteristic curve(SWCC)and shear strength of root-soil composites is expected to provide a scientific basis for revealing the strengthening mechanism of purple-soiled root-soil composites and maintaining the stability of soil bunds.The root-soil composites of herbaceous plants on the soil bunds of typical purple-soiled sloping farmlands in the Three Gorges Reservoir region was selected as the research object,and the effect of matrix suction on the shear strength of root-soil composites was constructed by using Hyprop2 soil moisture characteristic curve measuring instrument,filter paper method combined with the direct shear test.Major findings were:(1)SWCC of the root-soil composites could be divided into boundary effect zone,transition zone,and unsaturated residual zone,and the F-X model fitted best among the three commonly used models(B-C,VG,F-X).The saturated water content,air intake suction,residual water content,and suction at the same volumetric water content of the root-soil composites were all higher than those of the plain soil.(2)The cohesion of the root-soil composites first increased and then decreased with the decreasing volumetric moisture content,and the maximum cohesion of 51.25 kPa in the test range occurred at a volumetric moisture content of about 23%.At the same time,the angle of internal friction increased linearly.The cohesion of root-soil composites increased by 50%compared with plain soil at the same volumetric water content,and the internal friction angle was not greatly enhanced.(3)The enhancement effect of matrix suction on the shear strength of root-soil composites and its parameters had a stage-specific characteristic,and the critical suction value of each stage was consistent with the SWCC.The shear strength of soil in the transition zone(where the matrix suction was 3~500 kPa)was most obviously improved.After entering the unsaturated residual zone(matrix suction was greater than 500 kPa),the shear strength of soil increased at a slower rate due to the decrease of cohesion.In addition,the shear strength of the root-soil composites raised with increasing matrix suction to a greater extent than that of the plain soil.Establishing the relationship between SWCC and shear strength of the root-soil composites of purple-soiled bunds could estimate the shear strength of soil bunds under actual working conditions,which provides an important theoretical support for the construction,maintenance and management of slope cultivated land and the erosion control of slope cultivated land.