冻融作用对黄河源区曲流河岸土体抗剪特性的影响

Influence of freezing and thawing on the shear resistance of meandering riverbank soil in the Yellow River source region

河岸带土体的抗剪性能直接影响河岸稳定性,冻融作用对高寒草甸土体的结构和抗剪力学特性的影响直接关系到黄河源区河岸的崩退频率和横向迁移。为探究冻融作用下,黄河源区曲流河岸带含根土体抗剪强度指标的变化规律及其产生机制,通过室内重塑土冻融直剪试验,开展不同含根量和冻融循环次数对土体抗剪强度指标的影响研究。结果表明:(1)植物根系能显著增强土体黏聚力,且随根系含量增加,黏聚力增幅可达2.7%~77.9%;内摩擦角随含根量变化不明显;(2)冻融循环具有削弱土体黏聚力的作用,尤其冻融循环初期。3次冻融循环条件下,黏聚力下降最大,下降幅度达19.0%;随着冻融循环次数增加,其变化基本趋于稳定,内摩擦角则随冻融循环次数增加呈现略微增大的趋势;冻融作用对含根土体抗剪强度指标的影响较素土小,在同等冻融次数条件下,含根试样黏聚力降低幅度较素土试样小。(3)草甸植物根系能够在一定程度阻隔土体温差变化,减缓土体黏聚力下降幅度,且随含根量增加而增强,含根量达到11%时,其对土体黏聚力的削弱作用较素土小4.2%~27.7%。因此,黄河源区河岸带应加强保护滨河草甸植被,最大限度发挥根系增强河岸稳定性作用,保护河流生态。

Soil shear resistance in the Riparian zone directly affects riverbank stability.Furthermore,the influence of freezing and thawing on the structure and mechanical properties of alpine meadow soils is directly related to the collapse frequency and lateral migration of the river bank in the source region of the Yellow River.To investigate the change rules and generation mechanisms of the root bearing soil mass,the shear strength index in the meandering Riparian zone of the source region of the Yellow River under the effects of freezing and thawing were assessed.The subsequent impacts of different root contents on the soil mass shear strength index were also determined using an indoor freeze-thaw direct shear test with remolded soil.The experimental results show that plant roots can significantly and increasingly enhance soil cohesion,which can range from 2.7%to 77.9%.Variations in the internal friction angle with root content were not significant.The freeze-thaw cycle weakens soil cohesion,especially in the early stages.The maximum decrease in cohesion of 19.0%occurred with three freeze-thaw cycles,after which the changes stabilized,while the internal friction angle showed a slight increasing trend.The effects of the freeze-thaw action on the shear strength index of the rooted soil is smaller than that of the plain soil.Under the same freeze-thaw frequency conditions,the decrease in cohesion of the rooted samples was found to be smaller than that of the plain soil samples.The root systems of meadow plants can block the changes in soil temperature,reduce the decrease in soil cohesion,and increase with the root content.When the root content reaches 11%,its weakening effect on soil cohesion is 4.2%-27.7%less than that of plain soil.The Riparian zone,as the source area of the Yellow River,should strengthen the protection of riverside meadow vegetation,maximize the role of the root system in enhancing Riparian stability,and protect river ecology.