赣南崩岗侵蚀区不同部位土壤抗剪强度及影响因素研究

Soil Shear Strength of Collapsing Erosion Area in South Jiangxi of China Relative to Position of the Soil and Its Influencing Factors

为明确南方崩岗侵蚀区不同部位土壤抗剪强度的分布规律,探索在崩岗发育过程中土壤基本性质对抗剪强度指标的影响,以不同发育阶段崩岗各部位表层土(0~20 cm)为研究对象,对土壤基本性质和抗剪强度的差异进行对比研究。结果表明:(1)随着崩岗的发育,表层土壤基本性质逐渐恶化,容重逐渐减小,颗粒组成粗骨质化现象明显,土壤有机质的含量与根系密度的变化,均随崩岗的发育呈现出典型的退化特征;(2)崩岗各部位黏聚力和内摩擦角的变化规律相似,集水区部位达到峰值,沟道部位达到最小值,随崩岗的发育呈明显下降趋势;(3)根系密度与黏聚力有良好的线性相关关系,砾石含量、粉粒含量和黏粒含量对崩岗土体内摩擦角有显著影响,可以用幂函数表示它们之间的关系;(4)试验以根系密度、砾石含量、粉粒含量和黏粒含量来表征土壤饱和状态下的抗剪强度,建立了在崩岗发育过程中饱和抗剪强度的预测方程(R2=0.891,P<0.01),结果显示方程可信程度较高,预测效果较好。研究结果揭示了南方花岗岩崩岗区不同发育阶段抗剪强度的控制因素,为进一步防治水土流失提供理论依据。

【Objective】Soil shear strength is an apparent indicator of how easily shear deformation occurs under the action of external force,and a major index to characterize soil mechanical properties,as well as an important parameter of the process-based soil erosion model for prediction of hydraulic erosion.So far,little has been reported on soil shear strength at each collapse developing stage.The purpose of this study is to(1)investigate variation of soil shear strength with the process of soil erosion on typical collapsing mounds;(2)determine influences of basic physical and chemical properties on soil shear strength;and(3)establish an equation for prediction of variation of soil shear strength with development of collapsing.【Method】The experiment lot was set up in the Jingouxing watershed in Tiancun Town of Gan County,where there are quite a number of collapsing mounds.Three adjacent collapsing mounds of granite different in collapse developing stage(initial stage,active stage and stable stage)were selected for the experiment and a total of 15 sampling sites were set on each mound.Topsoil samples from the 0~20 cm soil layer of each mound and relevant environmental variables,were gathered,separately,for analysis of basic soil properties and soil shear strength.The data were processed with the classical statistic method for spatial variation of soil shear strength and variation of saturated shear strength with developing of collapse was predicted with the stepwise regression equation.【Result】(1)The physical properties of the soil in the collapse system are relatively poor with bulk density of the top soil layer varying in the range of 1.02~1.40 kg·m–3 and declining with the position lowering along the slope,particle size composition coarsening,soil organic matter content lowering and root density ranging from 0.27 to 3.57 kg·m–3,all of which demonstrate typical features of soil degradation with developing collapse;(2)Soil cohesion and internal friction angle,varies quite similarly,that is,both in a declining trend with development of the collapse,peaks at collecting areas,and bottoms in ditches.When collapse develops into a stable stage,restoration of vegetation promotes formation of root-soil complexes,which in turn increases soil cohesion and hence soil shear strength by a certain degree;(3)Statistical analysis shows that the contents of gravels,silt and clay are the optimal parameters to characterize soil internal friction angle of a collasping mound and their relationships can be well-described with a power function.Besides,a good linear correlation between root density and soil cohesive was observed;and(4)The experiment used root density and particle size composition to characterize shear strength of the soil under saturation,and established the equation(R2=0.891,P<0.01)for predicting soil shear strength of a developing mound.【Conclusion】With developing collapse,soil properties degrade obviously.Soil saturated shear strength varies significantly with soil particle-size distribution and root density across the collapsing erosion area,and is affected jointly by soil texture,topography,moisture and land use at the regional scale.It is recommended to use the functional equation based on parameters like particle-size and root density to predict soil shear strength,particularly for soil layers below 20 cm in the collapsed erosion areas in South Jiangxi.