农业灌溉作用下黄土边坡失稳引起耕地流失分析

为了明确在大面积农业灌溉作用下,水分入渗土壤进而渗入下部黄土体,改变临空耕地黄土边坡的稳定性状态,造成边坡失稳引起耕地流失的过程。在统计分析甘肃天水耕地流失面积、农田灌溉面积、地质灾害数量和由地质灾害造成耕地流失比例的基础上,在典型地层剖面上采集原状土壤和黄土试样,进行天然状态和灌溉作用下土体的物理力学性质和抗剪强度试验,采用理正岩土边坡稳定性分析系统,利用基于极限平衡条分法的瑞典法进行边坡稳定性定量分析。结果表明：在天然状态下,该边坡稳定性系数为1.074,处于基本稳定状态;而在灌溉作用下,随着水分入渗深度的增加,稳定性系数逐步降低,最后失稳。因农田灌溉仅使土壤层饱和,对该边坡稳定性影响不大;当灌溉水持续入渗使饱和层土体厚度大于2 m时,该边坡稳定性降低一个等级,处欠稳定状态;当饱和层厚度大于10 m时,该边坡失稳,发生滑坡,造成耕地流失。

The Analysis of Arable Land Loss Caused by Loess Slope Instability Under Agricultural Irrigation

The study aims to clarify the process of arable land loss caused by loess slope instability, in which the loess slope stability was changed by irrigation water infiltration into soil and loess under large-scale agricultural irrigation. On the basis of statistical analysis of the loss area of arable land, the farmland area under irrigation, the number of geological disasters and the proportion of farmland loss caused by geological disasters in Tianshui of Gansu, the author collected samples of undisturbed soil and loess from typical stratigraphic sections, and tested the physical and mechanical properties and shear strength of soil under natural condition and irrigation. The slope stability was quantitatively analyzed by Swedish method based on limit equilibrium method in combination with Lizheng rock slope stability analysis system. The results showed that the slope was steady and its stability coefficient was 1.074 under natural condition, but under agricultural irrigation, with the increase of water infiltration depth, the stability coefficient decreased gradually, and the slope became unsteady. If farmland irrigation only saturated the soil layer, it would have little effect on the stability of the slope. When the thickness of loess saturated layer was greater than 2 m due to continuous irrigation water infiltration, the slope stability would be reduced by one level and became unsteady. When the thickness of loess saturated layer was greater than 10 m, the slope would be unsteady and landslides would develop, causing arable land loss.