黄土塬边漫灌区土体水入渗过程研究

Infiltration process of loess in flood irrigation area

黄土漫灌区水入渗形成的饱和黄土层内极易产生液化型破坏,诸如积石山6.2级地震诱发的中川乡液化型黄土滑坡和甘肃黑方台黄土滑坡为典型案例;然而,黄土中水的渗流是以活塞式基质渗流为主还是以优势渗流为主,目前尚未定论。以甘肃黑方台典型滑坡后缘漫灌区土体为研究对象,开展现场漫灌入渗试验,借助三维高密度电法实时监测水的入渗过程;利用电阻率变化率表征水分的整体入渗过程,并用相邻测量时段电阻率变化率差值表征该时段内水分的关键渗流空间,分析漫灌作用下黄土中水的渗流模式,探讨不同补给强度对渗流模式的影响。主要得出以下结论:(1)固定电极的时序三维高密度电法能有效探测黄土中水的渗流过程;(2)试验区黄土中呈现基质流与优势流共存的渗流模式,其中基质流的均匀入渗为测量空间内的主要渗流模式且集中于近地表2m内,优势流表现为延伸至4m深度的优势通道内水分向周围以基质流形式逐渐渗流,渗流轨迹受优势通道分布的影响;(3)含裂隙黄土中水的渗流模式受水补给强度的影响,其中漫灌或降雨积水时,出露地表的裂隙内水分可直接下渗至裂隙延伸的区域形成优势流,而在无积水的降雨条件下,裂隙内无法形成明显优势流,水分以活塞式基质流的形式下渗。研究成果可为黄土中水渗流的现场观测及模式探讨提供借鉴。

The saturated loess layer is susceptible to liquefaction failure,as evidenced by the liquefaction loess landslide in Zhongchuan triggered by the Jishishan M6.2 earthquake,and the Heifangtai loess landslides serve as typical examples.Nonetheless,the infiltration mechanism in loess remains elusive.A field irrigation test was carried out at the rear boundary of a representative landslide in Heifangtai,with the water infiltration process monitored using the 3D electrical resistivity tomography method.The cumulative rate of resistivity change was employed to depict the overall infiltration process,while the disparity in resistivity change rates between adjacent measurement intervals was utilized to identify the primary seepage pathways.The infiltration mechanism in loess was examined under varying recharge intensities.The main conclusions are as follows:(1)The time-series 3D electrical resistivity tomography method can effectively detect the infiltration process in loess.(2)There co-exists matrix flow and preferential flow in the test,the matrix flow is the main infiltration mode during the test.The preferential flow shows the gradual seepage around the preferential channel extending to a depth of 4 m,and the seepage area is affected by the distribution of preferential channel.(3)The infiltration mode in the fissured loess is affected by the intensity of water recharge.With the flood irrigation or rainfall water ponding,the water in the fissures can directly penetrate into the deep soil forming a preferential flow.While in case of rainfall without water ponding,there is no obvious preferential flow observed,and the water infiltrate only with matrix flow.The results can provide reference for the study of field infiltration test and infiltration mechanism in loess.