泾河下游黄土台塬区滑崩灾害空间分异研究

Distribution Difference of Landslide and Collapse in the Loess Tableland Area at the Downstream of Jing River

近年来,泾河下游黄土台塬区滑坡、崩塌灾害频繁发生,严重威胁当地居民的人身安全和正常的生产生活秩序。通过现场调查发现,这些黄土地质灾害在空间上表现出"东滑西崩"的分布特征,与区内二级地貌单元具有极高的空间相关。已有研究表明,农业灌溉造成塬区东段斜坡带水文地质条件变化是诱发黄土滑坡的主要原因,但同为灌溉区的塬区西段却未能形成相同类型的地质灾害。为此,以东、西段地貌单元差异为线索,利用Modlfow水文地质数值模拟软件,分析2种地貌单元在灌溉条件下的水文地质响应。在此基础上,探讨了二级地貌单元差异对斜坡孕灾环境的影响,并利用CSD和RTC应力路径试验模拟了农业灌溉和工程挖方工况下斜坡土体的力学行为,探讨了斜坡的2种破坏模式及"东滑西崩"空间分布的成因。结果表明,研究区东段塬面完整,在长期农业灌溉条件下,斜坡带水位涨幅显著、水力坡度大、潜蚀作用强,斜坡土体中超孔隙水压力的不断增大,将导致土体在不完全排水条件下发生剪切破坏,甚至静态液化,从而诱发黄土滑坡灾害;研究区西段塬面破碎、冲沟发育、有效灌溉面积小,斜坡带径流排泄边界广、蒸发作用强、地下水位涨幅小,受工程挖方影响,干燥的斜坡土体在围向压力不断降低的条件下,将导致脆性破坏的发育和贯通,使得斜坡在节理裂隙面控制下发生突然垮塌,形成黄土崩塌灾害。

In recent years,the loess landslide and collapse have occurred frequently in the loess tableland area at the downstream of Jing River.These geological hazards threaten the safety,normal order of production and living of local residents.The field investigation has discovered that these geohazards have the distribution characteristic of＂East landslide,West collapse＂,which have close spatial correlation with the secondary geomorphic unit in this area.Previous studieshave shown that the agricultural irrigation causes the changes of hydrogeological conditions in the eastern slope belt of this study area,which is the main reason for the loess landslide.But,different types of geological hazards were occurred in the western slop belt of the irrigated area.Therefore,the hydrogeological models have been established to analyze the difference of hydrogeological conditions of different secondary geomorphic units under long-term irrigation.And then,based on the CSD and RTC stress path test,two failure models of slopes under the coupling effect of landform,agricultural irrigation and engineering excavation have been discussed in this paper.The results show that the long-term agricultural irrigation causes a significant increased groundwater level,increased hydraulic gradient,enhanced erosion and changed hydrogeological conditions,which provide favorable formative environment for the formation of loess landslide and become the main cause of loess landslide.In addition,the hydrogeological condition is not strongly affected by irrigation and not easy to induce landslide in the gully area of loess tableland.However,the frequent excavation makes the slope steep and destroys the slope structure,which is the main cause for the frequent occurrence of loess collapse.