Study On The Hydrogeological Structure Evolution And Disaster Control Mechanism Of Loess Slope In The Southern Jingyang Plateau

Irrational water irrigation would change the hydrogeological conditions of loess slope,which is an important triggering factor of loess landslide.In order to explore the effect of irrigation on the formation of loess landslide,this paper takes the loess slope of the Southern Jingyang Plateau of Shaanxi Province as the research object.Based on the investigation of hydrogeological and irrigation condition,according to the theory of variable-saturated seepage,the numerical model of the two-dimensional transient variable-saturated seepage flow was built to study the loess slope transient variable-saturated seepage pattern;the numerical model of the two-dimensional steady variable-saturated seepage flow of the loess slope was established,and the loess slope hydrogeological structure evolution under the effect of irrigation and fissure and its disaster control mechanism were proposed.The main findings are as follows:1.The results of hydrogeological survey show that the flow of groundwater flow direction in the survey area from 2014 to 2016 was from the Loess Plateau to the Jinghe River,while the hydraulic gradient obviously increased from the middle to the edge of the plateau area.Compared with that in 2014,the water level elevation in 2016 in the east and west of the southern plateau increased by 10-20 m while that in the central part reduced by 0-10 m.Unconfined water level of Southern Jingyang Plateau during the year 1976 to 2016 showed an average annual increase of 1.05 m.The main local irrigation way is canal irrigation,supplemented by well irrigation.The groundwater level is higher in the canal irrigation area,accompanied by frequent landslides,while that in the well irrigation area is lower with less landslide occurrence.2.The 360 days of intermittent irrigation results indicated that the soil moisture content changes significantly within the depth of 8m on the loess slope,while the wetting peak moves downwards constantly and reached 10 m after 360 days.The inflow and accumulation of water for a long period of time is considerable,which can explain the rising groundwater level in the Southern Jingyang Plateau plain under long term irrigation.3.Numerical simulation results showed that uder natural conditions,the water content of unsaturated zone was low and landslide was less likely to occur.After flood irrigation,the unconfined water level of the loess slope raised and the water level rose above slope foot.The trailing edge fissure extension and the migration of the water to the deep were mutually promoted,therefore the weak zone beneath the fissure was connected with that at the slope foot to form a penetrating weak zone.4.Landslide was likely to occur when the combination of penetration force,groundwater float and the self-weight of the slope exceeded the frictional resistance through the weak zone.After the landslide,the landslide body accumulated at the slope foot,which hindered the drainage of the groundwater in the original slope position and provided the favorable condition for the formation of the new landslide.Accordingly,the layout of the wells behind fissure on the loess plateau to reduce the water level could be a potential way to control loess landslides.