Study On Groundwater Dynamic Law And Deformation Response Mechanism Of Shiliushubao Landslide In Three Gorges Reservoir Area

Since the completion of the Three Gorges Reservoir area and the start of water storage,the annual change of the reservoir water level has reached 30m,which has changed the original geological environment of the reservoir bank.In addition,the reservoir area has heavy rainfall during the rainy season,and the geological conditions of the reservoir bank landslides are complex,which has caused great difficulties in the evaluation of landslide stability and the prevention and control of reservoir bank geological disasters.Due to the influence of regional geological structure and topography of the landslide area,accumulation landslides in the Three Gorges Reservoir area are very common.After the Three Gorges began to store water,many ancient and old landslides were affected by the dual factors of reservoir water level and rainfall.The original groundwater seepage field of the landslide changed,and the landslide revived during the process of stress redistribution.Some have undergone large deformations,and some have even slipped into the river.Therefore,it is very important to study the deformation response mechanism and stability of this type of landslide under the influence of reservoir water level and rainfall.In this paper,the Shiliushubao landslide is selected as the research object.Through multiple field geological surveys and surveys,combined with the on-site permeability test,the geological structure and permeability characteristics of the landslide are analyzed.The seepage field,stability and deformation under the conditions of water level rise and fall and rainfall were analyzed,and the following research results were obtained:?1?Through the combination of on-site investigation,drilling and geophysical exploration,the engineering geological conditions of Shiliushubao landslide were ascertained:The plane shape of the landslide is tongue-shaped,the slope surface is broken line,the slide surface is arc-shaped,the bedrock rock formation is 70°?20°,the landslide aspect is 181°,it is a tangential landslide;This landslide is a typical accumulation landslide in the Three Gorges Reservoir area.The main material of the landslide is the rock body with spalled structure and fragmented structure formed after strong movement of T₂b,The sliding distance reached more than 240 meters,and the material of the sliding body as a whole fell forward.?2?According to the permeability test in the field,the permeability of the sliding body varies greatly in space,and its permeability has a great relationship with the lithology and the degree of crushing of the sliding body.Seen from the plane,the permeability of the landslide increases first and then decreases,the permeability of the first-grade slope is the largest at 9.344m/d,and the permeability of the second-grade slope is smaller at 0.233m/d.From the profile,the mass of the sliding body is generally broken by the leading edge relative to the trailing edge,and the deep layer is broken relative to the surface layer.Limestone and dolomite debris soil,the front edge and the back surface of the landslide are generally covered with a layer of Quaternary slope deposits with greater permeability.Therefore,the permeability of landslides is generally that the leading edge is larger than the trailing edge,the middle deep layer is larger than the surface layer,and the leading edge and the posterior permeability first decrease and then increase.The permeability coefficient of each part is quite different,ranging from0.1 to 10m/d.?3?Through the monitoring and analysis of landslide groundwater,the groundwater in various parts of the landslide responds differently to the reservoir water level and rainfall:The groundwater level at the front edge of the landslide has the strongest correlation with the reservoir level,and is hardly affected by rainfall;The groundwater level in the front edge of the landslide is slightly higher than the reservoir water level,and has a strong correlation with the reservoir water level.When the reservoir water level is low,it will be increased by the impact of heavy rainfall;The groundwater level in the middle of the landslide is affected by the reservoir water level and rainfall,and the response to rainfall has a lag of 6-8d;The groundwater level in the middle and rear of the landslide is almost not affected by the reservoir water level,and it is basically in the range of 181-183m throughout the year.?4?Through dynamic simulation analysis of the seepage field of landslide:a.During the whole year of a hydrological year,the largest part of the seepage of the landslide body is at the middle front edge of the landslide.Rainfall will form a saturated zone with a thickness of about 1m at the back of the landslide and the surface of the platform body in the middle of the landslide.After the rainfall,the seepage in the sliding body generally increases,with a maximum increase of 34%;the increase in the reservoir water level will cause the seepage flow in the sliding body to decrease by 65%,and the resulting dynamic water pressure will also decrease accordingly.b.The slopes farther away from the reservoir water are less affected by reservoir water changes;The rise of the reservoir water level will form a"er"shaped seepage field in the landslide body,and will move as the reservoir water rises;The seepage field formed by the reservoir water level decline at the front edge of the slope body is similar to laminar flow.The hydraulic slope during this process is mainly in the middle of the landslide.?5?Through the monitoring data of surface displacement,deep displacement and groundwater,combined with numerical simulation,the results show that:The deformation of the landslide is related to both the rise and fall of the reservoir water and rainfall.The reservoir water and rainfall affect the seepage field in the landslide body,which causes the landslide to deform.When the reservoir water level rises and falls,the landslide deformation mainly occurs in the middle and front part of the sliding body.The largest area of deformation of the landslide during rainfall is mainly the rear of the landslide.When the reservoir water level drops from the high water level to the minimum water level+rainfall,the stability of the landslide is the lowest.