Study On Synchronized Drainage Technology And Its Performance For Exploitation-type Treatment Of Reservoir Bank Landslide

The Three Gorges Reservoir is one of areas where the landslides are most developed in China.During the routine operation of the reservoir,water-level changes between 145 m and 175 m annually.Two huge fluctuation belts formed,are the most ecological vulnerable zones in the reservoir.Violent changing of the water-level,make the water-level changing in slope lagging behind it in the reservoir.Enormous pore pressure difference may lead to landslide in the bank slope.Among the commonly used slope drainage methods,the horizontal drainage holes may be blocked up in long-term use because of insufficient hydraulic gradient;the inclined drainage holes may increase the drilling length and reduce the drainage point depth;the drainage tunnels require too much quantities of work;and the way of water-collecting wells cooperating with electric-pneumatic pumps needs a lot of additional power and regular maintenance.Siphon drainage pipe is suitable for bank slope drainage because of its small borehole depth and excellent drainage effect.However,due to the limitation of physical laws,the lift of the siphon drainage pipe can not meet the water level variation of up to 30 m in the Three Gorges Reservoir.a multistage siphon drainage system is proposed,siphon pipes are used for drainage and pressure reduction at each stage.The drainage water from the slope interception drainage system flows into the reservoir water body,reducing the pore pressure difference.Through theoretical analysis and numerical simulation of a hypothetical silty clay bank slope of the Three Gorges Reservoir with multistage siphon drainage system,it is concluded that the reasonable stage of the multistage siphon drainage system is 4,the siphon lift should be 7m,the siphon pipes' diameter should be 4mm,the top of the water-collecting pipe should be 145 m,155m,165 m and 175 m,the horizontal length should be 20 m,and the water-collecting pipes' diameter should be 10 cm.The multistage siphon drainage model experiment verifies the superiority of the multistage siphon drainage system for synchronous drainage of reservoir bank landslide.The exploitation-type synchronized drainage treatment system is put forward.The cut-off ditches where multistage siphons overflow are transformed into small-scale dike-ponds.The cash crops including algae,Trapa natans L.,Nelumbo nucifera,Cynodon dactylon(L.)Pers.,Glycine max(Linn.)Merr.and Morus alba L.are selected for planting in the dike-pond and on the slope surface.The discharged water is utilized to maintain the stability of the bank slope,the ecological system of the bank slope is restored and acquiring economic value at the same time.In order to prevent the possible break-off caused by long-term non-operation of the siphon,an automatic control system is used to dominate the opening and closing of both ends of the siphon.The control program and the flow of the instrument are studied,and the instrument suitable for automatic control is selected.Finally,the construction technology of the system is discussed,in which reasonable crop planting spacing,excavation depth of dike-pond and anti-seepage engineering measures are selected.