| Since the 21 st century,with the vigorous promotion of China’s western development strategy and the rapid development of infrastructure construction,a large number of large reservoirs represented by Three Gorges Reservoir(TGR),Jinping Reservoir,Xiangjiaba Reservoir,Xiluodu Reservoir,Wudongde Reservoir,Baihetan Reservoir,etc.have been built.The construction of such large reservoirs has greatly changed the original regional environment and geological conditions of the area,which has transformed a large number of slopes into reservoir banks,which in turn has triggered reservoir landslides.The largescale landslides have extremely high sliding driving forces and complex geological structures.During the operation of reservoirs,conventional engineering solution methods such as hand-dug piles and anchor piles often cannot play an influential role,so there is still an urgent need to develop new engineering solution methods.Due to its low construction environment requirements,good flexibility,high construction safety,and short construction period,the bored medium-diameter stabilizing piles have been gradually used in recent years.However,the mechanical distribution characteristics and stabilizing mechanism of medium-diameter stabilizing piles are still not clear,especially the mechanics and deformation characteristics under the action of reservoir water level(RWL)fluctuation have not been studied systematically.The application of bored medium-diameter stabilizing piles in reservoir landslides is in the initial stage,and the design method is still being explored.This thesis takes the Taping landslide in the TGR area as a case study;the filed investigation,in-situ comprehensive monitoring,machine learning,and numerical simulation were used to obtain the spatial and temporal deformation characteristics,subzones triggering factors and deformation mechanism of the large-scale reservoir landslide.The medium-diameter bored stabilizing piles group was then proposed to stabilize the Taping landslide.After that,the geotechnical centrifuge tests of the mediumdiameter stabilizing pile group-reinforced reservoir landslide were conducted to investigate the internal force distribution,load transfer,and deformation characteristics of the medium-diameter stabilizing pile group used in reservoir landslide,and the influence of different row spacing on the mechanical behavior and reinforcement effect of the medium-diameter stabilizing pile group in reservoir landslides were also explored.Then,a coupled "continuous-discrete" numerical analysis method was used to reveal the development characteristics of the soil arch effect within the medium-diameter stabilizing piles;the mechanical and deformation characteristics of medium-diameter stabilizing piles are discussed under the change of pile lateral spacing and row spacing.Finally,based on the analysis of the long-term RWL operation curve in the TGR area,two continuous fluctuation conditions of RWL are proposed,and the analytical solution of the landslide seepage line under the RWL continuous fluctuation was derived to optimize the design driving force of the Taping landslide;the two-dimensional design load distribution coefficient table is proposed to optimize the structural design of the medium-diameter stabilizing piles.The two-dimensional seepage field numerical modelings of the mediumdiameter stabilizing pile group reinforced reservoir landslide were carried out to optimize the planar layout scheme of the medium-diameter stabilizing pile group.We anticipate that our research can provide some theoretical basis and practical application reference for the prevention and control of large-scale reservoir landslides.The main conclusions are as follows:(1)Taping landslide is a large ancient landslide,the composition of the sliding body is fractured rock mass.The Taping landslide shows a typical step-like deformation pattern,characterized by alternating cycles of rapid movement in a short period and slow movement in a long period.The deformation of the rear part of the landslide is large,which is mainly controlled by the drawdown of the reservoir water level(RWL),and initiates when the RWL drops to 160 m.The deformation at the middle and rear parts of the landslide is small,which is controlled by the combined effect of heavy rainfall and RWL drawdown.The deformation initiates when the precipitation is >10mm/day.There are two sliding zones within the landslide,and the deformation of deep sliding zone is dominant.The factor of saferty along the shallow sliding zone is 1.05~1.10,and that along the deep sliding mass is 1.03~1.13.The later is mainly affected by the fluctuation of reservoir water level,and the former is more affected by heavy rainfall.(2)During the drawdown period of the RWL,the water pressure on the slope surface of the landslide disappears rapidly,and the internal pore pressure response lags behind,causing the effective stress decreasing rapidly,which induces the partial slump,and further causes the dislocation of the broken structure to produce excess pore pressure,eventually the overall failure occurred at the toe part.After that,overall failure at the toe part provides space for the instability of the middle and rear part,and the resistance of the front edge disappears,which may eventually induce failure at the middle and rear part failure.Taping landslide shows obvious seepage-induced progressive failure mode,and may overall failure in the future under the RWL fluctuation and heavy rainfall.(3)The thickness of the sliding body of Taping landslide is huge,and the downward driving force is large,and meanwhile sliding zone is below 145 m RWL,so there is no condition for slope cutting and foot pressing.In addition,the construction of conventional stabilizing piles is extremely difficult and the construction safety is low.In this paper,we propose a new engineering solution named buried medium-diameter bored stabilizing piles against the Taping landslide.(4)Centrifuge modelling results show that,the slope deformation is limited as RWL rising,and the earth pressure and bending moments on the piles are reduced.Under the high RWL,the earth pressure and bending moments on the piles increase slowly.As RWL drawdown,water pressure on slope decrease rapidly and seepage force within the slope increase fastly,causing the effective earth pressure and bending moments on the piles increase significantly.The downslope part of the pile group can change the mechanical transmission behavior of the multi-row stabilizing pile group.When this part is stable,the mechanical states of the pile group usually decrease from the first to the last row.When this part is unstable,the last row of the pile group may be subjected to a higher net soil pressure and associated bending and shear effect,even than the first and second rows of the pile group.In the piles group,the earth pressure on piles in the boundary column is greater than that of the middle column,and the driving force on the first row of boundary column is twice that on the middle column;the piles in the boundary column in the third row is 1.2 times than in the middle column.(5)The "continuous-discrete" coupled numerical simulation shows that the mediumdiameter stabilizing pile group resists the slope driving force through the triangular force chain structure composed of the frictional force on the pile side and the end-bearing force in the slope direction.Under the slope driving force,the geotechnical body between the medium-diameter stabilizing piles forms a complex frictional arching effect,which limits the slope deformation.The larger the pile spacing,the weaker the frictional arch effect between piles,and the slope driving force is more easily transferred within the different rows of piles.The smaller the row spacing,the more pronounced the overlapping effect of the frictional arching effect between the rows of piles,which can significantly enhance the mechanical connection between the rows of piles and further promote the stress transfer between the piles.(6)The deformation and failure mode of the medium-diameter stabilizing pile group is a "composite failure mode".The deformation at the top section of the front row of piles is easily supported by the rear row of piles,so the cantilever does not shows obvious bending deformation.Due to the small deformation at the lower part of the piles limited by the bedrock,the shear force on the piles is the largest near or below the sliding surface,so shear failure is most likely to occur at this position.The resistance in front of the cantilever of the rear row of piles is small,causing the net soil pressure on the upper section of the pile is larger than that on the lower part,and the bending failure is more easily developed at the cantilever.(7)The multi-year RWL operation curve condition and RWL operation curve during the 2019~2020 hydrological year are proposed to replace the RWL sudden drop conditions in the current code.This paper propose a method for calculating landslide seepage line and factor of safety under the effect of continuous fluctuation of RWL,and the numerical simulation and field monitoring verification show that the method is accurate.The design residual driving force of the Taping landslide has been optimized using the proposed conditions and the new calculation method.After optimization,the design residual driving force of the Taping landslide is reduced by 31-40%.(8)Based on the centrifuge modelling and numerical simulation,a two-dimensional load distribution coefficient table is proposed to optimize the structure of the mediumdiameter stabilizing piles group in reservoir landslides.The two-dimensional load distribution coefficient table improves the traditional one-dimensional load distribution coefficient table.The safety factor of the Taping landslide after implementing stabilizing piles group increased by 0.04-0.2,which is greater than the design safety factor.The twodimensional seepage numerical modeling of the Taping landslide with a mediumdiameter stabilizing pile group,was used to optimize the layout plan of the pile group.Finally,ten groups of stabilizing piles were used,and the pile group interval was 8 meters. |
