Coordinated Evolution And Mechanism Characteristics Of The Reservoir Landslide-Stabilizing Piles System

Landslides are widely distributed all over the world,especially in mountain areas,such as in the Himalayas,where more than 3600 landslides have been reported.As the hydropower project constructions were constructed,the problem of landslises has become more and more serious.Anti-slide piles,one of the most common stabilizing structures,are widely used around the world.For example,in the Three Gorges Reservoir area,over 725 landslides are stabilized by anti-slide piles and other structures.A new and more complex system is formed due to pile-landslide interaction.The deformation mechanism of this system is important to the long-term stability evaluation of the landslide.In practice,anti-slide piles need not be only rigid,but can be constructed to have intermediate to great flexibility.They have completely different deformation characteristics with landslides.However,there are few research on the long-term interaction mechanism and long-term stability evaluation of landslides stabilizing piles,so that the anti-slide piles design is static.Moreover,the coordinated deformation of piles and landslides is not considered.Therefore,in this paper,the Majiagou landslide was taken as an example.Based on the results of field monitoring,physical model tests are constructed to study the interaction of piles-landslides interaction and the codeformation characteristics of the system.The main research contents and results are followed:(1)After implanting 17 anti-slide piles,the Majiagou reservoir landslide still deformed and its' deformation was obviously affected by the reservoir water level and rainfall.The implantation of anti-slide piles divided the soft and hard rock layers into two parts,resulting in a new sliding surface developed under the pile bottom.As a result,the landslide at downhill side of piles gradually slide into reservoir.A field experiment system was constructed to study the pile-soil interaction.It was found that the anti-slide pile gradually deformed elastically.The soil in front of the pile was gradually separated from the pile under the effect of reservoir water level fluctuation,and the piles' top movement exceeded the soil around piles movement.Pile had obvious coordinated action deformation with landslide.Majiagou landslide has several potential shear surface,which are all developed in the purple-red mudstone layer.In order to understand the codeformation mechanism of anti-slide pile and landslide,several physical model tests were developed.(2)Based on the deformation characteristics of reservoir landslides stabilizing piles,a new approach of physical model test of reservoir landslide-stabilizing piles design to realize multi-field monitoring and complex conditions is proposed.Taking Majiagou landslide as a prototype,the physical model tests design of reservoir landslides are systematically described: Re-design the geometric size of real landslide by taking the stability coefficient as the control condition;Based on the similarity theory,the physical model was design;The orthogonal test and the fuzzy comprehensive evaluation method were used to determine the similar materials.Evaluating the relationship between the displacement of reservoir landslide and the water level fluctuation,the hydrological condition was designed.The comprehensive monitoring system is composed of model surface and deep deformation,pile stress and strain,infrared thermal temperature monitoring,earth pressure,pore water pressure and water content to obtain seepage,stress,deformation and temperature field.In addition,Based on the principle of electromagnetism,applying mutually perpendicular electric and magnetic fields in the landslide model,calculated the force formula of pore water.According to the theory of electroosmotic consolidation,calculated the resultant force of groundwater,and then the relationship between the migration rate and the voltage and magnetic field intensity is deduced,then the time similarity ratio is obtained.And improve the water migration rate of landslide model by controlling the voltage and magnetic field strength applied to the model,to provide the conditions for studying the influence of reservoir water level rise and fall on landslide.(3)Several physical model tests were constructed with different reservoir water fluctuation conditions and different inclination angles of the landslide.The results showed that during the initial impoundment,the intersecting-angle of cracks is negatively correlated with the inclination of the bedrock.The relationship of cracks development,pore water pressure,infiltration line and failure mode was quantitatively obtained.The greater the water level rate,the greater the rate of change of water pressure in the slope,which has the greatest influence on the underwater slope,which affects the stability of the landslide.The small landslide is destroyed from the local to the whole,showing a typical multi-slip progressive retrogressive mode.soil structure deterioration and water floatability is the key factor of the decline of the leading edge of the landslide model,and hydrodynamic pressure and effective stress reduction.(4)The implantation of anti-slide piles changed the stress distribution of the landslide,which in turn changed the evolution of the landslide and improved the stability of the landslide.In unreinforced landslides,the stress of the sliding mass was distributed in a triangular shape,and the elastic pile changes the distribution of the earth pressure behind the pile from a triangle to an inverted triangle,but the rigid pile controls the landslide thrust behind the pile,resulting in no obvious change occurrence in the stress in front of piles;The strain of the pile was consistent with the displacement change of the landslide,and it increased in a step-wise shape.The bending moment of the elastic pile was approximately triangular,but the rigid pile mainly concentrated to the upper part.During the deformation of the landslide-stabilizing pile,the temperature field on the model surface had obvious changes also occurred,especially when cracks generated or the displacement increases rapidly.Compared with rigid piles,elastic piles exhibit better coordinated deformation,resulting in landslide stress uniform and small,so the elastic pile system can withstand higher loads before failure.In terms of failure mode,the unreinforced landslide slide into reservoir along the sliding zone,but in the landslideelastic pile system,at least two slips are observed after the pile.At the same time,the landslide was gradually extruded,and the deformation of the pile body causes multiple shear outlets in the front of the pile.Under the action of rigid pile reinforcement,the deformation of the landslide is concentrated in.(5)Based on the multi-field evolution characteristics of the landslide-stabilizing pile system,several methods such as gray correlation,rate correlation,pile-landslide deformation relationship,temperature field,and stress field were used to divide the landslide-stabilizing pile system into four stages: initial,coordinated action,uncoordinated action and failure.Initial stage: the stress of the landslide is gradually balance,and as thrust force increased,the force is gradually transferred to the sliding mass around piles.The displacement correlation degree between pile and landslide increases first and then decreases.Coordinated action stage: the soil arch around the pile gradually generates.Piles showed co-deformation with landslide.The displacement correlation degree gradually increased and became stable.The deformation of the landslide and the piles increased linearly,and the energy gradually accumulated,caused temperature increasing.Uncoordinated action stage: the soil between the piles was gradually extruded,and the soil arch was gradually failure.The correlation degree value decreased rapidly,and the displacement of the landslide and the piles increased non-linearly.Moreover,the temperature of the landslide surface gradually decreased as the energy dissipated;As the force increased,the landslide surface temperature suddenly increased and then decreased.Meanwhile,the landslide had a sudden large displacement,and the landslide was failure.(6)Based on physical model tests and field monitoring results,a point on the trailing edge of the slope surface is used as a reference point to construct the slope surface displacement equation at the stage of coordinated deformation and uncoordinated deformation.The ground reaction coefficient method was used to obtain the cooperation based on the soil compression load test.The relationship between the pile deflection and the base point deformation in the uncoordinated deformation stage is derived,and the interaction force between the pile and the soil in front of the pile is derived;The relationship between the pile and the soil displacement can be expressed by the parabolic equation: In coordinated deformation stage,the parabolic opening is upward,but in uncoordinated action stage,the soil arching between piles changed to the opening downward,which means the displacement of the soil between the piles greater than the displacement of the piles.The soil between piles is gradually extruded;Based on the pilesoil interaction,the SW model is used to derive the formula of the interaction force between piles and the landslide behind the pile to determine the critical value of the system entering the uncoordinated action stage.The effect of group piles was also analyzed.Based on the pile deflection and the pile-soil interaction,elastic mechanics is used to calculate the stress formula of the pile in the coordinated action stage.The Filaman solution was used to deduce the stress formula of group piles and landslide.This study found that the upper part of the elastic pile was not subjected to the thrust,so that the thrust force distribution behind piles was simplified.(7)Four parameters: pile length ratio(embedded section / cantilever section),pile spacing,pile rigidity,and pile section were used to study the influence of anti-slide pile structure parameters on the co-deformation of the landslide-piles system.The relative stiffness of the pile has an important influence on the evolution of the anti-slide pile system and the stress of the pile.The research found that when the relative stiffness of the piles was 30-40,the piles stress could be more reasonable and sufficient,and made use of the anti-sliding pile's bending resistance.Besides,the embedded section's reinforcement performance can also be used,and the landslide and anti-sliding pile can fully deform together.For elastic piles,under the condition of 5 times the pile spacing,the elastic pile could fully cooperate with the landslide to deform.In rigid pile system,the 4-5 times pile spacing model has a longer coordinated deformation stage and a larger displacement increment.