Study On The Synergistic Mechanism Of The Pile-slab Wall Of The Newly-built Embankment And The Existing L-shaped Retaining Wall

With the continuous expansion of railway transportation volume,the phenomenon that the railway transportation capacity cannot meet the traffic volume has become more and more serious.Therefore,the reconstruction of existing railway lines and new construction projects near existing lines will increase year by year.Railway existing protective measures and supporting structure safety assessment and reinforcement utilization,existing roadbed deformation development law caused by the reconstruction of existing lines and the addition of second lines,design calculations and force analysis under the combined action of new and old supporting structures,etc.More and more attention has been paid.In this paper,under the complex construction environment of the newly-built Zhonglan Passenger Dedicated Railway Station-the study of the synergy of the new embankment pile-slab wall and the existing L-shaped retaining wall composite retaining structure as the background,using methods of field testing,numerical simulation and theoretical analysis to discuss the changing law of the earth pressure of the retaining wall during the process of the pile hole excavation and the influence of the pile hole stress release effect on the existing structure during the excavation;the study of the force and the synergistic mechanism of the combined retaining structure,the main conclusions are as follows:(1)By burying earth pressure sensors,rebar gauges and inclinometer tubes on the back side of the pile and the pile,and analyze the variation law of the pile bending moment,displacement and earth pressure under the action of the wide filling load of the subgrade side of the composite supporting structure.(2)Through the method of numerical simulation,the change law of the earth pressure of the retaining wall during the excavation of the pile hole is studied.The research results show that,in the process of pile hole excavation,the soil pressure of each retaining wall increases first and then stabilizes with the increase of depth.The depth of soil pressure of each retaining wall increases with the increase of retaining wall number.With the increase of the excavation depth,the increasing range of the soil pressure relative to the initial value of each retaining wall is smaller and smaller.When the excavation reaches 17 m,the final earth pressure of the retaining wall begins to stabilize.(3)Analyze the influence of the pile hole stress release effect on the deformation of the existing retaining wall and subgrade structure in the pile hole excavation.The horizontal displacement and vertical displacement at the existing cargo line shoulder first decrease and then increase with the increase of the pile hole excavation depth under the condition of diaphragm excavation,the horizontal displacement and vertical displacement at the existing L-shaped retaining wall first increase and then decrease.(4)Using MIDAS GTS NX and establishing a three-dimensional finite element model based on actual working conditions,the maximum bending moment of the new pile under the new line load is 1433.9k N·m,The maximum shear force is 230.3 k N,and the maximum horizontal displacement of pile top is 2.55 mm.Analyzing the internal force response,coordinated displacement and earth pressure changes of the combined structure under different construction steps,it is concluded that the load sharing of the newly-built pile and the existing L-shaped retaining wall under the action of the backfilled bench soil and the train load is4.3:1,and the pile-slab wall Withstand most of the fill and train loads.The accuracy of the numerical simulation results is verified by comparing the results of field test data processing with the numerical simulation results.Then the influence of pile length and pile section size is analyzed by numerical simulation,and the mechanical characteristics of composite retaining structure are obtained.(5)The distribution characteristics of the earth pressure of the L-shaped retaining wall under the conditions of the existing embankment and the combined retaining structure are analyzed,and its service state is checked.It is concluded that the retaining wall Kc=1.9,K0=8.1,σ=37.82 k Pa under the load of the existing cargo line;the retaining wall Kc=1.7,K0=7.2,σ=43.30 k Pa under the load of the new line,all meet the requirements of the specifications and are in good service condition.