Time Dependence Research On The Influence Of Foundation Seepage And Creepage At The Reclamation Area Of Coastal Beach On Bridge Piles

Reclamation of coastal beach has important significance for exploitation and utilization of land resources at coastal area,but the existence of border dike will produce certain influence to adjacent existing bridge piles after reclamation.On the one hand the construction of border dike will change foundation seepage and then lead to foundation deformation,on the other hand the foundation at coastal beach will be deformed under the load of border dike because of its creeping character.Foundation deformation will then lead to the change of foundation stress,and finally cause additional deformation and internal force in bridge piles.The change of foundation deformation and stress is slow and lasting,so the influence of additional deformation and internal force can't be ignored with the accumulation of time,severe cases can result in piles destruction and safety accidents.Applied basic research was performed in this thesis based on the scientific project from Zhejiang Provincial Communication Department named "space-time characteristic and countermeasure research on the influence of reclamation operations on coastal beach on adjacent bridge piles"(2014H39),laboratory tests and numerical simulations were conducted to research the temporal variation laws of the deformation and force of bridge piles at reclamation area after reclamation,the main contents of this thesis include the following aspects:Firstly,uniaxial compressive seepage-creep tests were conducted with the silt samples sampled from coastal beach area of Taizhou City,Zhejiang Province using the self-made test system,and the tests were conducted under one dimensional seepage condition.Creep curves and stress-strain isochronous curves under constant water head were obtained by the tests,permeability coefficients under different stress were also measured.Meanwhile,the creep constitutive parameters were obtained by data fitting.All this could provide evidence for the calculations and analysis of bridge piles under the condition of seepage and creep.Secondly,border dike-single pile-foundation analysis models which considered water invasion from open sea were created by the finite element software PLAXIS 3D,fluid-solid couple calculations were conducted under seepage condition which contained partial evaporation boundary.The laws of the influence of replenishment from open sea through the bottom of border dike on foundation seepage field and the deformation of single pile at reclamation area after reclamation were obtained,on the basis of which the calculations and analysis of different distance between border dike and single pile were conducted.The results showed that the deformation of single pile,affected by seepage field near border dike,was greater if the single pile was closer to the border dike.The deformation of single pile increased with time and the increasing trend alleviated with time.At the same time the closer the distance between border dike and single pile,the slower the increasing trend alleviated.But even if the distance between single pile and border dike was very small,the deformation of single pile was not large after a certain time when the reclamation was completed.Finally,border dike-pile groups-foundation analysis models which aimed at the creep characteristics of foundation were created by the finite element software ABAQUS,creep calculations were conducted under the load of border dike.Meanwhile,the scope and time history of the impact of border dike on pile groups after reclamation were obtained.The results of the calculations showed that:(1)The deformation of pile groups was greater if the pile groups were closer to the border dike.The deformation of pile groups increased with time and the deformation was mainly completed in the early period,the increasing amplitude became very gentle soon;(2)There were different deformation forms in pile groups with different distance from the border dike affected by the stress field of border and the creep characteristic of foundation.At the same time,partial body of the piles in front row and the piles in back row attracted mutually,here the front row and the back row were said relative to the position of the border dike.The attraction between partial body of the pile groups became significant with time;(3)A large axial tensile stress occurred in a small segment of the pile body near pile top because of the "buoyancy" in foundation on the condition of the big stiffness and large area of bearing platform,a relatively small axial tensile stress also occurred on other parts of the pile body because of the different deformation forms of the pile groups,and the tensile stress increased with time.The results of this thesis can provide a reference for long-term safety assessment of the bridge at reclamation area,so this thesis has a certain practical value.