Study On The Influence Of Sand Blasting Cofferdam On The Mechanical Performance And Construction Quality Of Cast-in-place Bridge

Blowing sand cofferdam is an artificial cofferdam,which takes "mold bag sand" as protection slope,and the middle of it is filled with blowing sand.As a new construction technology,blowing sand cofferdam is widely used in the cofferdam construction of the river,lake or sea.And in recent years,many projects have attempted to use the blowing sand cofferdam as the artificial foundation of cast-in-situ structural bridge.However,as the foundation of cast-in-situ bridge’s bracket,there are few researches on the bearing capacity and deformation performance of it.This thesis takes the 2#bridge of NaChao river in Tangshan city as the project background,studies the strengthening mechanism of geotextile tube,And use the ANSYS software to establish the finite element model of cofferdam,analyzes the deformation behavior of cofferdam under the action of support and superstructure,and also studies the influence of settlement on the different construction stages of the main girder.Firstly,based on the theoretical analysis,the thesis puts forward the calculation formula of equivalent cohesion for the sand filled bag,which is in different buried depth.And also the thesis puts forward a calculation formula about the shape of sand filled geotextile tube that under it’s own weight and the external loads.With the help of Matlab the thesis analysis the effects of cofferdam’s extrusion stability that causes by cofferdam’s top width,height,slope of the cofferdam,single tube bag’s width and height etc.At last the theory of ground settlement is briefly introduced.Secondly,establish finite element models of single sand filled geotextile tube,analysis the behavior of sand filled geotextile tube,which under it’s own weight and the external loads.Through the establishment of finite element model of geotextile cofferdam,the thesis studies the vertical and lateral deformation in the different thickness of the concrete slab and steel beam.And then according to the actual construction method of the bridge,the thesis analyzes the influence of the settlement of the cofferdam on the cracking of the bridge and the early age of the concrete.And also the thesis analyzes the mechanical behavior during operation under the influence of the linear error caused by the early settlement.According to the analysis results the thesis provides basis for further similar geotextile cofferdam design and construction to create social benefits and economic benefits.Finally,according to measuring results,the thesis find out that the naturally subside of geotextile cofferdam in the first 200 days is faster than later stage.And as time goes on the settlement goes slowly and finally reach a steady-state.By comparing the settlement measuring data between two sides and middle of cofferdam,it’s found out that the settlement rate in middle of the cofferdam is lower than that of the two sides.This is mainly because the drainage conditions are poor in the central of cofferdam,so consolidation settlement develops slowly.The sand blowing cofferdam has many advantages,such as convenient to get materials,simple construction,lower cost of project,less environmental pollution,and so on.As the sand blowing cofferdam has obtained good application effect in the 2#bridge of Nachao river,it can be used as a reference for similar projects...