Existing Piles Durability In Marine Environment Assessment Study

With the accelerated process of urban construction in China,building structure aging,degradation of mechanical properties,reduced service life,performance degradation of structural materials and other phenomena have become increasingly prominent.There are many researches on aboveground structure buildings in standardization construction,new materials development and computer simulation,but the underground structures,especially the existing pile foundation engineering research is relatively few.When the upper structure does not meet the requirements,the alteration or expansion will bring new challenges to the existing pile foundation and foundation treatment,especially for the golden section of the building structure of the impact is extremely prominent.In this paper,a coastal project in Qingdao as an example,for the re-use of the existing pile foundation,through the pile detection method and the corresponding technical means to the existing pile foundation in the project as the object of field tests and laboratory tests,the durability of the existing pile foundation is studied and the corresponding evaluation method is used to analyze.Through the comprehensive testing of the existing pile foundation,the concrete performance parameters of the existing pile foundation are obtained,which can be used as the basis for the analysis and appraisal,and then evaluate the engineering value possessed by the existing pile foundation.The main contents and conclusions are as follows:(1)According to the material factors such as the concrete carbonation of the pile,the corrosion of the steel bar,the chloride ion erosion and the stability caused by the calcium oxide.Analysis of these factors affect the mechanism of structural durability of concrete pile and comprehensive analysis on this basis.(2)Through the durability test of the existing pile foundation,the carbonization depth,steel corrosion degree,chloride ion content and calcium oxide content of the pile foundation concrete were detected and identified.Determination of these factors damaging effects on the pile and specific distribution law of development.(3)Through the detection of core sampling,concrete strength compression test,on-site static load test,low strain testing.Analysis of existing pile foundation bearing capacity and integrity.(4)According to the importance of factors influencing the durability of pile foundation,the factors of durability can be obtained under the influence of different factors.The grade of each influencing factor is weighted and the durability grade of the pile foundation is obtained.(5)Select the marine environment of chloride ion penetration as the main influencing factors,in order to deduce the life cycle of piles with the rate of chloride ion corrosion and the degree of corrosion of steel bars.The time of chloride ion eroding the concrete components of pile foundation was obtained respectively.(6)Through ABAQUS software for numerical simulation,comparative analysis of the pile at three different stages under the load the effect of the displacement of the settlement:(1)pile of concrete protection layer is not damaged,sedimentation and changes under load bearing capacity of the intact state.(2)Under the influence of chloride ion,the settlement and bearing capacity of the pile are changed after the failure of the protective layer.(3)Under the influence of chloride ion,the protective layer fails,and the settlement of the pile under the load and the change of the bearing capacity when the steel bar is corroded to 95% of the original cross section.By comparing the above three kinds of changes,the pile foundation settlement and stress analysis at different stages are analyzed,test values of the pile in the field and the changes of the three different stages.It is deduced that the limit values of the bearing capacity of the three stages are 6000 KN,5400KN and 5400 KN respectively.