Technical Scheme Design And Field Test Of Soft Foundation Treatment In The Fifth Contract Section Of Nanyi Expressway

In order to further find the treatment method of soft soil foundation suitable for Dongting Lake plain,the soft soil foundation of the north section of Nanxian-Yiyang e xpressway is selected as the research object,considering the complexity of geological st ructure,the depth of soft foundation treatment,the simplicity of construction,construct ion period and economy.Fromfive schemes of Drainage consolidation method,Riprap co mpaction withDynamic replacement,Bored pile,Cement-soil mixing pile,PHC tubular pil ecomposite foundation,the more suitable cement mixing pile composite foundation and PHC pre-stressed pipe pile composite foundation are selected as the treatment schem e of the soft soil foundation.The idea ofpile foundation selectionand design parameters of composite foundation in the north section of Nanyi Expressway are discussed.Drill ed core method andLow strain testare carried out on the treated foundation respectivel y.Through the analysis of the experimental results,the quality of piles formed by the t wo treatment methods can meet the design requirements,which can play an expected role in enhancing the bearing capacity of foundation and reducing the settlement of fo undation.Finally,the tatic Load Testingof soft soil foundation under two treatment meth ods is carried out.After obtaining the experimental results verified by theoretical calcul ation,according to the experimental results and the problems in the construction proce ss,the social and economic benefits brought by the two treatment methods,the more suitable treatment methods for soft soil foundation in Dongting Lake Plain be will sel ected.Through statistical analysis,4170 cement-soil mixing piles and 408 PHC piles a re tested under static load according to relevant codes,and the construction quality,co nstruction technology and economy of the two schemes are compared and analyzed.It is found that the former has advantages in economy,but the latter has more remarka ble reinforcement effect.It is concluded that the most economical and scientific treatm ent methods should be combined according to different geological conditions.The cont ents and results of this paper are as follows:(1)Through in-situ test in situ testing and laboratory test the physical and mechanical properties of soft foundation soil widely distributed in the treatment section,and the b earing capacity of natural foundation of rock.(2)According to the geological report of engineering survey and the experience of rel evant cases,cement mixingand PHC pipe pile composite foundation are selected from the five treatment schemes.(3)The design parameters of cement mixing pile and PHC pre-stressed pipe pilecomp osite foundationare determined,and their bearing capacity and settlement are calculated respectively.The calculation results are verified by field experiments.(4)Through the analysis of the results of field static load experiment,it is verified wit h the results of theoretical calculation.At the same time,the relevant conclusions of th eoretical calculation can be used to help improve the field experiment(5)From the perspective of construction technology,construction quality and economy,It is concluded that according to the actual situation,a scientific treatment scheme co mbining various treatment methods is the best one for soft foundation treatment.