Research On The Application Of Vacuum Preloading On Soft Foundation With Straight-Line And Long-Short Plastic Drainage Board

In recent years,vacuum preloading has been widely applied in the large area of sludge,mucky soil,dredger fill and other soft soil foundations reinforcement,due to its advantages of simple process,short construction period,large area of one-time reinforcement,low cost,no pollution,etc.And it has achieved good economic and social benefits in practice.However,the existing design and construction plans of vacuum preloading have mainly based on the approximate solution of Consolidation Theory and previous engineering experience,which has certain limitations.Therefore,it is of great theoretical value and practical value to further study the soft soil foundation reinforcement with vacuum preloading,which is helpful for the further development and improvement of vacuum preloading in engineering practice.This paper was based on the research background of a project that soft foundation was improved by vacuum preloading,which adopted a vacuum preloading method that had the combination of straight-line vacuum pre-compaction technology and long-short plastic drainage board.At present,there is not many articles on the analysis and research of this method.The research and analysis were carried out from the three aspects of field test data analysis,settlement prediction and numerical simulation,the research contents and conclusions were as fo lows:(1)Combining with on-site test data,the variation of under-membrance vacuum degree,surface settlement,layered settlement,and pore pressure in vacuum preloading process were analyzed in detail.Moreover,the reinforcement effect was evaluated.It was concluded that the application of straight-line and long-short plastic drainage board vacuum preloading reinforced the dredger fill foundations obviously,and can effectively relieve the phenomenon of soil co umn.(2)The applicability of these four methods was analyzed contrastively,by using Hyperbolic method,Three-point method,Asaoka method and LM-BP Neural Network for settlement fitting and prediction based on the measured data.For later construction settlement prediction,the prediction value of Three-point method and LM-BP Neural Network was smaller than the measured value,while the prediction value of Hyperbolic method was larger than the actual value,and the relative average error of the predicted results by these three methods were less than 0.6%,indicating that the prediction accuracy of the three methods can meet the requirements of this project.For the prediction of the final settlement,it was concluded that the predicted results of Three-point method and Asaoka method were less than Hyperbolic method,and Hyperbolic method was recommended for the higher engineering usage requirements of foundation.(3)Combining with project example,adopting the equivalent method of the sand wall and considering the attenuation law of negative pressure along the depth,the numerical calculation and analysis of vacuum preloading settlement and pore pressure were completed using by FLAC3D software.The settlement calculation precision was higher,it was verified for the foundation of long-short plastic drainage board that vacuum preloading settlement simulated calculation was feasible with the equivalent method of the sand wall,and there was a certain guiding effect on the settlement estimation of super large area vacuum preloading in the second phase.On the basis of the original model,the quantitative analysis of the influence of vacuum degree,drainage plate layout and spacing on the settlement of vacuum preloading foundation were completed.