Settlement Prediction And Numerical Analysis Of Dredger Fill And Soft Foundation Consolidated By Vacuum-loading Preloading

With the large-scale construction of national infrastructure and the rapid and steadily economic development,land resources are increasingly scarce.This phenomenon is particularly common in our developed coastal areas with a large population and scarce land.Seizing land resources into oceans is a common method for the development of coastal areas,and more and more land is composed of dredger fill formed by the reclamation project.Due to the characteristics of high filling rate,large void ratio,high compressibility,poor permeability,low natural strength and high sensitivity,dredger fillings themselves are underconsolidated soils.Under the action of self-weight stress,gravity of upper fill and consolidation settlement generated during construction,it is incapable to directly build industrial buildings,docks,airports,highways,houses and other structures on dredger fill.Because of its simple equipment,easy operation,large area for reinforcement,low energy consumption,good reinforcement effect,short pre-press time and no environmental pollution,vacuum preloading is an effective method and has been well applied to consolidate dredger fill.(1)This study analyzed the reinforcement effect of vacuum preloading combined with surcharge preloading on dredge fill foundation in a port dredging and filling project at Guangzhou,based on a large number of monitoring data,in-situ tests and indoor geotechnical tests.I also summarized the range and merit and demerit of various prediction models of foundation settlement,and select each individual model and combined models to predict the foundation settlement.In addition,the finite element simulation software Midas GTS NX was employed to conduct the numerical simulation of the whole process of vacuum preloading combined with surcharge preloading on dredger fill.The main content of this study are as follows:(2)This study analyzed geological conditions and soil characteristics of different areas of the study field and compared physical-mechanical parameters between the soft soil and dredger fillings,in order to understand engineering characteristics of the soft soil and dredger fillings.Combined with grain size analysis of laboratory experiment and physical-mechanical parameters of dredger fillings,this paper explored engineering characteristics of the soft soil and dredger fillings in the study areas.Through the analysis of the in-situ monitoring data and the data of in-situ test and indoorgeotechnical test of vacuum preloading combined with surcharge preloading on dredge fill foundation,this paper studied the vacuum degree,pore water pressure,surface settlement and stratified settlement.Drilling sampling for in-situ vane shear test and indoor geotechnical test were also carried out.These works revealed the settlement and consolidation of dredge fill foundation after the treatment of vacuum preloading combined with surcharge preloading,and the characteristic of strength increase of dredge fill foundation.The physical mechanical parameters of dredge fill foundation before and after reinforcement were analyzed in order to evaluate the effect of reinforcement treatment.(3)The exponeitial curve method,hushino method,asaoka method and hyperbolic method were used to predict the settlement separately.Then,three combined prediction models were proposed.Combined with the field data,this study compared the result of each single prediction model with the result of each combined model,and analyzed the prediction accuracy of various prediction models.Our result showed the accuracy of combined prediction models were higher than that of single settlement prediction model,and the entropy weight method was the best model with the highest accuracy to predict settlement in our study field.(4)Using the finite element simulation software Midas GTS NX,based on the Biot consolidation theory and elasto-plastic model,this study conducted numerical simulations using field engineering parameter data derived from vacuum preloading combined with surcharge preloading on dredge fill foundation.Comparative analysis showed that the simulation results are in good agreement with the field test results.