The Study On The Premeability And Foundation Improvement By Vacuum Preloading In Wenzhou Area

Dredge fill,which is generally distributed in the coastal areas as the special soft soil,has really some different properties,such as:high natural water content,low shear strength,poor permeability,consolidation for a long time and so on.It becomes one of the important contents in geotechnical engineering to study the characteristics and reinforcement of dredge fill,in order to meet the project needs.At present,vacuum preloading is the main method of foundation reinforcement.After several decades of development,although it has been more mature,there are still a lot of problems in projects,due to the particularity of the dredge fill and the defect of construction.The thesis which put the dredge fill in Wenzhou as the object of study,made some research about permeability characteristics and consolidation mechanism through the indoor test,on-site monitoring and theoretical analysis.The main contents and innovation as follows:For the indoor test,the influence factors of the permeability coefficient were analyzed one by one.The permeability coefficient is a direct parameter reflecting the permeability characteristics of the dredge fill.By various contrast experiments,the wall effect is confirmed which has made a significant change.The difference between the sampling methods has been tested.The water temperature has also been considered;the reasonable range of the height of water head was determined;the influence of the permeable stone has been observed on the experimental precision.It provides some data references and theoretical basis for the accurate determination of permeability coefficient of dredge fill.The changes of void ratio,permeability coefficient and the test of high water head were studied by modify the equipment under different consolidation pressures.The curve of void ratio and permeability coefficient was obtained during the consolidation process of dredge fill,and it also proved the applicability of Taylor formula in Wenzhou area.The situation of penetration test under high water head was analyzed,and some suggestions for improvement were given.Combined with the project,the principle and construction steps of the air booster vacuum preloading were described.The theory of consolidation of soft soil is explained,and the change of soil infiltration characteristics during the pressurization process is put forward by data analysis and cujrve fitting.The results show that there is about 1.5 times increment about the permeability coefficient,and it was verified by the analysis of the relevant literatures.Finally,an improved vacuum preloading method was proposed.Through the model test,the results show that the vacuum transfer efficiency is higher and the consolidation effect is better under the same drainage board spacing,compared with the traditional vacuum preloading method.It is of great significance to save the-project cost and shorten the construction period.In addition,the test also proved the change in permeability coefficient during vacuum preloading,that is,the permeability coefficient becomes smaller,the speed of soil consolidation gradually slows down.