Improvement Of Vacuum Preloading On Soft Clay Foundation By Hydraulic Filling And Its Clogging Mechanism

In the coastal area of Southeast China,a lot of soft clay brought by artificial hydraulic fill was produced by cofferdam reclamation and river dredging.At present,despite that the super soft soil foundation by the Hydraulic Filling is mainly strengthened by the vacuum-PVD consolidation method,Indeed,Vacuum preloading reinforcement effect is limited by clogging in practice of foundation reinforcement,which has plagued theoretical research and engineering practice.Although the new anti clogging materials and construction technology is the current hot spot to overcome the problem,however,the clogging problem and its microscopic mechanism have not been solved completely..In this paper,colloidal chemistry knowledge is introduced into this studyby means to indoor model test,colloid testing,microstructure test,calculation of the semi permeable boundary finite element consolidation,field testing,the mechanism of the existence and movement of the colloid in the vacuum preloading of soft soil foundation is discussed.The main conclusions are as follows:The new anti clogging indoor model test found that the time of vacuum in the soil is lagging behind the pump opening time,and achieve stability very soon;.The soil moisture content of 0-4cm was the largest,and the intensity was the highest,the soil particles are concentrated near the drainage plate,which shows that the phenomenon of 'soil column'.For the model test,the water content is almost equal as the vacuum time is more than 43 days,that is,the vacuum preloading time is not as long as possible,but there is an effective time.In contrast to the tail water properties under before and after the stoving experiment,and found water vacuum colloidal particles with different periods of Tyndall experiment of tail water;then,the Zeta potential test and the laser particle size analysis were carried out to determine the stability and distribution of colloids.Meanwhile,the mercury intrusion test is carried out to determine the pore size distribution characteristics of the 'soil column';According to the shape of the tail water colloid,the mechanism of soil column clogging is expounded.Numerical simulation of finite element calculation results show that the soil consolidation degree near the drainage plate increased rapidly at the initial stage of loading,while the permeability coefficient and consolidation strength of peripheral soil is basically no change;Radial soil of drainage plate consolidate from the near to the distant in turn.with the continuous vacuum pumping,the drainage performance of the soil around the plate is reduced,and the semi permeable boundary is formed.Therefore,the permeability coefficient varies with the size and distribution of leachate colloidal stability of morphological changes of the semi-permeable boundary consolidation model to improve the analysis precision and reliability of the results in the reclaimed soft soil consolidation calculation,and can verify the "soil column" phenomenon in the indoor model test and field test.Through the field test,the new anti clogging construction technology of vacuum preloadingdevelop that the traditional drainage plate was placed by the anti-clogging drainage plate,the horizontal bellows were replaced by wired hose with no holes in connection mode,at the same time,the traditional binding bundle has been improved into a three way sealing joint,which is the further improvement of the direct discharge vacuum preloading method.Dynamic monitoring and reinforcement quality detection in the vacuum preloading project of the Hengda Sea Flower Island in Hainan Province found that although the technology can improve the quality of vacuum preloading,the quality can be further improved after the introduction of colloidal treatment technology.