Experimental And Theoretical Study On The Treatment Of Dredged Slurry By Vacuum Preloading With Reverse Prefabricated Vertical Drain

In recent years,with the development of construction of coastal city waterways,river dredging,and port engineering,a large amount of dredged slurry will be produced annually.Due to the unfavorable engineering characteristics of such dredged slurry,such as high water content,low shear strength,and low permeability,it is not possible to construct production directly on such foundations.Therefore,a fast and effective foundation treatment method is needed to treat these high water content dredged slurry.Currently,vacuum preloading method has been widely used in engineering practice due to its low cost,simple construction process,and good treatment effect.However,through a large number of laboratory tests and analysis of engineering site test data,due to problems such as vacuum pressure loss and clogging effect,the treatment effect of the soil is often poor,leading to some engineering accidents.How to solve the engineering problems of conventional vacuum preloading method and achieve rapid consolidation of dredged slurry has become an important research direction in the field of vacuum preloading.This article focuses on the land reclamation project of Wenzhou City,Zhejiang Province,and conducts relevant research on the vacuum preloading-reverse prefabricated vertical drain method proposed by the Zhejiang Provincial Key Laboratory of Soft Soil Foundation and Coastal Reclamation Engineering Technology.A series of laboratory model tests and theoretical analyses were carried out,and the main research contents and achievements are as follows:1.A laboratory model test was conducted on vacuum preloading method and vacuum preloading-reverse prefabricated vertical drain method to explore the superiority of vacuum preloading-reverse prefabricated vertical drain method in treating dredged slurry.Through comparative analysis of the test results,it was found that the vacuum preloading-reverse prefabricated vertical drain method had a better treatment effect on the soil.2.In response to the clogging effect in the process of vacuum preloading method treating dredged slurry,this article proposes to use reverse prefabricated vertical drain for pressure increase.Different pressure increase durations were used to provide theoretical support and scientific evidence for the design and construction of large-scale dredged slurry foundation reinforcement treatment.The results showed that using reverse prefabricated vertical drain for pressure increase had a significant improvement effect on the clogging effect,and the optimal pressure increase duration was 45 minutes.3.Based on Hansbo’s sand well consolidation theory,a consolidation calculation method for vacuum preloading-reverse prefabricated vertical drain method considering vacuum pressure attenuation and clogging effect is proposed.Subsequently,a sensitivity analysis of parameters was conducted,and the numerical calculation results were compared and verified with the experimental results.The results showed that the lower the permeability coefficient or the larger the clogging radius in the clogging zone,the slower the consolidation rate.The larger the well diameter ratio,the longer the drainage path,and the poorer the reinforcement effect.The more vacuum pressure attenuation,the less dissipation of average pore pressure,and the worse the consolidation effect.4.Based on the assumption of equal strain,the consolidation equation considering linearly decreasing soil column radius with depth was derived.The calculation results show that the smaller the permeability coefficient of the soil column in the clogged zone,the slower the dissipation of pore pressure,and the slower the consolidation rate of the soil.The larger the radius of the soil column,the lower the consolidation rate of the soil.The smaller the residual coefficient of the soil column radius after decay,the greater the degree of decay of the soil column radius,and the faster the consolidation rate of the soil.Considering the decay of the soil column radius,the calculation results are in good agreement with the experimental results.