| At present,landfilling has become an important means and trend to solve the worsening scarcity of land resources in coastal areas,and has been widely used in coastal cities of China.Due to the extremely poor engineering properties of ultra-soft soil foundation formed by landfilling,its reinforcement treatment is a core technical issue of concern to engineering and academic circles.This paper takes the newly dredged fill soil in Tianjin Binhai area as the research object,and uses a series of laboratory tesst and basic theoretical research to change the chemical environment of the dredger fill by adding different chemical reagents,using direct shear test,one-dimensional compression test and three-axis test.A series of macroscopic tests such as shear test to explore the macroscopic mechanical properties of dredger fill under different chemical environments;combined with ICP elemental analysis experiments,XRD diffraction experiments,mercury intrusion experiments,SEM electron microscopy scans to analyze the chemical environment affecting the mechanical properties of dredger fill Micro-mechanism;using the indoor chemistry-vacuum pre-compression combined with the reinforcement of the model test of the dredger fill,provides a theoretical basis for effectively improving the reinforcement effect of the dredger fill and improving the reinforcement technology.(1)The test results show that in the acidic environment,the intergranular cement of the dredger fill is destroyed,the cementation strength is reduced,the shear strength is reduced by 1.72 kPa to 12.65 kPa,and the compressive deformation is increased by 10.4% to 47.9%.The stress is reduced by 7.5% to 50.7%.Under alkaline conditions,there are a large number of highly reactive hydroxide ions,which react with magnesium ions and silica in the soil to form a large amount of insoluble substances such as magnesium hydroxide and silicate.It has been improved.The microscopic test shows that the dredged soil particles aggregate to form agglomerate structure.The shear strength increases by 15.2~79.3kPa,the structural yield stress increases by 10.6%~252.2%,and the compressive deformation decreases by 3%~33%.The stress-strain relationship is the strain hardening type transition is a strain softening type.When the dredger fill is in a salty environment,due to the hydrolysis and crystallization of sodium sulfate,the influence on the strength and deformation of the dredger fill is significant,and the difference is obvious under different water content conditions.(2)Exploring the reasons for the failure of conventional vacuum preloading reinforcement,mainly because the soil particles migrate under the action of vacuum pressure,and the formation of silt mud layer near the drainage board leads to a decrease in the permeability coefficient;The microscopic characteristics can be found that the alkaline environment is conducive to the aggregation of soil particles to form agglomerate structure,and the large-diameter pore content of the pores larger than 2 μm in the soil increases by 6.8%,which can effectively improve the permeability of the dredger fill.Therefore,the alkaline environment has a significant effect on improving the vacuum preloading reinforcement effect.(3)The effective chemical modification treatment of the dredger fill by adding different amounts of sodium hydroxide,and then the vacuum preloading test,the results show that the drainage efficiency and reinforcement effect in the test process are greatly improved.The maximum increase of displacement is 17.6%,and the shear strength of soil cross-section after reinforcement is increased by 69.0%.For Tianjin Binhai newly-filled fill,the optimal addition amount of sodium hydroxide is 4%,and stable drainage is achieved during the test.Time calculation can save about 20%~30% of construction period and construction electricity consumption,and the economic and social benefits are remarkable. |
