Research On Soft Soil Reinforcement Method Of Vacuum Drainage Combined With MICP

Due to the poor engineering properties of silt soft soil,it is easy to cause problems such as foundation instability,foundation pit deformation and pile foundation failure,which lead to many geological disasters.Therefore,more effective measures must be taken to enhance the mechanical properties of soft soil and improve the bearing capacity and deformation resistance of soft soil foundation when construction is carried out on such soil.In this paper,a new method of vacuum sand well drainage combined with MICP is proposed to strengthen soft soil.The soft soil was strengthened through several joint strengthening stages under laboratory conditions,and the solidification effect and mechanism of vacuum drainage combined with MICP were analyzed through the basic physical parameters,shear strength,compression consolidation index,unconfined compressive strength and microstructure characteristics of soil samples.The influences of curing days,cementing fluid concentration and the number of sand well channels on the properties of solidified soil samples were investigated.The main research contents and conclusions are as follows:(1)In this paper,Bacillus pasteurii was used as the solidified strain in this experiment.Through activation and expanded culture of the strain,the variation curve of the concentration and urease activity of the microbial liquid with time was plotted,so as to select the appropriate growth conditions for the cultivation of bacterial liquid for the subsequent MICP grout test.(2)The traditional indoor vacuum drainage test was improved by replacing the film covering with the horizontal and vertical plastic drainage pipes,and the sand well drainage channels were set in the soft soil samples.The test results show that the basic physical parameters,shear strength,compression characteristics and consolidation rate of the soil samples are significantly improved after the vacuum sand well drainage treatment,and the more the number of sand Wells in the soil sample,the better the drainage effect is,and the more significant the strength improvement is.(3)MICP pressure grouting test was conducted on the samples after vacuum sand well drainage treatment.The results show that the vacuum sand well drainage combined with MICP grouting treatment can effectively improve the unconfined compressive strength,shear strength and compression performance of soft soil,and reduce its water content,porosity ratio and consolidation coefficient.It is found that the longer the curing age,the more sand Wells,the better the solidification effect of soil samples,and there is an optimal value of cement concentration ratio during MICP pressure grouting.(4)Scanning electron microscopy(SEM),X-ray diffraction(XRD)and calcium carbonate content determination were used to study and analyze the strengthening effect and influence mechanism of vacuum drainage combined with MICP grouting method from three aspects of microscopic morphology,phase composition and quantitative measurement.The results show that calcium carbonate is formed in the sand well and the surrounding soft soil area of about 10 mm in the vacuum drainage combined with MICP solidified soil sample.The calcium carbonate fills the soil pores,strengthens the bond between soil particles,and improves the soil integrity.This paper proposes and verifies the feasibility and effectiveness of the new method of soft soil foundation treatment,namely vacuum sand well drainage combined with MICP.At the same time,through a series of tests,the influence of curing days,the concentration of cementing liquid and the number of sand Wells on the curing effect was explored,and the related properties of solidified soil samples were analyzed.To a certain extent,it broadens the application scenarios of MICP in soft soil foundation and provides experimental and theoretical support for subsequent practical engineering applications.This paper proposes and verifies the feasibility and effectiveness of the new method of soft soil foundation treatment,namely vacuum sand well drainage combined with MICP.To a certain extent,it provides experimental and theoretical support for subsequent practical engineering applications.