| Microbial-induced calcium carbonate deposition to solidify dredged fill soft soil is a new way to treat dredged fill soft soil foundation.By injecting bacteria solution and nutrient salt solution,calcium carbonate is induced to deposit in the pores of dredged fill soft soil particles,and calcium carbonate minerals solidify and bond the soil particles to form a cementing body with certain strength.In this paper,the mechanical properties,macro-characterization and micro-mechanism of solidified soil under various influencing factors are systematically analyzed and studied through indoor soft dredger fill soil column layered grouting experiment,on-site soft dredger fill grouting solidification experiment and a series of geotechnical tests.Through the activation,culture and preparation of Bacillus pasteurianus freeze-dried powder,the number of bacteria and p H value of bacteria were measured.The change of p H value was positively related to the number of bacteria and urease activity.Through the density,permeability,calcium carbonate increment,unconfined compressive strength and freeze-thaw characteristics of laboratory solidified soil column,the interrelation under the influence of different factors is analyzed.The on-site curing effect is evaluated through the bearing characteristics and curing depth of soil.The mechanism and image of soil solidification were characterized and analyzed by optical microscope,scanning electron microscope and X-ray diffractometer.The ductility and deformation capacity of solidified soil are better than those of concrete and rock,and can still bear certain load after the soil column is damaged.The calcium carbonate increment and strength of calcium chloride sample are significantly higher than those of calcium acetate and calcium nitrate samples.Solidification strength of soil with high fine particle content is obviously lower than that of soil with high sand particle content,while calcium carbonate content will increase with the increase of fine particle content in soil.The damages occurred in 25 freeze-thaw cycles mainly occurred in the parts where the soil did not get good solidification.Silty fine sand layer in soft dredger fill can be effectively solidified on site,and mixed lumpy clay and silty clay layer have poor solidification effect on site.The microscopic mechanism shows that bacteria induce calcium carbonate to form and bind solidified soil particles,mainly in two aspects: on the one hand,bacteria attached to the surface of soil particles are used as nuclei to form calcium carbonate crystals to bind adjacent soil particles;on the other hand,flocculent substances are formed between the particle voids,which deposit and wrap some soil particles and gradually form calcium carbonate aggregates to bind soil particles. |
