Mechanical Properties of Microbial-induced Calcite Precipitation-improved Dredged Sediment as Road Subgrade Filling Material
Basic mechanical properties of microbial-induced calcite precipitation(MICP)-improved dredged sediment soil specimens made using a mixing method were investigated using various test techniques to investigate the feasibility of optimizing the improvement process and improving the road performance of a dredging sediment subgrade filler improved using MICP.Unconfined compressive strength(UCS),direct shear strength,and California bearing ratio(CBR)tests,and X-ray diffraction(XRD)and scanning electron microscopy(SEM)were employed to analyze the material composition and microscopic morphology of typical samples.The effects of different curing environments,curing times,percentages of bacterial solution dosing,and concentrations of cementing substance dosing on the mechanical properties of the MICP-improved dredged sediments were revealed.The results indicate that the mixed MICP method can be used for dredged sediment reinforcement,and the curing condition in a sound ventilation environment at 30 ℃ is more conducive for increasing the sample strength,which first increases and then decreases with an increase in cementing substance concentration.The shear performance gradually transitions from strain softening to strain hardening,and the UCS of the MICP-treated specimens increases from 0.16 to 0.96 MPa.The shear modulus E50,cohesion c,and internal friction angle φ also improve after curing for 14 d under the conditions of a 100％bacterial solution,1.0 mol·L-1 cementation level,30 ℃ ambient temperature,and favorable ventilation.The CBR,which typically characterizes the performance of road-filling materials,is improved by 5.0％.XRD and SEM analyses indicate that calcite crystallization formed between soil particles improves the mechanical properties of the specimens.The performance of the dredged sediment is significantly improved using the MICP-based mixing method,which satisfies the minimum requirements for roadbed fillers.Therefore,the improved dredged sediment soil can be used for roadbed filling.
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