The Mechanical Behaviors Of Microbial-induced Calcite Precipitation Sand

Microbiologically Induced Carbonate Precipitation?MICP?is a process that bacteria hydrolyse urea and carbonate is produced,which in turn results in the precipitation of calcium carbonate?CaCO₃?in the presence of a calcium source.Because of its sustainable and environment friendly characteristics,The precipitated calcium carbonate distributed spatially within the pore space in the form of stable bonded structure between soil particles.In recent years,the MICP is widely used as an alternative soil treatment technology to improve its engineering properties such as strength and impermeability.In this paper,the use of MICP technology to improve the sand,by comparing the mechanical properties of treated sand and pure sand,to explore the improvement effect of the method.In addition,the microbiological improvement process of sand was explored by numerical simulation to investigate the uniformity of the treated soil sample.,The main work in this study are as follows:1.By Using the MICP method to improve the standard sand,the treated sand was successfully prepared by grouting solution from the bottom of the sand column.The composition of the modified sand was analyzed by X-ray diffraction?XRD?.The results show that the calcium carbonate were foundin the composition.The microstructure of the treated sand was also analyzed by Scanning Electron Microscope?SEM?.The results suggest that calcium carbonate crystals were formed between the surface of the sand particles and the pores with a typical crystal size of 5–50um.These calcium carbonate crystals mainly acted as bridges between the sand particles and form stable bonded structure.2.Conventional triaxial tests under different confining pressue are used to investigate the mechanical properties of sand and MICP treated sand.The results suggest that the peak strength of treated sand is about 4-21 times of that of pure sand,indicating that the improvement effect of the is significant.Compared to sand,MICP treated sand shows the obvious strain softening after peak strength and strong dilatancy.3.MICP treated sand exhibit strong cohesion and bonded structure.Based on the super-loading and sub-loading yield surfaces,an elastoplastic constitutive model for MICP treated sand considering cohesive strength was established by introducing cohesion and its evolution law in the loading process.The model is used to predict mechanical behaviors of the pure sand and treated sand in the triaxial tests under different confining pressures.The results show that the proposed model can well describe the strain softening and dilatancy of the treated soil induced by failure of bonded structure.4.By using numerical simulations,involving convection,diffusion and reaction,.the whole process of MICP in continuous flow column system and the uniformity of treated sand sample are consideredThe results show that injection velocity greatly affects the uniformity of treated sand sample.