Study On Solidification Characteristic And Failure Mechanism Of Microbial Cemented Sand

Microbial induced calcite precipitation（MICP）technology is a microbial based foundation soil treatment technology,which has the characteristics of non-polluting,sustainable,low energy consumption,and this technology has been used in many different applications.Currently,the research of MICP to improve the macroscopic mechanical properties of sand are more focused on the impacts of cementation concentration,injection velocity,bacteria concentration and other single factors on the mechanical properties.Few studies have been conducted on the solidifacation effect under the comprehensive effect of multiple influencing factors.In addition,most of the current investigations are about the mechanical behavior of microbial cement sand from a macroscopic examination or analysis through physical experiments and the meso-structure of the cement-bound sand structure has not been fully considered.However,the mechanical properties of the microbial cement sand after cementing,such as the strength,crack resistance,are closely related to the meso-structure.Therefore,how to use the advanced technical means to systematically study the mechanism of cementation and fracture of the microbial cement sand under the comprehensive effect of multi-factor and to overcome the shortcomings of existing research have become the basic problems that need to be solved at present.In this paper,the analysis of multi-scale structural mechanics response under the comprehensive effect of multiple factors,the solidification mechanism of microbial cemented sand and the fracture characteristics of cemented structure under thermo mechanical coupling were studied.The main research results obtained are as follows:（1）The mechanical behavior of the cemented sand structure under the comprehensive effect of multiple factors was studied.The uniaxial compresson failure and stress-strain relationship of cement-bonded sand structure under different conditions were analyzed.Ultimately,the optimal scheme combination was determined through the sensitivity analysis of influencing factors,which provides a theoretical basis for obtaining high strength cemented soil.（2）The influence of spatial distribution,crystal content and crystal size of calcium carbonate on the response of structural mechanics,and the pore size distribution of microial cement sand was obtained.The process of mineralization and the effects of Ca²⁺concentration and OD₆₀₀ on the morphology of the crystals were analyzed.The four-stage process of microbial mineralization has been proposed and the intrinsic mechanism of the loose sand body of the microbial cement was revealed,which provides the basis for the further modeling of the microbial cement sand.（3）The mesoscopic modeling method for microbial cement sand structure has been proposed.An irregular particle generation algorithm that characterizes the irregular shape of calcite was developed.A microbial cement sand model was established to match the shape and proportion of the actual irregular calcite.The contact model between the meso-particles was determined,and the parameters of the meso contact model were calibrated.These investigations have provided reliable technical means for revealing the fracture mechanism of microbial cement sand structure from a mesoscopic examination or analysis.（4）The study on the failure mechanism of cement sand structure based on PFC simulation was conducted.Based on the moment tensor theory,an acoustic emission algorithm was developed.The distribution characteristics of moment magnitude under the uniaxial compression of the microbial cement sand were investigated.Considering the effect of temperature,the damage mechanism of the cemented sand body structure under various strains were analyzed.The results can be used to provide effective and controllable theory and technical support for the application of the consolidation of sand under complex geological conditions.