Studies On Soil Consolidation Performance And Control Of Microbe Induced Calcium Carbonate Mineralization

Microbial induced calcium carbonate precipitation（MICP）can be used to consolidate soil in geotechnical engineering.Compared with traditional chemical and physical soil consolidation,MICP technology has the advantages of easy operation and environmental friendliness.However,for different soil substrates,how to achieve excellent mineralization effects has not yet been studied in depth.In this paper,different soil bodies are used as the research object,and the Bacillus Pasteurella hydrolyzed urea is used to mineralize calcium carbonate to consolidate the soil.The influencing factors and soil-fixing performance of the MICP mineralization process are systematically studied,and the soil-fixing performance is explored.The interaction relationship between calcium carbonate and calcium carbonate;in addition,this article also innovatively uses small molecular substances as regulators to regulate the formation of calcium carbonate in the MICP system to improve the consolidation effect of small-sized soils.In this paper,the controllable adjustment of the mineralization process of MICP in different soil matrices is realized by controlling the mineralization process.Firstly,the influence and mechanism of different factors on the precipitation of calcium carbonate in the MICP system are explored.By changing the pH value of the environment and adjusting the ratio of different Ca²⁺and NH₄⁺,the concentration of the bacterial solution(OD₆₀₀),and the reaction time,the changes of calcium carbonate were explored.（1）Calcite-type calcium carbonate crystals are more likely to appear when pH>8;（2）When the initial urea concentration is 20 g/L and the molar ratio of Ca²⁺and NH₄⁺is4:1～1:1,vaterite-type carbonic acid is easily formed Calcium crystals;（3）With the prolongation of the reaction time from 6 h to 72 h,calcium carbonate crystals gradually transformed into calcite type.（4）As the concentration of the bacterial solution decreases from 2.0 to 0.6,calcium carbonate crystals change from a mixed crystal form of vaterite and calcite to a calcite type.Secondly,a free infiltration device and a flexible mold made of geotextiles are used to conduct experimental research on the consolidation of soils,and a series of analysis methods such as FTIR,SEM and unconfined compressive strength are used to explore the curing effect of MCP on different types of soils.（1）Under the reaction conditions of OD₆₀₀of 0.3 and Ca²⁺concentration of 0.3 mol/L,the consolidation effect on coarse sand is the best,with unconfined compressive strength of 2.15 MPa;（2）OD₆₀₀ of 0.6,and Ca²⁺concentration of 1.0 mol/L is the most suitable for the consolidation of fine sand,and the unconfined compressive strength is 3.42 MPa.The results also show that the consolidation strength of different soils is related to the size of calcium carbonate.The larger the size of calcium carbonate produced in coarse sand,the higher the unconfined compressive strength;on the contrary,fine sand produces calcium carbonate with small particle size and high unconfined compressive strength.In addition,this research innovatively adjusts the morphology and particle size of calcium carbonate by adding modifiers to the MICP system,which has a better consolidation effect on fine sand with a small particle size and soil with a smaller particle size.Studies have shown that:（1）the addition of citric acid and ammonium citrate has a better solidification effect on small-grain sand.The maximum mechanical strength of fine sand is 2.69 MPa,which is 3.5 times higher than the strength of fine sand without adding control agents;（2）The mechanical strength of the silt specimen can reach 1.86 MPa.