| Calcareous sand is a special geotechnical medium of marine biogenic origin,rich in calcium carbonate or other insoluble carbonate substances,widely distributed on the continental shelves and coasts of the Caribbean Sea,Red Sea,and South China Sea.In these areas,calcareous sand is usually used as the basic material for marine engineering construction.Compared to silica sand,calcareous sand has characteristics such as low particle strength and high porosity,which usually leads to particle breakage when subjected to external loads.Therefore,in the practical application of ocean engineering,it is often necessary to reinforce it.Microbial induced calcium carbonate precipitation(MICP)technology is a new type of soil reinforcement technology,which has the characteristics of low cost,low energy consumption,and environmental friendliness,and is very suitable for the construction needs of island and reef projects in China.In this paper,the statics and dynamic properties of calcareous sand strengthened by MICP in seawater environment are studied deeply and systematically through laboratory experiments.Using GDS fully automatic static triaxial apparatus,the calcium sand samples reinforced with MICP in freshwater and seawater environments were loaded,and the stress-strain relationship of calcium sand with solid was analyzed under different reinforcement levels,confining pressures,and compactness conditions.The dynamic response of MICP reinforced calcareous sand samples under long-term cyclic loading under different load frequencies,load amplitudes,confining pressures,reinforcement times,consolidation stress ratios,and bacterial immersion time was studied using a GDS fully automatic triaxial apparatus.The main conclusions are as follows:(1)Through static triaxial compression experiments,the peak strength of MICP reinforced calcareous sand samples under different reinforcement and loading conditions was obtained.The analysis results showed that the strength of MICP plus solid was significantly improved under different reinforcement conditions in seawater and freshwater environments,and the reinforcement strength of the samples in freshwater environments was higher than that in seawater conditions.The peak shear strength of the sample increases with the increase of reinforcement days,confining pressure,and density.When the reinforcement number is 7 times,the confining pressure is 100 k Pa,and the solid density is 1.38g/cm 3 The shear strength of the samples in seawater and freshwater environments reached 1760 k Pa and 2040 k Pa,respectively.(2)Based on the static triaxial compression experiment,the stress-strain relationship curves of MICP reinforced calcareous sand under different reinforcement days,confining pressure,density,and other conditions were obtained.A composite power exponential model(CPE model)with solid was established under different loading conditions.The theoretical curve calculated by the model was compared with the measured stress-strain curve,The results indicate that the CPE model can effectively describe the stress-strain relationship of MICP reinforced calcareous sand under different loading and reinforcement conditions.This study provides a theoretical basis for the study of the constitutive model of MICP reinforced calcareous sand.(3)To study the effects of load frequency,load amplitude,confining pressure,and consolidation stress ratio on the dynamic characteristics of MICP reinforced calcareous sand under long-term cyclic loading,long-term vibration loading tests were conducted on calcareous sand and solid under different working conditions.The results indicate that the dynamic elastic modulus of reinforced soil continues to increase with the increase of loading cycles,and gradually stabilizes when the loading cycles increase to a certain extent.The damping ratio of reinforced soil continues to decrease with the increase of cyclic loading times,and gradually stabilizes when the loading times increase to a certain extent. |
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