Anti-liquefaction Performance Study Of Sand Foundation Improved By Bio-grouting

Compared with the traditional ground improvement methods, one of advances inbio-mineralization enables the rapid microbial induced carbonate precipitation, which isintroduced by transporting the bacterial cells and nutrient solutions into loose sandfoundations for the purpose of ground improvement. This new ground improvementprocess is called bio-grouting. It is the leading edge of ground improvement research,which has many advantages such as small disturbance, short construction period,notable reinforcement and low energy consumption.This study is attempted to investigate whether the bio-grouting is applicable to theimprovement of liquefiable ground through dynamic triaxial tests and shaking tabletests. And besed on the problems found in the test, the bio-grouting scheme isadjusted.Firslyt, a brief introduction to the research, development of microbial inducedcarbonate precipitation and bio-grouting technology is presented, and a practicalbio-grouting treatment method applicable to improvement of liquefiable sandfoundations is described.Secondly, the anti-liquefaction performance and other dynamic performance of thebio-grouting sand ground are studied through dynamic triaxial and small scaled shakingtable tests, and a comparison between the bio-grouting and the traditional groundimprovement methods is made. The test results show that the anti-liquefactionperformance of bio-grouting samples and models is greatly improved.Finally, Besed on the problems and deficiencies in bio-grouting technique at homeand abroad study, such as,grouting batches too much, cured sample strength high,CaCO3crystallizationuneven distribution. We study the bio-grouting process in detail.This study found, the concentration of the fixation will infulence the transport of themicroorganisms in the sand soil, andeasily cause the non-uniform distribution ofmicroorganisms.According to the research results, the author re-design the microbialformulation and grouting scheme. The dynamic triaxial test, unconfined uniaxialcompression UCS test and the consolidated undrained triaxial compression CU test, areused to test the performance of the sample reinforced by the adjustment method. Testresults show that,after25mM/L fixation (CaCl2solution) mixed with the equal volumeof bacteria liquid, the mixed solution is transported into the sand column by1ml/min. the method can guarantee a certain bacteria liquid fixed rate, improve the uniformitydistribution of microorganisms in sand column, and improve theCaCO3crystallizationeven distribution phenomenon.Moreover, to lower strength curedsample, there is not a good corresponding relationship betweenCaCO3crystallizationproduction and the UCS of cured sample. But we can improve thebond strength of cured sample by reducing the concentration of bacteria and increasingbacteria and nutrient grouting batch times. The test result show that, Using the adjustedmicrobial formulation and grouting scheme, after2batches of bacteria and nutrientsgrouting reinforcement, the anti-liquefaction of the cured samples were equal to10%silica cured sand sample, and higher than that of Dr=85%dense sand.but silica curedsand sample need10-132batch times, and curied4-56d.After4batches times bacteriaand nutrient grouting, the axial strain of the cured sand sample is only0.3%, atCSR=0.5and dynamic loading3000times.and there is no obvious change in porepressure.but in reference,at the CSR=0.45, the cured sand sample is liquefaction underdynamic loading10times, whose bacteria amount is2times and the nutrient amount is3times to the4batch times cured sample in our study.So, the amount of bacteria andgrouting batchs times are substantially reduced to the adjusted MICP technique, thecured time is shortened to1-2day, the CaCO3crystallizationuneven distributionphenomenon is reduced, and bond strength can be brought into fullest play. The study isan important step to the MICP technology application in practical engineering.