微生物固化砂土强度增长机理及影响因素试验研究

Experiental study of the strength enhancing mechanism of bio-cemented sand and its influential factors

微生物诱导碳酸钙沉淀(MICP)可以显著改善砂土的工程力学特性,但其固化效果易受诸多因素影响。基于不同胶结水平微生物固化砂土试样,开展固结排水三轴剪切试验和扫描电镜测试,探讨了MICP技术的固化效果及其相关机理;在此基础上,研究了胶结液浓度、砂土初始密实度、胶结液浓度配比等因素对微生物固化砂土抗剪强度的影响。结果表明:随着胶结水平的提高,微生物固化砂土试样强度提高,试样的脆性也越显著。微生物固化砂土强度的增长主要源于碳酸钙晶体对土体黏聚强度的提高。微生物固化砂土的强度主要包括土骨架强度和碳酸钙晶体胶结强度两部分,前者受土体性质及相关参数影响,后者主要取决于碳酸钙晶体的含量。采用合适的砂土初始密实度,适当提高胶结液浓度以及胶结液中尿素的浓度占比,均可提高微生物固化砂土试样的胶结强度。

Microbial curing(MICP)can significantly improve the mechanical properties of sand.However,the curing effect is affected by many factors.In this study,the consolidated drained triaxial shear tests and electron microscope scanning tests were carried out to investigate the curing effect and the related mechanism of MICP.On this basis,the effects of cementation concentration,relative density and the proportion of cementation liquid’s composition on the shear characteristics of bio-cemented sand were studied.The results show that with the increase of cementation level,the strength and brittleness of bio-cemented sand samples are increased.The increase of the strength of the bio-cemented sand is mainly due to the increase of the cohesive strength provided by the calcium carbonate crystal.The strength of the bio-cemented sand consists of the strength of the soil skeleton and the cementation strength of calcium carbonate.The former is influenced by the properties of sand and related parameters,while the latter mainly depends on the content of calcium carbonate crystals.The strength of the bio-cemented sand sample can be improved by using appropriate initial relative density of sand,increasing the concentration and the molar concentration ratio of urea in the cementation liquid.