原位激发微生物成矿加固钙质砂的剪切与压缩特性研究

钙质砂广泛分布于热带海岸地区，其抗剪强度较低，在较高应力条件下极易破碎。因此，对以钙质砂为主要原料的地基材料进行加固，是海洋岩土工程领域的研究热点。基于尿素水解过程的碳酸钙成矿技术（MICP）是近年来地基材料加固领域的一项新技术。目前广泛使用的生物强化法实现MICP存在成本昂贵及环境适应性差等问题，制约了其大规模工程应用。研究采用原位生物激发MICP法对钙质砂进行加固，并对加固后试样开展直剪和一维压缩试验。结果表明：原位生物激发MICP方法可以在钙质砂中形成有效胶结，胶结水平最大可达6.26%。采用高浓度胶结溶液或增加注射次数可提高胶结水平。同时，加固后钙质砂的最大应力比、最大剪胀角以及残余内摩擦角均随胶结水平增加而显著增大，但竖向应力水平增大会抑制这些力学指标的增大。随胶结水平升高，试样压缩性显著减小；压缩后的原位激发MICP加固钙质砂中，细颗粒与粗颗粒的比例均随胶结水平的增加而增大。

Direct Shear and Compressibility Behavior of Bio-stimulatedMICP Treated Calcareous Sand

Calcareous sands are widely distributed in coastal areas around the world. They are considered as a material with low shear strength and high compressibility. Stabilizing calcareous sand has become a hot research topic in coastal geotechnics recently. Microbial induced calcite precipitation (MICP) is a new soil improvement technique. Currently, MICP is primarily implemented through the bio-augmentation approach, which is expensive and has a bad compatibility with the natural soil environment. This study focuses on the bio-stimulated MICP approach by enriching indigenous ureolytic bacteria to stabilize calcareous sand. Direct shear and one-dimensional compression tests are conducted on the bio-cemented samples. The results show that the bio-stimulated MICP approach could create up to 6.26% cementation level within the sand matrix. Increasing the concentration of cementation solution or treating multiple times could yield higher cementation level. during the direct shear test, the peak stress ratio, peak dilation angle, and near critical state friction angle increase significantly with elevated cementation level. However, these mechanical parameters could be suppressed at higher normal stress levels. Meanwhile, the compressibility of bio-cemented sand is significantly reduced with the increase in the cementation level. Upon the completion of the compression test, the proportions of both very fine and vary coarse particles increase with elevated cementation level.