微生物固化技术（MICP）是岩土工程领域新兴起的一种不良地基处理技术，不同地基土体之间的颗粒粒径并不相同，其固化效果也可能存在一定差别。选用3种不同颗粒粒径范围的砂土进行微生物固化处理，并基于无侧限抗压强度试验、孔隙体积测量和洗酸处理，从宏观角度分析颗粒粒径对微生物固化效果的影响。结合扫描电镜测试，从细观角度对微生物固化机制进行了初探。研究结果表明，微生物固化砂土中碳酸钙晶体以颗粒簇形式堆积在砂土颗粒表面及颗粒间接触处，其尺寸随碳酸钙晶体堆叠程度的增加而增大；对于颗粒粒径较小的砂土，颗粒间孔隙较易被碳酸钙晶体填充密实，固化试样内有效碳酸钙晶体比例较大，“结构性”较强，无侧限抗压强度较高。

Microbial-induced calcite precipitation(MICP) is a newly emerged ground treatment technique in geotechnical engineering to treat the soil with poor engineering properties. However, differences on the particle size may occur in different types of soil, which will have influences on the properties of treated soil. In this study, three different ranges of particle size are adopted to be treated by MICP method; and then the effect of particle size on the strength of bio-cemented sand is investigated based on the unconfined compressive strength(referred to as strength hereafter), porosity and calcite content of each sand specimen from macroscopic level, which are obtained via unconfined compression test, porosity measurement and acid treatment, respectively. Meanwhile, this effect is also analysed at the mesoscopic level according to the images of scanning electron microscope (SEM). The research results show that calcite crystals are precipitated on the surface of sand particles, as well as in particle-particle contacts. Calcite crystal clusters will be formed as the MICP process continues; meanwhile, its size increases with the superposition of calcite crystals. The pore space of sand with smaller particle size can be tightly filled and a higher proportion of effective calcite crystals can be obtained. Hence, the bio-cemented sand is able to present a higher strength due to the stronger structure established by the calcite crystal clusters.