微生物灌浆加固土体新技术的试验与应用研究

The technique of microbial improvement of soils is a novel ground treatment technique by biological technology that has recently emerged in geotechnical engineering. In this study, macro-micro experiments are conducted in the laboratory on Microbial Induced Calcite Precipitation (MICP) with bacterium strains being suitable for improving sand or silt. Discrete Element Method (DEM), as an effective method, is used to establish the numerical model of microbial grouting-cemented soils to reveal the mechanism of this special system from the microscomic view. The microbial grouting treatment technique is applied to improve the soft soil between piles in geogrid-reinforced and pile-supported embankment and a bio-seepage-chemo-mechanical-time model is developed. It can describe the variation laws of the dispersion, precipitation of grout containing microorganisms and the performance of bio-cemented soil. Additionally, for a geogrid-reinforced and pile-supported embankment, the method for calculating settlement in life cycle is proposed to evaluate the effect of microbial grouting-cemented subsoil. Meanwhile, aiming at the failure mode of soil between piles, a stability analysis method is presented. This study belongs to the interdisciplinary research field of traditional geotechnical engineering and modern biology engineering. The achievements obtained in this study will provide important theoretical and experimental basis for the application of biological treatment technology in expressway and high-speed railway engineering. Moreover, they have great significance for developing the green geotechnical engineering and building an environmentally friendly, resource-saving and sustainable society.

微生物加固土体技术是近年来国际岩土工程界开始研究的新兴的生物地基处理技术。本项目拟通过室内微生物菌种改性土体的宏观、微观试验，选择适合于加固砂土或粉土的微生物菌种；进行微生物灌浆改性土体的宏观、微观试验，采用离散元方法建立微生物灌浆改性土体系统的细观数值模型，揭示微生物灌浆改性土体的作用机理；采用微生物灌浆技术应用于加固桩承式加筋路堤的桩间土体，建立反映微生物浆液扩散、沉积与改良土体性能的变化规律的生物-渗流-化学-力学-时间耦合模型，提出基于微生物灌浆加固桩间土的桩承式加筋路堤的全寿命周期的沉降计算方法，并建立桩承式加筋路堤稳定性分析方法。本项目的研究内容属于传统岩土工程与现代生物工程技术学科的交叉研究领域，项目成果将为生物地基处理技术应用于高速公路和高速铁路工程提供重要的理论基础和试验基础，对发展我国绿色岩土工程，建立环境友好型、资源节约型的可持续发展社会具有非常重要的现实意义。

微生物固化（Microbially Induced Calcite Precipitation，以下简称为MICP）技术是岩土工程领域兴起的一种新型环保的地基处理技术，该技术利用土中微生物的新陈代谢产物诱导产生碳酸钙晶体，将松散土体颗粒胶结成为整体以改善土体的工程力学特性。然而，该新型地基处理技术存在固化土体的均匀性差、强度增长机理及承载变形特性不明确等问题，一定程度上制约了该技术在实际工程中应用的进程。通过开展室内无侧限抗压强度试验、固结排水/不排水三轴试验、扫描电镜测试和离散元数值模拟，探讨了微生物固化砂土的碳酸钙含量及化学转化效率、应力及孔压变化规律、抗剪强度参数、碳酸钙晶体胶结与砂土强度增长机理、破坏模式等，获得了微生物固化砂土强度及变形特性的系列创新成果，可为微生物固化技术在实际工程中的应用提供理论指导。针对现有微生物固化注菌方法存在的不足，研发出二阶段注菌技术，从宏细观角度及动力响应方面分析了二阶段注菌技术在改善固化砂土均匀性方面的有效性，并分析了胶结液浓度、化学处理方式、颗粒粒径和固化试样初始含水量对固化砂土强度的影响。研究结果表明二阶段注菌技术能够有效改善微生物固化砂土内碳酸钙晶体的空间分布均匀性，进而提高微生物固化砂土的强度。从微生物固化技术在实际工程中应用的角度出发，针对桩板式路基结构价格昂贵和传统桩承式加筋路堤变形控制效果不佳等问题，研发一种新型的“微生物固化加筋垫层-刚性桩”路基结构。研究结果表明“微生物固化加筋垫层-刚性桩”路基结构能够显著减小路堤填料及桩间土沉降，并显著提高路堤荷载传递效率。