微生物反硝化诱导固化和减饱和协同作用应用于砂土抗液化的方法与机理探索

Soil liquefaction induced by earthquakes often occurs in saturated non-cohesive soils. Microbial processes can be adopted to counter soil liquefaction. In previous studies, there are two microbial approaches to solve such a problem: 1) bio-cementation, that is, to induce cementation effect between soil particles and thus the strength and stiffness of soil can be enhanced; and 2) bio-desaturation, that is, to produce biogenic gases in soils to reduce the degree of saturation, and thus the increment of excess pore water pressure can be reduced and shear strength can be improved in undrained conditions. In this research project, we will explore a method for the remediation of soil liquefaction using synergetic effect of cementation and desaturation. This synergetic effect is achieved through microbial denitrification process. This method can potentially be more effective in reducing the liquefaction susceptibility, as compared to other microbial methods. The research will be carried out from two aspects. First, we will develop methods to achieve combined cementation and desaturation effects in soils. Some factors and conditions affecting the treatment result will also be investigated, such as the amount of substrates, the concentration of treatment solution, grouting methods, and pore water pressure. Second, we will examine the performance of the synergetic effect of bio-cementation and bio-desaturation for liquefaction mitigation and investigate its mechanisms. We will conduct static and cyclic triaxial tests. The underlying mechanisms of combined bio-cementation and bio-desaturation effect, and its comparison to single cementation or desaturation, for the mitigation of soil liquefaction are to be revealed.

地震引起的地基液化常见于饱和无粘性土中。微生物方法可以用来治理液化地基。过往的研究中有两种思路：一是微生物固化法，即给土颗粒提供粘结力，来提高土体的强度和刚度；二是微生物减饱和法，即用生物气泡来降低土体的饱和度，从而减低超静孔隙水压力的上升幅度同时提高土体的不排水强度。本项目采用微生物反硝化过程，来实现针对土体的固化和减饱和协同作用，起到抵抗液化的效果。本项目将开展两方面的研究。第一，微生物处理方法研究：利用微生物反硝化过程在土体中同时实现可控的微生物固化和减饱和，研究处理参数和条件（反应物添加量、处理液浓度、灌浆渗流方式、地下水压力等）对处理效果的影响规律。第二，微生物固化和减饱和协同作用下土体抗液化性能和力学机理研究：利用静、动力三轴试验，分析评估上述方法处理土体的力学特性和抗液化效果，揭示微生物固化和减饱和协同作用在抗液化中的工作机理，及其与单一的固化或减饱和作用的差异。

地震中的地基液化现象，会造成地基土的强度丧失和大变形发生，造成极大的建筑破坏和经济损失。新型的微生物技术可以为地基液化问题提供一种有效且廉价的处理方法。本研究采用微生物反硝化过程，在地基土中产生稳定的固化物和气泡，提升土体的强度，并减缓土体在地震动力荷载下的超静孔隙水应力上升。研究获得了能够稳定生成固化物碳酸钙和氮气的无害反硝化菌株，并理解了反硝化菌株的反应特点。取得了利用反硝化细菌进行土体固化处理、以及固化和气泡减饱和联合处理的方法。揭示了不同处理方法和程度下的土体的强度变化规律。研究也对土体处理效果的渗流稳定性进行了研究，试验发现反硝化细菌以静态的方式对砂土进行固化和减饱和联合处理会对减饱和气体的稳定性造成不利影响，但先对砂土进行固化，再使用反硝化细菌进行减饱和处理时，联合处理效果便会有显著的提高。本研究为现有工程中处理饱和地基土抗液化提供了新型处理方法，也为研究者们提供了新的研究思路。