火山灰增强微生物固化砂土效果的试验研究

Experimental study of MICP-treated sand enhanced by pozzolan

为了提升微生物固化砂土的效果,考虑火山灰的多孔结构及活性特征,设计进行了火山灰增强微生物诱导碳酸钙沉淀(MICP)固化砂土试验,综合宏观物理力学试验和微细观检测,系统分析了火山灰对微生物固化砂土的增强效果及增强机制。结果表明:(1)火山灰能够显著提高砂土微生物加固过程中的固菌率和胶结物产量,火山灰掺量在10%左右达到最佳,与常规MICP相比,固菌率提高了118.28%,胶结物生成量提高了29.55%。(2)火山灰的掺入提高了固化体的抗压强度和抵抗变形的能力,不同围压下固化体的抗压强度提升了52.26%~62.96%,破坏时的应变增加了100.00%~112.58%。(3)火山灰掺入后,固化体的孔隙大小及孔隙率明显减小,整体的密实性及抗渗性能进一步提升,孔隙率从20.12%减小为14.17%,渗透系数降低了一个数量级。(4)火山灰对微生物固化砂土的增强机制主要包括3个方面,一方面,火山灰在砂颗粒间起到了良好的充填作用,大幅减少了颗粒间的大孔隙,使得固化体的密实性增强;另一方面,火山灰良好的吸附作用有效提高了试样内细菌的含量,使固化体碳酸钙的产量及分布的均匀性均增加;第3方面,火山灰中的活性物质参与反应生成的胶凝物质与碳酸钙晶体形成复合凝胶体,使得固化体的胶结性能和密实程度进一步增强。

In order to improve the reinforcement effect of microbial induced calcite precipitation(MICP) technology on sand, the test of MICP-treated sand reinforced by pozzolan was designed and carried out considering the porous structure and activity characteristics of pozzolan. The enhancement effect and enhancement mechanism of pozzolan on the MICP-treated sand were systematically analyzed by integrating macroscopic physical and mechanical tests and microscopic tests. The results showed that: 1)Pozzolan could significantly improve the bacteria fixation rate and cementation material production in the process of sand microbial reinforcement, and the optimal amount of pozzolan content was around 10%, which increased the bacteria fixation rate by 118.28% and the cementation substance production by 29.55% compared with the conventional MICP. 2) The addition of pozzolan greatly improved the compressive strength and resistance to deformation of bio-cemented soil. Under different confining pressures, the compressive strength of the bio-cemented sand increased by 52.26%-62.96%, and the strain at failure increased by 100.00%-112.58%. 3) After the addition of pozzolan, the pore size and void ratio of the bio-cemented sand were decreased obviously,and the overall compactness and impermeability performance were further improved, with the void ratio decreased from 20.12% to 14.17% and the permeability coefficient reduced by an order of magnitude. 4) The enhancement mechanism of pozzolan on MICP-treated sand mainly included three aspects: for one thing, the pozzolan played a good filling effect between the sand particles,which significantly reduced the large pores between the particles and increased the compactness of the sample;for another, the good adsorption of pozzolan effectively increased the content of bacteria in the sample, which increased the production of calcium carbonate and enhanced the uniformity of distribution;on the third hand, the active substances in pozzolan participate in the reaction to generate gelling substances and calcium carbonate crystals to form a composite gel, which could further enhanced the cementation properties and compactness of the bio-cemented sand.