微生物矿化作用改善岩土材料性能的影响因素

基于微生物诱导碳酸钙沉淀作用（MICP）的土体改性技术近年来在岩土工程领域引起了人们的广泛关注。该技术在改善岩土材料的强度、刚度、抗液化、抗侵蚀及抗渗透性等性能的同时，还能维持土体良好的透气性和透水性，改善植物的生长环境。由于微生物矿化作用涉及一系列生物化学和离子化学反应，固化过程中的反应步骤较多，因此，MICP固化效果受许多因素的制约与影响。基于大量文献资料，系统总结了细菌种类、菌液浓度、温度、pH值、胶结液配比及土的性质等关键因素对微生物改善岩土材料性能的影响，讨论了这些影响因素的优化方式和未来的研究方向，主要得到了以下几点结论：菌种类型、菌液浓度、温度、pH、胶结液性质会从微观上影响碳酸钙的晶体类型、形貌和尺寸，进而在宏观层面影响岩土体的胶结效果；菌液浓度尽可能高、温度在20～40℃间、pH值在7.0～9.5左右、胶结液浓度在1 mol/L以内的因素条件对微生物加固岩土体具有较好的效果。上述范围内的低温、较高的pH值、低浓度胶结液有助于提高土体的抗渗性，而高温、较低的pH值以及中高浓度胶结液有助于提高土体的强度；MICP加固土体的有效粒径范围为10～1 000 ?m，相对密度越大、级配越好则加固效果越好。分步灌浆法、多浓度相灌注法及电渗灌浆法有助于提高土体固化均匀性，0.042 (mol/L)/h以下的注浆速度有利于提高胶结液利用率，砂土试样的灌浆压力一般在10～30 kPa之间，粉黏土试样的灌浆压力不宜超过110 kPa，过高的灌浆压力会破坏土体结构，降低固化效果。

Factors affecting improvement in engineering properties of geomaterials by microbial-induced calcite precipitation

Based on microbial induced carbonate precipitation (MICP), soil modification technology has attracted widespread concern in geotechnical engineering. This technology can not only improve the soil strength, stiffness, the properties of anti-liquefaction, anti-erosion and anti-permeability but also maintain good soil permeability and water permeability and improve the growth environment of the plants simultaneously. As the microbial mineralisation involves a series of complex biochemical and ion chemical reactions in the curing process, soil modification through MICP curing can be affected by many factors. In this paper, the effects of influence factors on the performance of microbial improved geomaterials were summarised, such as bacterial species, bacterial concentration, temperature, pH, the ratio of cement solution and soil properties, and their optimisation methods and future research direction were discussed as well. The conclusions are as follows. The bacteria type, bacteria concentration, temperature, pH, and the nature of the cement can affect the crystal type, crystal appearance, and size of calcium carbonates microscopically, and further affect the cementing effect of geomaterials macroscopically. The optimized conditions for strengthening the geomaterials are under the high bacteria concentration, the temperature from 20℃ to 40℃, the pH from 7 to 9.5, and the concentration of the cementation solution within 1 mol/L. In the optimised range of those factors, the soil permeability is improved by relatively low temperature, high pH value, and low concentration of cementation solution, while the soil strength is enhanced by the relatively high temperature, low pH value and high concentration of cementation solution. The effective grain size ranges from 10 to 1 000 μm, and the relatively large size and good gradation can promote the consolidation effect. The methods of multi-phase grouting, multi-concentration grouting and electroosmosis grouting improve the uniformity of soil solidification. The grouting speed below 0.042 mol/L/h is beneficial to improve the utilization ratio of the cement solution. The grouting pressure of the sand specimen is generally between 10 kPa～30 kPa bar, the grouting pressure of the silt and clay specimen should not exceed 110 kPa, and the high grouting pressure destroys the structure of soil and reduces the curing effect.