微生物诱导碳酸钙沉淀改性膨胀土试验研究

Experimental study of modifying expansive soils using microbial induced calcite precipitation

微生物诱导碳酸钙沉淀(microbial induced calcite precipitation,简称MICP)技术可能是有助于解决膨胀土胀缩行为的一种潜在方法。用细菌浓度和脲酶活性作为控制指标,研究了在不同培养条件下的巴氏芽孢杆菌的生长特性,确定了最有利于细菌生长的温度、pH和摇床震荡速率。用MICP技术对两种不同的膨胀土进行处治,通过比较处治前后土样的自由膨胀率、无荷膨胀率、黏聚力、内摩擦角以及抗剪强度等物理力学指标,验证处治效果,从微观角度解释了改性膨胀土的作用机制。结果表明:培养温度为30℃、pH为7、摇床震荡速率为200 r/min时,最适宜细菌生长。MICP处治后的膨胀土自由膨胀率和无荷膨胀率均有明显下降,黏聚力、内摩擦角以及抗剪强度均有明显增强,MICP过程中生成的碳酸钙起到了孔隙填充和土颗粒胶结作用,同时钙离子对低价阳离子的置换和碳酸钙对土颗粒的包裹效应,共同作用改善了膨胀土特性。研究可为微生物处治膨胀土技术和工程应用提供参考。

Microbial induced calcite precipitation(MICP)is a technique that can be a potential method to solve wetting swelling and drying shrinkage of expansive soils.With the bacteria concentration and urease activity as standards of measurement,the growth properties of Sporosarcina pasteurii in various conditions were studied,and the most favorable temperature,pH and vibration velocity were determined.Two different types of expansive soils were treated with MICP,and the effect of this method was studied by comparing expansive properties,cohesive force,internal friction angle and shear strength before and after the treatment.The mechanism of MICP treated expansive soils was explained through microstructure perspective.The results showed that the optimal culture conditions for the bacterial growth were as follows:the pH of 7,the vibration velocity of 200 r/min,and the temperature of 30℃.After treating with MICP,the free swelling ratio and unloaded swelling ratio were decreased significantly,while the cohesive force,internal friction angle and shear strength were increased.The calcium carbonate generated during MICP played the role of pore filling and soil particle cementation,and the replacement of low valence cations by calcium ions and the wrapping effect of calcium carbonate on soil particles improved the properties of expansive soils.The research can provide beneficial references for the technology and engineering applications of MICP treatment of expansive soils.