微生物沉积碳酸钙固化砂质黏性紫色土试验研究

重庆紫色土是一种砂质黏性土,地区降雨集中,水力冲蚀作用剧烈,极易产生水土流失,微生物诱导方解石沉积(MICP)技术因能耗低、污染小而广泛应用于土体加固中。通过正交试验优化了巨大芽孢杆菌(BNCC 336739)的培养基和培养条件,活菌数增长126%,活性良好。采用巨大芽孢杆菌,进行低水压(9.8kPa)灌注固化砂质黏性紫色土试验,探究了固化效果的变化规律。结果表明:随固化次数增加,碳酸钙生成量和干密度逐级增加,无侧限抗压强度与碳酸钙生成量正相关;碳酸钙有效沉积越来越少,强度提高趋于稳定,固化9次后强度提高77%;随孔隙被碳酸钙填充和上下碳酸钙硬壳的形成,渗透性不断降低,最终下降两个数量级;通过试样上、中、下三部分碳酸钙生成量C的样本标准差s来反映碳酸钙分布离散程度,发现割线弹性模量在s的影响下随C增加而波动上升,波动表现为在C相近或s相差很大时,s越小割线弹性模量越大。研究成果可以为MICP技术在紫色土地区的地基、边坡加固和水土流失防护等工程应用提供科学依据和参考。

An experimental study of sandy clayey purple soil enhanced through microbial-induced calcite precipitation

Due to the concentrated rainfall and severe hydraulic erosion, the loss of the sandy clayey purple soil in Chongqing region is serious. The microbial-induced calcite precipitation (MICP) has been widely used in the soil improvement owing to its low energy consumption and less pollution. In this paper, the culture medium and culture conditions of Bacillus megaterium (BNCC 336739) were optimized by orthogonal tests, and the number of viable bacteria increased by 126% with good activity. Under a water pressure of 9.8 kPa, the soil solidification tests using Bacillus megaterium were conducted to investigate the change rules of solidification effects with treatment times. The results show that calcium carbonate production and dry density increase progressively with the increase of treatment times, and the unconfined compressive strength positively correlates with the calcium carbonate production. The strength tends to be stable with less effective calcium carbonate precipitation and increases by 77% after nine times of treatment. As the pores filled with calcium carbonate and the formation of upper and lower crusts, the permeability decreases continuously and eventually drops by two orders of magnitude. The sample standard deviation (s) of calcium carbonate production (C) in the upper, middle and lower layers of the soil column was used to reveal the discreteness of calcium carbonate distribution. Besides, it is shown that the secant elastic modulus fluctuates with the increase of C under the influence of s. When C is close or s differs greatly, the smaller the s is, the greater the elastic secant modulus is. This study provides scientific basis and reference for the application of MICP technology in foundation, slope reinforcement and soil and water conservation in the purple soil area.