添加剂对微生物胶结砂渗流特性的影响研究

Effect of Chemical Agents on Seepage Characteristics of Microbial Cemented Sand

从MICP反应环境及细菌代谢过程分析出发,选取NH_(4)Cl与NaHCO_(3)作为添加剂,应用于砂土的微生物改性加固,研究结果表明:(1)NH_(4)Cl、NaHCO_(3)添加浓度为0.1 mol/L时,CaCO_(3)生成量显著增加,相较于添加前增加了68.30%,原因是NH_(4)Cl和NaHCO_(3)的添加,调节反应体系pH值,使其更趋近于脲酶最佳活性所需碱性环境,同时促进细菌活性及代谢过程,进而增加CaCO_(3)生成量;(2)核磁共振检测结果显示,添加NH_(4)Cl、NaHCO_(3)后固化砂柱的孔隙率减小了15.93%,渗透系数降低了2~3个数量级,与MICP固化结果相比也有明显改善,渗透系数降低了50%以上;(3)在渗流模型分析中,一方面考虑CaCO_(3)沉淀对孔隙的填充作用,将其等效为填充于砂颗粒间的小颗粒,提出了MICP固化效应系数表述灌浆加固前后砂颗粒平均粒径的变化,另一方面根据固化后微细观检测分析结果,考虑CaCO_(3)沉淀对砂颗粒表面形貌的改变,调整模型中的颗粒材料形状系数α的取值。综合这两个方面对Kozeny-Carman渗流模型进行了修正,验证分析表明,修正后的Kozeny-Carman渗流模型能够较好地描述加固体的渗流特性,这也为MICP固化砂土的渗流特性分析提供了一种便捷的思路,只需测试不同阶段CaCO_(3)的生成量,就可以比较准确地估算加固体的渗透系数。

This study starts from the analysis of the microbial induced calcite precipitation(MICP)re-action environment and bacterial metabolism process,NH_(4)Cl and NaHCO_(3)were selected as additives for microbial modification and reinforcement of sandy soil.The results showed that:(1)when the con-centration of NH_(4)Cl and NaHCO_(3)was 0.1mol/L,the amount of calcium carbonate increased signifi-cantly,which was 68.30%more than that before adding.The reason is that the adding of NH_(4)Cl and NaHCO_(3)adjusts the pH value of the reaction system to make it closer to the alkaline environment re-quired for the optimal activity of urease,and at the same time promotes bacterial activity and metabol-ic processes,which thereby increases the amount of calcium carbonate precipitation;(2)The results of nuclear magnetic resonance show that the porosity of the solidified sand column decreased by 15.93%and the permeability coefficient decreased by 2-3 orders of magnitude after adding NH_(4)Cl and NaHCO_(3).Compared with the conventional MICP curing results,the permeability coefficient de-creased by more than 50%;(3)In the analysis of the seepage model,on the one hand,the filling ef-fect of CaCO_(3)precipitation on the pores was considered,and it is equivalent to the small particles filled between the sand particles.The MICP solidification effect coefficient was proposed to express the changes in the average particle size of sand particles before and after grouting reinforcement.On the other hand,according to the microscopic inspection and analysis results after solidification,the change in the surface morphology of sand particles caused by the precipitation of CaCO_(3)was consid-ered,and the value of the shape coefficientαof the granular material in the model was adjusted.Com-bining these two aspects,the Kozeny-Carman seepage model was revised.The verification analysis shows that the revised Kozeny-Carman seepage model can better describe the seepage characteristics of solids,which also provides information for the analysis of the seepage characteristics of MCP-solidi-fied sand.A convenient way of thinking is that only by testing the amount of CaCO_(3)produced at differ-ent stages,the permeability coefficient of the solid can be more accurately estimated.