基于新型单相MICP技术改性黏性土力学特性的试验研究

微生物诱导碳酸钙沉积(MICP)是一种绿色低碳的新型土体改性技术.该技术当前主要适用于渗透性较好的砂土,普遍使用两相处理方法,即菌液和胶结液分开施用.然而,对于渗透性相对较差的黏性土,传统的两相处理方法难以适用.为此,引入新的单相胶结方法,即菌液和胶结液混合施用,通过调节溶液的初始pH值为细菌水解作用提供窗口期,避免微生物絮凝阻塞孔隙,使混合液均匀分布于土体一定深度范围内,从而达到显著提升胶结效果的目的.利用喷洒法将混合液喷洒至土体表层进行MICP处理,处理完成后使用超微型贯入仪SMP-1测试土体表层不同深度处的结构强度,分析土体力学特性的空间差异,对土体的胶结效果进行定量评价.此外,探究了胶结液浓度(0.2M、0.5M和1.0M)及胶结方法(调节pH与否)对于土体结构强度及MICP改性效果的影响.结果表明:采用单相MICP技术对黏性土进行改性,能够显著提高其结构强度,具有较好的适用性;在不高于1.0 M的胶结液浓度范围内,黏性土的胶结效果随着胶结液浓度增加而提升;相比较而言,调节pH的单相胶结方法对于提升土体胶结的深度和均匀性有明显积极作用.新型单相MICP技术简单易行,能够节约成本,在黏性土表层加固方面具有潜在推广应用价值.

MECHANICAL BEHAVIOR OF CLAYEY SOIL TREATED BY NEW ONE-PHASE MICP TECHNIQUE

Microbially Induced Carbonate Precipitation (MICP) is a new kind of green and low-carbon soil modification technique. At present, this technique is mainly applicable to sandy soil with good permeability. A two-phase treatment method is commonly used, where the bacterial solution and the cementation solution are applied separately. However, for clayey soils with relatively poor permeability, the traditional two-phase treatment method is difficult to apply. Therefore, a new one-phase cementation method is introduced in this paper. It is a mixed application of bacterial solution and cementation solution. It provides a lag period for bacterial hydrolysis by adjusting the initial pH value of the solution, avoids microbial flocculation blocking the pore, makes the mixed solution evenly distributed in a certain depth range of soil, and thus significantly improves the cementation quality. The mixed liquid is sprayed to the surface of soil to have it treated by MICP. After the treatment, the initial structural strength of soil surface at different depths is tested by SMP-1. The spatial difference of soil mechanical properties is analyzed. The cementation quality of soil is quantitatively evaluated. In addition, the effects of cementation solution concentration (0.2 M, 0.5 M and 1.0 M) and cementation method (adjusting pH or not) on soil structural strength and MICP modification quality are investigated. The results show that the one-phase MICP technique can significantly improve the structural strength of clay and has good applicability. Within the range of cementation solution concentration not higher than 1.0M, the cementing effect of clay increases with the increase of cementation solution concentration. Comparatively the one-phase cementation method of adjusting pH can improve the depth and homogeneity of soil cementation proactively. One-phase MICP technique is simple and easy to implement, can save costs, and has potential application value on strengthening the surface of clayey soil.