不同细菌注浆方法对MICP一相注工艺的影响

为了提高细菌和胶结液的利用率,并得到更好的土体固化效果,基于低pH一相注工艺,分析探讨低浓度细菌分次注入和高浓度细菌一次注入这2种不同的细菌注浆方法对微生物诱导CaCO₃沉积(MICP)技术固化效率的影响。通过水溶液、砂层过滤及砂柱固化试验,从CaCO₃生成量、注浆窗口期和固化强度及均匀性3个方面综合评价了2种注浆方法的优劣。结果表明:在细菌总量一定的情况下,低浓度的细菌(OD为0.45,活性为3 U/mL)分次注入比高浓度细菌(OD为3.6,活性为24 U/mL)一次注入所生成的CaCO₃总量更多,前者约为后者的3倍;一相浆液的pH降至4时,低浓度细菌不易絮凝,能够提供更长的注浆窗口期;低浓度细菌分次注入所形成的固化砂柱其CaCO₃分布更为均匀,且强度更高,当CaCO₃含量都为13%±1%时,其无侧限抗压强度约为高浓度细菌一次注入时的2.5倍。

Influence of different bacterial grouting strategies on MICP one-phase injection method

In order to improve the availability of bacteria and cementation solution for better solidification effect, the low-pH one-phase method was used to analyze and discuss the effects of two different bacterial grouting strategies, i. e. , multiple injection of low concentration bacteria and single injection of high concentration bacteria, on the solidification efficiency of microbially induced calcite precipitation(MICP)technology. Liquid solution, sand layer filtration and sand column bio-cementation experiment were carried out, and thereafter, three aspects including the calcium carbonate production, the grouting waiting period and the bio-cementation effect were evaluated. The result shows that with the same amount of bacteria used, the calcium carbonate produced by multiple injection of low concentration bacteria(OD=0. 45, activity=3 U/mL)is 3 times more than that produced by the single injection of high concentration bacteria method(OD=3. 6, activity=24 U/mL). When the pH of the all-in-one solution decreases to 4, the low concentration bacteria are not easy to flocculate and can provide a longer grouting period. This also results in a more uniform calcium carbonate distribution. It is found that when the calcium carbonate content is about 13%±1%, the unconfined compressive strength of bio-cementation sand column is about 2. 5 times greater than that treated with single injection of high concentration bacteria.