不同养护测试条件对微生物加固土体强度的影响

Influence of curing test conditions on the strength of microorganism reinforced soil mass

利用微生物诱导碳酸钙沉积(MICP)技术对岩土体进行加固,已成为学术界研究热点。根据已有研究,MICP加固能使土体强度显著提高,但不同文献中对试样在强度测试前的养护处理方法不尽相同。为了便于比较加固效果,需要研究养护测试条件对加固强度的影响。本研究采用微生物技术对粉土进行注浆处理,通过无侧限抗压强度和碳酸钙含量等评价加固效果,开展了不同养护条件对加固强度的影响试验。试验结果表明,养护条件不会影响试样中沉积的碳酸钙数量,但会影响无侧限抗压强度。室温条件下试样水分随着养护时间的延长而逐渐下降,而强度逐渐上升,试样含水状态对强度有显著影响。低温烘干条件下的加固强度随养护时间的延长而逐渐提高;而高温烘干条件时,养护1 d后的强度基本不变。相比烘干状态,试样在浸泡条件或干湿循环下的强度明显降低。无论试样处于浸泡或干湿循环条件,对试样进行烘干处理均可使强度显著提高。对比可知,高温烘干养护后测试得到的强度最高,浸泡养护后测得的强度最低。

Reinforced soil mass by microbially induced calcite precipitation(MICP)technology has become a research hotspot in engineering field.Based on the existing research,the soil strength can be greatly improved by MICP reinforcement,however,the specimen curing conditions and curing time prior to strength test are not consistent in different literatures.As is well known,the saturation strength of soil is lower than drying strength.For the sake of comparing reinforcement effect,the research and analysis of the influence of curing conditions on the strength of reinforced soil should be carried out.In this study,the marine silt was treated by MICP injection method,and the reinforcement effect was evaluated mainly through unconfined compressive strength test and calcium carbonate content.Experiments were conducted to discuss the effects of curing conditions such as drying temperature,soaking curing,and dry-wet cycles on treated strength.Before strength test,the specimens were cured under different conditions.The results indicated that curing conditions did not affect the amount of calcium carbonate deposited in the soil specimen,but affect the unconfined compressive strength.The specimen mass was reduced with the extension of curing time,while the strength was increased gradually at room temperature,which proved that the water content had marked impact on the strength.Compared with room temperature curing,the moisture evaporation was relatively slow during drying curing at the same temperature,so the strength increasement also became slower.For the case of high-temperature drying curing,the moisture and strength maintained constant after 1 d.The strengths of specimens in soaking curing or dry-wet cyclic curing were decreased significantly when compared with that of specimen in drying curing.Regardless of whether the specimen was under soaking or dry-wet cyclic conditions,the drying of specimen could significantly improve its strength,but the improved strength was lower than the strength of continuous drying curing specimen.This indicated that some lost strength caused by soaking could not be restored through drying.The comparison showed that the strength obtained after high-temperature curing was the highest one,and the strength tested after soaking curing was the lowest one.Therefore,the curing conditions are crucial for evaluating MICP reinforcement strength.From the perspective of time saving,the high-temperature drying curing can be used,but it is necessary to be aware that the high drying strength is not suitable for other situations.