改善MICP固化粉土均匀性的试验研究毕业论文

 2021-04-16 01:04

摘 要

近年来生物技术作为一门新兴技术飞速发展,各种利用微生物的新型技术开始萌芽。而本文所介绍的正是利用微生物诱导方解石沉淀来固化粉土的试验。

本文主要针对怎样选取最优菌种,通过试验的对比,分析不同胶结液注浆效果,比较出微生物加固粉土最优方案。通过对大尺寸试样的注浆,利用不同的注浆方案,如通过注纯菌液、上清液等胶结液来比较分析不同注浆条件下试样强度、均匀性的效果。

本文得到以下结论:

(1)在对巴氏芽孢杆菌培养过程中发现,菌种培养24小时,得到的细菌浓度、脲酶活性增长趋势明显,细菌浓度增长约211%,脲酶活性增长约467%。而在24小时到48小时之间细菌浓度增长不大,故菌种培养最优时间为24小时;

(2)在相同注浆方案下,注浆轮数越多的试样,其无侧限抗压强度越高。相同注浆方案下,取相同距离处比较,注浆4轮的试样其无侧限抗压强度较注浆6轮的试样相比要低50%,说明微生物加固粉土强度与注浆轮数紧密相关。而碳酸钙沉淀量占18%时,试样的无侧限抗压强度达到2800kPa,而碳酸钙沉淀量占9%时,试样无侧限抗压强度仅有180 kPa,说明试样无侧限抗压强度的值随着碳酸钙沉淀生成量的增加而增加;

(3)通过数据图可以看出,试样无侧限抗压强度的值与碳酸钙沉淀生成量波动基本一致。因为碳酸钙沉淀生成初期,土体内部空隙较大,碳酸钙沉淀大量生成,土体内部空隙越来越少,土体越来越密实,强度越来越大。到中期土体内部空隙越来越少,碳酸钙沉淀量开始趋于稳定;

(4)在相同注浆方案下,注完氯化钙静置的时间短的试样,其无侧限抗压强度要高,但试样的均匀性较差。注完氯化钙静置时间长的试样,其无侧限抗压强度要低一些,但试样整体的均匀性要好。对比分析相同注浆方案下注完氯化钙后静置8小时和静置16小时的试样发现,静置时间短的试样其无侧限抗压强度在同等距离范围内要高于静置时间长的试样,但其加固试样长度很短,平均加固长度只有15cm左右。强度最高值与最低值之差达到2607 kPa,其均匀性远远差于静置时间长的试样。说明试样的均匀性与其注完氯化钙后静置时间紧密联系。

关键词:微生物固土、微生物诱导方解石沉淀、注浆

Experimental study on improving homogeneity of MICP solidified silt

ABSTRACT

In recent years, biotechnology, as a new technology, has developed rapidly, and various new techniques using microorganisms have begun to germinate. What this article introduces is the test of solidifying silt by using microorganism to induce calcite precipitation.

This paper focuses on how to select the best bacteria, through the comparison of the test, analysis of different grouting fluid grouting effect, compare the best solution of microbial reinforcement powder. Through the grouting of large size specimens, different grouting schemes are adopted, such as the solution of pure bacteria, liquid and supernatant, to compare and analyze the effect of strength and uniformity of specimens under different grouting conditions.

The following conclusions are obtained in this paper:

(1) in the course of culture of Sporosarcina pasteurii, it was found that the bacterial concentration and urease activity increased obviously when the strain was cultured for 24 hours, and the concentration of bacteria increased by about 211%, and urease activity increased by about 467%. In 24 hours to 48 hours, the concentration of bacteria increased little, so the optimum time of culture was 24 hours;

(2) under the same grouting scheme, the more the number of grouting wheels, the higher the unconfined compressive strength. Under the same grouting scheme, the unconfined compressive strength of the sample with 4 rounds of grouting is 50% smaller than that of the 6 wheel grouting sample at the same distance, and the strength of the reinforced soil is closely related to the number of grouting wheels. The precipitation of calcium carbonate samples accounted for 18%, the unconfined compressive strength reached 2800kPa, and calcium carbonate precipitation accounted for 9%, the unconfined compression strength of the samples is only 180kPa, explain the unconfined compressive strength increases with increasing precipitation of calcium carbonate production;

(3) by data diagram, it can be seen that the value of unconfined compressive strength is basically the same as that of calcium carbonate precipitation. Because of the calcium carbonate precipitation in the early stage, the soil interior gap is larger, calcium carbonate precipitation generated a large number of soil voids are less and less, the soil is becoming denser and denser, the intensity is growing. By the middle of the period, the inner voids of the soil become less and less, and the precipitation of calcium carbonate begins to stabilize;

(4) there is no unconfined compressive strength for the specimens with a short resting time after calcium chloride injection, but the uniformity of the sample is poor. The specimens with a long resting time after calcium chloride injection have less unconfined compressive strength, but the overall uniformity of the sample is better. Comparative analysis of the same grouting scheme after calcium chloride bet after standing for 8 hours and 16 hours of incubation samples found that static sample time is short of the unconfined compressive strength is higher than that of static sample time in the same range, but the reinforced specimen length is very short, the intensity maximum value and minimum value the difference reaches 2607kPa, the uniformity is far worse than the sample holding time long. It is indicated that the uniformity of the sample is closely related to the settling time after the injection of calcium chloride.

Key words: soil cementation;microbial induction calcite precipitation; bio-grouting

目 录

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