Purpose

Instability of slope surface is a critical concern in Geotechnical and Environmental Engineering. MICP (Microbial-Induced Carbonate Precipitation), an innovative bio-cementation technique, has attracted the attention for slope surface protection. In this work, MICP was investigated to evaluate its durability under the exposure of acid rain and to advance the understanding on long-term performance of slope soil preserved by MICP.

Methods

MICP treatment was applied to a fine-grained slope soil using indigenous bacteria. Specimens treated to different cementation levels (% CaCO₃) were exposed to acid rain (of varying pH) through two sorts of mechanisms: (i) infiltration and (ii) immersion. The evaluations were based on corrosion of CaCO₃, mass loss, needle penetration tests, and scanning electron microscopy.

Results

The decrease in pH increased the corrosion of CaCO₃, resulting in considerable loss in aggregate and unconfined compressive strength. However, increased cementation level showed high durability of specimens. The soils treated to 12.5% CaCO₃ showed 19.9% soil loss, whereas it was reduced to 5.4% when cemented to 22.5% CaCO₃. The results also revealed that the contact time of acid rain significantly governed the rate of corrosion, i.e., specimens subjected to lower infiltration rate (20 mm/h) showed higher loss of mass compared to that of higher rate (100 mm/h).

Conclusion

The long-term performance of MICP treatment is determined by (i) cementation level, (ii) pH, and (iii) infiltration rate of acid rain. High cementation level promotes the longevity of the treatment. Therefore, MICP to higher cementation level is recommended for long-term preservation of slope surface.

中文翻译：

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酸雨作用下生物胶结边坡土的耐久性分析

目的

坡面的不稳定性是岩土工程和环境工程中的一个关键问题。MICP（Microbial-Induced Carbonate Precipitation）是一种创新的生物胶结技术，在斜坡表面保护方面引起了人们的关注。在这项工作中，研究了 MICP 以评估其在酸雨暴露下的耐久性，并促进对 MICP 保存的斜坡土壤长期性能的理解。

方法

使用本地细菌对细粒斜坡土壤进行 MICP 处理。处理到不同胶结水平（% CaCO ₃）的样本通过两种机制暴露于酸雨（不同 pH 值）：（i）渗透和（ii）浸没。评价基于CaCO _{3 的}腐蚀、质量损失、针刺试验和扫描电子显微镜。

结果

pH值的降低增加了CaCO ₃的腐蚀，导致骨料和无侧限抗压强度的显着损失。然而，增加的胶结水平显示出试样的高耐久性。用 12.5% CaCO ₃处理的土壤表现出 19.9% 的土壤流失，而当胶结到 22.5% CaCO ₃时，土壤流失减少到 5.4% 。结果还表明，酸雨的接触时间显着控制腐蚀速率，即，与较高速率（100 毫米/小时）相比，处于较低渗透速率（20 毫米/小时）的试样表现出更高的质量损失。

结论

MICP 处理的长期性能取决于 (i) 胶结水平、(ii) pH 值和 (iii) 酸雨的渗透率。高胶结水平促进了治疗的寿命。因此，对于坡面的长期保存，建议将MICP 提高到更高的胶结水平。