The effective parameters on deviator stress and stiffness of treated sands by microbial induced calcite precipitation (MICP)

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Authors

1 Department of Civil Engineering, langarud Branch, Islamic Azad University, langarud, Iran

2 Department of Civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran

3 Department of Civil Engineering, Roudsar and Amlash Branch, Islamic Azad University, Roudsar, Iran

10.22034/ceej.2025.62581.2398

Abstract

Due to the increase in population, one of the challenges of geotechnical engineers is access to grounds with suitable bearing capacity. Until now, various techniques such as compaction, injection, etc., have been used for soil treatment. Recently, innovative and environmentally friendly methods have been developed, such as microbial induced calcite precipitation, which necessitates research on factors affecting the improvement, increasing its efficiency. In this research, the effect of cementation solution molarity, optical density of bacteria and curing time on stress-strain behavior and stiffness changes of biologically treated sand was investigated by consolidated undrained triaxial compression test. The used soil was SP sand from Kohin region of Qazvin province, which has been improved by Sprosarcina Pasteuri bacteria as a catalyst in accelerating the reaction and sediment production. Also, a 4-phase injection was used to prevent clogging and control the uniform distribution of CaCO3 precipitation. The curves of deviator stress against axial strain showed that the cementation solution molarity had the greatest effect on the stress-strain behavior of the treated sand, resulting in a 45% increase in deviatoric stress. In contrast, the effect of curing time and optical density of bacteria is less in the process of biological improvement. On the other hand, no significant increase in deviator stress was obtained for improved sand with low molarity and optical density levels compared to clean sand. After the biological treatment of sand, the secondary modulus (Esec) and stiffness equal to 50% of maximum resistance (E50) increased by approximately 1.5 to 2 times.

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Journal of Civil and Environmental Engineering

Articles in Press, Accepted Manuscript
Available Online from 12 March 2025

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