Impact of Biocementation on Geotechnical Properties of Soils

Abstract

Microbially Induced Calcite Precipitation (MICP) has emerged as a promising and sustainable technique in the field of geotechnical engineering, offering environmentally friendly solutions for soil improvement and stabilization. This biological process not only enhances the mechanical strength of soils but also contributes to reducing soil erosion and permeability, making it an effective alternative to conventional chemical methods. The main objective of this research was to investigate the potential of MICP in improving soil stability by inducing calcium carbonate precipitation through microbial activity. The study specifically aimed to assess the effectiveness of this technique on both consolidated and unconsolidated soils collected from different locations to compare their behaviour under microbial treatment. For this purpose, consolidated soil samples were collected from Margalla Hills, while unconsolidated soil samples were obtained from B-17 Multi Gardens, Islamabad. The methodology involved isolating indigenous bacteria from the collected soils, which were later used for MICP treatment. Standard geotechnical laboratory tests were conducted to determine the physical and mechanical properties of the soil samples both before and after MICP application. Sieve analysis confirmed that the soil gradation met the ASTM D standards, ensuring the reliability of the sample preparation process. The Atterberg limits test revealed a liquid limit of 26% and a plastic limit of 29.5%, indicating low plasticity characteristics of the soil. The Modified Proctor compaction test showed a maximum dry density (MDD) of 152.25 g/cm³ and an optimum moisture content (OMC) of 24.8%, reflecting the soil's favorable compaction properties. The Unconfined Compressive Strength (UCS) test demonstrated significant improvement in strength after MICP treatment, with pH values recorded as 10, 11, and 12 on the 10th, 20th, and 30th days, respectively, indicating an alkaline environment conducive to microbial activity and calcite precipitation. Among these, pH 11 was found to be the most suitable for promoting optimal microbial activity and soil stabilization, resulting in enhanced strength development and calcite precipitation compared to other pH levels. Overall, the results of this study suggest that MICP can effectively enhance the strength and stability of loose soils, making it a viable technique for sustainable soil improvement in geotechnical applications.