STRENGTH ENHANCEMENT OF SILTY SAND VIA MICROBIAL-INDUCED CALCITE PRECIPITATION USING BACILLUS MEGATERIUM

Abstract

This study evaluates the strength enhancement of silty sand using Microbial-Induced Calcite Precipitation (MICP) with Bacillus megaterium. The soil, classified as A-3 (0) under AASHTO and SP-SM under USCS, was treated with varying bacterial suspension densities ranging from 1.5×108 cells/ml, 6 × 108 cells/ml, 1.2 × 109cells/ml, 1.8 × 109 cells/ml and 2.4 × 109 cells/ml and compacted using British Standard Light (BSL), West African Standard (WAS), and British Standard Heavy (BSH) energies. Laboratory investigations including unconfined compressive strength (UCS), California bearing ratio (CBR), durability assessment, and statistical analysis using ANOVA were conducted. Results showed significant improvement in strength characteristics of treated soils compared with control specimens. Peak UCS values of 448.84 kN/m², 689.98 kN/m², and 749.82 kN/m² were recorded for BSL, WAS, and BSH compactive efforts, respectively, at optimal bacterial density. Similarly, treated soils exhibited improved CBR values under both soaked and unsoaked conditions, with maximum performance observed at 6.0 × 10? cells/ml suspension density. Durability assessment indicated increasing resistance to loss in strength with higher bacterial density and compactive effort, although values remained below recommended durability thresholds. Statistical analysis confirmed that microbial treatment had a significant influence on the engineering properties of silty sand. The findings demonstrate the potential of MICP using Bacillus megaterium as a sustainable soil stabilization technique for improving the strength and load-bearing capacity of silty sand for geotechnical engineering applications.

Keywords: microbial soil stabilization, UCS, CBR, Bacillus megaterium, durability, compaction energy