Abstract
This study investigates the efficacy of microbial-induced carbonate precipitation (MICP) on the mechanical properties of poorly graded sand through a set of laboratory experiments. Unconfined Compressive Strength (UCS), Ultrasonic Pulse Velocity (UPV), Scanning Electron Microscopy (SEM), and calcium carbonate assessments were conducted to evaluate the influence of MICP under varying cementation concentrations, cementation ratios, and injection cycles. To this end, treated samples underwent 3, 14, and 21 injection cycles with cementation ratios ranging from 10–90% and molarities of 0.25, 0.5, 0.75, and 1 mol/L. Optimally stabilized samples were then subjected to 2, 4, 6, 8, 10, and 12 freeze-thaw cycles to evaluate their thermal durability. Correlation relationships were also developed to predict the compressive strength and stiffness of MICP-treated sand. Results demonstrated that MICP treatment effectively enhanced the UCS and stiffness by forming interlocking zones between the sand particles. Accordingly, the maximum UCS, secant stiffness, and constrained modulus were achieved at 14.98% calcite content using Sporosarcina pasteurii bacteria accompanied by a 50% cementation ratio and molarity of 0.75 mol/L over 21 injection cycles. Also, the optimally stabilized specimens exhibited 70% and 90% retention in USC and stiffness after 12 freeze-thaw cycles, confirming their sustainability under harsh thermal conditions.