Bacterial transport and treatment uniformity in Microbial Induced Carbonate Precipitation-treated calcareous sand foundations

Abstract

Microbial Induced Carbonate Precipitation (MICP) offers significant potential for strengthening calcareous sand foundations in island reclamation. However, controlling bacterial transport and uniformity within complex three-dimensional (3D) seepage fields remains a critical challenge. This study investigates bacterial transport under single-pipe grouting and double-pipe circulation modes by integrating 3D physical model tests with two-phase flow numerical simulations. Physical experiments revealed a competition mechanism between density-driven gravitational settling and pressure-driven radial advection. The reliability of the numerical model in predicting fluid migration was validated by correlating measured normalized penetration resistance with simulated normalized bacterial concentration. The comprehensive parametric study revealed a key finding for single-pipe grouting, increasing the injection rate markedly enhances radial driving forces. This increase, in turn, expands the treatment radius and improves vertical uniformity. Treatment efficacy, however, proved insensitive to the thickness of the overlying clay layer. For the double-pipe circulation cases, an effective hydraulic threshold for pipe spacing exists, beyond which the treatment zone becomes disconnected. Furthermore, adopting an asymmetric flow strategy, with a suction rate higher than the injection rate, effectively mitigates fluid accumulation near the injection, thereby significantly improving the treatment uniformity in the inter-well region. These findings provide a theoretical basis for optimizing MICP grouting in calcareous sand foundations.

Graphical abstract

Keywords

MICP / calcareous sand / bacterial transport / treatment uniformity

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