Laboratory Experiment and Micro-Mechanism Analysis on the Influence of Particle Size and Distribution on Micp Enhanced Soil

Abstract

Microbial-induced calcite precipitation (MICP) is an environmentally friendly alternative to conventional chemical grouting for enhancing geotechnical properties in soils. Certain particle size distribution soils can be effectively improved through MICP to enhance integration. Understanding the enhancing mechanisms and applicability of MICP on soils with different particle sizes distributions prior to its implementation is crucial. The previous studies of MICP enhanced soil focus on the particle size distribution for seismic liquefaction. Whether the MICP method can be used in the soil with other particle size distribution for reinforcement and seepage reduction instead of liquefication prevention has no perfect answer. The MICP method was suggested to be used in the reinforcement of the deep layer ⑨ in the deep foundation pit of Guanyuan project in Shanghai, China. Whether the MICP method fit the particle size distribution had to be determined. This study focused on investigating the effect of particle size distribution on the strength of biocemented sand through unconfined compressive strength (UCS) tests, porosity analysis, and calcite content measurements. A total of three typical particle sizes of sands was treated using the MICP method. The effects of particle size distribution were examined. Optimal size particle was added to typical sands to obtain certain particle size distribution. The particle size distribution effect was analyzed to assess the improvements in UCS, porosity and calcite content. Scanning electron microscope images were used to analyze the effects at the mesoscopic level. The particle size range of 0.25–0.5 mm is optimal for enhancing strength through MICP treatment because it provides a suitable void size for effective bonding. The increment of the optimal size content to the 1–2 mm column resulted in remarkable strength improvements, particularly at a 50% percentage content. However, the increment of the optimal size in the 0.075 mm column exhibits no considerable significant improvement due to minimal changes in void size. The failure modes of the MICP enhanced soils depended on the particle sizes and calcite content. High-strength specimens exhibiting diagonal shear, weak sample displayed split and block failure. The results provided criterion determining the possibility for the usage of MICP in the Guangyuan Engineering, which also can be referred by other similar engineering.

Keywords: sand, MICP, particle size, particle size distribution, MICP enhanced soil, failure mode