Salt-Cycle Durability of Biocemented Calcareous Sand under Repeated Shear

Abstract

Calcareous sand is a critical engineering material in marine and coastal infrastructure development. However, its high angularity, internal porosity, and susceptibility to particle crushing present significant geotechnical challenges. Microbially induced carbonate precipitation has emerged as a sustainable ground improvement technique, utilizing ureolytic bacteria to precipitate calcium carbonate and bind soil particles. Despite the promising application of biocementation, the long-term durability of treated calcareous sand in aggressive marine environments remains insufficiently understood. Coastal structures are continuously exposed to complex environmental and mechanical stressors, most notably cyclical salt crystallization and repeated shear loading induced by waves and tides. This paper provides a comprehensive investigation into the salt-cycle durability of biocemented calcareous sand subjected to repeated shear. Through a highly controlled experimental framework, the research evaluates the coupled effects of sodium chloride crystallization cycles and cyclic direct shear on the mechanical integrity of the biocemented matrix. The analysis explores the microstructural degradation mechanisms, highlighting how crystallization pressure induces micro-fractures in the calcite bonds, which are subsequently exacerbated by cyclic shear stresses. Findings demonstrate a non-linear degradation of shear strength and energy dissipation capacity as the number of salt cycles increases. This study contributes critical insights into the fatigue life and environmental resilience of microbially treated marine soils, offering predictive frameworks for the design and maintenance of sustainable coastal infrastructure.