Strength, stiffness, and microstructure characteristics of biocemented calcareous sand

TLDR

Calcareous sands are problematic soils, and microbially induced calcite precipitation offers an in‑situ biomineralisation technique to cement them. This study examines how varying the cementation solution‑to‑sample volume ratio affects the strength, deformation, and microstructure of biocemented calcareous sand. Laboratory tests—including unconfined compressive, splitting tensile, Brazilian tensile, and consolidated drained triaxial—were performed to evaluate these properties. Results show that unconfined compressive and splitting tensile strengths, as well as the tangent modulus at 50 % peak strength, increase exponentially with the cementation ratio, and microstructure analysis links higher calcite content to greater strength and stiffness, providing design‑relevant parameters such as peak cohesion and friction angle.

Abstract

Calcareous sands are known as problematic soils in nature and challenge geotechnical engineers in many practical projects. Microbially induced calcite precipitation (MICP) is an innovative soil improvement technique that uses biomineralisation processes to induce cementation in-situ. The work described in this paper investigates the strength, deformation, and microstructure characteristics of biocemented calcareous sand under different cementation solution to sample volume ratios. A series of laboratory experiments was conducted, including unconfined compressive strength tests, splitting, tensile (i.e., Brazilian) strength tests, and consolidated drained triaxial tests. The results indicate that an exponential function reasonably describes the unconfined compressive strength and splitting tensile strength with increasing cementation solution to sample volume ratios. The tangent modulus at 50% peak strength increases exponentially with an increase in cementation solution to sample volume ratio, whereas it increases linearly with an increase in strength. The strength parameters for this MICP-improved soil, including the peak cohesion and friction angle, are derived to facilitate engineering design. Microstructure analyses are used to illustrate the physical basis for the increase in strength and stiffness with increases in the calcite content, as demonstrated using the cementation solution to sample volume ratio.