Influence of fines on the hydromechanical properties of a biocemented uniform-size sand

¹ CERIS/ Instituto Superior Técnico, University of Lisbon, Av Rovisco Pais,1, Lisbon Portugal
² IBB/ Instituto Superior Técnico, University of Lisbon, Av Rovisco Pais,1, Lisbon Portugal

^* Corresponding author: rafaela.cardoso@tecnico.ulisboa.pt

Abstract

Microbially induced calcite precipitation (MICP) is a potentially sustainable and innovative soil improvement technique that utilizes urea hydrolysis driven by bacterial activity to precipitate calcium carbonate, thereby enhancing geotechnical properties. While most studies in this field focus on granular soils due to their high permeability and geometric compatibility between voids and bacteria, the natural diversity of soils requires a more comprehensive investigation into the applicability of this technique. The study presented aims to evaluate the influence of the presence of fines on the biocementation of a uniform- size quartzite sand prepared with or without 5% of kaolin clay. Control specimens prepared with water and with feeding solution without bacteria were also tested. The improvement in soil properties was assessed through variable water head tests to measure permeability, direct shear tests to measure shear strength and oedometer tests to measure compressibility, all performed in full saturated specimens. The presence of biocement and the efficiency of the treatment were confirmed through leaching tests, mercury intrusion porosimetry, scanning electron microscopy, and X-ray diffraction analyses. The results confirm the effectiveness of the treatment increasing soil strength and stiffness, which suggests void clogging and increased tortuosity due to biocement precipitation. The presence of fines significantly influenced the material behavior, overall reducing the improvement with the treatment.