Investigation of Mechanical Enhancements of EICP-Treated Soil

Abstract

In recent years, enzyme-induced carbonate precipitation (EICP) has emerged as a bioinspired and innovative technique that has captured the attention of geotechnical engineers specializing in soil stabilization. This method involves the utilization of urease enzymes combined with urea and calcium chloride to induce calcium carbonate precipitation. The effectiveness of the EICP treatment is influenced by the concentration of the chemical components and the urease enzyme. To identify the optimal formulation of the treatment, tube tests were conducted using 1 M urea and varying concentration of calcium chloride to identify the optimal formulation of the treatment, along with different amounts of urease enzyme. The identified optimal EICP formulation was then employed to investigate the uniform distribution of calcium carbonate precipitation in the prepared specimens before subjecting them to experimental testing. The research delves into monotonic drained triaxial tests, which were conducted to gain insights into the mechanical behavior of EICP-treated specimen after 7 days of curing time under three effective confining pressures: 50, 100, and 200 kPa. Biocementation through EICP significantly enhanced the deviatoric stress, dilatancy, and shear strength parameters in one treatment cycle. Microscopic analyses were performed to comprehend further the microstructural transformations resulting from calcium carbonate precipitation. These include field-emission scanning electron microscopy (FE-SEM) analysis, energy dispersive spectroscopy (EDS) elemental mapping, and X-ray diffraction (XRD) studies on calcium carbonate precipitate from tube tests, pure sand, and EICP-treated sample. The FE-SEM and EDS analysis revealed augmented strength particle-to-particle contact and particle-to-calcite precipitation due to EICP treatment. Notably, XRD results confirm that the crystals formed through EICP treatment are primarily composed of calcite.