Resonant Column Testing Procedure for Microbial-Induced Carbonate-Precipitated Sands

Abstract

Abstract One of the fundamental inputs to site response analysis is the characterization of the dynamic properties of the soil, namely the shear modulus and material damping ratio. Because of soil’s nonlinear behavior, these properties change with induced shear strains, and modulus reduction and damping (MRD) curves have been proposed to capture that cyclic shear strain dependency. Microbial-induced carbonate precipitation (MICP) is a natural cementation process that induces the precipitation of calcium carbonate, bonding soil particles together. Laboratory experiments have demonstrated that MICP can improve the mechanical behavior of soils and mitigate their liquefaction potential. However, MRD curves have not been developed for MICP-treated soils, which hinders further evaluations of their suitability as a ground improvement technique for geotechnical earthquake engineering applications. To the best of our knowledge, this paper provides the first empirical study measuring the shear strain–dependent dynamic properties of MICP-treated sands for different cementation levels (i.e., lightly to heavily cemented). Outcomes from this work include empirical models of the maximum shear modulus and minimum shear strain damping ratio of MICP-treated clean sands and the corresponding mean MRD curves. The experimental program includes MICP-treated specimens of Ottawa 20-30 sand tested with a resonant column (RC) device incorporating a modified RC porous disk that (1) minimizes the disturbance between treatment and installation of MICP-treated samples prior to being tested in the RC device, (2) prevents slippage between the specimen and the modified RC porous disk during RC shearing, and (3) enables repeatability of the MICP-treated sample preparation. We find that the level of cementation influences the MRD curves of MICP-treated sands. Linear elastic and volumetric shear strain thresholds for MICP-treated sands are smaller than those for untreated sands, whereas the initial shear modulus for treated soils is larger than its counterpart for untreated sands.