3D DEM modeling of biocemented sand with fines as cementing agents

Abstract

Microbially induced calcium carbonate precipitation (MICP) has attracted much attention as a promising green technique for soil improvement. Despite the significance of precipitation pattern in mind, constitutive relations or numerical models considering the finite-strain mechanical effects of the various precipitation patterns are rarely developed. In this paper, we propose a novel 3D DEM modeling scheme by using coarse particles to represent sand grains and fines as cementing agents, to reproduce the various precipitation patterns in MICPtreated sand. Based on the topological relations with adjacent particles and the contribution to the mechanical improvement, the cementing fines are classified into effective, partially effective, surface coating, and pore filling ones. The microstructural characteristics and their evolution upon external loading are investigated quantitatively after a careful calibration and validation. The microstructural variation in experiments can be well reproduced, pinpointing this variation as a possible cause for the fluctuation in experimental data. Massive coating fines are produced accompanying the microstructural degradation, which is initiated by the breakage of effective bonds. The breakage of partially effective bonds may become dominating later in the medium to strong cemented specimens. One weakly cemented specimen shows diffuse failure with simultaneous bond-breakage and friction. In contrast, the medium to strong cemented specimens show localized failure with the dominating mechanism transiting from bond-breakage to friction producing notable pore filling fines. We propose a relation between unconfined compressive strength and the equivalent effective volume fraction of cementing agents normalized by the pretreatment porosity, which reveals the coupling effects of the initial configuration and the precipitation pattern on the mechanical improvement.

Removal of ammonium by‐products produced during biocementation soil improvement using rinse injection strategies

“…However, when staged injections were used, which allowed for extended retention periods, both columns rinsed with solutions lacking Ca 2+ (S‐DI, S‐K‐200) exhibited the largest V s reductions observed in all columns near 50 m/s (≈10% of post‐treatment values) with more minimal V s reductions observed in the column receiving staged Ca 2+ ‐enriched solutions (S‐Ca‐200). Although minimal V s reductions were observed in all columns, potential differences in the particle‐level patterns of dissolution resulting from rinse injections (i.e., dissolution at particle contacts vs. dissolution of particle coatings vs. dissolution of free precipitates) have been shown to significantly alter relationships between V s values and soil CaCO 3 contents (Lin et al., 2020; Wu et al., 2023). Accordingly, potential differences in particle‐scale dissolution patterns resulting from different rinsing techniques may merit further investigation in future studies.…”

Simultaneous Biocementation and Compaction of a Soil to Avoid the Breakage of Cementitious Structures during the Execution of Earthwork Constructions

“…It should be noted that MICP occurs at the site of bacterial-cell nucleation or calcium-carbonate precipitation, which is associated with an increase in alkalinity originated by ureolysis, as reviewed by several authors [26][27][28]30]. In a very recent study, Wu et al [31] considered a novel 3D DEM (discrete element model) of biocemented sand with fines as cementing agents. Thus, it was a quantitative study designed to reproduce the different precipitation patterns in sand treated by MICP through an analysis of the microstructural characteristics and how they changed under external loading.…”

“…In a very recent study, Wu et al [31] considered a novel 3D DEM (discrete element model) of biocemented sand with fines as cementing agents. In order to replicate the diverse patterns of precipitation in sand treated by MICP, a quantitative investigation was conducted to examine the microstructural properties and how they changed in response to external loading.…”

Micromechanics of multiphase geomaterials based on micro-CT image analysis: unsaturated soil, vegetated soil, and bio-cementation

“…Numerical methods such as the discrete element method (DEM) are utilized to investigate the microscale behaviors of unsaturated granular soils, offering a potent means to explore the macroscopic mechanical properties of geomaterials at the micro-level [7][8][9]. However, DEM simulations fall short of accurately replicating the complex topological structures of multiphase geomaterials, and theories pertaining to the microscopic mechanism lack effective experimental verification.…”