Three-Dimensional Reconstruction of Biomineralized Sand and Particle-Flow-Code Numerical Simulation of Penetration Resistance Characteristics of Biomineralization Crust

When fine sand is treated with microbial-induced calcite precipitation (MICP), the connections of loose sand particles are reinforced by being filled with crystals of calcium carbonate (CC) caused by the presence of microorganisms. According to the research of scholars, in the process of MICP, the common anhydrous CC crystals are calcite, vaterite, and aragonite. To explore the factors that influence the penetration resistance (PR) of a biomineralization crust (BMC) and to consider the influence of sand particles and CC crystal morphology on strength, this paper reconstructs the sand particles and CC crystals by means of three-dimensional reconstruction from photographic images. Two numerical models based on a particle flow code were established using the discrete element method and were used to investigate separately (1) the unconfined compressive strength (UCS) of a biomineralized sand column; and (2) the PR of a BMC. The research shows that the UCS of an MICP sand column of calcite crystal form is 4.9 MPa, which is 2.39 times that of one of vaterite forms. It is found that the thickness of the BMC and its CaCO3 content has a great influence on the PR of the BMC. The PR shows an increasing trend due to the increase of CC content when the penetration speed is 1.5 m/s and the coating thickness of the coating layer is 2.5 cm. The PR test value at 2.5 cm in the soil layer increases from 52.8 to 103.9 kPa when the penetration speed is 1.5 m/s, the CaCO3 content is 12%, and the thickness of the BMC is increased from 2.5 to 4.5 cm. It is concluded that because the thickness of the BMC and the CC content increases, the PR of the test points in the soil also increases. The results of this study complement the test results of a field-scale experiment and have important value for the large-scale application of MICP technology to desert sites for desertification control.