Influence of MICP Mineralization on the Mechanical Behavior of Sand Considering Different Contact Types in the Discrete-Element Method

Abstract Microbially induced calcium carbonate precipitation (MICP) is a promising green soil improvement technology. The micro- and mesoscale deposition state of calcium carbonate influences soil strength, but existing numerical models often neglect precipitation patterns and particle contact modes, hindering the clarification of micro–meso–macro property relationships. In this study, we propose a novel discrete-element method modeling scheme that simulates calcium carbonate precipitation by generating microparticles between sand grains and at their contacts. The model accounts for three key interaction types: sand–sand contacts, sand–calcium carbonate particle contacts, and calcium carbonate–calcium carbonate particle contacts. The results indicated that selecting appropriate particle contact models based on interparticle mineralization effects could more accurately characterize the microscale interaction mechanisms and mineralization characteristics of calcium carbonate-improved soils. An analysis of the influence of varying calcium carbonate content on the mechanical properties of MICP-mineralized sand revealed that both the peak and residual strengths increased significantly with higher calcium carbonate content, reaching 1.2–8.7 times those of untreated samples. An increase in confining pressure was found to enhance the deformation modulus of the specimens, while the modulus exhibited a critical threshold effect with increasing calcium carbonate content: the increase was gradual below 3%, but became abrupt beyond this value. Cohesion remained low when the calcium carbonate content was below 3% but improved markedly once this threshold was exceeded, owing to the formation of a stable mineralization network. The internal friction angle initially experienced a slight reduction at low calcium carbonate content but increased substantially with further content increase.