Jie Yang

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.

Local scour around suction caisson foundations has emerged as a significant geotechnical hazard for offshore wind turbines as developments extend into deeper waters. This study quantitatively evaluates the scour-induced degradation of the bearing capacity of suction buckets in sand using a three-dimensional finite element model incorporating the Hardening Soil (HS) constitutive model. The HS framework enables realistic representation of stress-dependent stiffness, dilatancy, and plastic hardening, which are essential for simulating stress redistribution caused by scour. Parametric analyses covering a broad range of relative scour depths show that scour depth is the primary factor governing capacity loss. Increasing scour leads to systematic reductions in horizontal and moment capacities, evident stiffness softening, and a downward migration of plastic zones. A critical threshold is identified at S_d/L = 0.3, beyond which the rate of capacity deterioration increases significantly. The H–M failure envelopes contract progressively and exhibit increasing flattening with scour depth while maintaining nearly constant eccentricity. Empirical relationships between scour depth and key envelope parameters are further proposed to support engineering prediction. The results highlight the necessity of integrating scour effects into design and assessment procedures for suction bucket foundations to ensure the long-term performance and safety of offshore wind turbines.

This paper develops a novel erosion law that incorporates the influence of stress state into the mass exchange between the liquid and solid phases for suffusion, using the coupled computational fluid dynamics and the discrete element method (CFD–DEM) simulations. To achieve this, a series of CFD–DEM simulation tests are conducted on gap-graded soil samples, followed by the derivation of a new erosion law that considers the influence of seepage velocity and mechanical conditions. The proposed erosion law is then integrated into a four-constituent framework to enable hydromechanical modeling. Furthermore, a fines-dependent constitutive model based on the critical state concept is implemented to account for the influence of suffusion on the mechanical behavior of the soil. The new model is assessed through a series of laboratory hydromechanical tests, yielding satisfactory estimation results. Subsequently, the model is utilized to investigate the influence of soil initial state, including void ratio, friction angle, fine content, and size ratio, on the evolution of erosion. Finally, the mechanical behavior of soils before and after suffusion is modeled using the proposed framework. The results demonstrate that the CFD–DEM-based erosion law, as well as the hydromechanical model, effectively capture the main characteristics of soils subjected to suffusion.