In this study, a series of undrained multidirectional cyclic simple shear tests were conducted using the discrete element method. Various stress paths, including figure-8, circular, teardrop, and straight-line shapes, were considered. Realistic and irregular particles were generated by integrating the theory of random fields for spherical topology with the Fourier-shape-based method. The influence of particle shape irregularity was assessed using a synthetic parameter derived from four common descriptors: aspect ratio, roundness, convexity, and sphericity. The study revealed that the liquefaction resistance of samples subjected to a constant cyclic shear stress ratio predominantly depended on the stress trajectory and particle shape. Numerical results demonstrated that the sample undergoing the unidirectional simple shear exhibited the highest liquefaction resistance, whereas the figure-8 shape exhibited the lowest. Furthermore, greater irregularity in particle shape corresponded to increased resistance to failure. Additionally, microstructural evolutions of granular samples were quantified throughout the simulation using the contact-normal-based fabric tensor. This allowed for a comprehensive exploration of the interplay between internal structure and external loading, leading to a more comprehensive understanding of the macroscopic observations discussed above.

The wave-induced liquefaction of seabed is responsible for causing damage to marine structures. Particle composition and consolidation degree are the key factors affecting the pore water pressure response and liquefaction behavior of the seabed under wave action. The present study conducted wave flume experiments on silt and silty fine sand beds with varying particle compositions. Furthermore, a comprehensive analysis of the differences and underlying reasons for liquefaction behavior in two different types of soil was conducted from both macroscopic and microscopic perspectives. The experimental results indicate that the silt bed necessitates a lower wave load intensity to attain the liquefaction state in comparison to the silty fine sand bed. Additionally, the duration and development depth of liquefaction are greater in the silt bed. The dissimilarity in liquefaction behavior between the two types of soil can be attributed to the variation in their permeability and plastic deformation capacity. The permeability coefficient and compression modulus of silt are lower than those of silty fine sand. Consequently, silt is more prone to the accumulation of pore pressure and subsequent liquefaction under external loading. Prior research has demonstrated that silt beds with varying consolidation degrees exhibit distinct initial failure modes. Specifically, a dense bed undergoes shear failure, whereas a loose bed experiences initial liquefaction failure. This study utilized discrete element simulation to examine the microscopic mechanisms that underlie this phenomenon.

Aiming at the problems of coastal ecological damage and low yield of mudflat aquaculture caused by the invasion of M. alterniflora, in order to improve the operational efficiency of mudflat wet and soft ground, and to promote the ecological balance and the development of coastal agriculture, a walking device with twin spiral propellers for muddy wet and soft ground was designed. Using EDEM simulation software to simulate and analyze, the discrete element model of muddy soil particles is established to analyze the interaction mechanism with the spiral propeller and the operation propulsion effect, and it is concluded that the spiral propeller will not produce congestion phenomenon during the operation; data are collected through several simulation tests, and the optimal parameter design of the spiral propeller structure is derived from the response surface analysis, and the spiral propeller is designed to operate at a speed of 2.416 mph in the simulation with the optimal parameter of structural design. The field test shows that the optimal height of the spiral blades is 50 mm, the total length of the drum is 2,970 mm, the helix angle of lift is 30 degrees, the pitch is 453 mm, and the propelling speed is 2.36 m/s. The data collected through several simulation tests are used to find the optimal parameter design of the spiral propeller structure, and the simulation speed of the spiral propeller in the optimal structural design parameter is 2.416 m/s.