The micromechanical mechanism of upward pipe-soil interaction in unsaturated soil remains unresolved. This study investigates the upward pipe-soil interactions in dry and unsaturated granular soil through a sequence o...
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The micromechanical mechanism of upward pipe-soil interaction in unsaturated soil remains unresolved. This study investigates the upward pipe-soil interactions in dry and unsaturated granular soil through a sequence of coupled discrete element method and finite element method (DEM-FEM) simulations. The capillary suction effect was simulated using the Johnson-Kendall-Roberts (JKR) adhesive model, while the pipe segment was simulated with finite element mesh. A comparison was conducted between the behaviors of pipes and soil in dry, unsaturated soils at various depths of burial. The findings reveal that discontinuity and large deformation in unsaturated granular soil can be modeled successfully. In addition, the capillary suction effect on the stress and deformation of pipes is effectively explained by the wide contact force distribution and the weak particle collision behaviors around pipes. Meanwhile, the study identifies differences in soil arching effects as the essential reason behind the different modes of soil deformation in dry and unsaturated soils. Moreover, an exploration of particle-scale behaviors yields several conclusive mechanistic modes of upward pipe-granular soil interaction at different burial depths. The study demonstrated that suction in unsaturated granular soil significantly improves the upward pipe-soil interaction force and changes the failure mode of pipe-soil interactions.
The micro-mechanism of local scour around circular piles in granular soil under steady flows remains unclear. This study investigates local scour around circular piles with the coupled Smoothed Particle HydrodynamicsD...
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The micro-mechanism of local scour around circular piles in granular soil under steady flows remains unclear. This study investigates local scour around circular piles with the coupled Smoothed Particle HydrodynamicsDiscrete Element Method (SPH-DEM) for the first time, taking the effects of scour lengths and flow velocities into consideration. The granular soil and piles are modeled using DEM elements, while the water is modeled using SPH elements. The flow regularity and scour holes in numerical simulations are compared with those in experiments, while detailed pile-water-soil interactions are analyzed. The findings demonstrate that the flow behaviors evolve with the development of scour holes. Large deformation and turbulent flow occurrences surrounding piles are successfully simulated using the SPH-DEM approach and their relationships to scour lengths are discovered. Besides, relationships between local flow direction, vortexes, and soil erosion are established by analyzing the streamlines and fluid force on particles. Furthermore, detailed investigations of particle transportation and scour holes under both flow and flow-stop conditions lead to an identification of conclusive modes of soil erosion around piles. This study provides novel insights into local scour behaviors around pile foundations in granular soil.
A novel ground improvement method that combines grid prefabricated horizontal drains (PHDs) with prefabricated vertical drain (PVD) assisted by vacuum preloading is proposed for the beneficial reuse of dredged clayey ...
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A novel ground improvement method that combines grid prefabricated horizontal drains (PHDs) with prefabricated vertical drain (PVD) assisted by vacuum preloading is proposed for the beneficial reuse of dredged clayey slurry for reclamation purpose. To assess the feasibility of this innovative method, physical model tests are designed and conducted using high-water content Hong Kong marine deposits as the clayey slurry material. Furthermore, the impact of the spacing configuration of the grid PHD on the effectiveness of the proposed method is investigated through a series of model tests. A test without the installation of PVD was set, and in this case, two phases of vacuum preloading are applied sequentially through the PHD layer installed in stage. The other three tests involve three phases, with the addition of a vacuum preloading stage through PVD and variations in arrangement pattern of grid PHD layer. Results show that this proposed approach yields a final average undrained shear strength of soil of approximately 30 kPa, meanwhile reducing the average water content to around 50%. Furthermore, it is observed that decreasing the vertical spacing of grid PHDs results in growing final settlement. Reducing the horizontal spacing has less impact on the final settlement.
A frequently overlooked aspect in previous research on bearing capacity of reinforced foundations is the prevalent unsaturated properties of soils. This paper provides an analytical framework for evaluating the bearin...
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A frequently overlooked aspect in previous research on bearing capacity of reinforced foundations is the prevalent unsaturated properties of soils. This paper provides an analytical framework for evaluating the bearing capacity of strip footings with single-layer and double-layer reinforcement in unsaturated soils. Four classical nonlinear expressions are used to determine the additional cohesion induced by matric suction. Solutions for the reinforcement layer undergoing tensile failure and sliding failure are provided separately. In the former case, where the bearing capacity depends on the reinforcement's tensile strength, the Prandtl mechanism is employed. In the latter case, where the bearing capacity is influenced by the characteristics of the reinforcement-soil interface, a multi-block mechanism is adopted. Additionally, sliding failure exhibits different mechanisms depending on the reinforcement's embedded depth. By comparing the results of different failure mechanisms, accurate upper bound solutions for bearing capacity are obtained. In the case of sliding failure, the optimal reinforcement depths that maximize the bearing capacity are identified for both single-layer and double-layer reinforcement. To facilitate engineering use, the optimum depths and corresponding bearing capacity factors are given in tabular form. The effectiveness of the framework is demonstrated through comparisons with previous theories, experiments, and finite element simulation results.
This research investigates the particle-scale stress transmission characteristics at the end of isotropic consolidation stage for sand-rubber mixtures, focusing on the effects of particle size disparity, density, and ...
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This research investigates the particle-scale stress transmission characteristics at the end of isotropic consolidation stage for sand-rubber mixtures, focusing on the effects of particle size disparity, density, and stress levels. The discrete element method was adopted with total 450 simulations being conducted for sand-rubber mixtures with increasing size disparities to quantify the particle-scale stress distribution between sand and rubber materials. This study reveals that the variation of coordination number and void ratio for sand-rubber mixtures align with those observed in conventional gap-graded soils, while the inclusion of deformable rubber clumps significantly increases coordination number values. A complex interplay between packing density and stress level was evident, illustrating the nuanced role of rubber in stress transmission. As packing density and stress levels decrease, the efficacy of deformable rubber clumps in stress transfer increases. An inverse relationship between the efficiency of stress transmission and particle size disparity was observed for all these sand-rubber mixtures. The findings indicate that, despite variations in size disparity, the proportion of stress transferred by rubber remains consistently lower than their volumetric contribution. This study underscores the complexities of using sand-rubber mixtures and highlights that the effect of particle property disparity outweighs the that of particle property disparity.
This paper develops a novel Hybrid Particle Element Method (HPEM) to model large deformation problems in solid mechanics, combining the strengths of both mesh-based and particle approaches. In the proposed method, the...
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This paper develops a novel Hybrid Particle Element Method (HPEM) to model large deformation problems in solid mechanics, combining the strengths of both mesh-based and particle approaches. In the proposed method, the computational domain is discretized into two independent components: a set of finite elements and a set of particles. The finite elements serve as a temporary tool to compute the spatial derivatives of field variables, while the particles are used for storing history variables and establishing equilibrium equations. Spatial derivatives of field variables on particles are obtained by averaging the surrounding Gauss points of finite elements with a smoothing function. When the finite element mesh becomes distorted, it can be arbitrarily adjusted or completely regenerated. No global variable mapping is required when mesh adjustment or regeneration is performed, thus avoiding irreversible interpolation errors. The proposed method is validated through six typical examples, assessing its accuracy, efficiency, and robustness. The superior performance of the proposed method is comprehensively demonstrated through comparisons with several existing numerical methods.
Accurately describing the solid-like and fluid-like behaviors of granular media is crucial in geotechnical engineering. While the unified frictional-collisional model, integrating rate-independent frictional and rated...
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Accurately describing the solid-like and fluid-like behaviors of granular media is crucial in geotechnical engineering. While the unified frictional-collisional model, integrating rate-independent frictional and ratedependent collisional stresses, is widely used for solid-fluid phase transitions, an effective model is still under investigation, and comprehensive analyses are lacking. This study addresses these gaps by developing an enhanced elastoplasticity-based frictional-collisional model. The frictional stress is modeled using a critical-statebased elastoplasticity approach, and the collisional stress is formulated through an enhanced kinetic theory incorporating particle stiffness. Subsequently, comprehensive element simulations are conducted to explore the effects of concentration, particle stiffness, and strain rate paths on the model. The proposed model's effectiveness is also validated against experimental data. Finally, a detailed comparison with the typical mu(I) rheology model and a state-equation-based phase transition model is conducted. Our analyses show that the developed model effectively captures strain rate path and particle stiffness through the collisional stress component, while concentration-dependent characteristics are captured through both frictional and collisional stress components. Through comparative analyses, we also found that both the state-equation-based and elastoplasticity-based models depict solid-like behavior and replicate the rheology of granular media in a fluid-like state, similar to the mu(I) model. However, they differ in implementing critical state theory: the state-equation-based model acts as a partial-range phase transition model, describing stress evolution from the critical state to the fluid-like state, while the proposed elastoplasticity-based model serves as a full-range phase transition model, covering stress evolution from the initial to the fluid-like state.
This study systematically investigates the small-strain stiffness of sand-rubber mixtures, focusing on combined particle disparity-both larger sand with smaller rubber and smaller sand with larger rubber-using the dis...
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This study systematically investigates the small-strain stiffness of sand-rubber mixtures, focusing on combined particle disparity-both larger sand with smaller rubber and smaller sand with larger rubber-using the discrete element method. The effectiveness of various state variables in capturing stiffness behavior across different rubber contents and size disparities (SDs) is evaluated. Conventional state variables developed for natural sands, such as void ratio and mechanical void ratio were found to be less effective in describing the small-strain stiffness characteristics of sand-rubber mixtures due to distinct properties of rubber. This study then demonstrates that the stiffness contribution of rubber materials could be negligible, emphasizing that particle property disparity is more significant than SD between sand and rubber materials. Therefore, an adapted state variable, considering only active sand particles, shows improved performance for capturing the correlation between small-strain stiffness with increasing rubber contents, suggesting its potential utility over conventional variables. Additionally, a refined void ratio, including inactive sand particles but excluding rubber, offers a practical alternative for capturing small-strain stiffness in experimental and engineering practices, aligning with previous experimental observations. These findings underscore the need for developing more effective state variables that accurately reflect the interactions within heterogeneous materials like sand-rubber mixtures.
The importance of yield surface for clays lies in describing compression behaviour, shear strength, and induced anisotropy. Various yield surfaces were proposed and adopted in modelling, but they are not consistent on...
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The importance of yield surface for clays lies in describing compression behaviour, shear strength, and induced anisotropy. Various yield surfaces were proposed and adopted in modelling, but they are not consistent on describing anisotropic consolidation and/or undrained shear with both compression and extension stress paths of K0-consolidated clays. This study proposes a new generalized anisotropic yield function for K0-consolidated clays. First, limitations of existing yield surface are discussed based on comparisons with measurements of yield surfaces on various clays. Taking the more flexible isotropic yield function of Hardin and introducing the inclination angle of yield surface, a new generalized anisotropic yield surface is then proposed. The new anisotropic yield function is successfully examined on the predictive ability on the eta-constant compression behaviour, and both the g(theta )-method and the TS-method (Transformed stress-method) can be adopted for taking into account the Lode angle effect in three-dimensional strength. Next, the new yield function is applied to develop an anisotropic elasto-plastic bounding surface model. The predictive performance is finally evaluated by comparing experimental and predicted results of anisotropic consolidation and shear tests on two reconstituted K0-consolidated clays.
The complex morphologies of particles are a crucial factor influencing suffusion in gap-graded granular soils. However, the micro-mechanism of soil suffusion composed of irregular concave particles remains unclear. To...
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The complex morphologies of particles are a crucial factor influencing suffusion in gap-graded granular soils. However, the micro-mechanism of soil suffusion composed of irregular concave particles remains unclear. To this end, a systematic numerical simulation that considers particle concavity and aspect ratio is performed with the resolved discrete element method (DEM) and computational fluid dynamics (CFD) approach. The macro responses of suffusion of particles with varying morphologies, e.g., cumulative eroded particle mass and sample profile, are revealed and interpreted from a microscopic view, e.g., particle rotation, average number of contact points, and moment. It is found that the rotation of irregularly shaped particles during suffusion requires overcoming the moment applied by the surrounding particles. Particles with bigger contact force or irregularity require a higher moment to be overcome, thus significantly increasing their suffusion resistance. Irregularly shaped particles can adjust their orientation to reduce the moment and drag force applied to them. At the same aspect ratio, particles with larger concavity are more likely to interlock with each other, with increasing the average number of contact points of the soil packing and shrinking the pore channel for particle migration. A shape parameter considering both concavity and aspect ratio is finally proposed to characterise the influence on suffusion.
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