Search Results (40)

Accurate prediction of the load–settlement response of axially loaded piles remains challenging because the pile–soil interface undergoes progressive elastoplastic shear deformation accompanied by stress-dependent volumetric changes. Conventional one-dimensional load-transfer models are computationally efficient but usually rely on empirical or hyperbolic fitting functions, making it difficult to explicitly describe the coupled evolution of interface shear hardening, volumetric hardening, and radial effective stress. Although three-dimensional elastoplastic models provide a more rigorous mechanical representation, their high computational cost limits routine engineering application. To address this gap, this study develops a double-hardening elastoplastic load-transfer model for axially loaded piles based on a physically interpretable pile–soil interface constitutive formulation. In the proposed model, the Hardening Soil model is used to characterize interface shear hardening, while the Modified Cam-clay model is introduced to describe volumetric hardening. These two mechanisms are coupled through a stress–dilatancy relationship. According to the loading direction and the position of the current stress point relative to the shear and volumetric yield surfaces, the p′–q stress plane is divided into elastic, shear-hardening, volumetric-hardening, and coupled double-hardening regions. The corresponding incremental constitutive equations are derived and embedded into a conventional load-transfer framework. The model is validated using interface direct shear tests and field-scale static pile load tests. The predicted shear stress–displacement curves and pile-head load–settlement responses agree well with the measured data. Quantitative evaluation shows that the MAPE values are lower than 5%, the maximum relative errors are below 7.6%, and the R² values exceed 0.96 for all validation cases. Full article

This paper proves that existing implicit integration schemes for the modified cam-clay (MCC) cannot handle the dependency of critical state stress ratio on Lode angle, because the coaxiality between the deviatoric strain rate tensor and the deviatoric stress tensor, on which these algorithms are built, no longer holds when the Lode angle effect is considered. A more appropriate algorithm is proposed based on closet point return mapping, and a consistent tangent modulus is calculated. After detailed mathematical derivations, the proposed method is examined via four computational examples. The first example includes a series of numerical triaxial tests, for demonstrating the appropriateness of the employed constitutive equations. The second and third examples are convergence tests at the material (integration point) level and finite element (FE) level, respectively. The resulting quadratic converging rate proves that the Jacobian matrix for return mapping and the consistent tangent modulus for finite element implementation are correctly computed. The last example concerns drained penetration of a surface footing. The proposed method is demonstrated to be more efficient and robust in this case than the Abaqus built-in MCC model, which aborted halfway when simulating the same problem. Full article

Anti-toppling helical piles exhibit superior load-bearing performance due to enhanced interaction between the helices and the underlying soil; however, rigorous theoretical frameworks for their compressive analysis remain scarce. To address this limitation, this study proposes a computationally efficient analytical model utilizing the Modified Cam-Clay (MCC) constitutive framework to calibrate plane strain elements for pile–soil interaction simulations. Wedge-shaped and bulb-shaped fictitious soil pile models are introduced to accurately capture vertical capacity mobilization beneath the helix and pile tip, respectively. After successfully validating the framework against 3D finite element simulations and field test data, extensive parametric analyses were conducted. The key findings reveal that (1) unlike conventional piles, skin friction for anti-toppling helical piles increases monotonically with depth; (2) an optimal helix-to-pile diameter ratio of approximately 1.5 maximizes coordinated bearing capacity; (3) increasing pile length below a fixed helix depth provides negligible additional capacity; and (4) the critical state parameter M strictly controls the ultimate bearing threshold. Full article

The simulation accuracy of triaxial tests for oversolidated clay in transient finite element analysis is affected by soil constitutive model, permeability coefficient, overconsolidation ratio, shear rate and mesh size. This study introduces the concepts of overconsolidation parameters, potential strength, and hardening parameters from the unified hardening model into the modified Cam-Clay model. By integrating the generation mechanism of pore water pressure, a constitutive model for overconsolidated clay incorporating pore water pressure was developed, and its accuracy was validated through triaxial tests. By invoking the UMAT subroutine, accurate simulation of the undrained triaxial tests of overconsolidated clay was achieved in the static/general analysis in Abaqus. Based on this, model parameters for simulating triaxial tests of overconsolidated clay in transient analysis (Soils) were calibrated. The relationships between shear rate, mesh size, and soil parameters were quantified, providing a reference for similar engineering numerical simulations. Full article

Soil compaction in grassland and agricultural soils reduces water infiltration, root growth and ecosystem services. Conventional deep tillage and coring can alleviate compaction but are energy intensive and strongly disturb the turf. This study proposes an earthworm-inspired subsurface robot as a low-disturbance loosening tool for compacted grassland soils. Design principles are abstracted from earthworm body segmentation, anchoring–propulsion peristaltic locomotion and corrugated body surface, and mapped onto a robotic body with anterior and posterior telescopic units, a flexible mid-body segment, a corrugated outer shell and a brace-wire steering mechanism. Kinematic simulations evaluate the peristaltic actuation mechanism and predict a forward displacement of approximately 15 mm/cycle. Using the finite element method and a Modified Cam–Clay soil model, different linkage layouts and outer-shell geometries are compared in terms of radial soil displacement and drag force in cohesive loam. The optimised corrugated outer shell combining circumferential and longitudinal waves lowers drag by up to 20.1% compared with a smooth cylinder. A 3D-printed prototype demonstrates peristaltic locomotion and steering in bench-top tests. The results indicate the potential of earthworm-inspired subsurface robots to provide low-disturbance loosening in conservation agriculture and grassland management, and highlight the need for field experiments to validate performance in real soils. Full article

This study numerically investigates the deformation and consolidation behavior of high-water-content river sediment improved by a combined vacuum preloading and internal air-bag pressurization (VPA) system. A 2D axisymmetric finite-element model in Abaqus 2021 with the Modified Cam-Clay constitutive law is established to simulate the treatment process. Key design parameters—air-bag pressure, pressurization timing, embedment depth, and staged loading—are systematically analyzed. Results show that: (1) Under a −80 kPa vacuum, an additional 20 kPa air-bag pressure reduces the maximum inward horizontal displacement by over 20%, while effective stress increases linearly with pressure; (2) Early pressurization (20 days) better controls lateral deformation and accelerates strength gain; (3) Staged pressurization (20 kPa upper, 40 kPa lower) outperforms uniform loading in both displacement control and cost-effectiveness; (4) Compared to 30 kPa surcharge preloading, VPA further reduces horizontal displacement by 10–18% under equivalent total load. The hybrid “vacuum–air-bag–surcharge” scheme yields the highest effective stress and smallest lateral deformation. The VPA method enhances sediment engineering properties, providing a viable approach for resource utilization of dredged materials. Full article

Because of its specific nature, mining activity causes numerous negative impacts on the environment, both during the exploitation phase and after it has ended. An important source of income in the Jiu Valley is represented by the Lupeni Mining Exploitation. Like any mining activity, coal exploitation causes various negative effects on the environment. The subsidence phenomenon represents a significant issue associated with coal mining in the Jiu Valley. Underground extraction of mineral deposits induces displacement of the overburden strata. Such displacements result in ground subsidence and modifications of the surface topography. The larger the voids created following the exploitation of useful mineral deposits, the more they affect the surface of the land above the exploitation through sinking, displacement, deformation, and even cracks. Secondary deformations refer to post-mining surface movements induced by delayed rock mass adjustment, manifesting as ground collapse, localized subsoil failure, or uplift driven by groundwater rebound after drainage cessation. In this paper, we aim to study the subsidence phenomenon produced by coal mining at the Lupeni Mining Exploitation using the COMSOL simulation software and applying the Barcelona Basic Model (BBM) and Modified Cam-Clay (MCC) models. Following the simulation, the behavior of the rocks could be observed in order to improve prediction accuracy to support sustainable land management in post-mining areas. Full article

This study introduces an innovative deflection-controlled design method (DCM) for evaluating the bearing capacity of offshore mono-bucket foundations (MBFs) in clay, integrating advanced numerical simulations using FLAC3D with the modified cam clay (MCC) soil model. Departing from conventional ultimate bearing capacity approaches, the proposed method prioritizes serviceability limits by constraining foundation deflections to ensure optimal structural performance and turbine efficiency. A systematic investigation revealed that the MBF performance is predominantly governed by eccentricity ratios and soil–structure interaction, with vertical loads exhibiting a minimal impact in a serviceability limit state. Key findings include the following: (1) the rotation center (RC) stabilizes at approximately 0.8 times the skirt length (L) under loading; (2) thin, deep MBFs (aspect ratio > 1.0) exhibit up to a 30% higher bearing capacity compared to wide, shallow configurations; (3) increasing eccentricity ratios (ε = 0.31–1.54) enhance the moment capacity but reduce the allowable horizontal force by 15–20%; (4) compressive vertical loads (υ = −0.30) slightly reduce the normalized bending moments (ω) by 5–10% at low eccentricities (ε < 0.5). The numerical framework was rigorously validated against centrifuge test data, demonstrating high accuracy (error < 3%) in predicting foundation behavior. By bridging geotechnical mechanics with practical engineering requirements, this study provides a robust and efficient design framework for MBFs, offering significant improvements in reliability and cost-effectiveness for offshore wind turbine applications. The proposed DCM successfully guided the design of an MBF in southeastern China, demonstrating its efficacy for use with homogeneous clay. Full article

This study investigates the full penetration simulation of piles from the ground surface, focusing on frictional contact modeling without mesh distortion. To overcome issues related to mesh distortion and improve solution convergence, the Arbitrary Lagrangian–Eulerian (ALE) adaptive mesh technique was implemented within both explicit and implicit time integration schemes. The numerical model was validated against field experiments conducted at Bothkennar, Scotland, using the Imperial College instrumented displacement pile (ICP) in soft clay, where the soil behavior was effectively represented using the modified Cam-Clay model and the Mohr–Coulomb model. The primary objectives of this study are to evaluate the ALE method performance in handling mesh distortion; analyze the effects of soil–pile interface friction, pile dimensions, and various dilation angles on pile resistance; and compare the effectiveness of explicit and implicit time integration schemes in terms of stability, computational efficiency, and solution accuracy. The ALE method effectively modeled pile penetration in Bothkennar clay, validating the numerical model against field experiments. Comparative analysis revealed the explicit time integration method as more robust and computationally efficient, particularly for complex soil–pile interactions with higher friction coefficients. Full article

In order to consider the effect of fabric anisotropy in the analysis of geotechnical boundary value problems, this study proposes a modified model based on a fabric-based modified Cam-clay model, which can account for the anisotropic response of soil. The major modification of the original model aims to simplify the equations for numerical implementation by replacing the SMP strength criterion with the Lade’s strength criterion. This model comprehensively considers the inherent anisotropy, induced anisotropy, and three-dimensional strength characteristics of soil. The model is first numerically implemented using the elastic trial–plastic correction method, and then it is encapsulated into the FLAC^3D 6.0 software, and tested through conventional triaxial, embankment loading, and tunnel excavation experiments. Numerical simulation results indicate that considering anisotropy and three-dimensional strength in geotechnical engineering analysis is necessary. By accounting for the interaction between microstructure and macroscopic anisotropy, the model can more accurately represent soil behavior, providing significant advantages for geotechnical analysis. Full article

Cemented paste backfill (CPB) is a cemented void filling method gaining popularity over traditional hydraulic or rockfill methods. As mining depth increases, CPB-filled stopes are subjected to higher confining pressures. Due to the soil triaxial apparatus limitations, as the conventional method of triaxial testing on CPB, no confining pressures higher than 5 MPa can be applied to CPB over a range of curing time. This lack of data introduces uncertainty in predicting CPB behavior, potentially leading to an overestimation of the required strength. To address this, this study introduces a new testing method that allows for higher confinement beyond traditional limitations by modifying the Hoek triaxial cell to accommodate low-strength materials. This study then investigates the coupled influence of confining pressure and curing time (hydration) on CPB characteristics, specifically examining the impacts of different curing times and confining pressures on the mechanical and rheological properties of CPB. A total of 75 triaxial tests were conducted using 42 mm cylinder shape samples at five various curing times from 7 to 96 days, and applied at low and high confinement condition levels (0.5 to 30 MPa). The results reveal that hydration and confinement positively impact the CPB strength. The modified structured Cam-Clay model was selected to predict the behavior, and its yield surface was updated using the experimental results. The proposed yield model can be utilized to describe CPB material subjected to various curing and pressure conditions underground. Full article

Accurate estimation of in-situ stresses is a critical parameter for geo-mechanical modelling. In-situ stresses are estimated in the field from logs and frac tests. Laboratory tests are performed with cored material to estimate horizontal stress changes under defined boundary conditions to complement field data. Horizontal stress path coefficient is used to estimate a change in in-situ stresses as the reservoir undergoes depletion or injection. Uniaxial Strain boundary conditions are representative of far field stress state. The laboratory data provides the change in horizontal stress with a change in pore pressure. It is used to complement the field data acquisition of absolute stress values to predict the value of total stresses. This experimental study provides a novel method of simulating geological compaction for fabricating representative samples from unconsolidated sands. It investigates the variability of horizontal stress path coefficient as a function of changing pore pressure (depressurization and re-pressurization) in unconsolidated sandstone reservoirs. Synthetic sandstones samples were made from sand packs by consolidating them under an isostatic stress path at ambient pore pressure. After getting to initial reservoir conditions, a series of pore pressure depletion and injection tests with varying magnitudes (injection and depletion) were performed to study the effects of stress path direction and associated hysteresis. The magnitude of the stress path coefficient under depletion is lower than that under injection for the first load-unload cycle. In subsequent load-unload cycles, the stress path coefficient values remain constant until the sample is depleted to a new level of pore pressure. A Modified Cam Clay model is fit to the data to map the expansion of the yield surface and quantify the model parameters. Application of this research includes accurate prediction of changes in-situ stresses during depletion and injection stress paths for simulating unconsolidated reservoirs behavior under fluid injection or further depletion. Full article

The water sensitivity and structural characteristics of collapsible loess are two typical factors that significantly influence its mechanical behaviors. This paper presents a simple and practical elastic-plastic model based on the modified Cam-Clay model to well capture the essential behavior of unsaturated intact loess. The model employs deviator stress and spheric stress as the stress variables, with the water content serving as the moisture variable. The critical state surface of the model can be determined by utilizing the shear strength parameters of unsaturated soil under axisymmetric stress conditions. An initial yield surface equation is established by incorporating structural strength into the elliptical yield surface equation, which is used to determine the starting point for elastic-plastic deformation calculations under different humidity and stress combinations. The model comprises several parameters, each of which has a clear physical interpretation and can be conveniently obtained through conventional triaxial tests. The validity of the model for unsaturated intact loess is confirmed through a comparison with the stress–strain relationship of unsaturated intact loess in the axisymmetric stress state. This work has the potential to significantly enhance our ability to predict and mitigate potential geotechnical disasters, such as foundation deformation under axisymmetric conditions and slope stability problems under non-axisymmetric conditions. Ultimately, the application of this model could contribute to the safety and stability of infrastructure and construction projects in loess regions. Full article

This paper provides the process of incremental constitutive integration for the unified hardening model combined with the transformation stress method. The dimension-extending technique takes the hardening function of the hardening/softening model as the same position as the stress components, so that the constitutive integration of the plasticity can be reduced to an initial value problem of differential–complementarity equations, which is solved using the Gauss–Seidel algorithm-based Projection–Correction for the mixed complementarity problem. The Gauss–Seidel based Projection–Correction algorithm does not require the calculation of the Jacobean matrix of the potential function, making it relatively easy to implement in programming. The unified hardening model is proposed based on the modified Cam–Clay model and the sub-loading surface model, and the elastic properties are pressure-dependent. Two processing methods, backward Euler integration and exact elastic property, are used for the variable elasticity properties. The constitutive integration of the increased dimensional unified hardening model is reduced to a special mixed complementarity problem and solved by the proposed algorithm, which does not need to calculate the Jacobean matrix of the potential function, and greatly simplifies the derivation process. Several numerical examples are given to verify the feasibility of the incremental constitutive integration in the unified hardening model, including the single integral point and the boundary value problems. The research results have expanded the scope of use of the Gauss–Seidel based Projection–Correction algorithm. Full article

Rapid sedimentation is widely recognized as a crucial factor in initiating the instability of submarine slopes. Once the slope fails, the subsequent landslide poses a significant threat to the safety of underwater infrastructures and potentially leads to severe damage to seabed pipelines, offshore foundations, and oil and gas exploitation wells. However, there is currently a lack of numerical methods to effectively assess the real-time stability of submarine slopes under rapid sedimentation. This study firstly employs a calibrated finite element (FE) model-change approach to reproduce the rapid sedimentation processes and proposes a concise method to calculate the safety factors for the real-time stability of sedimenting submarine slopes. Further, a parametric analysis is carried out to evaluate the effect of varying sedimentation rates on slope stability, and the critical sedimentation rate is numerically solved. Moreover, the effect of seismic events with different occurring times on the stability of rapidly sedimenting slopes is investigated in depth, and the most critical seismic loading pattern among various acceleration combinations is achieved. The results indicate that the presence of weak layers during sedimentation is a critical factor contributing to slope instability. The introduced rate of decrease in the safety factor proves valuable in assessing slope safety over a specific period. As the occurrence time of seismic events is delayed, the seismic resistance of the slope decreases, increasing the likelihood of shallower sliding surfaces. The findings offer insights into the mechanisms by which rapid sedimentation influences the stability of submarine slopes and provide valuable insights for predicting the potential instability of rapidly sedimenting slopes under specific seismic activity levels. Full article