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The progression of marine resource exploration into deepwater and ultra-deepwater regions has intensified the requirement for precise quantification of the undrained shear strength of clay. Although diverse in situ testing methodologies-including the vane shear test (VST), cone penetration test (CPT), T-bar penetration test (TPT), and ball penetration test (BPT)-are widely utilized for the assessment of clay strength, systematic discrepancies and correlations between their derived measurements remain inadequately resolved. The aim of this work is to provide a systematic comparison of strength interpretations across different in situ testing methods, with emphasis on identifying method-specific biases under varying soil behaviors. To achieve this, a unified numerical simulation framework was developed to simulate these four prevalent testing techniques, employing large-deformation finite element analysis via the Coupled Eulerian-Lagrangian (CEL) approach. The model integrates critical constitutive behaviors of marine clays, specifically strain softening and strain rate dependency, to replicate in situ shear strength evolution. Rigorous sensitivity analyses confirm the model's robustness. The results indicate that, when the stain rate and softening effects are neglected, the resistance factors from the CPT and VST remain largely insensitive to shear strength variations. However, T-bar and ball penetrometers tend to underestimate strength by up to 15% in high-strength soils due to the incomplete development of a full-flow failure mechanism. As a result, their application in high-strength soils is not recommended. With both the strain rate and softening effects considered, the interpreted strength value Sut from the CPT increases by 13.5% compared to cases excluding these effects, while other methods exhibit marginal decreases of 4-5%. The isolated analysis of strain softening reveals that, under identical softening parameters, the CPT demonstrates the least sensitivity to strain softening among the four methods examined, with the factor reduction ratio Ns/N0 ranging from 0.76 to 1.00, while the other three methods range from 0.65 to 0.88. The results indicate that the CPT is well suited for strength testing in soils exhibiting pronounced softening behavior, as it reduces the influence of strain softening on the measured results. These findings provide critical insights into method-specific biases in undrained shear strength assessments, supporting a more reliable interpretation of in situ test data for deepwater geotechnical applications.

期刊论文 2025-05-09 DOI: 10.3390/jmse13050935

The shear deformation characteristics of the pile-soil interface is significantly influenced by the water content due to the structural strength and water-sensitive nature of loess, leading to strain-softening behavior during shear deformation. Effective saturation and Bishop's effective stress were employed as direct driving variables to reflect the effects of saturation on the structural strength of loess, based on the water-stress coupling characteristics of the pile-loess interface. Structural parameters such as cohesion, friction angle, and compression index, along with their evolution equations, are developed to reflect the degradation of structural strength with plastic strain and effective saturation. On the basis, by equating the plastic deformation of unsaturated structural loess with saturated non-structural loess under lateral confinement, a load-collapse function is developed for the pile-loess interface in the effective stress-effective degree of saturation space. An elastoplastic hydro-mechanical coupling model for the pile-loess interface is developed by integrating a soil-water characteristic curve. The model is validated using direct shear test data from unsaturated structural Lanzhou loess and field pile test data from Shanxi unsaturated loess. The results show that the proposed model effectively. represents the hydro-mechanical coupling behavior of the pile-unsaturated loess interface, reflects the effects of saturation on shear strength, and captures the variation of strain-softening characteristics at the pile-soil interface with saturation. The model offers aneffective approach for disaster prevention design, analysis, and assessment of the load-carrying behavior of piles in unsaturated loess.

期刊论文 2025-05-01 DOI: 10.16285/j.rsm.2024.0978 ISSN: 1000-7598

The soil-rock mixture is a heterogeneous material consisting of high-strength rocks and a low-strength soil matrix, with complex interactions among its mesoscopic components under loading. Considering the mesoscopic structural characteristics, the interface between soil and rock, as well as the interior of the soil matrix, are identified as the material's weak points. Using the cohesive model, the initiation, expansion, and fracture of cracks at weak points are described, and a cohesive element insertion program is developed. Subsequently, using the results of direct shear tests, the material parameters for the cohesive elements in the soil matrix and at the soil-rock interface are determined. A mesoscopic numerical method for soil-rock mixtures based on the cohesive model is then established. Based on this, biaxial compression numerical tests on soil-rock mixtures with varying mesoscopic structures were conducted. The influence of different mesoscopic factors on mechanical properties was clarified by analyzing the failure state of cohesive elements. Results indicate that the maximum nominal stress in shear direction of cohesive elements can be determined by the peak shear stress of the load-displacement curve in direct shear tests. The maximum effective displacement is determined by one-fifth of the maximum shear displacement, and the tangential friction coefficient is calculated by the ratio of residual shear stress to normal stress. The numerical method based on cohesive elements can effectively describe the mechanical properties and deformation behavior of soil-rock mixtures, particularly for the strain softening behavior under low confining pressure.

期刊论文 2025-05-01 DOI: 10.16285/j.rsm.2024.1109 ISSN: 1000-7598

Two earthquakes, Mw = 7.8 Kahramanmaras,-Pazarcik, and Mw = 7.6 Elbistan, occurred on February 6, 2023, approximately 9 h apart. These earthquakes caused devastating effects in a total of 11 nearby cities on the east side of T & uuml;rkiye (Adana, Adiyaman, Diyarbakir, Elazig, Gaziantep, Hatay, Kahramanmaras,, Kilis, Malatya, Osmaniye, and S,anliurfa) and the north side of Syria. These earthquakes provided an outstanding prospect to observe the effects of liquefaction in silty sand and liquefaction-like behavior in clays (cyclic softening) on the stability of structures. This paper specifically presents the post-earthquake reconnaissance at three sites and evaluations of four buildings within these sites in Adiyaman Province, Golbas, i District. First, important role of post-earthquake piezocone penetration test (CPTu) in characterizing the subsurface conditions was presented. Then, the effect of soil liquefaction and cyclic softening on the performance of four buildings during the earthquakes was evaluated. These structures represent the typical new reinforced concrete buildings in T & uuml;rkiye with 3 to 6-story, situated on shallow (raft) foundations, and demonstrated diverse structural performances from full resilience to moderate and extensive damage during the aforementioned earthquakes. Based on the interim findings from these sites, the potential factors that caused moderate to severe damage to buildings were inspected, and preliminary-immediate insights were presented on the relationship between structural design, soil properties, and the performance of buildings with shallow foundations.

期刊论文 2025-05-01 DOI: 10.1016/j.soildyn.2025.109300 ISSN: 0267-7261

This paper presents the findings from a series of constant suction triaxial tests conducted on compacted sand and silty sand under unsaturated conditions. These tests were carried out using a fully automated double-walled triaxial cell employing the axis translation technique. The net mean stresses applied ranged from 50 to 250 kPa, while matric suctions were maintained at 0, 100, and 200 kPa. The primary objective of this study was to elucidate the mechanical behavior of the two compacted soils under triaxial conditions, particularly focusing on the influence of suction on variables such as peak stress, apparent cohesion, critical state stress, postpeak softening, and strain-induced dilatancy. The experimental results were utilized to calibrate and validate two prominent critical state-based models for unsaturated soils: the Barcelona basic model (BBM) and the Morvan model. While the BBM accurately predicted the deviatoric stress values at the critical state under controlled suction conditions, it did not adequately capture the postpeak softening behavior. Conversely, the Morvan model, after appropriate calibration and validation, successfully replicated both the critical state and postpeak behaviors, demonstrating a strong correlation between its predictions and the experimental data for both soil types.

期刊论文 2025-05-01 DOI: 10.1061/IJGNAI.GMENG-10584 ISSN: 1532-3641

In marine environments, monopiles of offshore wind turbines (OWTs) are often subjected to horizontal cyclic loads caused by wind and wave. Due to cyclic loading, the stiffness and strength of clays degrades, further affecting the serviceability limit state of OWTs. This study developed a 3D finite difference model for the OWTmonopile-seabed system under real wind and wave conditions. A nonlinear cyclic constitutive model was demonstrated to be effective in describing the degradation of strength and stiffness of the soft clay under irregular cyclic loading. The monopile-clay interaction was validated against a centrifuge model test in term of the load-displacement relationship. The aerodynamic wind loading is calculated using the Kaimal spectrum, and the wave loading is computed using the JONSWAP wave spectrum and Morison equation. It was found that the peak the horizontal displacement and rotation angle of the monopile at the mudline were primarily influenced by the amplitude and combination of wind and wave loads and were also significantly affected by the pile-soil interaction related to the cyclic softening of clays. The cumulative peak horizontal displacement of monopiles caused by wind and wave underscores the importance of continuous structural health monitoring and risk assessment of OWTs.

期刊论文 2025-04-01 DOI: 10.1016/j.oceaneng.2025.120449 ISSN: 0029-8018

Dynamic triaxial tests were conducted to clarify the dynamic deformation characteristics of silty clay in flood irrigation areas under cyclic loading, using single-sample stepwise and multiple samples of constant amplitude. The effects of confining pressure, bias consolidation ratio, drainage conditions, dynamic load frequency, and cyclic stress ratio on the development law of cumulative plastic strain and residual dynamic pore pressure, the evolution characteristics of the hysteresis curve, and the change law of softening index of silty clay were studied. The results show that the development of cumulative plastic strain and residual dynamic pore pressure of soil under dynamic load is consistent. According to the stability theory, the dynamic behavior of samples under different test conditions can be divided into three typical cases: plastic stability, plastic creep and incremental failure. Under the basic conditions of this test, the boundary cyclic stress ratios of the three dynamic states of plastic stability, plastic creep, and incremental failure are around 0.30 and 0.40, respectively. The hysteresis characteristics of undrained specimens in the plastic stable state are obvious, and the hysteresis curve shows an S shape. With the progression of loading, soil experiences stiffness degradation. The cumulative plastic deformation of undrained specimens is smaller than that of drained specimens, and the softening index of soil under drained and undrained conditions remains stable at around 1.15 and 0.91, respectively, under lower cyclic stress ratios. Through grey relational analysis, it is found that the cyclic stress ratio has the greatest influence on the cumulative plastic strain and pore pressure ratio. The confining pressure exerts the greatest influence on the softening index. The parameters of the cumulative plastic strain model suitable for silty clay in flood irrigation areas have been determined, and the prediction effect is good.

期刊论文 2025-04-01 DOI: 10.16285/j.rsm.2024.0865 ISSN: 1000-7598

Each individual bucket of multi-bucket foundations sustains mainly the vertical upward and downward cyclic load during its lifetime. It is evidenced from centrifuge test and engineering experience that the behaviour of individual bucket under upward and downward load is not identical - usually the capacity and stiffness of downward direction is stronger than the upward. This anisotropic behaviour is mainly due to the different failure mechanism and soil strengths mobilized. In this paper, a macro element model is established to reproduce the anisotropic behaviour of individual bucket under vertical cyclic loading, expanded from previous study of the cyclic-softening macro element model. The model is formulated based on multi-surface plasticity and a combined isotropic and kinematic hardening rule. The anisotropy is implemented by establishing the oval yield surfaces and non-symmetrical hysteresis loops. The parameters of the macro element model are calibrated by a small amount of FE analyses, where an anisotropic soil constitutive model and an attached or separated soil plug are adopted to highlight the anisotropy. The performance of the model is demonstrated by a series of numerical cases and is compared to parallel FE analyses. The new macro element model is capable of capturing the anisotropic load-displacement loops real-timely during a cyclic load sequence, with high computational efficiency and reasonable accuracy.

期刊论文 2025-03-01 DOI: 10.1016/j.compgeo.2024.106964 ISSN: 0266-352X

The seepage of groundwater and the strain-softening of rock mass in a submarine tunnel expand the plastic region of rock, thereby affecting its overall stability. It is therefore essential to study the stress and strain fields in the rocks surrounding the submarine tunnel by considering the coupled effect of strainsoftening and seepage. However, the evolution equation for the hydro-mechanical parameters in the existing fully coupled solution is a uniform equation that is unable to reproduce the characteristics of rock mass in practice. In this study, an updated numerical procedure for the submarine tunnel is derived by coupling strain-softening and seepage effect based on the experimental results. According to the hydro-mechanical coupling theory, the hydro-mechanical parameters such as elastic modulus, Poisson's ratio, Biot's coefficient and permeability coefficient of rocks are characterized by the fitting equations derived from the experimental data. Then, the updated numerical procedure is deduced with the governing equations, boundary conditions, seepage equations and fitting equations. The updated numerical procedure is verified accurately compared with the previous analytical solution. By utilizing the updated numerical procedure, the characteristics of stress field and the influences of initial pore water pressure, Biot's coefficient, and permeability coefficient on the stress, displacement and water-inflow of the surrounding rocks are discussed. Regardless of the variations in hydro-mechanical parameters, the stress distribution has a similar trend. The initial permeability coefficient exerts the most significant influence on the stress field. With the increases in initial pore water pressure and Biot's coefficient, the plastic region expands, and the water-inflow and displacement increase accordingly. Given the fact that the stability of the tunnel is more sensitive to the seepage force controlled by the hydraulic parameters, it is suggested to dewater the ground above the submarine tunnel to control the initial pore water pressure. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

期刊论文 2025-03-01 DOI: 10.1016/j.jrmge.2024.05.060 ISSN: 1674-7755

For rock structures exposed in the natural condition, water-induced weakening (including water softening and chemical weathering) is thought to be the main reason for its' stiffness and strength degradation, thus it is of great significance to study the mechanical properties of rocks under the influence of water. In this study, a hexagonal close-packed particle assembly (2D) composed of bonded circular particles with same diameter is considered to approximate a typical soft rock, where the composite contact model for rock materials considering the water-induced wakening is adopted to define the microscopic mechanical reactions between particles. Based on homogenisation theory and lattice model, the stress-strain relationship and strength criteria for rock considering water-induced weakening, as well as the quantitative correlation between macroscopic elastic and strength parameters with microscopic parameters are obtained. The effects of water softening and chemical weathering respectively characterised by saturation and mass loss ratio on macroscopic mechanical behaviours of rock are analysed in detail. The long-term ageing effects of water-induced weakening are also analysed. All results are in good agreement with the laboratory test results, verifying the applicability of the theoretical solution for analysing the effect of water-induced weakening on mechanical behaviours of rock.

期刊论文 2025-01-02 DOI: 10.1080/19648189.2024.2370855 ISSN: 1964-8189
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