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.

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.

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.

This paper deeply couples the exponential-type nonlinear strain softening with the anisotropic method of microstructure tensor combined stress invariants, proposing an effective strength formula that reflects the anisotropy evolution of soil. Furthermore, an expression for the anisotropy ratio k of strength as an equivalent plastic strain-related variable is derived. For natural clay, this evolution of strength anisotropy is incorporated into the Mohr-Coulomb-matched Drucker-Prager (MC-matched DP) yield criterion within the Cosserat continuum framework, resulting in a more refined soil constitutive model. The main strength parameters required for this model can be conveniently obtained based on conventional soil tests, and the model functionality can be degraded through parameter adjustments. The detailed procedure of stress updating algorithm and the elastoplastic tangent modulus matrix are provided for the constitutive integration. Through the finite element implementation, the superiority of the model is demonstrated compared with existing literature. Also, a biaxial compression example is systematically analyzed to prove that the model can effectively reflect the sensitivity of soil to loading direction. Moreover, the evolution of the shear band morphology, particle rotation in the shear band, and the anisotropy degree presented by the model are consistent with previous experimental studies and discrete element method (DEM)-related literature results. Furthermore, the proposed model effectively addresses numerical convergence issues and mesh size dependence usually encountered in classical models during the simulation of strain localization occurred in the soil.

Mudstone is a common rock in underground engineering, and mudstone with fractures, have the certain self-closing capability. In this paper, we employed experiments and numerical analyses to investigate the mechanism of such a characteristic, and also examined the permeability pattern of mudstone overburdens. The experiments were performed with the MTS815.02 testing system, involving material properties under different water contents and their crack-closing behaviors. The principal task of numerical analysis is to determine the permeability of fractured mudstone layers, working with the COMSOL platform. The experimental results show that the Young's Modulus of water-saturated mudstone is just 2.2% of that of natural mudstone, and the saturated also exhibit a remarkably obvious creep behavior. As the surrounding pressures increase, the permeability coefficient of fractured mudstone decrease exponentially, even dropping by two orders of magnitude corresponding to over 2.0MPa pressures. Based on these experiment outcomes, we can easily infer that rapid or complete fracture-closing is the main reason of permeability drop, and furthermore, both softening and creep are the major factors of self-closure of mudstone fractures, and especially, the softening behavior plays an absolutely fundamental role. The numerical analyses show that either a higher in-situ stress or lower fracture density can obviously become one of the advantageous conditions for fractured mudstone layers to restore towards impermeability. These results are also verified by the engineering observation in Yili No. 4 mine of China. There obviously existed the recovery of water-blocking capacity of overlying strata after a period of time. We hereby recommend this investigation as refences for underground mining or engineering construction involving mudstone.

This study presents a comprehensive investigation into the mechanical properties of lime-stabilized lateritic soil, with a focus on developing an improved constitutive model that incorporates both curing time and strain-softening effects. Current constitutive models fail to accurately capture the stress-strain behavior of lime-stabilized soils, particularly over extended curing periods. To address this, unconfined compressive strength (UCS) tests were conducted using lime contents of 0%, 1%, 3%, 5%, 7%, 9%, and 11% revealing that 7% lime content optimally enhances the compressive strength of the soil by 1202.66% compared to untreated soil. Triaxial consolidated-drained tests were then performed with the optimal 7% lime content, considering curing times of 3, 7, 14, and 28 days under confining pressures of 100 kPa, 200 kPa, 300 kPa, and 400 kPa. The results demonstrated that the shear strength, cohesion, internal friction angle, and initial tangent modulus of lime-stabilized lateritic soil increased with longer curing times and higher confining pressures. These findings were integrated into a re-modified Duncan-Chang model, which incorporates both strain softening and curing time as key factors. The revised model was validated through comparisons with experimental data, achieving an average relative error of 2.12% at 7 days, 1.46% at 14 days, and 17.55% at 28 days. This validation demonstrates the model's ability to accurately predict the stress-strain behavior of lime-stabilized lateritic soil under different curing conditions. The novelty of this research lies in the successful integration of curing time and strain-softening effects into the Duncan-Chang model, providing a more accurate tool for predicting the long-term mechanical performance of stabilized soils. The findings have significant implications for engineering applications, particularly in the context of soil stabilization for infrastructure projects in tropical and subtropical regions.

The purpose of this paper is to study the intensity attenuation characteristics of fault zone under the action of blasting accumulation and its influence on the evolution law of bedding rock landslide. Through the comprehensive method of field test, indoor shaking table test, theoretical model analysis and FLAC3D numerical simulation, we analyzed the evolution stage of landslide under different accumulative action, and established the evolution stage identification and vibration safety criterion of landslide by using the theory of H index and energy probability entropy. The results show that the internal mechanical characteristics and state changes of slope have significant influence on landslide risk, especially in the early stage of dynamic external force, dynamic load parameter strength plays a decisive role in slope stability. Based on numerical simulation, we determined the number of cyclic loads corresponding to slope critical instability under different stability coefficients, which provides an important reference for landslide warning.

The rotational-translational loess landslides are widely distributed in northwest China, usually posing threats to the surrounding residents and infrastructure. These loess landslides are characterized by the formation of multiple slip surfaces during the run-out process, and the mechanisms of this phenomenon in loess landslides have not been sufficiently investigated. Therefore, in this paper, we integrated the elastic-plastic strain softening constitutive law into the original DualSPHysics code to extend its application in simulating rotational-translational loess landslides. Two benchmark cases are studied to validate the model, the failure process of a cohesive soil slope without strain softening and that of a sensitive clay slope with strain softening. The results illustrate that our model can effectively predict large deformation. Then, the run-out process of the Caijiapo landslide in northwest China is analyzed by the modified model to investigate its failure mechanism. The results illustrate that the failure pattern of the Caijiapo loess landslide is very different from the typical retrogressive failure of clay landslides. The main slip surface of the Caijiapo landslide is controlled by the pre-existing structural plane. The second and third slip surfaces of this landslide are formed inside the sliding mass due to stress redistribution during the run-out process. Three scarps are formed in the landslide deposit because of the formation of multiple slip surfaces. This deposition morphology can be well reproduced by the SPH model taking strain softening into account, while the results using an SPH model without considering strain softening cannot capture this essential deformation characteristic.

Slope stability analysis is a classical mechanical problem in geotechnical engineering and engineering geology. It is of great significance to study the stability evolution of expansive soil slopes for engineering construction in expansive soil areas. Most of the existing studies evaluate the slope stability by analyzing the limit equilibrium state of the slope, and the analysis method for the stability evolution considering the damage softening of the shear zone is lacking. In this study, the large deformation shear mechanical behavior of expansive soil was investigated by ring shear test. The damage softening characteristic of expansive soil in the shear zone was analyzed, and a shear damage model reflecting the damage softening behavior of expansive soil was derived based on the damage theory. Finally, by skillfully combining the vector sum method and the shear damage model, an analysis method for the stability evolution of the expansive soil slope considering the shear zone damage softening was proposed. The results show that the shear zone subjected to large displacement shear deformation exhibits an obvious damage softening phenomenon. The damage variable equation based on the logistic function can be well used to describe the shear damage characteristics of expansive soil, and the proposed shear damage model is in good agreement with the ring shear test results. The vector sum method considering the damage softening behavior of the shear zone can be well applied to analyze the stability evolution characteristics of the expansive soil slope. The stability factor of the expansive soil slope decreases with the increase of shear displacement, showing an obvious progressive failure behavior. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.

The soil surrounding bucket foundations that are subjected to vertical cyclic loading would become softened but not consolidated. This would reduce the uplift resistance and even cause foundation failure. The paper firstly investigates the development, especially the dissipation of excess pore pressure and base suction (the suction between the bucket lid and soil) under vertical cyclic loading through 1 g model tests. The test results demonstrate that although base suction can bear 54 % of the uplift resistance of the bucket foundation at the beginning, the upward movement of foundation causes cracks at the soil surface, which accelerates excess pore pressure dissipation and leads to faster foundation failure. Therefore, the base suction should not be considered in the foundation design under long-term cyclic uplift loading. Then, an amended kinematic hardening model that can consider the strain softening effect of soil is employed to obtain the uplift resistance under vertical monotonic and cyclic loadings for various soil softening parameters and cyclic load level (the ratio of cyclic mean load to the monotonic ultimate uplift resistance). Through extensive fatigue analyzes with tens of thousands or even hundreds of thousands of cyclic loadings in each analysis, it is concluded that the fatigue cyclic number increases as the cyclic load level decreases or softening parameters (xi 95 and delta rem) increase. A prediction formula of fatigue curve of bucket foundation is proposed and verified to predict the fatigue cyclic number. The prediction error is within 10 %, and the formula can provide a convenient reference for the design of bucket foundation.