International Journal for Numerical and Analytical Methods in Geomechanics最新文献

This paper proposes an improved discretization-based kinematic approach (DKA) with an efficient and robust algorithm to investigate slope stability in nonuniform soils. In an effort to ensure rigorous upper-bound solutions which may be not satisfied by the initial DKA based on a forward difference method (DKA-FD), a central and backward difference “point-to-point” method (DKA-CD and DKA-BD) is proposed to generate discretized points to form a velocity discontinuity surface. Varying (including constant) soil frictional angles along depth are discussed, which can be readily considered in the improved DKA-CD. Work rate calculations are performed to derive upper-bound formulations of slope stability number, and critical failure surface is correspondingly obtained at limit state. The comparison with forward and backward difference methods clearly reveals that the improved DKA-CD could significantly reduce the mesh-dependency issue and enhance efficacy of slope stability analyses in nonuniform soils.

Laminar flow phenomena may occur when pore water flows at low velocities across the interfaces between soils of different properties, thus causing flow contact resistance. To explore the impacts of interfacial flow contact resistance and rheological characteristics on the thermal consolidation process of layered viscoelastic saturated soil foundation featuring semi-permeable boundaries. This paper established a new thermal consolidation model by introducing a fractional order derivative model, Hagen–Poiseuille law and time-dependent loadings. The semi-analytical solutions for the proposed thermal consolidation model are derived through the Laplace transform and its inverse transform. The reliability and correctness of the solutions are verified with the experimental data in literatures. The influence of constitutive parameters, flow contact resistance model parameters on thermal consolidation process and the interfacial flow contact resistance on foundation settlement, is further explored. The results indicate that the impact of the constitutive parameters and permeability coefficient on the thermal consolidation of viscoelastic saturated soil is related to the flow contact resistance. The enhanced flow contact resistance effect leads to a significant increase in pore water pressure and displacement during the consolidation process.

The dynamic interaction between granular flowing masses and rigid obstacles is a complex phenomenon characterised by both large displacements and high strain rates. In case the flowing mass is modelled as a continuum, its numerical simulation requires both advanced computational tools and constitutive relationships capable of predicting the mechanical behaviour of the same material under both fluid and solid regimes. In this paper, the authors employed the open-source ANURA3D code, based on the Material Point Method (MPM), and a multi-regime constitutive model. A series of impacts characterised by different velocities, initial void ratios, front inclinations and impacting mass lengths have been simulated. The MPM numerical results are critically compared with those obtained by using a Discrete Element Method (DEM) numerical code. The model capability of simulating material regime transitions, from fluid to solid and vice versa, is shown to be crucial for reproducing the mechanical response of the flowing mass put in evidence by DEM data.

This paper mainly discusses the dynamics of poroelastic media using the finite element analysis based on the u-v-p full formulation, where $�u$, $�v$, and p denote the solid displacement, relative fluid velocity with respect to solid velocity, and pore fluid pressure. It incorporates the effect of relative fluid acceleration with respect to solid acceleration on soil dynamic response. The $�u$-$�v$-p formulation is first verified through the comparison with the analytical solution. After that, the response of one-dimensional saturated soil column and two-dimensional partially saturated soil layer subjected to vertical loading with different combinations of soil permeability and loading frequency are investigated using the analyses with the $�u$-$�v$-p and $�u$-p formulations, based on which the effect of relative pore fluid motion is discussed and the differences in the soil response between two kinds of analysis approaches are examined. Results reveal that the rapid fluid flow has a pronounced effect on soil dynamics and the soil with a greater degree of saturation is more sensitive to the increase of loading frequency and soil permeability. The soil dynamic response can basically be divided into two main categories that represent insignificant and significant flow motion depending on loading frequency and soil permeability. Furthermore, despite vertical loading, horizontal soil response can also be affected by the large relative pore fluid flow when loading frequency and soil permeability are large. In addition, the simplified formulation can still be applicable to predict dynamics of poroelastic media in cases with high loading frequency and low soil permeability.

Soil arching is one of the main load transfer mechanisms of geosynthetic-reinforced and pile-supported (GRPS) embankments. This study established a numerical spring-based trapdoor model that can consider the coupling effect between embankment filling, horizontal geosynthetic, piles, and soft soil between piles by the discrete element method (DEM). The effects of multiple factors on the deformation pattern, load transfer, and the settlement at the top surface of GRPS embankments were analyzed, such as soft soil stiffness, geosynthetic stiffness, fill height, and pile clear spacing. The multiple spring-based trapdoor (MS-TD) model effectively replicated the actual deformation of soft soil between piles in engineering practice by elucidating the nonuniform settlement of the fill on the trapdoor. Although the geosynthetic indirectly reduces the load transferred to the pile top by weakening the soil arching, it can directly increase the load transferred to the pile top by the membrane effect, thereby increasing the total load transferred to the pile top. The effect of the geosynthetic on reducing settlement decreases with the increase of soft soil stiffness, and the displacement reduction ratio at the top surface remains unchanged when it exceeds a certain value. In addition, the shape of the soil arch evolves rather than unchanged during the growth of pile clear spacing.

This study aims to provide substantial theoretical support for employing vacuum preloading-airbag pressurization (VP-AP) to enhance soft soil foundations. By integrating the airbags and prefabricated vertical drains (PVDs) within the analytical framework, the consolidation models are developed to accommodate double smear zones and well resistance. Analytical solutions for various airbag pressurization scenarios are derived under the equal-strain assumption. A model test is subsequently conducted to investigate the settlement process of soft soil using the VP-AP method. The validity of the proposed theoretical model is corroborated through comparison with existing analytical solutions and experimental data. The accuracy of the predictive model is further substantiated by the model test results. Lastly, this research offers an in-depth analysis of soil consolidation behavior under diverse influencing factors. The findings indicate that the VP-AP method demonstrates superior efficacy over conventional vacuum-surcharge preloading when the airbag pressure matches the external load pressure. Additionally, an increase in the radius of airbags enhances the soil consolidation efficiency. The analytical model presented in this study elucidates the consolidation mechanisms of the VP-AP method, with experimental research confirming the efficacy of this approach and the predictive model established herein.

Site investigation provides essential geotechnical parameter information for analysis and design. However, three conflicting objectives, namely exploration effort, robustness and parameter uncertainty, pose a challenge to the development of an optimal site investigation program. In this study, a three objective optimization framework for the site investigation program is proposed based on the Bayesian approach and the non-dominated sorting genetic algorithm (NSGA-II). The only inputs required by the proposed framework are prior distribution of geotechnical parameters and error information. The prior distribution of geotechnical parameters is derived from integrating engineering experience and measurements from basic exploration boreholes. The error information is obtained based on literature and expert judgment related to the specific project. Firstly, a design pool of candidate investigation programs is generated using Bayesian approach to determine the locations and number of exploration boreholes. The NSGA-II is then applied to identify the optimal program that balances lower cost, higher robustness, and lower uncertainty. The proposed multiobjective optimization framework is illustrated and validated through a real site investigation case in Chongqing, China, aimed at determining the ultimate bearing capacity of the rock foundation. The spatial correlation of parameters within the study area is also considered. The optimal program is represented by the location and number of exploration boreholes. By comparing measurements with predictions from different site investigation programs, the efficiency of the proposed multiobjective framework is demonstrated. Additionally, the influence of engineering experience and random field modeling on the investigation program is discussed.

This paper presents a multiscale experimental study integrated with numerical simulations examining the mechanics of polydisperse granular mixtures composed of coarse-grained particles mixed with varying percentages of fines. The study includes macroscale wave propagation tests using bender elements on isotopically compressed granular samples to investigate the stiffness variation with changes in size ratio (SR) and fines content (FC). Empirical equations were developed to predict stiffness based on the experimental data, using the concept of equivalent void ratio to represent the influence of void ratio on stiffness. A newly introduced parameter called size disparity indicator was used to consider the coupled effects of size disparity and fines content on stiffness. Microscale assessment of the individual contacting grains revealed that stiffness (at grain scale) is affected by changes in grain size, even when the SR is less than 6, however, the experimental observations of the shear modulus behavior from the macroscale test results reveal minimal effect of FC. Furthermore, numerical simulations using the discrete element method were conducted on the polydisperse granular mixtures to demonstrate the coupled effect of SR and FC on the structural matrix formation, thereby influencing the force transfer among contacts resulting in varying stiffness behavior. Our findings provide valuable insights into the behavior of polydisperse granular mixtures in engineering applications.

The dilatancy behavior of overconsolidated (OC) clays is a key factor in determining their strength and deformation characteristics. Recognizing the limitations of previous dilatancy relations for OC clays, a novel dilatancy relation is proposed that can effectively capture the changes in dilatancy point, volume dilatancy and contraction with the overconsolidation ratio (OCR). As OC clays revert to the normally consolidated (NC) state, the proposed dilatancy relation smoothly transitions to that of the modified Cam-clay (MCC) model, ensuring a unified description of the dilatancy relation between OC and NC clays. The dilatancy relation can be easily incorporated into the constitutive model of different theoretical frameworks. Subsequently, this advanced dilatancy relation is integrated into a new elastoplastic constitutive model for OC clays within the framework of bounding surface and generalized plasticity theory. The validity of the proposed model is confirmed through drained triaxial compression and extension, undrained triaxial compression and extension, as well as complex stress path tests for clays with various OCRs, and the simulation results of the proposed model are compared with those of the SANICLAY model. The comparative analysis demonstrate that the model performs well in simulating the behavior of OC clays.

The vacuum preloading technique is extensively employed for ground improvement, particularly for slurry ground characterized by high-water content and low strength. Such ground frequently exhibits a delay in pore water pressure dissipation when treated with prefabricated vertical drains. To clarify the drainage and consolidation behaviour of high-water content slurry ground under vacuum preloading, this study proposed a two-stage combined model that integrates both filtration and consolidation processes. Initially, an axisymmetric filtration model was used to describe the formation of the soil column through the radial migration and compaction of the particles. The end-of-filtration radial distributions of void ratio, permeability coefficient, and effective pressure served as initial conditions for the consolidation stage analysis. This stage was depicted using a large strain consolidation model based on the free strain condition. The results showed the necessity of incorporating the filtration stage to capture the overall drainage mechanism and characteristics of slurry ground with vacuum preloading treatment.