Search

Studying the interaction between energy piles and saturated soil can provide guidance for the design, construction, operation, and maintenance of energy piles in soft soil areas. In this paper, the interaction between energy pile groups and layered transversely isotropic saturated soils under vertical loading is investigated based on the coupled FEM-BEM method. Firstly, the stiffness matrix equations of pile group are established by discretizing each pile with rod elements. Subsequently, the boundary of saturated soils is discretized to obtain the flexibility matrix of soils under thermo-mechanical loads. Then, by introducing displacement coordination conditions at the interface between piles and soils, as well as force balance conditions at the cap, the solution to the thermo-mechanical response of energy pile group in layered transversely isotropic saturated soils is obtained. Based on the theoretical derivation, MATLAB programs are developed, and the calculation results are compared and verified with the finite element software to demonstrate the efficiency and correctness of the work in this paper. Finally, effects of factors such as the pile spacing, arrangement of the pile group, time of loading application, soil stratification, and the ratio of soil skeleton modulus on the vertically loaded energy pile groups in saturated soils are analyzed. [ABSTRACT FROM AUTHOR]

This paper studies the undrained face stability of dual circular tunnels with the use of three-dimensional lower bound finite element limit analysis (3D LB-FELA) method based on a node-stress-based mesh adaptive refinement strategy. The effectiveness and correctness of the proposed 3D adaptive LB-FELA are proven through extensive comparison. In this paper, the non-homogeneous feature of the shear strength increases linearly with depth for the undrained clay is considered, and the dimensionless coefficient N s is adopted to assess the face stability. Through extensive calculations, the influences of depth C / D , the distance between dual tunnels S / D , soil gravity parameter γD / c 0 , and the strength coefficient ρD / c 0 on the face stability coefficient N s are deeply discussed. The research results show that the proposed 3D adaptive LB-FELA method can effectively evaluate the undrained face stability, and the evolution characteristics of failure mechanisms of dual circular tunnels can be studied according to the proposed method. The research results can also provide data support for evaluation of the face stability and formulating the reinforcement scheme for the dual circular tunnels. [ABSTRACT FROM AUTHOR]

In actual reservoirs, hydraulic fracture networks typically exhibit a complex state characterized by intersecting and non-planar features, posing significant challenges to hydraulic fracturing simulation. In this paper, we present an innovative numerical model based on the extended finite element method (XFEM) for simulating arbitrarily complex intersecting fractures in 3D. For the XFEM simulation of 3D fracture networks, one of the major challenges is the stiffness matrix singularity caused by the complex intersection of fractures. After a detailed discussion of the causes, this paper proposes, for the first time, an efficient and robust strategy to address the stiffness matrix singularity issue, which avoids the need for element subdivision in the integration of enriched elements. A dual-layer Newton-Raphson iteration is established to simulate the fluid–solid coupling process. Besides, a conjugate gradient solver with a Hughes-Winget preconditioner is adopted to solve the discrete linear system of equations using an element-by-element architecture. Another contribution is the proposal of a new algorithm to describe the contact between compressive-shear natural fractures based on the penalty function method. After validating the proposed numerical model, the final example is presented to show its capacity to simulate 3D hydraulic fracturing simulation in which complex crossing fractures are considered. [ABSTRACT FROM AUTHOR]

This paper proposes a modified Hybrid Finite-Element Material-Point Method (HFEMPM) for analyzing reinforced slopes. The method discretizes the soil using material points, and employs bar elements in the finite-element method to represent geosynthetics that can only withstand tensile loads. The interaction between geosynthetics and soil is naturally captured using the same background grid by HFEMPM. To capture their frictional contact more precisely, a specific procedure to evaluate the maximum frictional force of the bar exerted by the soil is proposed in this paper, which makes the modified HFEMPM more applicable in modelling reinforced soil. The μ (I) rheology from granular mechanics is introduced for stress updating of soil. The method is applied to simulate the experimental collapse of rod piles and centrifuge tests of reinforced slopes. Incorporating the μ (I) rheology for stress updating into the HFEMPM not only enables including the influence of particle size and initial soil strength on the stability of slopes, but also describing the effect of strain rate strengthening during the collapse process. Based on calculated results of stability with various reinforcement lengths and number of layers, a reference chart designed to summarize the optimal reinforcement scheme is provided as a guide in reinforced-soil engineering. [ABSTRACT FROM AUTHOR]

Suction-induced seepage flow can significantly reduce the soil resistance during the installation of suction buckets, thereby ensuring their intended penetration depths and the designed in-service capacities. However, the lack of analytical models describing seepage flow behavior in the literature poses a significant challenge, primarily due to the complexity of seepage boundary conditions and the anisotropy and spatial variation of soil permeability. This paper addresses this gap by presenting a novel analytical solution for analyzing suction-induced seepage flow around buckets, with a particular focus on the general multilayered soil profile featuring anisotropic permeability. The method of separation of variables is used initially to derive general solutions, and the final solutions are subsequently obtained by combining continuous conditions with the orthogonality of Bessel functions. The accuracy of the solutions is confirmed through comparisons with the results obtained from finite element analysis. Furthermore, this study discusses the seepage flow behavior in several typical scenarios, including permeability anisotropy, increased permeability within the bucket, and the presence of an overlying low-permeability layer. The analytical solutions presented in this paper provide a rapid and accurate method for the analysis of suction-induced seepage flow during suction-assisted installations across a wide range of complex soil permeability conditions. [ABSTRACT FROM AUTHOR]

Winkler modelling offers a flexible and computationally efficient framework for estimating suction caisson capacity. However, there is a limited understanding of the local soil resistance acting on caissons at capacity under combined six degrees-of-freedom (6DoF) loading, which is essential for accurately estimating caisson failure envelopes. Furthermore, existing simplified design models for caissons cannot assess capacity under non-planar lateral and moment loading, which is common in offshore wind applications. To address these limitations, this paper presents a comprehensive three-dimensional (3D) finite element analysis (FEA) study, which investigates the local soil resistance acting on the caisson at capacity in undrained clay under combined 6DoF loading. The paper introduces the concept of 'soil reaction failure envelopes' to characterise the interactions between soil reactions at capacity. Closed-form formulations are derived to approximate these soil reaction failure envelopes. An elastoplastic Winkler model is then developed, incorporating linear elastic perfectly plastic soil reactions based on these formulations. The results demonstrate that the Winkler model can provide efficient and reasonably accurate estimations of caisson capacity under combined 6DoF loading, even for irregular soil profiles that pose much uncertainty and challenges to existing macro-element models. [ABSTRACT FROM AUTHOR]

Shield-soil rotary friction is one of the reasons that cause asymmetrical settlements about the central axis of tunnel center line. This paper focuses on analytical analysis of the shield-soil rotary friction on tunnelling-induced ground mechanical reactions. According to the working principle of the shield machine, the way and process of the shield torque acting on the soil is proposed. Based on the calculation model of a spatial curved shield tunnel and the rewritten of the Mindlin solutions, this paper derives the analytical solutions of the effect of shield-soil rotary friction on the soil displacement field and the additional stress field, respectively. The derived theoretical solutions are verified and compared with the shield project of Beijing East Sixth Ring Road renovation project, and relevant parameters are analyzed in this paper. The numerical model analysis based on the finite element software and the field monitoring data verify the correctness of the method proposed. The theoretical study in this paper further improves the study of the construction load of shield machine. [ABSTRACT FROM AUTHOR]

This paper describes an advanced coupling method of finite element and discrete element called the Continuum-Discontinuum Element Method (CDEM). In this study, the Barton-Bandis model(BB model) for joint non-linear deformation is introduced into the CDEM to investigate the propagation of stress waves in jointed rock masses. The paper provides a detailed account of the development process of the BB model. Then, the developed model is utilized to simulate several representative cases of stress wave propagation in jointed rock masses, revealing the principles of stress wave propagation in jointed rock masses. The findings of this study demonstrate that the simulation results of the CDEM exhibit favorable consistency with experimental and theoretical results. This confirms the capability of the CDEM to accurately and effectively simulate stress wave propagation in jointed rock masses, thereby expanding the applicability of the CDEM. This research provides powerful support for further understanding and analysis of stress wave propagation problems in jointed rock masses. [ABSTRACT FROM AUTHOR]

Modelling the interaction between rigid and deformable bodies holds significant relevance in geotechnical engineering, particularly in scenarios involving stiff engineering objects interacting with highly deformable material such as soil. These processes are challenging due to the combined nonlinear mechanisms including large deformation, elasto-plasticity, and contact with friction. For highly deformable material, the Material Point Method is a natural choice over the Finite Element Method due to its ability to handle large deformations without remeshing by carrying material information at points. This paper uses the Implicit General Interpolation Material Point Method (GIMPM) to demonstrate a new approach for modelling this type of interaction, and exploits the GIMPM's inherent definition of the boundary of a deformable domain to formulate a consistent contact formulation, negating the need for boundary reconstruction. The formulation is demonstrated through validations and comparisons to alternative methods for simulating contact. The combination of the contact formulation with an implicit framework is shown to be an efficient method for modelling geotechnical problems. The proposed method exhibits optimal convergence for contact problems, accurately captures stick–slip Coulomb friction, and ensures consistent stress fields at the contact surface of a rigid body. [ABSTRACT FROM AUTHOR]

The Bisection Method is a common search strategy implemented as part of the shear strength reduction procedure for finite element slope stability analysis. Despite the Bisection Method's simplicity and reliability as a root finding technique, it is generally accepted to achieve slower rates of convergence than many alternatives. The aim of this paper is the description of an efficient method for performing shear strength reduction using root bracketing techniques, specifically for Finite Element slope stability analysis. The False Position (regula falsi) Method enables computationally intensive slope models to be simulated by minimising the total number of solver iterations required to determine the factor of safety. Several finite element models are presented to highlight the applicability of the given methods, with significant savings made (in the order of 50 percent) with respect to two of the most common strength reduction procedures − uniform incrementation and the Bisection Method. In all cases, strong agreement in safety factors is observed between traditional strength reduction methods and the proposed techniques. [ABSTRACT FROM AUTHOR]

With the increase in computational capabilities in recent decades, the possibility of modeling complex phenomena has continued to grow, inevitably increasing the number of calibrated parameters. Determining these parameters for complex coupled models can be challenging due to inherent nonlinearities, couplings, and uncertainties. This paper aims to provide a reliable methodology for calibrating and validating large-scale transient models through a rigorous assessment of model uncertainties. The methodology consists of performing a "one variable at a time" (OVAT) sensitivity analysis to identify the main effects, followed by a variance-based (VB) sensitivity analysis to uncover the most relevant model cross-couplings over the entire parameter domain. The outcomes of the sensitivity analysis are then used to identify the most influential parameters for model calibration. The calibration process leverages deterministic gradient-based methods in conjunction with a probabilistic treatment of the data using a Bayesian approach to rigorously quantify modeling uncertainties. A pivotal aspect of the Bayesian approach lies in its incorporation of the prior parameter distribution, enabling the quantification of the impact of deviating from their respective best-known values. This results in the establishment of 95% model confidence bounds around the optimized solution, reflecting the model uncertainties. [ABSTRACT FROM AUTHOR]

When modelling the phenomenon of strain localisation in strain-softening soils with the finite element (FE) method, nonlocal approaches have been commonly employed to avoid mesh dependency and numerical instability. This paper first presents the FE formulation of a critical state model for highly overconsolidated clays incorporating a nonlocal method. The performance of the nonlocal strain regularisation is subsequently assessed through a series of coupled hydro-mechanical (HM) analyses of undrained and drained triaxial compression tests on London clay. The mechanism behind the evolution of strain localisation in triaxial tests is investigated and a comparison with equivalent plane strain analyses is discussed. Finally, a comprehensive sensitivity study is presented, investigating the influence of the two nonlocal parameters, in the adopted nonlocal algorithm, on the predicted stress–strain responses. A key outcome is the derived linear relationship between the two parameters, which enables a unique stress–strain response to be achieved in either axisymmetric or plane strain analyses with multiple combinations of the two parameters. Such a modelling capability is essential in applications of the proposed nonlocal strain regularisation in large scale boundary value problems in which restrictions on element size exist. [ABSTRACT FROM AUTHOR]

Single-point mooring (SPM) system has been used in offshore engineering for its superiority in overcoming severe sea conditions. However, researches focused on the interaction mechanism between the anchor pile and soil in SPM systems remains insufficient, especially regarding the calculation method for oblique pullout bearing capacity that considers padeye depth. Based on the p-y curve method and load transfer method, this paper presents a simple prediction method for the behavior of anchor piles embedded in sand under oblique pullout load. The theoretical predictions are validated through comparing with results from the three-dimensional finite element method and existing centrifuge model tests. The effect of the loading angle and the padeye depth are analyzed and discussed. A negative bending moment peak and axial force discontinuity phenomenon appear at the padeye depth. The optimal padeye depth for anchor piles in this study ranges from approximately 0.53 to 0.80 times the pile length. When the padeye depth is less than 0.33 times of the pile length, the ultimate bearing capacity of the anchor pile increases with increasing load angles. Conversely, when the padeye depth exceeds 0.33 times the pile length, the ultimate bearing capacity decreases with the increasing load angles. [ABSTRACT FROM AUTHOR]

Deep geological disposal is the preferred solution for radioactive waste management in many countries, including Belgium, where the Boom Clay is one of the potential candidate host formations. Over the long term, corrosion mechanisms are expected to release large amounts of gas that will rise in pressure and activate different gas transport processes in the system and the surrounding geological formation. Assessing which transfer mode prevails under which range of pressure conditions in the sound rock layers remains a major issue. This paper presents a multi-scale Hydro-Mechanical (HM) model capturing the influence of the microstructure features on the macroscopic gas flow, and especially the emergence of preferential gas-filled pathways. A detailed constitutive model for partially saturated clay materials is developed from experimental data to perform the modelling of a Representative Element Volume (REV), and integrated into a multi-scale scheme using homogenisation and localisation techniques for the transitions to the macroscopic scale. Using this tool, numerical modelling of a gas injection test in the Boom Clay is performed with the aim of improving the mechanistic understanding of gas transport processes in natural clay barriers. [ABSTRACT FROM AUTHOR]

The design of buried pipelines against permanent ground displacements is usually performed numerically with the use of bi-linear elasto-plastic springs that simulate the soil-pipe interaction. If the pipe is buried in liquefied soil, then current practice considers bi-linear springs with reduced values of ultimate load and elastic stiffness in the order of miniscule percentages (e.g., 3%) of their values for stable (free-draining) soil. This paper employs 2D finite difference analyses to validate the accuracy of these assumptions when the pipe moves transversely (horizontally or vertically) with respect to its axis, in cases that the surrounding soil is (partially or fully) liquefied. It shows that although the soil deformation mechanism around the pipe is severely affected by the pipe displacement direction and the excess pore pressure regime, the use of reduction factors for the ultimate load and the elastic stiffness of the bi-linear springs per transverse direction is valid. These reduction factors are shown to reduce gradually with reducing factor of safety against liquefaction, taking their minimum values at liquefaction. As illustrated by 3D finite element analyses for a buried steel pipeline crossing a laterally spreading watercourse, these findings allow for a more realistic pipeline design in comparison to current practice. [ABSTRACT FROM AUTHOR]

Two primary types of numerical instabilities often occur in low-order finite element method (FEM) analyses of thermo-hydro-mechanical (THM) phenomena: (1) pressure oscillations arising improper interpolation of pressure and displacement fields; and (2) spatial oscillations induced by nonlinear convection terms in convection-dominated scenarios. In response to these issues, this paper proposes a novel stabilized edge-based smoothed FEM with a bubble function (bES-FEM) for THM analysis within saturated porous media. In the proposed framework, a cubic bubble function is first incorporated into ES-FEM to efficiently mitigate pressure oscillations that breach the Inf-Sup condition, and then the Streamline Upwind Petrov-Galerkin (SUPG) scheme is adopted in bES-FEM to effectively reduce the spurious oscillations in convection-dominated heat transfer scenarios. The accuracy of the bES-FEM with SUPG formulation for THM coupled problems is validated through a series of five benchmark tests. Moreover, the simulations of open-loop ground source energy systems demonstrate the proposed method's exceptional capability in tackling complex THM challenges in real-world applications. All the obtained results showcase the superiority of proposed bES-FEM with SUPG in eliminating the spatial and pressure oscillations, marking it as a promising tool for the exploration of coupled THM issues. [ABSTRACT FROM AUTHOR]

Percussive driving in low-to-medium density chalk creates a thin annulus of fully de-structured 'putty' chalk around pile shafts and an outer annular zone where fracturing is more intense than in the natural chalk. This damage and the related generation, and subsequent equalisation, of excess pore pressures impacts the piles' time-dependent axial loading behaviour, as do other ageing processes. This paper presents finite element analyses of open steel tubular piles driven for the recent ALPACA and ALPACA Plus research projects under monotonic axial loading to failure after extended ageing periods. A nonlinear elastic stiffness model with a nonlocal deviatoric strain-based Mohr-Coulomb failure criterion was employed, with different sets of properties to represent the de-structured, fractured chalk and intact chalk. It is shown that the piles' axial responses are mainly controlled by the puttified chalk annuli. A simplified but efficient means is adopted to impose pre-loading chalk effective stress conditions that explicitly capture the effects of installation damage and subsequent ageing. The potential for strain-softening in the brittle chalk is examined and the effective stress paths developed in representative chalk elements throughout the loading are considered in conjunction with the mobilisation of accumulated deviatoric strains. The simulations indicate 264% higher shaft capacity in compression than in tension, which is mainly attributed to the internal chalk plug. [ABSTRACT FROM AUTHOR]

The calculation of vertical bearing capacity plays a crucial role in the design of suction caissons, particularly under more complex loading conditions. In this paper, a series of three-dimensional axisymmetric finite element limit analyses were carried out to measure vertical bearing capacities of circular footings and suction caissons in cohesionless soils. The empirical shape and depth factors were derived by analyzing bearing behavior of cohesionless soil. Considering the presence of friction on imaginary cylindrical retaining wall for the active–passive Coulomb wedge mechanism, the theoretical bearing capacity equation of suction caissons was established based on limit equilibrium of sliding bodies to provided new predictive solutions. The results showed that for a shallow foundation, the empirical equations obtained by regression methods can better depict the mathematical relationship between the factors (s γ , d γ and s q d q) and the affected parameters (ϕ' and L/D) as a result of that the error is less than 5%. The friction angles along virtual cylindrical retaining wall were given by combining the above empirical equations. Due to a corresponding change in surcharge load caused by the friction force acting on outer wall, the theoretical equation is relatively conservative for predicting the bearing capacity of suction caissons. [ABSTRACT FROM AUTHOR]

By incorporating the bedding orientation of soil, this paper numerically investigates the effects of soil's anisotropic and heterogeneous behavior on strip footing under eccentric loading. The lower bound finite element limit analysis in association with second order cone programming is implemented to carry out the analysis by modeling cohesive soil as spatially random field. In order to generate the spatially random discretized soil domain, the well-known Cholesky decomposition technique is utilized. The probabilistic response is obtained by using the Monte Carlo simulation technique. The mean bearing capacity factor, failure probability of the footing for wide ranges of eccentricity, and soil heterogeneity are provided in design charts with respect to different bedding orientations. With the increase of eccentricity, the magnitude of the bearing capacity factor decreases in deterministic as well as probabilistic cases. At lower magnitudes of correlation lengths and eccentricity having different bedding orientations, significant variations are observed both in the magnitudes of mean bearing capacity factor and probability of failure; however, the variations are found to be minimized with the increase in the magnitudes of correlation lengths and eccentricity. Based on the obtained results, required factor of safety is evaluated for corresponding target probability by varying different bedding orientations. [ABSTRACT FROM AUTHOR]

This paper studies the time-dependent behavior of a pile drilled in layered saturated viscoelastic rock-soil mass due to a vertical load. By virtue of the finite element method (FEM), the pile is discretized into three-node axial bar elements. On the basis of the consolidation solution of layered transversely isotropic saturated rock-soil mass, the fractional Poyting-Thomson model and fractional Merchant model are used to simulate the rheological properties of rock and soil, respectively. The viscoelastic solution of layered saturated rock-soil mass under annular linear loads is derived according to the elastic–viscoelastic correspondence principle. Taking the above solutions as the kernel functions of the boundary element method (BEM), and combining with the stiffness matrix equation of a pile, a coupling formula of pile-soil-rock interaction is further established by the FEM-BEM coupling method. A MATLAB code is developed for numerical calculation, and the correctness of the present theory and calculation method are verified by comparing with the existing solutions, field tests and ABAQUS analyses. Finally, the key factors influencing the time-dependent behavior of piles are in-depth discussed. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical approach for analyzing the dynamic response of saturated media. Our approach provides a stabilized implementation of the u - w formulated Biot equation within the framework of the finite element method (FEM). Such a goal is achieved through modifications of both the solid and fluid phases based on the assumed strain method (ASM). Furthermore, the computational cost is remarkably reduced by the utilization of a reduced integration (RI) scheme. The proposed element has been implemented in ABAQUS as a user element subroutine (UEL), which can be straightforwardly incorporated with various user material subroutines (UMAT). The accuracy and stability of the developed element are verified through three numerical tests. Compared to the widely used u - p formulated elements, the developed element exhibits remarkable accuracy over all ranges of loading frequencies and soil permeabilities. Particularly noteworthy is its stability in the incompressible-impermeable limit without the need for additional stabilization parameters, which is further proven through a series of numerical inf-sup tests on progressively refined finite element meshes. Additionally, the applicability and efficiency of the proposed element are exhibited through the seismic analysis of a tunnel situated in a liquefiable field, underscoring its potential for complex geotechnical engineering simulations. [ABSTRACT FROM AUTHOR]

The pore pressure inside oil and gas reservoirs compartmentalized by sealing faults increases during injection processes. The rise in the pore pressure can induce fault reactivation, leading to hydraulic issues such as fluid leakage from the reservoir to other layers and seismicity. Therefore, it is essential to accurately model the mechanisms involved in this problem, primarily related to the presence of a strong discontinuity, a fault, inside the domain. Several numerical approaches can be used to represent the presence of discontinuities. The embedded finite element method (EFEM) has recently gained attention because it does not require the mesh to conform with the discontinuities, thus circumventing the typical mesh generation challenges of modeling faulted domains. The current EFEM formulations cannot properly model a hydromechanical problem such as fault reactivation, due to simplifications in their derivation. Hence, this work proposes a new fully coupled hydromechanical EFEM formulation based on the Strong Discontinuity Approach that can represent discontinuities acting as preferential flow paths or barriers for the fluid flow. The formulation is applied to a fault reactivation problem, showing the main reactivation mechanisms. This paper also discusses the presence of spurious oscillations along the discontinuities and their relations with the mesh discretization. [ABSTRACT FROM AUTHOR]

This paper investigates the roof collapse of deep circular cavities in jointed rock masses using adaptive finite element limit analysis. The rock mass strength is described by the generalized Hoek-Brown failure criterion. The calculated results of the stability number N s are presented in the form of dimensionless stability charts and are compared to the transformational results of an analytical upper bound solution by former investigators. The transformations are conducted using an algorithm proposed in the appendix of this paper. Parametric studies are performed to investigate the impacts of the Hoek-Brown parameters on the stability number and failure mechanism of underground cavities. In particular, different levels of rock mass disturbance are considered by adopting various rock mass disturbance factors D in the analyses. [ABSTRACT FROM AUTHOR]

The aim of the paper is to simulate the response of a deep excavation supported by sheet pile walls and lime-cement columns. The application of the deep mixing technique using lime-cement products in deep excavations changes the initial state of the natural soil and creates substantial displacements associated with the installation effects. In this paper, the influence of lime-cement stabilisation was investigated using the finite element method for an instrumented braced excavation. The 2D finite element analyses were performed with advanced constitutive models for both natural clay and stabilised soil, exploiting the laboratory test made on both field mixed and laboratory mixed stabilised clay samples. The numerical results show that taking account of installation effects provides realistic predictions of deformation, excess pore water pressure evolution, as well as the structural forces in the struts. [ABSTRACT FROM AUTHOR]

This paper provides a numerical framework for seismic analyses for layered saturated ground under inclined plane P1-SV waves. A unified stiffness matrix method (SMM) formula for both u - w - p and u - p formulations is first derived to obtain the dynamic response of saturated fields. Then, the domain reduction method (DRM) is extended to two-phase media to reproduce the target wavefield within the numerical models. The accuracy of the proposed SMM-DRM framework is verified by comparisons with analytical solutions and other numerical methods. Its applicability in complex boundary value problems is also proven by solving a typical SSI problem. The numerical framework is especially advantageous in the analyses of complex subdomains under obliquely incident seismic waves. With the procedure given in the paper, the framework can be implemented into existing finite element models straightforwardly. [ABSTRACT FROM AUTHOR]

The swelling of clayey rocks originates at different scales of the material. Clay mineral swelling is governed by two different phenomena: crystalline and osmotic swellings. In this paper, we adapt a multiscale numerical model that considers both crystalline swelling and interlayer osmotic swelling (four water layers and more) to efficiently implement it in a finite element method code. To this end, we itemize the different interactions arising in the interlayer space with respect to the disjoining pressure, and in the interparticular space considering the capillary effects. The overall model is based on the upscaling of the constitutive law from the nanoscopic scale to the macroscopic scale by adding all the different interactions that appear while upscaling. Additionally, the general model adapted in this paper can be considered as a new definition of the effective stress governing the chemo-hydromechanical behavior of clayey rocks. The numerical model is then implemented in Code_Aster software. The validation of our model is conducted by reproducing constant-volume swelling test. Simulation results for different pore size distributions demonstrate fair agreement between the experimental results and the numerical modeling in comparison with linear elasticity that overestimate the final swelling pressure compared to the model developed herein. [ABSTRACT FROM AUTHOR]

Geosynthetic-reinforced embankments founded on piled beams have emerged as a new ground modification technique for supporting earth embankments over deep soft subsoil. This paper presents an analytical model for this technique that combines parts of two existing analytical design models. The soil arching behaviour that divides the vertical embankment load into a part that is transferred to the piled beams directly, and the residual load part that rests on the geosynthetic, is described by the 3D part of the Concentric Arches (CA) soil arching model of van Eekelen et al. (2013 and 2015), which was adopted in CUR226:2016. The paper also compares the difference between adopting the 2D or the 3D part of this CA model. The tensioned geosynthetic effect was described by the membrane action equation of Pham (2020b). This equation calculates the geosynthetic strain and includes load–deflection behaviour, adhesion, and friction along the geogrid/soil interface. Two field studies and fully coupled hydromechanical finite element analyses were used to verify the proposed analytical approach and its assumptions. The paper compares the effect of founding geosynthetic-reinforced embankments on piles or piled beams. Finally, a parametric study showed the impact of beam width, center-to-center pile spacing, and geogrid stiffness on load transfer efficiency. [ABSTRACT FROM AUTHOR]

This paper presents a dual-modified implicit time integration method (DMITIM) for three-dimensional impact modelling within the framework of the scaled boundary finite element method (SBFEM). Controlled by a single parameter, this method effectively dissipates high-frequency responses in impact problems without affecting low-frequency responses, ensuring time integration stability. To address the issue of false oscillations during impacts, additional Lagrange multipliers are introduced to supplement the velocity and acceleration corrections at each time integration step. For nonmatching meshes, by leveraging the mesh flexibility of the SBFEM, a rapid and straightforward remeshing method is utilized to establish a node-to-node contact scheme. The numerical results demonstrate that the DMITIM significantly reduces false oscillations in the velocity and contact force during impact events. It also showcases the flexibility of the SBFEM in handling nonmatching meshes. The combination of the SBFEM with the DMITIM provides enhanced simulation accuracy and stability for impact problems compared to the results from ABAQUS using the HHT-α time integration algorithm. [ABSTRACT FROM AUTHOR]

This paper proposes a new method for computing the undrained lateral capacity of Reinforced Concrete (RC) piles in cohesive soils, overcoming inherent conservativeness of classical Broms' theory. The proposed method relies on a new theoretical distribution for the limiting soil resistance, simple enough to derive closed-form solutions of the undrained lateral capacity, for different restraints at the pile head and for all possible failure mechanisms. After validation against numerical results and experimental data, the model is used to compute the failure envelope of RC piles under generalised loading. 3D FE analyses are used as benchmark to identify the main factors governing the ultimate response of RC piles. To this purpose, the Concrete Damaged Plasticity model is adopted to reproduce nonlinear concrete behaviour, which is an essential ingredient when modelling pile behaviour under horizontal loading. FE analyses show that, contrary to what observed for rigid and elastic piles, the ultimate response of RC piles relies on the soil strength mobilised at shallow depths, where the normalised lateral soil resistance basically depends on the sole adhesion factor. The proposed solutions are readily applicable to the design of single piles, as well as to the computation of three-dimensional interaction domains of pile groups. [ABSTRACT FROM AUTHOR]

Abstract The bearing capacity of offshore foundations, subject to combinations of vertical, horizontal and moment loading, is generally defined through failure envelopes. These envelopes are commonly determined assuming a spatially homogeneous soil which is an unrealistic hypothesis. In this paper, probabilistic failure envelopes of strip foundations are determined taking into account the spatial variability of soil shear strength through a random finite element method (RFEM). The proposed approach combines finite element analysis, random field theory and Monte Carlo simulations. Through a strip foundation case-study, this paper shows the influence of soil spatial variation on ultimate capacities, failure mechanism and failure envelopes. [ABSTRACT FROM AUTHOR]

Over the past 5 years, a substantial research effort aimed at optimising the design of offshore wind turbines has led to significant reductions in the projected cost of developing offshore wind. Optimising the geotechnical design of these structures, through modern analysis techniques such as 3D Finite Element Modelling (FEM), has played a key role in helping to reduce costs. This paper presents a methodology for accurately modelling monopile behaviour using Cone Penetration Test (CPT) data to calibrate the non-linear stress dependent Hardening Soil (HS) model. The methodology is validated by comparing the modelled behaviour to field tests on a range of pile geometries. The paper also demonstrates how the soil-pile reaction response curves can be extracted from the FE model by isolating the stresses on each element of the pile. The contribution of each component to the overall lateral resistance is shown to vary with the pile geometry and is examined using the extracted soil reaction curves. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to enhance the current design practice of stiffened slab foundations on reactive soils through an advanced numerical modelling study. The paper presents sophisticated three-dimensional (3D) hydro-mechanical finite element (FE) numerical models using coupled flow-deformation and stress analyses capable of simulating the complex behaviour of reactive soils and slab foundations. The decisive parameters of the developed FE models are described in detail and the modelling efficacy is verified through three case studies. The ability of the FE models to simulate the moisture diffusion and suction variations in relation to climate changes is validated through two case studies involving field observations. A third case study involving a hypothetical stiffened slab foundation on reactive soil is used for comparison with one of the traditional design methods. The developed FE models are found to perform well and overcome some of the most significant limitations of available traditional methods, leading to more reliable design outputs. [ABSTRACT FROM AUTHOR]

A test embankment was established on the soft Ballina clay and practising engineers and academics were invited to make predictions of the behaviour of the embankment. Comprehensive geotechnical investigations were performed and the testing data were provided to the predictors. This paper presents Class A and Class C predictions made by the authors for the embankment. In Class A prediction, the soft clay was modelled as a single homogeneous layer. The Class A prediction showed good agreement with measurements for settlement, but not for pore pressure and lateral ground movement. Class C prediction divided the soft clay into two layers based on the information of ground investigation, and achieved better predictions for settlement, pore pressure and lateral movement. Finite element analysis using Plaxis 2D was carried out for the prediction, and Soft Soil Creep model was used for the soft clay. Consolidation parameters were assessed by statistical analysis of the oedometer test data. Sensitivity studies were performed to investigate the influence of parameters on the analysis results. Results of the predictions and sensitivity studies are discussed in the paper. [ABSTRACT FROM AUTHOR]

The paper summarises key results of a class A prediction obtained from 2D and 3D finite element analyses performed for the Embankment Prediction Symposium 2016. In addition class C predictions are included and the changes in input parameters for the finite element model are discussed. Although different constitutive models have been employed in the class A prediction where short term displacements, i.e. after embankment construction, have been considered in addition to long term consolidation and creep settlements only long term displacements are dealt with in this paper. Thus, only results obtained with the Soft Soil Creep model implemented in the finite element code Plaxis are presented. Input parameters have been chosen based on laboratory and in situ experiments and verified by back calculation of undrained triaxial tests and CRS tests. 3D FEA have been carried out confirming that a 2D representation is sufficient for this problem. [ABSTRACT FROM AUTHOR]

The tetrahedrons offer advantages in terms of its adaptability to complex geometries and high-efficiency of automated discretization. However, the performance is greatly limited by the weak accuracy suffered from first-order elements, as well as the significant computational burden required for quadratic cells. In this paper, a flexible mixed-order tetrahedron element is constructed on the basis of SBFEM theory, specifically, a formula for the interpolation of circumferential boundary is developed with the union of quadratic and first-order seamlessly, benefiting the combination of triangle area coordinates and the line drawing approach. Additionally, a flexural angle index of tetrahedral edges and regional customization are proposed as the modification method for determining order conversion. Subsequently, the accuracy of the proposed method in addressing various issues is investigated. The results show that the performance of tetrahedrons is satisfactorily enhanced through the utilization of 64 distinct order combination modes; and compared with its quadratic form, the calculation workload has been effectively decreased with no loss of accuracy. In summary, the analytical performance of tetrahedrons can be enhanced reasonably, which provides an effective approach for rapid and accurate analysis for critical structures. [ABSTRACT FROM AUTHOR]

The presence of discontinuities, such as fractures or geological faults, can significantly influence the fluid flow in a porous medium. In general, the discontinuities can act as preferential flow paths. However, depending on their aperture and filling material, they can act as barriers to fluid flow. To model these different possibilities, this paper presents an embedded approach in the context of the finite element method to model the presence of discontinuities inside a porous medium in transient analyses. The formulation is attractive since it does not require the mesh used to discretize the porous medium to conform to the discontinuities. The derivation of the formulation is based on the Strong Discontinuity Approach by enriching the pressure field of the finite element with a Heaviside function. The enriched part of the pressure field is discretized based on the pressure jumps evaluated at the nodes where the discontinuity intersects the finite element. The discontinuity internal pressure is taken as an independent field, allowing the modeling of high pressures inside the discontinuity. A strategy to condense the discontinuity internal pressure degrees of freedom is presented. Numerical examples are presented showing the flexibility of the formulation to capture the influence of discontinuities on the fluid flow in porous medium. The results obtained with the proposed formulation are compared with interface element models, showing a good agreement between the two approaches. • New fluid flow embedded formulation for conductive and impermeable fractures. • The formulation is successfully applied to steady-state and transient problems. • The formulation can be applied to problems with high pressures inside discontinuities. • The discontinuity internal pressure can be statically condensed. • The embedded formulation shows a good agreement against discrete fracture models. [ABSTRACT FROM AUTHOR]

The effect of pile installation is a critical issue in the analysis and design of pile foundations but it is commonly ignored due to various numerical difficulties. In this paper, the installation process of an open-ended pipe pile into a sand deposit is simulated by using the zipper technique combined with the Arbitrary Lagrangian-Eulerian (ALE) method in the framework of three-dimensional (3D) finite element modeling. The subsequent lateral load response of the pile is also simulated and compared with that without consideration of the pile installation. The state dependent behavior of sand in associated with the pile installation and the subsequent lateral load is described using an advanced constitutive model. The study shows that for a relatively loose sand deposit, the sand surrounding the pile exhibits contraction and the disturbance zone takes the form of a trapezoid, whereas for a dense sand deposit, the sand near the pile will dilate and the disturbance zone takes the form of an inversed trapezoid. Furthermore, the deformation mode of the surrounding sand under the lateral load differs to some extent from that without consideration of the installation effect. Particularly, the location of the rotation point for the laterally loaded pile tends to move downwards when the pile installation process is considered. [ABSTRACT FROM AUTHOR]

Considering the spatial variability of rock masses in tunnelling analysis is a challenge in geotechnical engineering. This paper focuses on predicting collapse loads and probabilities of design failure for dual circular tunnels constructed in anisotropic rock masses. This study employs the random adaptive finite element limit analysis method, which incorporates rotated anisotropic random fields, to model uncertainties in rock mass properties. The generalised Hoek–Brown constitutive model is employed to define the yield failure criteria of a rock mass. The adaptive finite element limit analysis is first validated against a previous study, demonstrating good agreement. Then, the probability of design failure for dual circular tunnels is comprehensively investigated. This study emphasises the importance of considering both geometric parameters and rotated anisotropic random fields in comprehensive probabilistic analyses. The results provide insights into the mean and coefficient of variation of the stability numbers, as well as the probability of design failure for different geometric configurations and rotated anisotropic random fields. In conclusion, the variation in failure probability for practical applications is presented, highlighting the significance of accounting for spatial variability, rotation angle and anisotropy in rock mass properties in tunnelling. [ABSTRACT FROM AUTHOR]

In this paper, a hydromechanical coupled XFEM approach is developed for simulating 3D nonplanar hydraulic fracturing, fracture–vug interactions and natural crack intersection problems. The extended finite element method associated with a high-order tip enrichment function is used for describing rock deformation, and the finite element method is chosen for discretizing fluid flow at the fracture surface. Rock deformation and fluid flow are coupled and solved by the Picard iteration method. The hybrid explicit–implicit representation method is adopted to represent 3D nonplanar fracture surfaces, and the displacement correlation method is chosen for extracting the mixed-mode stress intensity factor. A new mixed-mode failure criterion is introduced for determining 3D nonplanar fracture growth. Analytical solutions and experimental investigations are employed to verify the validity and effectiveness of our model. The simulations of fracture–vug interactions show that fracture surface growth on the side without vugs is constrained, while vugs can aggravate the tortuousness of the fracture surface on the side with vugs. In addition, four new intersection patterns (penetration, partial arrest, partial diversion, full arrest, and vertical propagation) are found in the 3D nonplanar fracture intersection simulations. The numerical examples highlight the considerable impacts of vertical growth and the mixed-mode effect on hydraulic fracturing. [ABSTRACT FROM AUTHOR]

Proper evaluation of seismic-induced excess pore water pressures in saturated sandy soils is still an open issue, which can be tackled with fully coupled to uncoupled approaches. The former are more accurate but computationally onerous, while the latter require seismic demand and pore pressure build-up to be computed in two successive steps, typically employing simple constitutive assumptions. Starting from the work by Seed et al. (1975) , this paper presents a novel uncoupled procedure to compute excess water pressures developing in a 1D soil column under partially drained conditions, when subjected to horizontal seismic excitations. Fundamental modifications are introduced to account for: non-uniform distribution of equivalent loading cycles; soil stiffness degradation; and modification of the frequency content of ground motion due to pore pressure build-up. The approach was implemented in Matlab via the Finite Difference Method and validated against both fully-coupled Finite Element analyses and one centrifuge test. An extensive parametric study was also performed for a two-layer soil column, by varying the thickness and hydraulic conductivity of the shallow layer, as well as the seismic input. The good agreement with both numerical and experimental data demonstrates that key features of liquefaction are well-captured by the proposed uncoupled approach. [ABSTRACT FROM AUTHOR]

Ground-borne vibrations are increasing at a rapid rate due to the rise in urban expansion and industrial activities. The current solution to mitigate the unwanted vibrations is limited to the use of single trenches that require unrealistic depths. This paper presents the possibilities of using dual open and infilled trenches to mitigate the vibrations generated due to continuous harmonic motions. Full-scale field tests and comprehensive numerical studies were performed to systematically design dual trenches. The field vibration tests were performed under a wide range of frequencies using the Lazan-type mechanical oscillator. Similarly, numerical studies have been performed using finite element analysis software, PLAXIS 2D. Expanded polystyrene (EPS) geofoams of different densities, bentonite, ceramsite, concrete, and sand-rubber mixture were used as the infill materials. The normalized depths of 0.40 and 0.50 were observed as the optimal values to reach an average amplitude reduction ratio (average ARR) of 0.25 for the dual open and EPS15-infilled trenches, respectively. The isolation efficiency of EPS15-infilled trenches was observed to be 178 % higher compared to the EPS48-infilled trenches. The performance difference between EPS15 and ceramsite-filled dual trenches was observed to be only 4 % in terms of average ARR , the former being superior. [ABSTRACT FROM AUTHOR]

In this paper, a novel numerical simulation approach based on the finite element method for dynamically modeling the excavation process of shield tunneling is proposed, with the shield-ground interactions well captured. This method is capable of mimicking the alternating modes of advancing and stopping of a shield boring machine during underground construction, with the important effects of the cutterhead rotation and slurry support pressure considered. Under the cutting action, the soil at the excavation face would experience irreversible deformation and damage, such that additional support needs to be provided by the cutterhead blades and slurry to maintain stability. The impacts of key construction parameters are examined, including cutterhead rotary speed, advance rate, and slurry support pressure, on shield tunneling operations and ground responses. The numerical model is rigorously validated against physical model experiments. This work provides useful insights into the mechanistic processes in the stratum during shield tunneling, including the spatiotemporal evolution of ground deformation patterns and stress redistributions. The results offer valuable guidance for optimizing shield tunneling operations and enhancing tunneling safety and efficiency. [ABSTRACT FROM AUTHOR]

A selective review is provided of the methods and solutions used to predict the response of various geomaterials in cavity expansion problems, both cylindrical and spherical cavities. As many authors have recognized, the solutions to these problems have numerous applications in geotechnics, and the more significant of these have been addressed in this paper. Some of the more important solutions already available in the literature are presented in addition to some novel results illustrating the effects of some unique features of soil behaviour, such as softening, rate-dependency, density dependent response and dilation. Some of the solutions are available in closed form, while others have required the use of numerical methods such as the finite element method. It is contended that the relatively simple problem of cavity expansion, be it either a cylindrical or a spherical cavity, is capable of revealing important aspects of the mechanical behaviour captured in both simplified and complex soil constitutive models. [ABSTRACT FROM AUTHOR]

The initiation, propagation, and coalescence of fractures in frozen rocks plays an important role in determining the deterioration and stability of the geotechnical engineering structure in cold regions. This study proposes a numerical method to consider the interaction of multiple fractures in frozen rock based on the volumetric expansion theory and extended finite element method (XFEM). The effective expansion coefficient is adopted in this paper to describe the volume change of ice-water mixture. To accurately determine the magnitude of frost-heaving pressure during the deformation and propagation of fractures, two iterative methods have been proposed. The correctness of the numerical method is verified by the analytical solution of frost-heaving pressure within a single fracture. In addition, the secant method shows the higher efficiency in solving the problems considering the fracture interaction. The evolution of frost-heaving pressure and cracking behavior under different geometric conditions were studied by the proposed method. The numerical results suggest that stress interference may promote the propagation of fractures and accelerate the deterioration of rock mass when the fractures are located in the favorable zone. After considering the multi-fracture interaction, the configuration of two fractures has a significant influence on the evolution of the frost-heaving pressure. [ABSTRACT FROM AUTHOR]

Taking non-Darcian flow and multi-stage loading into consideration, a semi-analytical solution for one-dimensional consolidation of multi-layered soil under continuous drainage boundary based on a linearization method was derived in this paper. The correctness of the proposed solution was verified by comparing with the existing solutions and finite element method results. Accordingly, the influence of soil properties, load parameters, interface parameter and flow parameters on the consolidation characteristics of multi-layered soil was further analyzed. The results showed that the permeability coefficient and flow exponent of the first layer of soil has the most significant influence on the consolidation of multi-layered soil, while the volume compression coefficient of the bottom layer of soil has the greatest influence on the consolidation of multi-layered soil. Continuous drainage boundary, non-Darcian flow and multi-stage loading can all prolong the consolidation process of layered soil. However, the influence of continuous drainage boundary on soil consolidation is reduced when considering non-Darcian flow or multi-stage loading. [ABSTRACT FROM AUTHOR]

This paper investigates the role of basement depth on the response of framed buildings to tunnel construction in sandy soil using finite element modelling. Six frames are considered to explore the influences of tunnel cover depth, building width, eccentricity, and the number of storeys on the role of basement depth. The numerical models adopt the hypoplastic constitute model to simulate the behaviour of the sand. The results suggest that basement depth plays an important role in determining the settlements of the raft foundations and soil displacements due to tunnelling. Its effect on the structural shear distortion primarily depends on the ratio of tunnel depth to building width (C / B); an increase in basement depth decreases and increases building maximum shear distortion for C / B < 0.3 and for C / B > 0.35, respectively. The basement considerably increases the shear distortion of short eccentric structures by preventing tilt of the building, causing a divergence from existing empirical envelopes and modification factors for shear distortion. The applicability of the meta-model is extended to the embedded structures by linking the building tilt freedom coefficient with the basement depth parameter, achieving good agreement between the predicted results and calculated data. Limitations and practical implications of the research are briefly discussed. [ABSTRACT FROM AUTHOR]

This paper describes a thermo-hydro-mechanical framework suitable for modelling the behaviour of unsaturated soils. In particular, this paper focuses on bentonite clay subjected to a thermo-hydro-mechanical load, as in the case of nuclear waste engineering barriers. The paper gives a theoretical derivation of the full set of coupled balance equations governing the material behaviour as well as an extended physical interpretation. Finally, a finite element discretisation of the equations and number of simulations verifying their implementation into a custom finite element code is provided. Some aspects of the formulation are also validated against experimental data. [ABSTRACT FROM AUTHOR]

The paper illustrates the development of metamodels of the response of steel piles driven in sand and subjected to pull-out. The metamodels are created for the prediction of the pile tensile capacity and secant stiffness. They were developed using the results of finite element analyses, which made use of finite element models of robustness assessed employing a selection of available data from large-scale model pile tests. Four hundred finite element analyses allowed for the calibration of very accurate metamodels, which were also demonstrated to closely track the outputs of the experimental results. Once calibrated, the metamodels can be used independently from the finite element models they stemmed from. The outcomes of the study show that metamodels of piles response can yield very accurate results within a wide and realistic range of soil-pile configuration, avoiding the laborious implementation and computational cost which underpins the use of finite element models. As the use of metamodels in this context is new, the paper relies on particularly simplified problem, but the procedure could be extended to accommodate modelling features of higher complexity. [ABSTRACT FROM AUTHOR]

Suction caissons are attractive solutions to support offshore structures. Their capacity, both pull-out and bearing, grows with their embedment depth. However, higher embedment depths increase risks of installation failure due to uncertainty of seabed condition, increased chance of piping and structural buckling. For the first time, this paper investigates installation of structurally enhanced caissons (SECs), in the form of flanges attached to the caisson shaft, through developing a numerical procedure based on finite element analysis. The SEC has the potential to offer additional (over 20%) pull-out and bearing capacity compared with standard caisson and can have substantial positive impacts on torsional capacity. Using the proposed numerical procedure, the impact of adding the flanges on the installation resistance was studied and compared against a standard caisson. A piping criterion was defined which allows tracking the soil region where piping develops and evolves as the installation proceeds. The impacts of flange base sizes and sand compaction on the required suction for installation were studied. The results of this paper can be used as guidance to predict the required suction to install flanged caissons and can facilitate the uptake of the proposed SEC. The proposed numerical framework is applicable to other SEC geometries. [ABSTRACT FROM AUTHOR]

The finite element (FE) method may suffer from numerical instability and mesh dependency when modelling the formation of shear bands using strain-softening constitutive models. Nonlocal methods have been shown to be capable of avoiding these numerical issues effectively. This paper proposes a novel generic algorithm for incorporating existing nonlocal methods into the FE formulation of elasto-plastic constitutive models with volumetric hardening laws. Using the example of the modified Cam Clay (MCC) model this paper shows that instabilities are inevitable if the nonlocal plastic volumetric strains are directly used to update the hardening parameter. The paper further proposes a robust regularisation algorithm to overcome this issue. This algorithm has been implemented into a bespoke FE code and its capability in significantly reducing mesh dependency while maintaining numerical stability is verified through a series of numerical analyses of biaxial compression tests for highly overconsolidated clays. The performance of various existing nonlocal methods is also critically assessed. [ABSTRACT FROM AUTHOR]