| 1. |
- Abed, Ayman, 1976, et al.
(författare)
-
3D simulations of deep mixed columns under road embankment
- 2021
-
Ingår i: Rakenteiden Mekaniikka. - 0783-6104 .- 1797-5301. ; 54:1, s. 1-20
-
Tidskriftsartikel (refereegranskat)abstract
- When column stabilisation is meant to function as a ground improvement under an embankment, the design cases to be considered consist of overall stability, compression resistance of the column heads, arching of the embankment on the columns and settlements. This paper focuses on the compression resistance of the columns. The proper geotechnical design of deep mixed (deep stabilised) columns under road embankment requires good estimation of the stress-strain behaviour of the columns and the surrounding soil under the embankment and traffic loading. Earlier Finnish design approaches relied on an even traffic load of 10 kN/m2 on the road surface. The dimensioning methods for column stabilised soil are also based on the idea of an even traffic load. Due to Eurocode recommendations a more realistic scenario is introduced, which remarkably increases the magnitude of the traffic loading. After deriving suitable material properties and stiffness parameters for static and dynamic traffic loading, three-dimensional finite element calculations are performed to achieve better understanding of the mechanical interaction between the embankment, columns and soil under the new loading configuration. Even though more investigations are needed before delivering a final statement, the calculations show that, for the considered case in this paper, the new loading scenario has no relevant consequences on the design compared to the earlier design approach.
|
|
| 2. |
- Abed, Ayman, 1976, et al.
(författare)
-
A study on how to couple thermo-hydro-mechanical behaviour of unsaturated soils: Physical equations, numerical implementation and examples
- 2017
-
Ingår i: Computers and Geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 92, s. 132- 155
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 3. |
- Abed, Ayman, 1976, et al.
(författare)
-
FEniCS simulation of a partially saturated slope under varying environmental loads
- 2023
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a numerical simulation of the response of a partially saturated slope under the impact of a long heavy rainfall event. The results are shown as a chart of varying safety factor over time. The powerful FEniCS finite element framework is employed to solve the governing coupled Hydro-Mechanical (HM) balance equations. An extended version of the Mohr-Coulomb failure criterion that accounts for partial saturation is implemented in Fortran and called from within FEniCSscript to carry out the stress integration and plastic correction. The safety calculations are performed using the strength reduction technique, firstly using Bishop’s effective stress, and secondly using two independent stress measures (i.e., net stress and suction). The impact of the chosen stress measures on the results is briefly discussed. The results highlight the importance of considering the unsaturated soil behaviour in the estimation of the safety margin, and to answer the important question of when and where the failure might occur.
|
|
| 4. |
- Abed, Ayman, 1976, et al.
(författare)
-
Finite element method algorithm for geotechnical applications based on Runge-Kutta scheme with automatic error control
- 2020
-
Ingår i: Computers and Geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 128
-
Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a novel explicit algorithm to solve the finite element equation linking the nodal displacements of the elements with the external forces applied via means of non-linear global stiffness matrix. The proposed method solves the equation using Runge-Kutta scheme with automatic error control. The method allows any Runge-Kutta scheme, with the paper demonstrating the algorithm efficiency for Runge-Kutta schemes of second to fifth order of accuracy. The paper discusses the theoretical background, the implementation steps and validates the proposed algorithm. The numerical tests show that the proposed method is robust and stable. In comparison to the iterative implicit methods (e.g. Newton-Raphson method), the new algorithm overcomes the problem of occasional divergence. Furthermore, considering the computation time, the fifth-order accurate scheme proves to be competitive with the iterative method. It seems that the proposed algorithm could be a powerful alternative to the standard solution procedures for the cases with strong nonlinearity, where the typical algorithms may diverge.
|
|
| 5. |
- Bozkurt, Sinem, 1990, et al.
(författare)
-
Finite element analysis for a deep excavation in soft clay supported by lime-cement columns
- 2023
-
Ingår i: Computers and Geotechnics. - 0266-352X .- 1873-7633. ; 162, s. 1-19
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Gramegna, Liliana, et al.
(författare)
-
A constitutive framework for the chemo-mechanical behaviour of unsaturated non-expansive clays
- 2023
-
Ingår i: E3S Web of Conferences. - 2555-0403 .- 2267-1242. ; 382
-
Konferensbidrag (refereegranskat)abstract
- Both osmotic and matric suction changes have a significant influence on the mechanical behaviour of clays. Despite the different types of interactions at the microstructural level, both suctions havea relevant effect on the fabric of non-expansive clays. Starting from experimental observations at the laboratory scale, it is possible to identify some common features characterizing the mechanical response of non-expansive clays to salinity and degree of saturation changes. This paper presents an elastoplasticframework to reproduce the behaviour of unsaturated clayey soils upon changes in the salt concentration of the pore fluid. In particular, it presents a strategy to include osmotic suction induced by pore fluid salinity in BBM-like models [1]. The model was implemented in the Thebes code and it was calibrated on experimental data performed on Boom clay [2] and remoulded loess [3].
|
|
| 7. |
- Gramegna, Liliana, et al.
(författare)
-
An Elastoplastic Framework Accounting for Changes in Matric and Osmotic Suction in Unsaturated Non-expansive Clays
- 2023
-
Ingår i: Springer Series in Geomechanics and Geoengineering. - 1866-8763 .- 1866-8755. ; , s. 311-318
-
Konferensbidrag (refereegranskat)abstract
- The mechanical behaviour of clays is significantly influenced by their salinity and degree of saturation, which are expected to change in both natural and anthropogenic environments. This influence is triggered by fabric changes. Capillary forces, related to changes in the degree of saturation, and electrochemical interactions, related to changes in salinity, affect differently the interaction between particles. However, at the continuum scale, it is possible to pinpoint some common characteristics. This paper focuses on the modelling capabilities of an elasto-plastic framework formulated to reproduce the behaviour of unsaturated non-expansive clays exposed to changes in matric and osmotic suction, by introducing osmotic suction on BBM-like models in terms of its effects on the normal compression line. The model, calibrated on experimental data on Boom clay (Mokni et al., 2014) and remoulded loess (Zhang et al., 2022), has been implemented in the Thebes code and used to predict material response under selected chemo-hydro-mechanical paths.
|
|
| 8. |
- Gupta, Abhishek, et al.
(författare)
-
Identification of key thermal couplings affecting the bentonite behaviour in a deep geological nuclear waste repository
- 2023
-
Ingår i: Engineering Geology. - 0013-7952. ; 324
-
Tidskriftsartikel (refereegranskat)abstract
- Deep geological nuclear waste repositories use the multi-layer Engineered Barrier System (EBS) to isolate nuclear waste from the environment. The key component of the barrier is densely compacted bentonite, closely resembling claystone. Therefore, to ensure safety, we need a numerical model for the bentonite and the barrier that predicts EBS behaviour during transient thermal, hydraulic, mechanical and chemical conditions. The paper identifies key mechanisms and processes affecting the bentonite in the barrier due to temperature changes (thermal couplings) based on advanced fully-coupled Finite Element Method simulations. The paper investigates 1) non-isothermal infiltration experiment on FEBEX bentonite (Villar and Gomez-Espina, 2009) and, 2) Centro de Investigaciones Energeticas Medioambientales y Tecnologicas (Ciemat) test (Martin et al., 2006), presenting 10 simulation configurations that are set up by inactivating one thermal coupling/variable at a time. The difference between these simulations and the baseline model results, examined in terms of the net mean stress (swelling pressure), suction and fluid flow, give insights into the significance of investigated coupling. Results suggest that thermal couplings related to vapour density, viscosity, water retention curve, and molecular diffusivity are among the most influential. The study additionally highlights the importance of water transport as liquid and gas, and water evaporation and condensation.
|
|
| 9. |
- Gupta, Abhishek, et al.
(författare)
-
Implementation and validation of pressure-dependent gas permeability model for bentonite in FEM code Thebes
- 2023
-
Ingår i: E3S Web of Conferences. - 2555-0403 .- 2267-1242. ; 382
-
Konferensbidrag (refereegranskat)abstract
- In an Engineered Barrier System of a nuclear waste repository, gas migrates through: a) diffusion/advection of dissolved gases, b) two-phase continuum flow, c) dilatant pathway flow and d) single-phase gas flow through macro-fractures in the soil. The gas production rate and the corresponding gas pressure accumulation affect the clay material behaviour and its properties such as air entry value. For the safe design of the EBS system, computational models need to account for the identified transport mechanisms. This study presents an enhancement in the finite element code Thebes [1, 2] that replicates the observed increase in permeability at higher gas pressures, e.g. due to pore dilatancy and gas fracture as proposed by Xu et al. [3]. The formulation links permeability to gas pressure and threshold/critical pressure. For model validation, the study utilizes a gas injection experiment carried out in IfG (Institute for Rock Mechanics, Germany) on Opalinus Clay [4]. The results show a good fit against the measurements while giving insight into gas flow through clays.
|
|
| 10. |
- Lei, Xiaoqin, et al.
(författare)
-
A generalized interpolation material point method for modelling coupled thermo-hydro-mechanical problems
- 2021
-
Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825. ; 386
-
Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a Generalized Interpolation Material Point Method (GIMP) for modelling coupled thermo-hydro-mechanical (THM) processes within unsaturated porous media. The governing equations for the coupled thermo-hydro-mechanical problems are derived based on the conservation laws of mass, momentum and energy, and are discretized within the framework of the explicit three-phase single-point GIMP. The proposed THM-coupled GIMP is validated against available analytical solutions and FEM-based numerical solutions, and is used for simulating a climate-driven slope failure process involving both temperature variation and rainfall infiltration. The proposed THM-coupled GIMP is proved to be capable to capture the fully coupled thermo-hydro-mechanical process within unsaturated porous media associated with large deformations.
|
|
