| 1. |
- Abed, Ayman, 1976, et al.
(författare)
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FEniCS simulation of a partially saturated slope under varying environmental loads
- 2023
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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.
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| 2. |
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| 3. |
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| 4. |
- Amavasai, Amardeep, 1988, et al.
(författare)
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Towards consistent numerical analyses of embankments on soft soils
- 2022
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Ingår i: European Journal of Environmental and Civil Engineering. - : Informa UK Limited. - 2116-7214 .- 1964-8189. ; 26:7, s. 2616 -2634
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Tidskriftsartikel (refereegranskat)abstract
- A consistent automated parameter derivation method for an advanced constitutive model, Creep-SCLAY1S, which considers anisotropy, structure and creep in soft soil is presented. The algorithms are implemented in a general purpose numerical framework and are robust for noisy data. The accuracy of the derived parameters are benchmarked against a well known test case: the Haarajoki test embankment. The results show that using the proposed methodology, a consistent parameter set is derived that enables accurate laboratory data and boundary value level simulations with limited to no major user intervention. The only remaining user input relates to the adjustment of the pre-consolidation pressure with 3 kPa. This difference between the laboratory and boundary value simulations is attributed mainly due to somewhat low quality of the samples.
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| 5. |
- Becker, P., et al.
(författare)
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Volume Averaging Technique in numerical modelling of floating deep mixed columns in soft soils
- 2013
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Ingår i: Proc. International Conference on Installation Effects in Geotechnical Engineering, Rotterdam, NL, 23-27 March 2013. - 9781138000414 ; , s. 198-204
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Konferensbidrag (refereegranskat)abstract
- The deformation behaviour of deep mixed columns in anisotropic soft soil is a threedimensional problem which has to be considered adequately in numerical modelling. However, in literature simplifications are often to be found due to computational costs of fully coupled 3D analyses by either modifying geometry of the problem or material parameters in 2D-plainstrain or -axisymmetric conditions. This paper uses an enhanced 2D volume averaging technique for numerical modelling of deep mixed columns. The method enables mapping the 3D problem in two dimensions, and yet modelling the two constituents (column and soft soil) appropriately within a homogenized material. The performance of the technique is demonstrated by considering unit cell simulations of floating columns in soft soil, in which the results from 2D finite element simulations utilizing volume averaging technique are compared against conventional and fully 3D coupled finite element analyses. It is shown that the quality of the match is very good but depending on the number of columns and stiffness ratio between columns and soft soil.
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| 6. |
- Bozkurt, Sinem, 1990, et al.
(författare)
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Finite element analysis for a deep excavation in soft clay supported by lime-cement columns
- 2023
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Ingår i: Computers and Geotechnics. - 0266-352X .- 1873-7633. ; 162, s. 1-19
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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.
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| 7. |
- Castro, J., et al.
(författare)
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Influence of stone column installation on settlement reduction
- 2014
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Ingår i: Computers and Geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 59, s. 87-97
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents numerical simulations investigating the settlement reduction caused by stone columns in a natural soft clay. The focus is on the influence of the soft soil alteration caused by column installation. A uniform mesh of end-bearing columns under a distributed load was considered. Therefore, the columns were modelled using the "unit cell" concept, i.e. only one column and the corresponding surrounding soil in axial symmetry. The properties of the soft clay correspond to Bothkennar clay, which is modelled using S-CLAY1 and S-CLAY1S, which are Cam clay type models that account for anisotropy and destructuration. The Modified Cam clay model is also used for comparison. Column installation was modelled independently to avoid mesh distortions, and soft soil alteration was directly considered in the initial input values. The results show that the changes in the stress field, such as the increase of radial stresses and mean stresses and the loss of overconsolidation, are beneficial for high loads and closely spaced columns but, on the contrary, may be negative for low loads, widely spaced columns and overconsolidated soils. Moreover, whilst the rotation of the soil fabric reduces the settlement, in contrast the soil destructuration during column installation reduces the improvement.
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| 8. |
- Castro, J., et al.
(författare)
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Numerical analyses of stone column installation in Bothkennar clay
- 2013
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Ingår i: Proc. International Conference on Installation Effects in Geotechnical Engineering, Rotterdam, NL, 23-27 March 2013. - : CRC Press. - 9781138000414 ; , s. 212-218
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Konferensbidrag (refereegranskat)abstract
- The paper presents the results of numerical simulations studying the installation effects of stone columns in a natural soft clay. Stone column installation is modelled as an undrained expansion of a cylindrical cavity, using the finite element code PLAXIS that allows for large displacements. The properties of the soft clay correspond to Bothkennar clay, a soft Carse clay from Scotland (UK). The complexity of this material is simulated via two advanced recently developed constitutive formulations able to account for the soil structure, namely S-CLAY1 and S-CLAY1S. Modified Cam Clay model is also used for comparison purposes. The paper shows the new stress field and state parameters after column installation and the subsequent consolidation process. This sets the basis for including installation effects in studying the settlement reduction caused by stone columns.
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| 9. |
- Castro, J., et al.
(författare)
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Numerical modeling of stone columns with installation effects
- 2014
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Ingår i: Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, Delft; Netherlands; 18 June 2014 through 20 June 2014. - 9781138026872 ; 1, s. 523-528
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Konferensbidrag (refereegranskat)abstract
- Stone column installation modifies the state of the surrounding soil, and therefore, influences the ground improvement achieved with the stone column treatment. The paper presents numerical simulations investigating the settlement reduction caused by stone columns in a natural soft clay, accounting for the modification of soil state caused by stone column installation. These installation effects have been previously studied by modelling the installation as an undrained expansion of a cylindrical cavity. A "unit cell", i.e. only one endbearing stone column and its corresponding surrounding soil, is modelled in axial symmetry using the finite element code Plaxis. The properties of the soft clay correspond to Bothkennar clay, a soft (Carse) clay from Scotland (UK). The complexity of this material is simulated via an advanced constitutive formulation able to account for the soil anisotropy, namely S-CLAY1. The results show that the changes in the stress field, such as the increase of radial and mean stresses, and the loss of overconsolidation have a positive influence on the settlement reduction, excepting for low loads. Furthermore, column installation and subsequent loading cause several changes in the soil fabric. Those changes have a positive effect in reducing the settlement because energy is dissipated in the evolution of anisotropy. Parametric studies of the influence of the coefficient of earth pressure at rest after column installation are also presented.
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| 10. |
- Castro, J., et al.
(författare)
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Numerical simulations of stone column installation
- 2010
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Ingår i: Canadian Geotechnical Journal. ; 47:10, s. 1127-1138
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the results of numerical simulations investigating the installation effects of stone columns in a natural soft clay. The geometry of the problem is simplified to axial symmetry, considering the installation of one column only. Stone column installation is modelled as an undrained expansion of a cylindrical cavity. The excess pore pressures generated in this process are subsequently assumed to dissipate towards the permeable column. The process is simulated using a finite element code that allows for large displacements. The properties of the soft clay correspond to Bothkennar clay, modelled using S-CLAY1 and S-CLAY1S, which are Cam clay-type models that account for anisotropy and destructuration. Stone column installation alters the surrounding soil. The expansion of the cavity generates excess pore pressures, increases the horizontal stresses of the soil, and most importantly modifies the soil structure. The numerical simulations performed allow quantitative assessment of the post-installation value of the lateral earth pressure coefficient and the changes in soil structure caused by column installation. These effects and their influence on stone column design are discussed.
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