- Title
- Applications of large deformation finite element method to geotechnical problems with contact
- Creator
- Ansari, Yousef
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2014
- Description
- Research Doctorate - PhD (Doctor of Philosophy)
- Description
- Geotechnical problems can be very complex because they involve sophisticated issues such as material nonlinearity, large deformations, changing boundary conditions and time-dependent behaviour. The nonlinear finite element method allows a rigorous solution to such complex problems, where analytical solutions cannot be easily obtained. Although much research has been conducted over the last five decades to improve solution algorithms within the nonlinear finite element method, application of these advances to real geotechnical problems has a short history. This PhD thesis is founded on five research articles. These research articles aim to shed some light into a number of complex mechanisms involving nonlinear geometric effects and interaction of two or more contacting bodies. Emphasis is put on practical findings, and on presenting simplified methods of estimation and valuation. These research articles demonstrate the ability of the Large Deformation Finite Element (LDFE) method to analyse highly nonlinear problems with a minimum of simplification. Achieving solution convergence within these highly nonlinear finite element analyses is one of the challenges encountered during the modelling stage. The main constraint is, however, to establish new methods of estimation and valuation based on the collected data. Critical data analysis, delicate sensitivity analysis and efficient parameter normalisations are some of the helpful tactics incorporated to meet the goals within the selected problems. The mechanical behaviour of a soilbag assembly under vertical compression and cyclic shear is first investigated. The compression capacity of soilbags is influenced by several factors including the bag thickness, bag tensile capacity and the soil strength parameters and this is investigated in detail in this paper. The ability of soilbags to reduce vibrations under cyclic horizontal shearing is also presented. The effects of the soil plasticity and the soil-bag interface frictional behaviour on the energy absorption capacity are also addressed. It is demonstrated that the available analytical models cannot capture the behaviour of soilbags when they are subjected to vertical compression and can produce unconservative predictions. On the contrary, finite element method is introduced as an effective replacement to investigate the mechanical behaviour of soilbag assemblies. In the next three technical papers, cone and piezocone penetration tests are numerically analysed. In this set of papers, finite element models are presented to obtain an in-depth study of penetration tests in soft clays. In the second study, a critical reliability analysis of the two analytical methods most widely-used to interpret piezocone dissipation tests is conducted. The outcome of this study reveals that the analytical predictions cannot accurately interpret data for the cases considered. The range of applicability of these analytical models is also found to be limited and inconsistent with the majority of the cases encountered in practical situations. A necessity to develop more robust methods of piezocone dissipation test interpretation with extended applications was induced from this work.In the third research article, a new cone factor is obtained using a full-penetration finite element model. This equation is calibrated to account for the effect of such influential parameters as the soil friction angle and the soil overconsolidation ratio by taking advantage of two distinct soil models. In the fourth technical paper, piezocone penetration and dissipation tests are numerically modelled since there are no robust interpretation methods for soil permeability estimation. By eliminating the majority of simplifications inherent within the previously reported methods, a new interpretation method is proposed. The method presented is applicable to monotonic and dilative dissipation data. A balance between accuracy and simplicity has been achieved in the proposed interpretation method to encourage its application in practice. In the last article, pipeline resistance for partially embedded pipelines against vertical penetration and axial walking is numerically investigated in the context of effective stress. A detailed parametric study on the response of partially embedded offshore pipelines under vertical penetration and axial movement is presented using 2-D plane strain and full 3-D models. In the first part of this study, the numerical simulation of pipelines under vertical penetration is discussed and validated against published centrifuge test results and numerical limit analysis solutions. Vertical penetration resistance of pipelines and surface heave generation process with respect to the rate of penetration are then investigated. In the second part, a parametric study is conducted to determine the axial resistance of partially embedded pipelines via a simplified expression. The factors influencing both the evolution with time and the ultimate value of axial resistance are outlined. The second part of this study also discusses the assumptions within the previously presented analytical models in the light of numerical results. These investigations, carried out during the course of this PhD, demonstrate the efficiency of the LDFE analysis in conjunction with contact mechanics in analysing complex geotechnical problems with minimum approximations. More importantly, it demonstrates in a practical manner how these numerical results can be used to improve design methods or present new methods of analysis and interpretation. Application of the nonlinear finite element method in the context presented in these studies is new and should become the basis for studying many complex geomechanics problems in the future.
- Subject
- large deformations; contact mechanics; finite element method; geotechnical problems; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1042247
- Identifier
- uon:14029
- Rights
- Copyright 2014 Yousef Ansari
- Language
- eng
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| View Details Download | ATTACHMENT02 | Thesis | 9 MB | Adobe Acrobat PDF | View Details Download |