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Modeling Vacuum Cconsolidation with Finite Elements

Numerous applications in which the vacuum pre-loading method has been used to improve soft clayey deposits have been reported in the literature. The new version of Plaxis 2D EA released in February 2014 contains new facilities in order to allow for the analysis of vacuum consolidation. The aim of this report is to give users a generic procedure to implement vacuum drains, simulate vacuum loading in the latest version of Plaxis and evaluate the modeling features. Moreover, a case study will be elaborated and a comparison between experimental data and F.E.M. results will be analyzed. In this work we will use a two-dimensional (2D) finite element analysis. The general procedures for the creation of a geometry model, the execution of a finite element calculation and the evaluation of the output results are described here in detail. The major topics that are useful to the research are analyzed in the introduction. To figure out and to get familiar with the Plaxis features to model vacuum consolidation a generic validation will be performed in chapter 2. Very simple 1D and 2D examples are used to start to start to deal with vacuum consolidation and understand the basic procedures. For all those examples, before approaching the software calculations, a hand calculation is performed. After that a complete analysis will be developed on a case of study in chapter 3 and through, the comparison of the numerical results with experimental data, a more further validation of the features validation is provided as well as a practical guide for the user who intends to model vacuum consolidation in Plaxis.
Furthermore in the appendix A special features of the Plaxis kernel useful to implement vacuum consolidation will be discussed in detail. In the appendix B the principles of vacuum consolidation will be discuss and the different techniques that are generally used will be described giving indications on the specific modeling. Lastly in the appendix C a generic overview on the practical uses of vertical drains and the theoretical studies on its is given.

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Chapter 1 Introduction 1.1 Ground Improvement Techniques One of the first and the more important considerations in most of civil engineering projects is the selection of a suitable site for construction. A suitable site usually means, from a geotechnical point of view, one where the foundation material has sufficient strength and stiffness to carry the loads imposed without unacceptable large deformations or stability problems, or else has drainage properties suitable for the particular construction application. In practice the most suitable site is determined by social or economic requirements, rather than purely engineering considerations and in many cases the mechanical properties of the soils (strength, stiffness or hydraulic conductivity) need to be improved through different engi- neering methods called ground improvement techniques. Due to increased urbanization there is now a growing shortage of available land in many cities which leads to the search for ways to build on land previ- ously thought unsuitable. Indeed for example there are airports, sea ports or even skyscrapers that have been developed on land reclaimed from the sea. Another example of applications for which ground improvement is almost inevitably re- quired occurs in railway and highway construction. Because these transportation routes often pass through regions underlain by deposits of soft or weak soils. The mechanical properties of these softer soils often have to be improved in order to adequately support the associated earth structures and to reduce the residual set- tlements that occur during the useful life of the transport infrastructure. Those are the main reason for which many ground improvement techniques have evolved during the years. All those techniques seek to improve those soil characteristics that match the desired results of a project, such as an increase in density and shear strength to aid problems of stability, the reduction of soil compressibility, influencing permeability to reduce and control ground water flow or to increase the rate of consolidation, or to improve soil homogeneity. In ground improvement, distinction is made between methods of compaction or densification and methods of soil reinforcement through the introduction of additional material into the ground. Bergado et al. [1] classified the various ground improvement methods according to whether or not additives are used to directly 1

Tesi di Master

Autore: Alberto Guidi Contatta »

Composta da 99 pagine.

 

Questa tesi ha raggiunto 91 click dal 20/07/2015.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.