Upper bound of tunnel face stability using asymmetric yielding

Although significant advancement has been made over recent years with respect to three-dimensional upper bound calculations of tunnel facing, a considerable difference still exists between analytically and empirically based stability values. The current work suggests that the difference may well be the outcome of the traditional use of Tresca yield criterion for the upper bound calculations, which, by definition, does not distinguish among the shearing modes (compression, extension, plane strain). Consequently, this paper suggests and discusses a new yield function, which allows for asymmetric yielding. Such yielding is only beneficial in the case of three-dimensional and continuous velocity fields, and therefore a numerical procedure that generates relevant kinematically admissible fields for classical upper bound calculation is suggested. The procedure involves conversion from a load controlled boundary value problem to a velocity controlled problem at the limit state of collapse. The analysis results in significantly lower upper bound values than those presented earlier (for Tresca material), and the values are much closer to the stability curves of Kimura and Mair (1981), which are commonly used in design. Keywords: Tunnels, Plasticity, Stability, Upper boun

Gas hydrate technology: state of the art and future possibilities for Europe

Interest in natural gas hydrates has been steadily increasing over the last few decades, with the understanding that exploitation of this abundant unconventional source may help meet the ever-increasing energy demand and assist in reduction of CO2 emission (by replacing coal). Unfortunately, conventional technologies for oil and gas exploitation are not fully appropriate for the specific exploitation of gas hydrate. Consequently, the technology chain, from exploration through production to monitoring, needs to be further developed and adapted to the specific properties and conditions associated with gas hydrates, in order to allow for a commercially and environmentally sound extraction of gas from gas hydrate deposits. Various academic groups and companies within the European region have been heavily involved in theoretical and applied research of gas hydrate for more than a decade. To demonstrate this, Fig. 1.1 shows a selection of leading European institutes that are actively involved in gas hydrate research. A significant number of these institutes have been strongly involved in recent worldwide exploitation of gas hydrate, which are shown in Fig. 1.2 and summarized in Table 1.1. Despite the state of knowledge, no field trials have been carried out so far in European waters. MIGRATE (COST action ES1405) aims to pool together expertise of a large number of European research groups and industrial players to advance gas-hydrate related activity with the ultimate goal of preparing the setting for a field production test in European waters. This MIGRATE report presents an overview of current technologies related to gas hydrate exploration (Chapter 2), production (Chapter 3) and monitoring (Chapter 4), with an emphasis on European activity. This requires covering various activities within different disciplines, all of which contribute to the technology development needed for future cost-effective gas production. The report points out future research and work areas (Chapter 5) that would bridge existing knowledge gaps, through multinational collaboration and interdisciplinary approaches

Elastic continuum solution for tunneling effects on buried pipelines using Fourier expansion

Notum sit omnibus presentes litteras inspecturis, das ist er nun, mein erster Blog-Artikel. Die ersten Gehversuche fühlen sich noch etwas seltsam an und das „verdammte weiße Blatt“ feeling sitzt gleich beim ersten Artikel frech im Nacken. Der Wechsel vom wissenschaftlichen Schreiben zum Bloggen wird mir nicht leicht fallen, so viel steht schon jetzt fest. Zum Einstig versuche ich daher erst mal ein paar einfache aber dennoch wichtige Fragen zu klären: Wer bin ich, was will ich und was erwarte..

Three-dimensional analysis of lateral pile response using two-dimensional explicit numerical scheme

Abstract: A procedure for exploiting a two-dimensional ͑2D͒ explicit, numerical computer code for the 3D formulation of dynamic lateral soil-pile interactions is considered. The procedure is applied to two models using simultaneous computation of a series of plane strain boundary value problems, each of which represents a horizontal layer of soil. The first model disregards the shear forces developed between the horizontal layers, and may be considered as a generalized Winkler model. The second model takes account of these forces by coupling the behavior of the horizontal layers. Several verification problems for a single pile and pile groups in a homogeneous soil layer modeled as a viscoelastic material were solved and compared to known solutions in order to assess the reliability of the models. Excellent agreement was observed between results of the present analyses and existing solutions

Nonlinear elasto-plastic formulation for tunneling effects on superstructures

The paper presents a formulation for evaluating the effect of tunneling on existing buildings. The formulation involves the matrix condensation method to represent the response of a linear elastic building and macro-elements to represent the nonlinear elasto-plastic soil behavior. The formulation includes new features that allow interaction between macro-elements, both through the soil continuum and the structure, to result in the final displacements of the foundations due to tunneling. One of the advantages of the formulation is its ability to incorporate a general input of a greenfield field displacement for the interaction analysis, allowing consideration of various tunneling scenarios. The formulation is evaluated by a comparison to a continuum based solution obtained using the finite difference method. The formulation is then used to conduct a parametric analysis of tunneling-soil-superstructure interaction, considering three different approaches: (1) the suggested elasto-plastic formulation, (2) purely elastic analysis, and (3) simplified analysis in which the foundations are forced to displace as the greenfield. It is shown that the vertical settlements of the foundations, due to tunneling, are the greatest when the first approach is considered. This is an outcome of the combined vertical and horizontal yielding, depicted in the formulation by the coupled yield function and plastic flow potential. Yet damage, which relates to differential settlement, appears to be smaller in the elasto-plastic formulation.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Design oriented linear-equivalent approach for evaluating the effect of tunneling on pipelines

The process of tunneling is associated with ground movements which may lead to stressing of nearby existing buried infrastructure, and potentially poses a risk of damage. The need for an effective evaluation method of the potential risk increases with the ongoing expansion of underground space utilization. This paper presents a new approach for evaluating the interaction between an assumed input of greenfield tunneling displacements and an existing buried pipeline. The approach integrates new developments with previous research findings to establish a practical interaction analysis methodology that can be used in design. It involves the use of an elastic-continuum analysis to solve the soil-pipeline interaction together with an iterative calculation of the equivalent stiffness in order to consider soil nonlinearity. A set of simplified closed-form expressions, which can be used to evaluate maximum pipeline bending moments within the suggested framework, are presented in the paper. A comparison of the new method results against centrifuge test data and advanced discrete element-method simulations is presented in the paper. The obtained agreement provides validation of the new method over a wide range of tunneling-induced volume losses and pipeline parameters