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Numerical analysis of ground-shotcrete interaction in tunnelling
No full textThe increasingly frequent use of shotcrete as primary support in tunnelling is not always accompanied, at the design stage, by analyses capable of describing its mechanical behaviour. In the first part of this paper the experimentally observed behaviour of shotcrete and its main properties as a supporting material are outlined, together with a critical overview of the general approaches adopted in modelling ground-support interaction in tunnelling. The results of three-dimensional parametric analyses of tunnel excavation and support are then presented. The analyses have been performed in axi-symmetric conditions, assuming an elastic constitutive law characterised by a time-dependent stiffness for the shotcrete. The numerical results are then compared in order to determine the influence of the following factors: constitutive law, strength parameters, tunnel advancement rate, relative ground-support stiffness. In the final part of the paper, simplified techniques are proposed to introduce the main features that emerged from the axi-symmetrical approach in the standard two-dimensional analysis
Stabilità del fronte di gallerie scavate con EPB in terreni stratificati di diversa permeabilità
No full text
Interazione tra una struttura esistente e lo sviluppo dell'ambiente urbano circostante: l'esempio della ex Vasca Navale di Roma.
No full textPatron Editor
Previsione dei cedimenti indotti dallo scavo meccanizzato di gallerie poco profonde – alcuni casi di studio.
No full textA strain applied method for FEM-2D modelling of TBM tunnels in coarse-grained soils with comparative analysis of case histories
No full textSimplified behavior models of tunnel faces supported by shotcrete and bolts.
No full textGround-support interaction in the vicinity of a tunnel face is a typical three-dimensional problem, nevertheless the tunnel support design is usually based on simplified plane strain analyses. The results of such analyses strongly depend on the choice of ground stress release at the time of lining installation. The paper focuses on tunnels excavated in difficult ground conditions, where the application of shotcrete and face reinforcement by fiber-glass bolts is widely used as a primary measure to reduce ground deformation and ensure safe working conditions. The results of an exhaustive parametric study based on 3D axisymmetric models are presented, taking into account the effect of shotcrete hardening and density of reinforcement. An Italian case history of a tunnel driven in difficult conditions is also reviewed. Finally on the basis of the results, a strategy is proposed in order to enhance the capability of two-dimensional analyses to give a more realistic prediction of stress conditions in lining and reinforcement systems
Progetto degli interventi di messa in sicurezza della parete rocciosa sovrastante l'abitato di Perticara (Italia)
No full textFEM 3D Analysis of Settlements Induced by Shallow Tunnels in Coarse-Grained Soils
No full textThe paper is focused on some aspects of 3D numerical modelling of shield-driven tunnels in coarse-grained soils. Different approaches for modelling soil-shield interaction are considered and their impact on the predicted settlement trough is analyzed. These approaches have been applied for modelling two well documented case histories of one tunnel bored in green field conditions. The tunneling process has been simulated step-by-step in order to represent relevant features, such as, application of face pressure, installation of a segmental lining, grout injection and time-dependent variation of grout stiffness. The soil mechanical behavior has been modelled by the Hardening soil model with small strain stiffness implemented in the Plaxis 3D software. Soil deformation around the shield has been modelled by three different approaches: Shield contraction, E-modulus reduction and Strain applied method. Settlement distributions obtained by E-modulus reduction and imposed strain methods are generally in better agreement with field monitoring data but require a specific calibration. Numerical results concerning the structural forces in the lining and the stress paths of representative soil elements are also discussed
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