3-D Nonlinear Numerical Analysis to study the Performance of Twin Tunnel System

S.A. Mazek

Dans les comptes rendus d’articles de la conférence: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Buried Structures & Subsurface Systems

ABSTRACT: Tunneling in loose soil is a sophisticate process leading to unexpected collapse for surface and subsurface structures. However, it is necessary to investigate the geotechnical problems related to tunnelling. Tunnelling process needs to more engineering insight analysis. Several numerical analyses have been conducted to model soil-structure interaction behavior. However, this study presents a case history along El-Azhar road tunnels. In the present study, the finite element model (FEM) is proposed to predict performance of tunnel system based on the twin tunnel construction. The case history presented and discussed in this study gives a rare opportunity to understand the performance of the twin tunnel system. The constitutive model for this analysis utilizes elasto-plastic materials. A yielding function of the Mohr-Coulomb type and a plastic potential function of the Drucker-Prager type are employed. A linear constitutive model is employed to represent the tunnel liner. The response of El-Azhar road tunnels system is described and presented to investigate the ground movement caused by tunnelling. The ground movement is calculated using 3-D finite element analysis (FEA). The results obtained by the 3-D nonlinear numerical model are compared with those obtained by the field measurement to assess the accuracy of the proposed 3-D FEM. A good agreement between the results obtained by the 3-D FEA and those by the field measurements is obtained.

RÉSUMÉ: Tunneling dans un sol meuble est un processus sophistiqué et provoquent l'effondrement inattendu des structures de surface et souterraines. Toutefois, il est nécessaire d'enquêter sur les problèmes géotechniques liés à effet tunnel. Tunneling processus besoins d'une analyse technique plus de perspicacité. Plusieurs analyses numériques ont été menées pour modéliser le comportement d'interaction sol-structure. Cependant, cette étude présente une histoire de cas le long des tunnels routiers Azhar El-. Dans la présente étude, le modèle éléments finis (FEM) est proposé pour prédire la performance du système de tunnel sous la construction du tunnel jumeaux. L'histoire de cas présentées et discutées dans cette étude offre une rare opportunité de comprendre la performance du système de tunnels. Le modèle constitutif pour cette analyse utilise-plastique des matériaux élasto. Une fonction de rendement de l'Mohr-Coulomb type et une fonction de potentiel plastique du type Drucker-Prager sont employés. Un modèle linéaire est constitutive employés pour représenter le revêtement de tunnel. La réponse du système de tunnels routiers El-Azhar est présentée et décrite pour enquêter sur les mouvements de terrain causés par effet tunnel. Le mouvement du sol est calculée en utilisant 3-D d'analyse par éléments finis (FEA). Les résultats obtenus par le modèle 3-D numériques non linéaires sont comparés avec ceux obtenus par la mesure sur le terrain pour évaluer l'exactitude de la proposition de FEM 3-D. Un bon accord entre les résultats obtenus par la FEA 3-D et celles de mesures sur le terrain a été obtenu. KEYWORDS: twin tunnels, numerical model, finite element analysis, deformations. 1. INTRODUCTION El-Azhar road tunnels have been constructed by tunnel boring machine (TBM) in a densely populated historical area in Cairo city. The twin road tunnels extend from Salah Salem street to Opera square at downtown. Each tunnel is 2.7 km long. Only one-km span of the twin road tunnels were constructed using cut-and-cover technique. Tunnelling leads to ground movement due to the associated soil stress changes. The numerical techniques have been widely used to predict the ground movements (Abdel Meduid et al., 2002; Abu- Farsakh et al., 1999; Berant and Cambou, 1998; El-Nahhas, 1986; Galli et al., 2004; Mazek et al., 2004; Mazek et al., 2009; Mroueh and Shahrour, 2008). Finite element method is considered the most appropriate analytical technique to solve geotechnical problems (Addenbrooke and Potts, 2001; Karakus and Fowell, 2005; Mazek, 2004; Mazek et al., 2006; Migliazza et al., 2009; Oettl and Hofsetter, 1998). Modelling of geotechnical properties and tunnelling procedure are a sophisticated problem (Contini et al., 2007; El-Nahhas, 1999; Mazek and Tehawy, 2008). In this study, El- Azhar road tunnels in central Cairo city are considered. The twin tunnel system performance is studied. The tunnel system is modelled using 3-D nonlinear finite element analysis (FEA) under the shadow of the case history so as to understand the performance of the twin tunnels system. In the 3-D nonlinear FEA, tunnelling process and interaction effects between twin tunnels and soil around the tunnels are investigated. The 3-D nonlinear FEA is used to estimate the vertical displacement at ground surface due to tunnelling. A comparison between the results calculated by the 3-D nonlinear FEA and the results recorded by field measurements is conducted to assess the accuracy of the proposed 3-D nonlinear FEA. The typical geotechnical properties used in this study are

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