1793
Numerical modeling of NATM urban tunnels and monitoring-Case study of Niayesh
tunnel
M
odélisation numérique de tunnels urbains construits par la méthode NATM et étude de cas du
contrôle du tunnel Niayesh
Zolghadr E., Pasdarpour M., Majidian S.
MSc of Civil (Geotechnique) Engineering, Department of Underground Structures, P.O.R. Consulting Engineers
Company, Iran
Golshani A.
Assistant Professor in Geotechnical Engineering, Department of Civil & Environmental Eng., Tarbiat Modares University,
Tehran, Iran
ABSTRACT: The New Austrian Tunnelling Method (NATM) has been adopted extensively as the method of tunneling in Iran. In this
study, some numerical models were developed using three-dimensional Finite Element software to analyze behaviour of the east
portal of the Niayesh road tunnel that is being constructed in Tehran, with the width of about 14 meters and the height of about 11.5
meters. Stability and performance analyses carried out for initial conditions, during and after construction conditions.
The Eastern portal of the north tunnel located under a reinforced soil slope that is loaded under 4 to 6 story buildings and streets
vehicles. Regarding condition of the entrance of the east portal, the pile system in addition with NATM stage construction for tunnel
has purposed to stabilize portal area. This procedure of design was controlled by monitoring results which provided by several
settlement points on the surface of the highway and some convergence stations placed in the initial lining of the tunnel.
RÉSUMÉ : La Nouvelle Méthode Autrichienne (NATM) a été adoptée largement comme méthode de creusement de tunnel en Iran.
Dans cette étude, des modèles numériques ont été développés en utilisant un logiciel par éléments finis en trois dimensions pour
analyser le comportement du portail Est du tunnel de l'autoroute Niayesh qui se construit à Téhéran, de largeur environ 14 mètres et
hauteur environ 11,5 mètres. Des analyses de stabilité et de performance ont été effectuées pour les conditions initiales, pendant et
après construction.
Le portail Est du tunnel Nord est situé sous une pente en sol renforcé chargé par des immeubles de 4 à 6 étages et des véhicules dans
les rues. Concernant la condition de l'entrée du portail Est, un système de pieux associé à une construction par étapes par la méthode
NATM a été utilisé pour stabiliser la zone du portail. Cette conception a été contrôlée par les résultats d’une instrumentation
comprenant plusieurs points de tassement à la surface de l'autoroute et des stations de convergence placées dans le revêtement initial
du tunnel.
KEYWORDS: Urban tunnels, NATM, Numerical modelling
1 INTRODUCTION
The project site is located at Tehran. Geotechnical studies have
been performed to recognize subsurface layer conditions and to
assess the geotechnical parameters. It should be noted that, there
is a need to take into account the stability of the portal in the
entrance of the tunnels. The main scope of this study is to
analyze the stability of the portal of north tunnel-Eastern adit.
The demand for more travel facilities in major cities has led
to a significant increase in the interest in development of
underground rail or road systems in Iran. The new Austrian
tunnelling method (NATM) has often been applied for
construction method of many tunnels in alluvial ground. The
NATM is a technique in which ground exposed from excavation
is temporarily supported by shotcrete as the lining (Sauer and
Gold 1989). Outstanding flexibility of NATM is the main
advantage of this method over conventional tunnelling
techniques. In this method many different support techniques
can be adopted to deal with various ground conditions.
Produced ground deformations due to urban tunnels is very
important, because urban tunnels are surrounded by highways,
buildings, installations and lifelines that are sensitive to
deformations.
Ground deformations can be evaluated using numerical
analysis methods such as finite element and finite difference. In
spite of the widespread use of numerical analysis, most of the
analyses used are mainly two-dimensional (2D) analyses that
cannot consider for 3D situations such as entrance ramp and
tunnel portal. Another issue is the modelling of the forepoles
that cannot be considered in 2D modelling. Steel pipe forepoles
are often used to bridge the unsupported gap as the tunnel face
advances. Its action is longitudinal and therefore cannot be
captured by a 2D analysis modelling just the tunnel section.
Considering a NATM tunnel as a case study, this paper tries
to illustrate how 3D numerical analyses can be applied to
stability analysis and to foresee the ground settlement.
2 PROJECT SPECIFICATION
The Niayesh parallel twin tunnels that are located in Tehran,
connect the crowded Niayesh and Sadr highways. The north
tunnel is excavated by the NATM and oval cross section with a
height of about 11.5 m and a width of about 14 m at the eastern
portal. The north tunnel at the eastern portal is located under a
reinforced soil slop that is abut 4 to 6 storey buildings and
streets.
Regarding project specifications 1 [m] diameter reinforced
concrete piles were performed in vicinity of buildings and
tunnel entrance. As it shown in figure 1, two lanes bored
concrete piles used with 2.5 [m] spans. Stability analyses
carried out for initial conditions and during and after
construction conditions.
