1687
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Application of Ductile Segments to Tunnels in Close Proximity
Utilisation de voussoirs ductiles à des tunnels très proches
J.F. Chang, D.J. Chen & Z.C. Moh
MAA Group Consulting Engineers, Taipei, Taiwan
N.T. Yu
Central District Project Office Department of Rapid Transit Systems, TCG, Taipei, Taiwan
ABSTRACT: Establishing or expanding a mass rapid transit (MRT) network has been a challenge in the urban area. With limited
space and cityscape issues, the network would be chosen to be built below ground by virtue of bored tunneling with precast reinforced
concrete (RC) segments. While the twin tunnels for the up- and down-track lines are in close proximity, the driving effect of the
succeeding tunnel may become significant on the preceding one, thus threatening the lining system. This paper presents a case history
in the Taipei MRT projects where limited space led not only the twin tunnels to a nearly stacked alignment but the clearance to as
close as about 1.5 m. A series of numerical simulations was conducted to investigate the proximity effects, and reinforcement of the
lining system was evaluated. Considering the high degree of strength, ductility, and anticorrosion features, ductile segments were
introduced for the first time in Taiwan. The basic information of the ductile segments is briefed, followed by the design consideration.
Monitoring results are further provided for validation and as retrofits for lining analysis and design.
RÉSUMÉ :
L’é
tablissement ou l'expansion d'un réseau de métro (MRT) a été un défi dans
l’espace urbain
. Avec un espace limité et
des contraintes de paysage urbain, la solution retenue est un tunnel foré sous terre, avec des voussoirs en béton armé (RC)
préfabriqués. Alors que les tunnels jumeaux des lignes de métro haute et basse sont très proches,
l’influence du creusement du tunnel
en cours sur le tunnel existant peut devenir significative, menaçant ainsi le système de revêtement. Cet article présente une histoire de
cas des projets de Taipei MRT où
l’
espace limité a provoqué non seulement
une quasi superposition de l’alignement des tunnels
jumeaux,
mais aussi jusqu’à
1,5 m
d’espacement entre les deux tunnels
. Une série de simulations numériques a été réalisée pour
étudier les effets de proximité, et le renforcement du système de revêtement a été évaluée. Étant donné le degré élevé des
caractéristiques de résistance, de ductilité et anticorrosion, des voussoirs ductiles ont été introduits pour la première fois à Taïwan. Les
informations de base sur les voussoirs ductiles sont présentées, suivies de considérations sur la conception. Les résultats de la
surveillance sont ensuite fournis pour validation et rétro-
analyse de l’analyse et
de la conception du revêtement.
KEYWORDS: ductile segments, proximity effect, Taipei MRT projects.
1 INTRODUCTION
With the first stage of Taipei Rapid Transit System (TRTS)
completed and set out for revenue services in 2009 (while the
first line started operation in 1996) and the second stage
finished by 2018, the system is now serving more than 1.7
million passengers a day within a total of 102 stations and about
113 km of routes (TRTC 2012) around the Taipei Metropolis.
As the MRT network keeps expanding, it would be more
frequent to encounter site constraints. The up- and down-track
lines of the underground routes may have to not only shrink the
in-between spacing but adjust the typical, parallel alignment to
a stacked pattern. In such situations, driving effect of
succeeding tunnel on the preceding one becomes significant and
requires additional consideration in design and construction.
General speaking, the effect of tunnel driving can be ignored
if the clearance between the existing structures, such as tunnels,
buildings, and facilities, is beyond one diameter of the tunnel.
As more and more routes constructed in the urban area,
however, it becomes much more frequent to encounter such
situations that twin tunnels are excavated with the in-between
clearance less than one tunnel diameter. Additional surcharge
has been suggested in the lining design guide to account for
such a proximity effect on the succeeding tunnel for the
clearance between 0.5 and 1.0 times of tunnel diameter (e.g.
JRCEA 1977). Ground improvement and temporary bracing
would be applied as the protection measure. Besides, the lining
system can be reinforced by replacing the commonly-used,
precast reinforced concrete (RC) segments to high strength
materials. This paper presents a case history in the Songshan
Line of Taipei MRT projects where the clearance between
tunnels is as small as about 1.5 m (about 0.25 times of tunnel
diameter) and the routes for clearance smaller than 0.5 times of
tunnel diameter is as long as more than 350 m. Since most of
the abovementioned sections are beneath either existing
buildings or roads of heavy traffic, implementation of ground
improvement (even from the boring machine) may not be able
to meet the protection requirement. Considering the high degree
of strength, ductility, and anticorrosion features, the spherical
graphite cast iron segments (or ductile segments) were first
introduced in Taipei MRT projects. The background of the case
history is first illustrated, followed by numerical simulation for
proximity effect and design consideration for ductile segments.
Measurements obtained from the automatic monitoring system
are provided, and concluding remarks are given at the end of the
paper.
2 BACKGROUND
The Songshan Line, which is part of the Green Line in the
second stage of TRTS, consists of 9 underground stations and
about 8.5 km of routes. The Construction Lot CG291 (Figure 1)
of the Songshan Line was first planned to cover Stations G15
and G16 and twin tunnels of about 930 m long between Stations
G14 and G16. The Station G15 was finally cancelled as a result
of site constraints and tremendous construction cost and risks
involved. As illustrated by the figure, the twin tunnels are
designed to pass underneath a street block between Stations
G14 and G15. Structures above the routes includes a
underground parking lot, one official building, and a series of
Application of Ductile Segments to Tunnels in Close Proximity
Utilisation de voussoirs ductiles à des tunnels très proches
Chang J.F., Chen D.J., Moh Z.C.
MAA Group Consulting Engineers, Taipei, Taiwan
Yu N.T.
Central District Project Office Department of Rapid Transit Systems, TCG, Taipei, Taiwan
