Actes du colloque - Volume 3 - page 193

1995
A Case Study of 3D FE Analysis of a Deep Excavation Adjacent to a Tunnel
Construction
Une étude de cas d'une simulation tridimensionnelle d'analyse par éléments finis d'une excavation
profonde adjacente à une construction d'un tunnel
Guler E.
Bosphorus University, Istanbul, Turkey
Osmanoglu U., Koç M.
ELC Group Inc. (Royal HaskoningDHV Turkey), Istanbul, Turkey
ABSTRACT: This paper describes the 3D geotechnical FE analysis and design of a deep excavation bracing system. The location is
situated in a very dense business area in Istanbul. The maximum height of the excavation is ~23 m to accommodate 7 basement floors.
The layout has a non-uniform shape, surrounded with existing high rise structures with multi-basement floors, and an underpass
connection to E-5 Motorway. In addition to these, the most outstanding characteristic of this design is the pedestrian tunnel and the
shaft that is very close to the excavation pit. Both of these underground structures were being constructed throughout the same
construction period as the deep excavation. At the non-anchoring zones adjacent to the tunnel and shaft, steel struts have been used.
As a compound engineering service, soil investigation – design – site supervision – geotechnical instrumentation works was carried
out. Therefore a comprehensive data for comparison between design results and in-situ performance could be gathered. This paper
focuses on the details of the sophisticated 3D FE analysis and the comparison with the in-situ performance of the shoring system.
RÉSUMÉ : Ce document décrit l'analyse géotechnique 3D par éléments finis et la conception d'un système de contreventement utilisé
dans l'excavation profonde. L'emplacement est situé dans un quartier très dense à Istanbul. La hauteur maximale de l'excavation est de
23 m pour 7 sous-sols. Le site a une forme non uniforme, entouré de structures existantes de grande hauteur avec multi-sous-sols, une
connexion souterraine de l'autoroute E-5. En plus de cela, la caractéristique la plus remarquable de cette conception est le tunnel pour
piétons et l'arbre qui est très proche de l'excavation. Ces deux structures souterraines ont été construites pendant la même période que
la construction de l'excavation profonde. Au niveau des zones de non-ancrage adjacentes au tunnel et à l'arbre, des entretoises en acier
sont utilisées. En tant que service d'ingénierie l'étude du sol, - la conception - la supervision de chantier - les travaux en
instrumentation géotechnique ont été réalisées. Par conséquent un ensemble de données complètes pour la comparaison entre les
résultats de la conception et de la performance in-situ aurait pu être recueillie. Ce document se concentre sur les détails d'une
simulation 3D sophistiquée d'Analyse par éléments finis et la comparaison des performances in-situ du système d'étaiement.
KEYWORDS: 3D FE Analysis, Deep Excavation, Case Study, Excavation-Tunnel-Shaft interaction.
1 INTRODUCTION
The deep excavation retaining system project is located at the
European side of Istanbul. The plan view of the site is presented
in Figure 1. The depth of the excavation is 23 m. The ongoing
construction of a pedestrian tunnel and entrance shaft adjacent
to this excavation makes the design of the retaining system
complicated. Interaction with this deep excavation work was not
considered in the design of the tunnel and shaft. Hence, the
shoring design for the deep excavation had to consider the very
close tunnel and shaft which were still being constructed and
standing with their temporary support systems during the
excavation works. Since the interaction between the deep
excavation and the simultaneously constructed shaft and tunnel
cannot be modeled with only a 2D analysis (plain-strain model),
a 3D Geotechnical FE analysis (especially for the shaft location)
had to be conducted.
The pedestrian tunnel has a span of 7 m at a distance of 7 m
to the piles of the shoring system. The shaft has a diameter of 6
m at 2.5 m distance to the piles of the shoring system. The
tunnel and shaft’s temporary support system was composing of
~20 cm shotcrete facing and rock bolts. In the tunnel 4 m long
rock bolts were used only at the top heading. In the shaft 2 m
long radial rock bolts were used. The temporary excavation
system of the building is designed with micro piles, pre-stressed
anchors and steel struts at non-anchoring zones due to tunnel
and shaft. The elevation corresponds roughly to the foundation
level of the excavation pit.
The software used in this project were TNO DIANA for 3D
modeling and Plaxis V.11 for 2D modeling (for the analysis at
the tunnel side).
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Figure 1. Site layout with surrounding structures
2 DESIGN PHASE
The design works were carried out based on the geological &
geotechnical data obtained from the site investigations.
Surcharge loads were considered wherever necessary.