1967
Top
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Down Construction Alongside Of Bosphorus – A Case Study
Construction en « Top
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Down » le long du Bosphore
–
Une étude de cas
Durgunoglu T., Kulac F., Ikiz S., Akcakal O.
Zetas Zemin Teknolojisi A.S., Istanbul, Turkey
ABSTRACT: Hatice Sultan and Fehime Sultan Residences are two historical Ottoman waterfront mansions placed on the European
shore of Bosphorus in Istanbul. Within the restoration campaign of these mansions, it is planned to add four basement levels under the
complete plot with the exception of preserved two corners where Hatice Sultan Residence and an old and large tree exist. The depth of
the excavation needed for the basements is about 24 m below ground surface of which 21.20 m will be below groundwater level. The
excavation should take place just 75 m far from the southwest pylon of the Bosphorus Suspension Bridge. Soil profile consists of
uncontrolled fill, marine alluvium layer and bedrock which is sloped towards the seaside with a varying inclination. Steel propping
system was set forth by the geotechnical design group of the Client, though this method was eliminated later during the bidding stage,
because it was found impractical due to their obstacle in basement construction. The method of top-down construction of the
basement levels with permanent diaphragm wall and bored piles socketed into bedrock was agreed to be realized by the Client based
on the alternative proposal given by the foundation subcontractor during the bidding stage. THY -Do&Co JV Ortakoy Hotel Project is
an interesting case-study where a challenging supporting system is being implemented near the Bosphorus in very poor soil
conditions, under high seismicity.
RÉSUMÉ : Les Résidences de Hatice Sultan et de Fehime Sultan sont deux yalis Ottomanes historiques situées sur la côte
Européenne du Bosphore, à Istanbul. Le projet de rénovation de ces yalis prévoit d’ajouter quatre étages en sous-sol sous l’ensemble
du terrain, à l’exception de deux zones préservées où sont situés la Résidence de Hatice Sultan et un arbre centenaire. Une excavation
de 24m sous le niveau du terrain naturel est requise pour la réalisation des sous-sols dont environ 21,20 m sous le niveau de la nappe
phréatique. L’excavation aura lieu à tout juste 75 m du pylône sud-ouest du Pont sur le Bosphore. Le profil du sol est constitué de
remblais non contrôlés, de couches d’alluvions marins reposant sur un substratum rocheux s’enfonçant avec une inclinaison variable
en allant vers le Bosphore. Cependant, le design initial du client basé sur la mise en œuvre d’un système de soutènement en acier a été
plus tard écarté car ne permettant pas la réalisation ultérieure des niveaux de sous-sol. La méthode de construction en « top-down »
utilisant une paroi moulée et des pieux forés ancrés dans le substratum rocheux a finalement été sélectionnée par le Client, sur la base
de la proposition alternative remise par le sous-traitant lors de l’appel d’offres. Le Projet de THY - Do&Co JV Ortakoy Hôtel est une
étude de cas intéressante pour lequel un soutènement a dû être mis en œuvre à proximité du Bosphore, avec des conditions de sol très
difficiles et en prenant en compte de forts risques sismiques.
KEYWORDS: Top-Down Construction
1 INTRODUCTION
Fehime Sultan and Hatice Sultan Residences are one of the
historical Ottoman waterfront mansions constructed alongside
the Bosphorus. These residences were constructed in the second
half of the 19th the Century by Sultan Abdulhamid II as a
wedding present for two daughters of Sultan Murat V. Later on,
Fehime Sultan Residence was given as a gift to Gazi Osman
Pasha for his success in Plevne Defense against Russian Army.
During the Turkish Republic period this mansion served as a
primary school and unfortunately was seriously damaged in a
recent fire in 2002. On the other hand Hatice Sultan Residence
served as an orphanage and then as private swimmers club in
the later periods. The plot has been recently purchased by
Turkish Airlines - Do&Co JV on BOT basis and is planned to
be restored and developed to serve as a boutique hotel. Ruins of
the Fehime Sultan Residence have been transferred to the
restoration workshop. This beautiful and historical mansion is
planned to be re-constructed using its original fragments.
Within this restoration campaign, it is also planned to add four
basement levels under the complete plot with the exception of
two corners where Hatice Sultan Residence and an old and large
tree exist. This deep excavation is agreed to be implemented
with the Top-Down construction method because of the poor
soil conditions, high ground water table and important
neighboring infrastructures. On the date of the paper
submission, the diaphragm wall construction was just finalized.
Therefore, only findings and implications of design and
methodology together with diaphragm wall construction are
presented within this paper.
2 PROJECT DESCRIPTION
Fehime Sultan and Hatice Sultan residences are located in
district of Ortakoy alongside of Bosphorus and approximately
75 m away the southwest pylon of the Bosphorus Suspension
Bridge in Istanbul (Figures 1a and 1b). Within the restoration
campaign of these residences four basement floors are planned
to be constructed in the entire plot. The periphery of the
basement floors encloses the plot limit, except two corners on
where Hatice Sultan residence and a historical tree exist (Figure
2). Basement excavation will be realized under Fehime Sultan
residence location at the left in Figure 2 because ruins of this
residence as a result of fire have been removed to restoration
workshop area before the commencement of the works. The
perimeter of the excavation plot is about 372 m and the area of
the plot is approx. 6064 m². Site elevations are varying between
+1.00 m to +3.00 m. Excavation elevation is 21.20 m below the
