2095
Comparative study of different deep excavation retaining systems
Etude comparative de différents systèmes de soutènement de fouilles profondes
J. Josifovski & S. Gjorgjevski
Department for Geotechnics, Faculty of Civil Engineering-Skopje, University Ss. Cyril and Methodius - R. Macedonia
ABSTRACT: In the past period a building expansion and rapid construction in highly urbanized city centre of Skopje (capital of the
R. Macedonia) has been witnessed. In most cases the structures are small administrative buildings which do not exceed 800m
2
with
underground often used for offices or parking. This has been an inspiration to investigate the comparative advantages of different
deep excavation retaining systems. In fact three designer tasks, very similar by many parameters, had been used to draw the general
conclusions. The selected construction sites are located closely to each other, thus share similar ground conditions. The following
retaining systems were considered: (1) system of solder H piles with lagging, (2) reinforced concrete diaphragm wall, (3) secant pile
wall with primary (reinforced concrete) and secondary (concrete) piles. Although systems are different in general they can still be
compared, especially from the economic point of view. All retaining systems had been calculated numerically and controlled
according to the Eurocode provisions. The concluding remarks offer a preferred solution for underground construction on narrow and
build-up sites.
RÉSUMÉ: Le centre-ville très urbanisée de Skopje (capitale de la république de Macédoine) a été témoin ces derniers temps de
nombreuses constructions de bâtiments neufs. Dans la plupart des cas, ce sont de petits bâtiments administratifs qui ne dépassent pas
800m
2
avec des sous-sols souvent utilisé pour des bureaux ou le parking. Cela a été l’occasion d’enquêter sur les avantages
comparatifs des différents systèmes de soutènement de fouilles profondes. En fait, trois principes de soutènement, très semblables par
de nombreux paramètres, ont été utilisés pour tirer des conclusions générales. Les chantiers de construction sélectionnés sont très
proches les uns des autres avec des conditions de sol similaires. Les systèmes de soutènement suivants ont été considérés: (1) Système
de poutres en H soudée après-coup, (2) paroi moulée en béton armé, (3) pieux sécants avec pieux primaire (béton armé) et secondaire
(béton). Bien que les systèmes soient différents, en général, ils peuvent encore être comparés, en particulier du point de vue
économique. Tous les systèmes de soutènement ont été calculés numériquement et contrôlés selon les dispositions Eurocode. Les
conclusions offrent une solution pratique pour la construction souterraine en zone densément construite.
KEYWORDS: deep excavation, retaining system, supporting elements, finite element analysis.
1 INTRODUCTION
The problem of deep excavation in highly urbanized area such
as the city centre of Skopje has proved to be quite formidable
engineering task. In particular the greater depth and the built-up
surrounding make it especially difficult. The ever growing prize
of a square meter has led to extensive utilization of the
underground. Such an idea has been very attractive for the
investors which always look for the most economic solution of
the underground works, generally constrained by the excavation
depth and retaining system.
The tendency to optimize the structures has been an inspiration
for the authors to investigate the comparative advantages of
different deep excavation retaining systems and their supporting
elements. The objective has been to offer a qualitative study
which considers all relevant aspects of the underground
construction in urban areas.
The paper presents case studies of three different retaining
systems used to secure the excavation pits which do not exceed
800m
2
in base. All of them are located in the area of around
2km, thus share similar ground conditions. There are different
limitations and/or specifics on every site, as to the surrounding
e.g. existing structures or very frequent streets. The depth of the
excavation pit varies from 6.5 to 18m. All retaining systems had
been calculated numerically and controlled according to the
Eurocode provisions.
1.1
System of solder H piles with lagging
In the first case example a 7m deep pit should be excavated for
the construction of the new National theatre. Larger part of the
structure has been already finished, only the part adjacent to the
street is left to be erected. The excavation pit is rather narrow
only 3.05m in width (enlarging to 6.1m) and 36.65m long, see
Figure 1.
Figure 1. Site location No.1 in front of the new National theatre.
osi
f
ovski J., Gjorgjevski S.
