2079
Aspects on designing and monitoring a deep excavation for a highly important
structure
Aspects de conception et de suivi d’une excavation profonde d’une très importante structure
Popa H., Manea S., Batali L., Olteanu A.
Technical University of Civil Engineering of Bucharest, Geotechnical and Foundations Department, Romania
ABSTRACT: Building large and deep excavations in urban areas is always a complex problem. The geotechnical investigation should
be very detailed and the design rigorous. As well, the monitoring of such a work is mandatory. The paper presents a retaining
structure from Bucharest, Romania for a deep excavation of 66 x 127 m size in plan and a maximum depth of over 16 m. This open
pit was required for building the infrastructure of the largest Cathedral in Romania, the National Redemption Cathedral. The paper
presents aspects regarding the geotechnical investigations and interpretation, soil parameters, calculation of the diaphragm wall,
anchors and dewatering system, as well as displacement monitoring.
RÉSUMÉ : Les excavations profondes et de grandes dimensions réalisées en milieu urbain représentent toujours un problème
complexe. L’investigation géotechnique doit être très détaillée et la conception rigoureuse. De même, le suivi d’un tel ouvrage est
obligatoire. L’article présente une structure de soutènement de Bucarest, Roumanie pour une fouille de plus de 16 m de profondeur et
ayant 66 x 127 m dimension en plan. Cette excavation a été nécessaire pour construire l’infrastructure de la plus grande Cathédrale de
Roumanie, la Cathédrale de la Rédemption du Peuple. L’article présente des aspects concernant l’investigation géotechnique et son
interprétation, les paramètres du sol, le calcul de la paroi de soutènement, des ancrages et du système de rabattement de nappe, ainsi
que le suivi des déplacements.
KEYWORDS: retaining structure, diaphragm wall, deep excavation.
1 INTRODUCTION
At the present, in Bucharest is under construction the larger
orthodox cathedral in Romania, the National Redemption
Cathedral. The location of the Cathedral is in the city centre,
next to another very large building, the People’s House, on a
high area called the Arsenal Hill.
The size of the future Cathedral is: length and height of more
than 120 m and a width of over 60 m. The Cathedral basement
has 2 stories and the total surface of the future cathedral plus the
adjacent buildings is of about 11 000 sqm. Figure 1 presents the
photo of the concept design of the future cathedral.
Figure 1. Concept design of the future National Redemption Cathedral.
Based on previous analyses of various foundation solutions it
was chosen as final solution a cellular raft (basement walls as
part of mat) of 4 – 6 m thickness. The raft thickness plus the
basement height let to the necessity of excavating a pit of up to
16 m depth. Taking into account the pit depth, as well as its
large size (~ 127 m x 66 m) it was chosen as retaining structure
a diaphragm wall supported by anchors.
The Cathedral project, including also the deep excavation
retaining structure has been submitted to a national contest for
choosing the best option.
Paper presents aspects regarding the geotechnical
investigation of the site, the design of the diaphragm walls,
construction and monitoring the deep excavation.
2 SITE INVESTIGATION
Geotechnical investigation was performed in two stages:
- a preliminary geotechnical study (2008) based on which
several preliminary projects were draw in order to participate to
the national contest;
- after selecting the best project, a new detailed geotechnical
study was performed by the Technical University of Civil
Engineering of Bucharest for the final design of the Cathedral
foundations and open pit diaphragm walls.
This geotechnical study comprised the following site
investigations: 8 boreholes 25 – 70 m deep, SPT tests, hydro-
geological measurements (permeability, analysis of the
groundwater flow regime).
Laboratory tests comprised static and cyclic triaxial tests, for
determining both shear strength and dynamic parameters of
soils. As well, were carried out tests with various stress paths,
with unloading – reloading cycles for determining the
calculation parameters for the retaining wall. Table 1 presents
the main soil parameters obtained from the site and laboratory
investigations.
