2629
Subgrade improvement measures for the main rescue roads in the urban
redevelopment area HafenCity in Hamburg
Mesures d’amélioration du sol de fondation des principales routes de secours dans la zone du
réaménagement urbaine de la HafenCity à Hamburg
Weihrauch S., Oehrlein S.
Grundbauingenieure Steinfeld und Partner GbR, Hamburg
ABSTRACT: The level of many streets in Hamburg's HafenCity is being raised by around 3 m to ensure safety from flooding. The
marshy soils in this area– mainly clay (a soft clay) and peat – necessitate the use of different foundation-soil improvement concepts for
the limitation of settlement; these have to take account of the surrounding infrastructure (buildings, river-bank structures, services). The
Honkongstrasse serves as a good example of such concepts. Stress and deformation measurements were carried out on the site, in which
the concept of a "pile-supported, geogrid-reinforced sand sub-base layer" was used; this paper reports on the results.
RÉSUMÉ: Dans le quartier d’HafenCity à Hambourg, la plupart des routes seront surélevées jusqu’à 3 mètres pour atteindre le niveau de
protection contre les eaux. Les sols en place, d’origine marécageuse, sont constitués d’argile et de tourbe. Du fait de l’hétérogénéité des
sols, et en fonction des ouvrages existants (bâtiments, murs de rive, tuyaux enterrés), différentes approches ont été appliquées pour
améliorer les sols et limiter les tassements. Dans cette communication, le cas d’étude de la rue « Hongkong » sera présenté. Dans ce
projet, des géogrilles sont utilisées en renforcement d’une couche de forme sableuse pour la répartition des contraintes. Une
instrumentation complète a été mise en place. Des mesures de contraintes et de déformation ont été effectuées. Les résultats de cette
instrumentation sont présentés dans cette communication.
KEYWORDS: urban redevelopment, soil improvement, geogrid, piled embankment, expanded clay, pre-loading
1. INTRODUCTION
At the HafenCity in Hamburg, previously part of the harbour area,
the current inner-city area south of the historic warehouse district
is being extended by some 40 % to a total of 157 hectares (Figure
1). 5,500 dwellings for 12,000 residents are to be constructed,
along with office space for 40,000 employees.
In the course of these infrastructure projects, the trafficked
areas – with the exception of the quay and embankment
promenades – are being raised from the current MSL +5 m to
MSL +7.5 m to + 8.0 m, to make them safe for flood events.
Figure1: City-planning concept of the HafenCity
Hamburg (as of January 2008)
The soil conditions around today's Honkongstrasse (formerly
Magdeburger Strasse) are typical for the HafenCity Hamburg.
Fill material of low bearing capacity overlies soft organic
layers of clay and peat which in turn overly firm sands (Figure
2). Raising the level of the road embankment by approximately
3.0 m would have resulted in long-term settlements of between
300 and 400 mm, and significant differential settlements would
have been expected.
The following subgrade-improvement methods are used to
limit settlement in the HafenCity:
-
pre-emption of settlement with a sand pre-loading layer
and vertical drains
-
use of lightweight materials (expanded clay)
-
construction of a piled, geogrid-reinforced sand layer
The choice of method depends largely on the local boundary
conditions. On the Honkongstrasse site, all three methods were
used on different sections. Measurements of stresses and
deformations were carried out on the section with the piled,
geogrid-reinforced sand layer. The paper therefore concentrates in
greater detail on this method.
Vollmert L.
BBG Bauberatung Geokunststoffe GmbH & Co. KG, Espelkamp
2. METHOD DESCRIPTION AND CONCEPT
2.1 Sand pre-loading layer and vertical drains
If the local boundary conditions e.g. space available, existing and
planned services, local structures (buildings, river-bank structures,
sewers) and the time constraints permit, the use of a sand pre-
