i137 GEO binnen - GeoTechniek

DEFORMATION MONITORING OF THE UNDERGROUND METRO STATION ROTTERDAM CS
the required measuring range of the measuring
instrument;
the required accuracy and frequency of measuring;
the hazard warning levels;
the way of communication.
This paper will focus on the deformation monitoring
of the metro station only. All other monitoring
parameters are beyond the scope of this paper and
will not be discussed.
HAZARD WARNING LEVELS
In order to make corrective actions effective, it is
essential to compare the measured parameters with
predefined hazard warning levels. These levels form
an important part of the monitoring specifications
(Berkelaar, 2006).
The main criteria for the hazard warning levels were
to assure the structural integrity of the station and
safe operation of metro traffic. The structural
engineers of RPW determined the levels based on the
structural integrity whereas the RET provided
specifications for safe metro operation. Two types of
hazard warning levels were defined:
the call or warning value; when exceeding this limit
the contractor has to communicate this with RPW
and take actions to prevent further exceeding of
this value;
the intervention value; when exceeding this limit
FIGURE 4
BUILDING PIT CONTOURS NEW METRO STATION.
40 GEOinternational – October 2008
the contractor has to communicate this immediately
with RPW, works have to be stopped and in
consultation with RPW further actions and
measurements will be defined.
The hazard warning levels of the metro station are
based on possible deformation of the underground
station, Table 1. The most vulnerable part of the station
to deformation results from the track deformation
requirements. A displacement of 10 mm between
station sections in vertical direction is critical as the
rail is directly fixed to the concrete station sections
i.e. no ballast bed construction.
FOLLOW-UP
A monitoring system is as good as the way data and
signals are processed and interpreted. Therefore a lot
of attention has been given to implementation and
communication of the hazard warning levels. For the
most critical part of the project, deformation of the
metro station, a fully automatic measurement system
was installed. Crucial with systems like this is that the
alarm signal has to reach the contractor at all times.
MONITORING SYSTEM
GENERAL
Monitoring the station was a challenge for the
contractor, because of the geometry, construction,
utilisation of the station and contractual requirements
like hazard warning levels and measuring frequency.
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TABLE 1 HAZARD WARNING LEVELS
METRO STATION
CRITERIA PARAMETER INTERVENTION
VALUEa SAFE METRO DIFFERENTIAL SETTLEMENT 10 MM
OPERATION OVER STATION SECTION
JOINTS
ROTATION OF STATION 1:1000b OR
SECTIONS 1:750c MM/MM
BANKING OR CANT
OF TRACKS
5 MM
TWIST OR DISTORTION
TOLERANCE OF STATION
SECTIONS
1:600 MM/MM
STRUCTURAL DIFFERENTIAL SETTLEMENT 16 MM
DEMANDS NORTH TO SOUTH
ABSOLUTE SETTLEMENT 50 MM
a Warning value is 75% of the intervention value.
b Around vertical axis.
c Between 2 station sections around horizontal axis
perpendicular to station section length.
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The main part of the station (W12 to W15) was built
in 1965 by immersing station sections in an artificial
channel. Sections B and A1 to A4 were constructed
from an open pit in 1978, Figure 5. Because of the
composition of the soil in Rotterdam the station is
founded upon concrete driven piles. The joints
between the station sections need to be water tight,
as groundwater level is just below surface level. The
station sections are very stiff ‘concrete boxes’.
Therefore the station sections were assumed to be
rigid for monitoring purposes. All station sections
could be surveyed by monitoring points near the
joints on both sides. This meant four points per
section, one on every corner.
SYSTEM SETUP
In an ideal situation a single tachymeter (theodolite
with internal distance measurer) could be used to
monitor all points. Measuring with a tachymeter
requires mutual visibility of the points to be
measured. Because of the metro traffic, its passengers,
pillars and other constructions in the station, it
was impossible to position the tachymeter in such a
position that mutual visibility between all points,
north and south, and the tachymeter could be
achieved. Therefore a tachymeter was positioned on
the north side of the station from where it was
possible to measure all joints (19 points, numbers
101 to 119) on the north side of the station and 4
points on the south side of the station (numbers 211
to 214), Figure 5.