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Because of the assumed stiffness of the station
the vertical displacement of the south side of the
station, which can not be ’seen’ entirely by the
tachymeter, could be computed from the measured
vertical displacement on the north side and the tilt of
the station sections. For this purpose 19 electronic
electro level tilt meters were placed along the north
side of the station next to the points measured with
the tachymeter. The 4 points which could be
measured by the tachymeter on the south side were
used to control the computed vertical displacement
at these locations.
With the described system it was possible to
measure the x, y, z deformation of all points on the
north side, the z deformation on the south side and
detect relative displacements. To measure absolute
displacements reference points on the outside of the
station had to be measured. The reference points
outside the station were also measured automatically
with another tachymeter which was also in use
monitoring buildings near the station.
After processing, the results were made directly
available on-line through the internet application
Argus Monitoring Software, Figure 6. In case of
exceeding hazard warning levels Argus provided
automated notification to the contractor by e-mail
and SMS text messages. On screen alarms were given
colour codes, green: below warning level, yellow:
warning level exceeded, red: intervention level
exceeded.
MONITORING RESULTS
GENERAL PERFORMANCE
The monitoring system of the contractor fulfilled all
contractual requirements (Huisman and Berkelaar,
2006). From the primary monitoring results (x, y, z
and tilt) secondary parameters, like differential displacement,
rotation, banking and twist could be
calculated. All measured and calculated results were
checked on-line on the hazard warning levels by
Argus. The accuracy level, relative accuracy less than
1 mm, matched the requirements. A monitoring
frequency of 20 minutes was reached.
The on-line presentation and automatic warning
system made it possible to guard the safety of the
station during all building activities and intervene
when necessary. The graphical on-line representation
of the results made it easy to interpret the results of
the monitoring system and evaluate the effect of the
construction activities on the station.
DEFORMATION MONITORING OF THE UNDERGROUND METRO STATION ROTTERDAM CS
MONITORING AS RISK CONTROL
Some examples will be given of typical monitoring
results in relation to the construction activities.
Illustrated is how monitoring has been used to
control risks during building.
Absolute vertical deformations due to pile driving
One of the first building activities was pile driving
just north of station section A4. Within 4 weeks time
a vertical deformation of 22 mm was detected, Figure
7. This deformation was directly related to the pile
driving. Exceeding of the warning level could be
expected shortly considering the trend of deformation.
It was therefore decided to change the installation
method of the piles by pre-drilling. This was a very
successful way to control the deformation as can be
seen in Figure 7. No additional significant settlement
occurred thereafter.
FIGURE 6
FIGURE 5
TOP VIEW OF THE STATION
WITH MONITORING POINTS AND
STATION SECTION NUMBERS
ON-LINE VISUALISATION WITH ARGUS
MONITORING SOFTWARE (BOART LONGYEAR)
Relative vertical deformation
over station section joints
An important hazard warning value for safe metro
operation was the differential settlement over station
section joints. Figure 8 shows the development in
deformation over some joints. When the warning
value was exceeded the operator of the station was
informed. The operator decided to execute track
corrections at the moment the intervention value was
reached. After the track corrections on joint W13-
W14 the hazard warning value for this joint was reset
(not shown in Figure 8).
MONITORING INCIDENTS
Verification measurements by RPW
Before the building activities had started, RPW had
already performed regular tachymetric measure-
GEOinternational – October 2008 41