Page 7 - Tunneling

www.moniterra.engineering TUNNELING

• Externally • During the installation of the metal brackets on one side
of the tunnels, there were metal pipes that impeded the
To unify the elevation networks of the tunnels, due to correct selection of the installation point that would meet
their great elevation differences, the method of Special the requirement of visibility with the other bases.
Trigonometric Levelling was used.
• The methane fumes inside the tunnels and the landslide
• Complete survey of tunnels with laser scanning and
compilation of cross-sections. problems due to water erosion were some of the other
problems presented and dealt with by observing the
After the establishment of the Trigonometrical Network and the necessary security measures, such as special masks,
breakthrough, the joined tunnel was scanned, using Amberg protective helmets, etc.
Profiler 5003 laser scanner.
5. COMPLETION TIMES
The following methodology was used:
The following survey crews were employed:
At each scan, targets were placed in the front and in the back of
the Laser Scanner, which were thus located inside the scanning • OOne six-member crew undertook the measurements
field and were part of the survey. The same targets were of the horizontal network at the 11km long Drakotrypa to
surveyed at the same time by the S6 Trimble total station, which Argithea tunnel, which were completed in three days.
was installed on a fixed metal bracket with known coordinates. • Another crew of two people undertook the levelling
This meant that the specific targets were oriented based on measurements of the levelling network, which were
the new trigonometrical network, and with them all the imaging completed in three days.
points were oriented through the scanning. This procedure was • The five-member crew that worked for the horizontal and
repeated at every 20 meters to allow the best possible and levelling network at the Petroto to Argithea tunnel required
more detailed surveying and supporti of the necessary overlap two days, covering 3 km.
of the consecutive scans.
• The five-member crew that worked for the horizontal and
For the process the data from the digital scans, we used levelling network at the access gallery required three days
the Cyclon software by Leica. This software carried out the for 2km + 4km in the main tunnel.
registration, to allow the correct georeferencing of the surveyed
sections in space. Based on this surveying and the axis of the • Three persons were needed for the special trigonometric
tunnels, cross-sections were produced every 6.67 meters levelling, which was completed in one day.
except for a 2,061-meter section of the Petroto-Argithea tunnel, • The complete imaging of the total length of the final tunnel
where sections produced every 9 meters. with the digital scanning method required approximately
4. THE PROBLEMS PRESENTED fifteen days to complete by a survey crew of three.
• The basic problem dealt with was the constant workflow • It should be noted that for the surface measurements of the
within the tunnels on a 24-hour basis, which therefore horizontal network with GPS geodetic receivers eight hours
required the organization and installation of the survey were needed and four people were employed.
works when no workers or machinery would be inside the 6. EQUIPMENT USED:
tunnels. Thus, the time when the works were carried out
was holidays and days of leave of the permanent staff. • Geodetic Stations LEICA 1201, 1’’,+/- (2mm+2ppm) ,
LEICA 2003, 0,5’’, +/- (1mm+1ppm) , and Trimble S6 High
• The tunnels were very narrow aprox. 4.5m – 5.0m, so the Precision, 1’’, +/- (1mm+1ppm).
geometry of the network was not the appropriate one.
• 2 Digital Levels TRIMBLE Dini (0,3mm/km)
• Due to rock mass collapse in the past, access gallery
alignment had very close and narrow curves. So in many • Laser Scanner 5003 AMBERG
cases the network’s side length didn’t exceeded 15m. This • 4 dual frequency GPS TRIMBLE R8 and 7 single frequency
was a very dangerous situation, because an 18km tunnel TRIMBLE R3.
breakthrough depended on 15m measurements.
• Huge amounts of water were entering the tunnel from
all sides, so measurements were taken through water
curtains.
• Along the length of the Drakotrypa to Argithea tunnel rails
were installed, which served to transport staff and materials.
These rails were covered on their greater part by water and
mud and thus work in this section required special attention
during the levelling and total station’s measurements. The
digital scan survey at this section was carried out with the
use of a special wagon where the Laser Scanner was
mounted. Ag. Stefanos tunnels

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