TERRATEC’s tight radius TBMs are enabling a highly
challenging project alignment for Bangkok’s Metropolitan Electricity Authority
in one of the city’s busiest downtown areas.
In May, TERRATEC joined representatives of Bangkok’s
Metropolitan Electricity Authority (MEA) and contractor Italian-Thai
Development PCL (ITD) to celebrate the successful breakthrough of one of two
TERRATEC Earth Pressure Balance Tunnel Boring Machines (EPBM) at work on the
complex Chidlom Cable Tunnel Project, in Bangkok, Thailand. The 3.2m diameter
S48B machine completed a challenging portion of the project that included an
extremely tight (35m-radius) curved drive.
Running from the Central Embassy ‘ultra-luxury’ mega mall,
located on Phloen Chit Road within the former gardens of the British Embassy
site, and MEA’s Chidlom Terminal Electrical Station, southwards to Lumphini
Park, the project is located in one of the most exclusive and built up areas of
downtown Bangkok.
In order to remain within public road easements, as well as
negotiate building foundations and the deep piles of the BTS Sukhumvit Skytrain
that run along Phloen Chit Road, the tunnel alignments are subject to strict
constraints that require several tight radius curves to bring them into MEA’s
Chidlom Terminal station. To achieve this, the TERRATEC EPB machines have been
designed with a unique extreme X-type articulation system, which can
accommodate very tight curves.
“We have worked closely with Terratec on several projects in
the past and were keen to work with them again,” explains ITD’s Project
Manager, Supak Khunviriya. “They have experience from similar projects in
Bangkok, so there was a close collaboration from the tender stage. The TBMs are
designed to achieve a high level of performance in difficult circumstances and
we have trust in Terratec’s team, who have assisted us throughout the
tunnelling operations.”
The TBMs’ soft ground cutterheads feature an open spoke
design with the addition of knife bits to assist break-in and break-out of the
concrete shaft eyes. Universal tapered precast concrete segments are typically
installed as the machines progress, with shorter steel segment sets utilised
during the course of the sharp radius curves. The geology along the project is
typical for Bangkok, generally comprising stiff to very stiff clay, with lenses
of sand and a groundwater head of about 2 bars.
Tunnelling on the project commenced last September: “We
started out straight into the 35m radius curve with the S48B machine, going
under a busy five-lane road and around the corner of an exclusive department
store at the intersection with Phloen Chit Road,” explains Khunviriya. “This is
an old building, so the foundation piles extend down about 20m. The tunnel is
at exactly the same level, so we had to be very careful not to cause any
settlement. We also had to negotiate the BTS Skytrain foundations on the other
side, giving us a window with about 1m either side of the machine through the
intersection.”
ITD had an array of monitoring equipment in place to check
for any tunnelling induced settlement during the curved drive, but zero
movement was recorded. ITD credits much of this to the skill of Terratec’s
field service team, whose experienced TBM operators steered the TBM throughout
the curve and are assisting TBM operations and maintenance throughout the
project.
Focus on the project has now switched to the other TERRATEC
machine, the 4.27m diameter S69 TBM, which was launched in January and is
currently excavating a 1,349m-long tunnel from Lumphini Park to the MEA’s
Chidlom Terminal Station. It is due to complete this drive in September. Each
machine will then execute a further short curved drive to complete tunnelling
on the project.
Designed to accommodate a new high-voltage cable system, the
Chidlom Cable Tunnel Project is one of a series of tunnelling projects being
undertaken by the MEA, which are being built to answer increased power demands
in the Thai capital. The projects will also improve the reliability of the
power transmission system and reduce the risk of physical damage to
conventional above-ground power lines as a result of accidents and storms.
TERRATEC has a well-established regional base in Thailand,
having sold its first machine in the country eight years ago for the
Metropolitan Rapid Transit (MRT) Blue Line Extension Project. Since then,
Terratec has become the country’s leading TBM supplier, with nine machines
supplied to Thai projects in recent years.
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For more information visit: www.terratec.co
