Terratec celebrates the successful factory acceptance test of a new-design 3.2m diameter EPBM destined for the tight radius curve demands of the Phra Khanong Cable Tunnel Project in Bangkok, Thailand.
The event, held on 26 September (2016), was attended by representatives of Bangkok’s Metropolitan Electricity Authority (MEA) and its Thai contractor Nawarat Patanakarn PCL.
Designed to accommodate a new high-voltage cable system, the Phra Khanong Cable Tunnel Project is the first of a series of planned tunnelling projects by the MEA that are being built to meet increased power demands in the Thai capital.
The project is situated in one of the busiest areas of downtown Bangkok and is subject to tight alignment constraints. The machine will be launched from a 7m diameter shaft that is currently being constructed beneath the Ram Inthra – at Narong Expressway toll road ramp, and with little working headroom.
The first of two drives for the project will see the EPBM head 495m south at an upgrade of 1.2%, terminating at a reception shaft located under the BTS Skytrain structure just short of On Nut Station. From there, the machine will be lifted and transported back to the launch shaft under the expressway ramp.
In order to negotiate the foundation piles of the ramp – and complete its second, 293m-long, drive northwards under the Phra Khanong canal – the EPBM will be launched onto a sharp 32m radius curve on a 2% upgrade.
To achieve this, the Terratec machine is designed with an X-type articulation system that provides a maximum articulation angle of 6.6-degrees to accommodate a minimum radius curve of 30m. Although this type of extreme articulation is uncommon in the global market, it is popular in Japan. Terratec therefore teamed up with Japanese manufacturer JTSC to develop the design, with the aim of exporting this technology to other countries.
The EPBM’s back-up systems are also tailored to accommodate the tight project requirements, including a mucking system that conveys spoil from the screw conveyor to a transfer pipe using air pressure.
Geological conditions along the alignment consist of fine sand and stiff clay, with an average overburden of 26m and a groundwater head of approximately 2 bar.
The TBM’s soft ground cutterhead features an open-spoke design with the addition of knife bits to assist break-in and break-out of the steel fibre reinforced concrete shaft eyes. Traditional tapered precast concrete segments (left/right/straight) will typically be installed as the machine progresses, with shorter steel segments utilised during the course of the sharp radius curve.
Following the successful factory acceptance test, the machine will now be shipped to Thailand and is expected to arrive by the end of October. Excavation is due to commence in mid-December.
Machine operation will be assisted at all times by Terratec’s highly-experienced field service staff, providing quality after-sales support to ensure optimum performance and successful project completion. The tunnel is scheduled to go into operation at the end of 2017.