TERRATEC has announced the delivery of a 4.27m EPBM for the South Bangkok Cable Tunnel Project by the Metropolian Electricity Authority (MEA) in Thailand. Following the successful Factory Acceptance Test (FAT), the machine is now ready to be shipped to the site where contractor Nawarat Patanakarn PCL will build a cable tunnel to supply the electricity from South Bangkok electrical substation to Samuth Prakan Province.
The 4.27m EPBM machine features a classic soil configuration with a spoke-style cutterhead and a 70% opening ratio. TERRATEC designed a robust high flow cutter head specifically for the expected ground conditions.
Designed to accommodate a new high-voltage cable system, the South Bangkok Cable Tunnel Project is one of a series of planned tunneling projects by the MEA that are being built to meet increased power demands and ensure reliable supply in the Thai capital. The project includes the construction of underground power transmission tunnels under the Chao Phraya River from the Southern Bangkok electrical substation to Suksawat Road.
TERRATEC EPB TBM will be deployed by contractor Nawarat Patanakarn PCL to cross Chao Phraya River which is 500m wide and approximately 30m deep. The cable tunnel will be 950m long. This new electricity tunnel will increase the capacity of the existing horizontal directional drilling (HDD) electrical cable nearby.
Major challenges on the project will include crossing the 500m river as well as excavating alongside with the existing live HDD cable supply which is the most challenging part of this project. Therefore, the TBM will be operated in an alert mode throughout the whole excavation of the cable tunnel to ensure that the excavating process will go smoothly.
Geological conditions along the tunnel alignments will consist of mixed faces of silt, clay and fine sand with an average overburden of 35m (114ft) and a groundwater head of about 3 bars. The TBM’s soft ground cutterhead therefore features a spoke design and the addition of knife bits to assist break-in and break-out of the concrete shaft eyes.
Traditionally reinforced, 300mm thick by 1200m wide and universal tapered precast concrete segments (4 + key) will be installed as the machine progresses and muck removal, segment transport and machine supply will be via rail bound equipment.
As the water pressure is high, the TBM has been designed to remove the muck by using the TERRATEC trademark “Non tuck hose” plus belt conveyor. It has been proven that this system is the most suitable for Bangkok sand stratum.
Located at the south of Bangkok sub-urban, the machine will be launched from a 12m (39ft) diameter shaft which is currently being constructed near the Chao Phraya River.
The shield of the TBM and backup systems are also tailored to accommodate the tight curve project requirements. This includes a mucking system that conveys spoil from the TBM’s screw to the “Non-tuck hose”. With the machine designed of 40-meter turning radius, it will comfortably swerve around any obstruction.