Terratec delivers TBM for Bangkok cable project

Following the successful Factory Acceptance Test, the machine is now ready to be shipped to the site where contractor Nawarat Patanakarn PCL, on behalf of the Metropolitan Electricity Authority, will build a cable tunnel to supply electricity from South Bangkok electrical substation to Samuth Prakan Province.

The 4.27m EPB TBM 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 tunnelling projects by the MEA to meet increased power demand 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.

The Terratec EPB TBM will be deployed by Nawarat Patanakarn 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.

The most challenging part of the project will be excavating alongside the existing live HDD cable supply so the TBM will be operated in an alert mode throughout excavation.

Geological conditions along the tunnel alignments will consist of mixed faces of silt, clay and fine sand with an average overburden of 35m and a groundwater head of about 3 bars. The TBM’s soft ground cutterhead therefore features a spoke design and knife bits to assist break-in and break-out of the concrete shaft eyes.

Traditionally reinforced, 300mm-thick, 1200m-wide and universal tapered precast concrete segments (4 + key) will be installed as the machine progresses. 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 Terratec’s “Non tuck hose” plus belt conveyor. 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-diameter shaft which is currently being constructed near the Chao Phraya River.

The TBM shield and back-up 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". The machine is designed with a 40m turning radius to swerve around any obstruction.

Terratec sold its first machine in Thailand 10 years ago for the Metropolitan Rapid Transit (MRT) Blue Line Extension Project.