Breakthrough on Bangkok’s Chidlom Cable tunnel

1 July 2019

Thailand – A 3.2m diameter Terratec TBM completed a challenging section of a drive for the Chidlom Cable tunnel project in Bangkok this month. The drive included a 35m-radius curve

Tunnelling on the project started in September 2018.

To avoid any issues with public roads, building foundations or the deep piles of the BTS Sukhumvit Skytrain that runs along Phloen Chit Road, the tunnel alignment had strict constraints that require several tight radius curves to bring them into MEA’s Chidlom Terminal station. To achieve this, the EPB machines have been designed with an X-type articulation system which can accommodate very tight curves.

A spokesperson for the manufacturer said, “The 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 includes stiff to very stiff clay, with lenses of sand and a groundwater head of about 2 bars.”

ITD’s project manager, Supak Khunviriya said, “We started out straight into the 35m radius curve with the machine, going under a busy five-lane road and around the corner of a department store at the intersection with Phloen Chit Road. This is an old building, so the foundation piles extend down about 20m. The tunnel is at 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.

The attention is now focused to the other machine, a 4.27m diameter 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.