This was the last of a series of tunnel drives on which the machine has been deployed by contractor Italian-Thai Development (ITD) and is one of three underground civil works contracts for the first 23km-long East phase of the project which comprises 11.38km of twin, single-track tubes. ITD’s E3 contract – awarded in May 2017 – involved 6.6km of mined tunnel and three underground stations. Along its way, the machine has installed a precast concrete segmental lining comprising rings of 5.7m internal diameter made up of five 1,400mm-wide Universal segments plus key.

Breakthrough on the eastbound tunnel of contract E3 has been achieved 118 days ahead of schedule. In March 2020, the TBM holed through on its 3.3km westbound tunnel drive after cutting through 10 diaphragm walls and numerous break-ins and -outs.

Throughout, the Terratec machine has encountered a complex and variable soft-ground geology, ranging from soft and medium, to stiff and very stiff clays, with lenses of dense sand and the potential for high-pressure groundwater inflows. Tackling these challenging conditions required a spoke-style cutterhead with 43% opening ratio plus back-loading knife bits to aid in the break-in and break-out of concrete shaft eyes at stations. The TBM also had an active bentonite face-support injection system and double-gated screw to ensure face stability and mitigate ground settlement within areas of flowing sands and high groundwater pressure.

When it opens in March 2024, the Orange Line will be 35.9km long, of which 26.2km and 22 stations will be underground, while another 9km and seven stations will be on elevated structures. The line will provide a vital link from Bangkok’s city centre to eastern districts, reducing traffic congestion and facilitating improved accessibility, economic growth and new residential and commercial opportunities along the alignment.