Early breakthrough on Bangkok Orange Line 09 Apr 2020

An early breakthrough has been celebrated on one of three underground civil works contracts for the first 23km-long east section phase for the Mass Rapid Transit Authority of Thailand (MRTA) Orange Line Project in Bangkok.

A Terratec 6.39m diameter EPBM made the breakthrough on the westbound tunnel of Contract E3 for contractor Italian-Thai Development (ITD) a month ahead of schedule, giving hope for an early breakthrough on the upcoming eastbound drive.

Breakthrough on Bangkok Orange Line Contract E3

Contract E3, which was awarded to ITD in May 2017, comprises more than 6km of TBM driven tunnel and three underground stations, extending from Hua Mak to Khlong Ban Ma. The Terratec EPBM started its journey westwards from the Khlong Ban Ma station box on 12 January 2019 and was up to speed quickly following its initial drive. By late March, the TBM was achieving progress rates of up to 18 rings/day and had already achieved its first intermediate breakthrough. July 2019 marked the best month of progress, achieving a total advance of 663.4m and a best day of 40.6m.

The Terratec EPBM was designed to manage the variable soft ground geology of the city which ranges from soft and medium to stiff and very stiff clays, with lenses of dense sand and the potential for high pressure groundwater inflows. The TBM will also excavate through the diaphragm walls of numerous shafts, potentially cutting through concrete piles.

In order to handle these challenging conditions, the TBM features a soft ground spoke-style cutterhead and the addition of back-loading knife bits to assist break-in and break-out of the shafts. In addition, the machine is fitted with an active bentonite face support injection system and a double gated screw, to ensure face stability and mitigate settlement during excavation in areas of flowing sands and high groundwater pressure.

As the machine progresses along the alignment, it has installed a precast concrete segmental lining consisting of five x 1.2m wide universal style segments plus a key in each ring for an internal diameter of 5.7m. These are being produced by ITD at the factory that was used for segment manufacture during its MRT Blue Line underground works contract five years ago, which also employed a Terratec TBM.

Celebrations at the westbound tunnel breakthrough

In total, TBM tunnelling operations for the ITD Orange Line East contract are expected to take about two years and are being assisted at all times by Terratec field service staff to ensure optimum performance and successful project completion.

“We have worked closely with Terratec since 2012, when we won our MRT Blue Line extension contract,” said Prakin Arunotong, Senior Vice President of the ITD MRT Business Unit. “Terratec has a very similar working style to our own and because of this we consider our partnership with them as more of an alliance than that of the traditional contractor-TBM manufacturer relationship.”

“Due to extensive project planning we were well prepared for the 3.3km long drive and any challenges had pretty much been solved on paper before the TBM commenced,” said Bunjerd Emnuch, Terratec Tunnel Manager. “The only remaining challenge was obstruction cutting. The TBM had to cut through 10 diaphragm wall panels during break ins and break outs.”

The Terratec EPBM is now being prepared for the 3.3km long eastbound drive on Contract E3 and is expected to relaunch this month (April).

The new Orange Line for Bangkok will eventually total about 35.4km with 26.2km and 23 stations aligned underground and another 9km and seven stations on elevated structures. When complete, in 2023, the Orange Line will provide a vital transportation link from Bangkok city centre to districts in the east, reducing traffic congestion and paving the way for improved accessibility, economic growth and new residential and commercial opportunities along the alignment.