Orange Line Metro Project Bangkok: Breakthrough of the Westbound Tunnel on Contract E3
In January 2020, TBM manufacturer Terratec joined workers and officials in celebrating the breakthrough of the 6.39 m diameter S70 EPB machine by contractor Italian-Thai Development PCL (ITD) on one of three underground civil works contracts for the first 23 km-long (East Section) phase of the Mass Rapid Transit Authority of Thailand’s (MRTA) Orange Line Project. The Westbound tunnel breakthrough on Contract E3 took place a full month ahead of schedule putting the project on a good footing for the upcoming Eastbound tunnel drive.
Contract E3, which was awarded to ITD in May 2017, totals over 6 km of TBM driven tunnel and three underground stations, extending from Hua Mak to Khlong Ban Ma. The S70 machine began mining westwards from the Khlong Ban Ma station box on January 12, 2019, and quickly got up to speed following its initial drive. By late-March, the TBM was achieving progress rates of up to 18 rings per day and had already undertaken its first intermediate breakthrough.
The Terratec S70 TBM was designed to tackle 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 – as well as the need to mine through numerous diaphragm wall shafts and, potentially, concrete piles. In order to handle these challenging conditions, the TBM’s soft ground cutterhead features a spoke style 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 to ensure face stability and mitigate settlement during excavation in areas of flowing sands and high groundwater pressure.
As the machine progressed along the alignment, it installed a precast concrete segmental lining with an internal diameter of 5.7 m. The segments are being produced by ITD at the same factory used for segment manufacture during its MRT Blue Line underground works contract five years ago, which also employed a Terratec TBM.
In total, TBM tunnelling operations for ITD’s Orange Line (East) contract are expected to last approximately two years. The S70 TBM is now being prepared for Contract E3’s 3.3 km long Eastbound tunnel drive and is expected to relaunch in April 2020.
Bangkok’s new Orange Line is expected to be completed in 2023 and will eventually total about 35.4 km with 26.2 km aligned underground with 23 underground stations and another 9 km and seven stations on elevated structures.