In late March, Contractor Italian-Thai Development PCL (ITD) on Contract E3 of the Mass Rapid Transit Authority of Thailand’s (MRTA) Orange Line Project, reported a 400m advance of its 6.39m diameter Terratec S70 EPBM since its launch on 12th January 2019, with progress rates of up to 18 rings per day. The EPBM has alreadyundertaken its first intermediate breakthrough into a ventilation shaft (IVS 17) where it underwent a cutterhead inspection.
Contract E3 is on one of three underground civil works contracts for the first 23km-long (East) phase of the Orange Line Project, and was awarded to ITDin May 2017. It totals over 6km 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.
The EPBMwas 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.
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“We are in a very congested area of the city, tunnelling underneath a busy highway that has a flyover directly above it and buildings with deep foundations on both sides,” says Prakin Arunotong, Senior Vice President of ITD’s MRT Business Unit. “So we need to carefully protect those structures during tunnelling and station construction.”
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 and 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 is installing a precast concrete segmental lining consisting of five x 1200mm wide Universal style segments plus key, with an internal diameter of 5.7m. These are being produced by ITD at the same factory used for segment manufacture during its MRT Blue Line underground works contract five years ago.
In total, TBM tunnelling operations for ITD’s Orange Line (East) contract are expected to last approximately two years.
Bangkok’s new Orange Line will eventually total about 35.4km with 26.2km aligned underground with 23 underground stations and another 9km and seven stations on elevated structures. When complete, in 2023, the Orange Line will provide a vital transportation link from Bangkok’s 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.