Bangkok MRT Orange Line project reaches another tunnelling milestone

Final TBM breakthrough has been achieved at Hua Mak Station on the 3.3-km MRT Orange Line (East section) project in Bangkok, Thailand. This landmark event took place way ahead of schedule, said Terratec, the TBM manufacturer.

A 6.39-m-diameter S70 earth pressure balance (EPB) machine from Terratec has been chosen 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.

Contract E3, which was awarded to ITD in May 2017, totals over 6 km of TBM driven tunnel and three underground stations, extending from Khlong Ban Ma to Hua Mak. After completing the Westbound tunnel on 20 January 2020 with progress of 663.4 m, the Terratec S70 machine began mining eastwards from the Khlong Ban Ma station box on 26 April 2020, and quickly got up to speed following its initial drive. By mid-June 2020, the TBM was achieving the best rates of 33 rings per day (46.2 m/day) and had already undertaken its first intermediate breakthrough.

According to Terratec, in March 2020 the Westbound tunnel breakthrough on Contract E3 was carried out a full month ahead of schedule, while the Eastbound tunnel breakthrough on Contract E3 was reached 118 days ahead of schedule.

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 the 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 has been installing a precast concrete segmental lining consisting of five 1,400-mm-wide Universal style segments plus key, with an internal diameter of 5.7 m. 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, which also employed a Terratec TBM.

In total, TBM tunnelling operations for ITD’s Orange Line (East) contract has lasted two years.

Bangkok’s new Orange Line will eventually total about 35.9 km, featuring 26.2 km aligned underground with 22 underground stations and another 9 km and seven stations on elevated structures. The line is scheduled to open in March 2024.

Upon completion, 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.

A video of the TBM breakthough can be seen here.