Extreme articulation for Bangkok flood prevention 04 May 2017

Following successful factory acceptance tests, two new 5.7m tight radius EPBMs from Terratec are headed to Bangkok to facilitate a challenging curved alignment on the Bueng Nong Bon to Chao Phraya river diversion tunnel project for the Bangkok Metropolitan Administration (BMA). The ceremonies were attended by representatives of the BMA and Thai contractor Sino-Thai Engineering & Construction Public Company Limited (STECON).

Terratec articulated tight radius EPBM

Located in the south-east of Bangkok, the 9,187m long river diversion project is the third of four major flood prevention tunnels to be built in the long term plan to manage the severe flash floods that currently plague the Thai capital during the rainy season.

Due to the densely developed nature of the city, the east-west route between the Bueng Nong Bon reservoir and the Chao Phraya River has largely been dictated by the need to stay within public road easements, which has imposed a number of very tight radius curves on the tunnel alignment. To achieve these, the Terratec tight radius machines have been designed with an extreme X-type articulation system that provides a maximum articulation angle of 7.5 degrees to accommodate a minimum radius curve of 35m.

The first machine to start work on the project (TBM1) will be launched into a 65m radius curve from a 15m diameter shaft at the Bueng Nong Bon reservoir intake and travel southwards towards the Klong Nong Bon inlet station. Following an intermediate breakthrough at Klong Nong Bon, the TBM will be turned 90 degrees within the 12m diameter shaft and re-launched westwards to the Klong Kled inlet. The third and final run for TBM1 will require a sharp 40m radius curve mid-drive to turn the TBM northwards to the Sukhumvit 101/1 shaft, where it will be dismantled. The total length of this first section is 5,523m.

Witnessing factory acceptance

Specially designed cutterheads with open spoke design

Meanwhile, the second machine (TBM2) will complete the two remaining sections of the tunnel. Launching from the 15m diameter Bang Aor pump station (inlet) shaft which, along with the Bang Aor pump station (outlet) shaft, has been constructed within a large diaphragm wall groundwater cut-off structure, this TBM will also commence its 2,975m drive with a 65m radius curve, heading eastwards to the Sukhumvit 66/1 inlet shaft. Here, the machine will need to negotiate a challenging, double 40m radius, S-shaped spiral curve before completing its drive to the Sukhumvit 101/1 shaft, where it will be dismantled and transported back to the Bang Aor pump station (outlet) shaft. Following reassembly, TBM2 will complete a final 690m drive westwards from the Bang Aor pump station (outlet) shaft, again starting on a 65m radius curve, to the Chao Phraya River outlet shaft. Geological conditions along the alignment consist of soft to medium sandy clays, stiff clays and very dense sands, with an average overburden of 30m and a maximum groundwater head of about 1.5 bar.

The TBMs’ soft ground cutterheads feature an open spoke design with the addition of knife bits to assist break-in and break-out of the shafts. Traditionally reinforced 1.2m thick, 5m id, precast concrete segments will be installed as the machines progress, with shorter steel segments used during the course of the sharp 40m radius curves.

Excavation is due to start later this year and machine operation will be assisted at all times by Terratec field service staff to ensure optimum performance and successful project completion.

When complete, the tunnel will have a drainage capacity of 60m³ per second, providing much needed flood relief to an area of approximately 85km².