Thai river diversion scheme accepts TBMs

5 May 2017

Thailand – April saw factory acceptance for the two 5.7m-diameter Terratec EPBMs that will bore the Bueng Nong Bon to Chao Phraya River Diversion Tunnel Project in Bangkok. These will be the newly-branded ‘Terratec Tight Radius Shields’ alluded to in a previous news article.

Located in the southeast of Bangkok, the 9,187m-long Bueng Nong Bon to Chao Phraya River Diversion Project is the third of four major flood prevention tunnels to be built under the Bangkok Metropolitan Administration’s long-term plan to manage the severe flash floods that currently plague the Thai capital during the rainy season.

A number of tight curves necessitated an X-type articulation system, providing a maximum angle of 7.5 degrees to accommodate a curve radius of 35m.

A spokesman for the manufacturer elaborated on the drives: “The first machine to get going on the project will be the S54 machine, which will be launched into a 65m radius curve – from a 15m diameter shaft at the Bueng Nong Bon reservoir intake – southwards towards the Klong Nong Bon Inlet Station. Following an intermediate breakthrough at Klong Nong Bon, the TBM will then be turned 90 degrees within the 12m diameter shaft and re-launched westwards to the Klong Kled Inlet. The third and final run for the S54 machine will require a sharp 40m radius curve mid-drive to turn the TBM northwards to the Sukhumvit 101/1 Shaft, where the TBM will be dismantled. The total length of this first section is 5,523m.

“Meanwhile, the S55 machine 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, the S55 machine 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 breakout of the shafts.

Traditionally reinforced 1.2m thick, 5m internal diameter, precast concrete segments will typically be installed as the machines progress, with shorter steel segments utilised during the course of the sharp 40m radius curves.

Excavation is due to commence later this year. When complete, the tunnel will have a drainage capacity of 60 cubic metres per second, providing much needed flood relief to an area of approximately 85 square kilometres.