Tight Bangkok cable tunnel breakthrough18 December 2017
Thailand - On 22 September the first drive for the Phra Khanong Cable Tunnel Project broke through. The project, carried out by contractor Nawarat Patanakarn called for a 32m-radius curve as the TBM exited the launch shaft to avoid some existing piles. The TBM used was a 3.2m Terratec EPBM, which is now excavating the second drive.
According to a spokesperson for the manufacturer “the machine was manufactured with an extreme X-type articulation system that provides a maximum articulation angle of 6.6-degrees… The TBM was launched on its first, 495m long, drive in early February from a 7.0m diameter shaft located beneath an elevated expressway ramp with limited working head room. At the end of the drive, the machine had to execute a second, 30m long 99m-radius, curve on its approach to the reception shaft.”
The lining initially consisted of 300mm wide x 125mm thick steel sets before transitioning to a tapered precast concrete segment lining of 1.2m width and 225mm thickness.
The manufacturer said of the machine setup: “[It has] a classic soft ground open spoke cutterhead design, with knife bits to assist break-in and break-out of the steel fibre reinforced concrete shaft eyes, the EPBM has coped extremely well with the geological conditions along the alignment, which consist of fine sands and stiff clays with a groundwater head of about 2 bars.”
The second, 293m-long drive began from the launch shaft in November with a 43.7m radius curve and on a 2% upwards gradient.