The Thai contractor built the tunnel, designed to alleviate flooding, using a refurbished Terratec S48C EPBM.

Terratec says the EPBM, featuring 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, coped well with the geological conditions along the alignment. They consisted of dense sand, stiff to hard clay and decomposed rocks with a groundwater head of about 2 bars.

The 5x9m receiving shaft was located at the bottom of two hills where flooding lies. The flood water will be drained through the new tunnel and connected with a 500m open canal to the sea. With Terratec’s non-tuck hose system, muck can be easily transferred to muck cars and out to the surface.

Samui Island, off the east coast of Thailand, is the country’s second largest island after Phuket. It attracts more than 2.7 million tourists a year. Samui faces severe flood problems and the tunnel is intended to ease flood waters. As part of the main Ring Road revitalisation and improvement project, the tunnel will improve rainwater collection from roadway run-off along Samui's main ring road.

Prior to the Samui Island Water Tunnel project, the 3.20m diameter EPBM was operated for Bangkok Metropolitan Electricity Authority’s Phra Khanong Cable Tunnel Project. Thai contractor Nawarat Patanakarn PCL excavated a sharp 32m-radius curve as it exited the project’s launch shaft in order to negotiate the piles of an adjacent expressway ramp.

To achieve the challenging curved alignment, the EPBM featured an extreme X-type articulation system that provided a maximum articulation angle of 6.6 degrees. Designed to accommodate a new high-voltage cable system, the Phra Khanong Cable Tunnel Project was the first of a series of tunnelling projects to meet increased electricity demand in the Thai capital.