Xe-Pian Xe-Namnoy project holes through early

7 April 2017


Laos – The headrace tunnel has been completely mined on the Xe-Pian Xe-Namnoy Hydroelectric Project in southern Laos. The feat is three months ahead of schedule and was accomplished by Seli Overseas using a Terratec TBM.

SK E&C is undertaking the engineering, procurement and construction (EPC) contract for the project, while Italian tunnelling specialist SELI Overseas was awarded the subcontract to excavate the TBM driven section of the headrace tunnel, along with the construction and operation of the project’s on-site pre-cast tunnel segment manufacturing facility.

The 5.74m-diameter double shield broke through into a drill-and-blast-excavated reception chamber on 18 March 2017, marking the end of an 11.5km low-pressure headrace drive. The bore began in March 2015 and was predominantly through mudstones, sandstones and siltstones.

A spokesman for Terratec added: “The TBM’s cutterhead features 39 x 17in back loading disc cutters and four large bucket openings. A 2,000kW electric VFD main drive provided maximum speeds of 7rpm in hard rock zones, while delivering a torque of 8,000kNm to cope with a number of fractured fault zones along the alignment. In order to mitigate potentially difficult ground conditions within these fault zones, a high-power probe drill was also installed within the TBM, in order to conduct any drilling or grouting deemed necessary.

“The use of pea-gravel to backfill the annulus behind the project’s pre-cast hexagonal segment lining rings also prompted some unique design features, including a hydraulic lift within the pea-gravel bays on the back-up to lift and empty the gravel cars; and a double capacity pea-gravel pumping system to facilitate the anticipated high advance rates of the machine.”

The peak production month was July 2016 where the team advanced 1,005m and advance rates were generally high, according to the manufacturer.