A JV of Wayss & Freytag AG and Sollazzo Hnos SA has successfully completed the 15km, $65m tunnel on the Rio Subterraneo Saavedra-Moron water supply system in Argentina, a new branch of the existing Buenos Aires potable water distribution system. The tunnel comprises four drives with lengths varying from 3.4km to 4.2km and was excavated using two 4.3m dia. Herrenknecht EPBMs.

Construction of the 3.5m i.d tunnel began with two drives in opposite directions. First from Shaft 1 to Shaft 2 and second from Shaft 1 to Shaft 5. Upon arrival at Shaft 2, the first TBM was removed and refurbished and then transported to Shaft 3 to begin a drive back to Shaft 4r. Upon arrival at Shaft 5, the second TBM was refurbished and then continued to Shaft 4. The length of each drive is: Shaft 1-2, 3.56km;Shaft 1-5, 4.2km; Shaft 3-4, 3.7km; Shaft 5-4, 3.8km. Both TBMs were removed from Shaft 4.

The tunnels were excavated at a depth of 35m through variable Buenos Aires ground conditions ranging from quick sands under 2.5b water pressure to hard consolidated silts (with calcareous nodules) passing through green sandy clays.

After the first two drives (1-2 and 1-5) had been completed, both TBM cutterheads were adapted to the unforeseen ground conditions by increasing the opening in front to allow a better flow of plastic material to the auger screw. The TBMs were also equipped with a fully integrated bentonite injection system which enabled the TBM operator to choose between foam and bentonite or a mix of the two at any time during the advance to find the best soil conditioning compromise. Refurbished machines averaged 19 and 21 rings/day with a best of 30 and 35 rings respectively.

Potable water flow in the tunnel is about 20m³/s, and the tunnel is designed with a watertight, single pass, 300mm thick, 1.2m wide, universal segmental lining. Gap grout and EPDM Phoenix gaskets have been used to maximise waterproofing. Client for the project was the Aguas Argentinas (Lyonnaise des Eaux), with Safege-Montgomery/Watson as Engineer.



Related Files
Subterraneo Saavedra-Moron