The tunnel boring machine digging the tunnel for the North Shore Connector in Pittsburgh, Pennsylvania, reached the banks of the Allegheny River on 3rd April, 2008 as it followed a sloping path beneath the river bed toward Downtown.
The tunnelling project then reached a milestone on 11th April, 2008 as the Herrenknecht machine started digging beneath the Allegheny River and heading for the Golden Triangle. Although the work is progressing quickly, it is also moving along cautiously. Safety training for the workers is becoming more and more important as the work progresses. Visit www.herrenknecht.com
The project is built by Obayashi and Trumbull Corp. for the Port Authority of Allegheny County. As part of a three-firm joint venture named TriGold and including HDR, Sverdrup Civil and the Kwame Building Group, HDR is directing the programme management and construction management of the project. Visit www.obayashiusa.com, www.hdrinc.com and www.kwamebuildinggroup.com
The further in tunnellers get, they find ground that has not been exposed to oxygen for a number of years, decades perhaps and longer and at that point there is organic decomposition and the main gas is methane. And methane in small quantities can be explosive so it is one of the major concerns.
When the crews have to access the machine’s cutter disk, it is almost like a submarine, they wear special suits and they have to go through hatches because it is pressurized and because of that pressurization, there is a decompression chamber on site in case a worker has a problem or should they have to escape in a hurry.
The crew building the tunnel is conscious of safety every second. A ventilation ducting along the roof brings in a constant flow of air. A hardwire phone provides a link outside even if everything fails. Monitoring air quality is the top priority. View a video at http://kdka.com/video/?cid=9
Everyone going under the North Shore must first spend some time in a construction site safety trailer. It is approved for self-rescue or escape, giving tips of some reality. A bit like on board a jetliner when passengers view a film on safety instructions or look at the cabin crew during the safety demo, a film describes the MSA W-65 self-rescuer respirator and a TriGold safety manager shows how to use it. This prepares for the worst case scenario: the total failure of the air entering system or possibly a fire. The MSA W-65 provides emergency respiratory protection against carbon monoxide gas resulting from underground fires or explosions. It is a device for escape purposes only. Visit www.msanorthamerica.com
Meanwhile, the tunnel boring continues chewing away about 210 metres in and 15 metres below the surface of the Allegheny River's north shore. As tunnellers are proceeding across the river, they are going to make a left turn and another right turn to line up with Stanwix Street where the receiving pit is almost constructed right now. The machine is supposed to emerge around the first week of June at the receiving pit. Then it would be turned around to dig a parallel tunnel back to the north shore. Click us/66. Visit www.boretotheshore.com and www.portauthority.org/PAAC/Portals/Capital/NorthShore/index.asp
Pittsburgh’s North Shore Connector light rail project will extend the existing light rail system 1.9 kilometres from Gateway station underneath the Allegheny River via twin bored tunnels to an underground station on the North Shore. The underground alignment will transition to an elevated section and will subsequently end at a second station near Heinz Field. 16/08.
