Slow Start for Tunnel Boring Machine

By [Dan Rivoli] The tunnel boring machine that was supposed to dig through 50 feet of bedrock a day to make room for the new subway has had a rocky start. Since the 485-ton machine started crushing bedrock below Second Avenue June 8, only 135 feet has been drilled. That is less than 10 feet a day, out of the 15,000 feet that needs to be mined. But the MTA says that in the first 700 feet of mining, the tunnel boring machine is in a â??start up phase according to spokesperson Aaron Donovan. â??We anticipated lower mining numbers during this phase, Donovan said. â??The tunnel boring machine has just been launched and we are still evaluating the performance. A patch of highly-fractured rock has slowed the machine down. Crain"s Insider reported that an electronics problem kept the grippers's which hold the machine in place under hydraulic pressure while it mines's from putting too much pressure on the walls of the tunnel. The MTA wanted to avoid crushing the rock pillar between the two starter tunnels for the Second Avenue Subway. The entire tunnel mining is scheduled to be complete by the end of 2011. Once the machine gets through the fractured rock, mining is expected to pick up to an overall average of 50 feet per day. The MTA will then establish a daily average of progress and reevaluate the projected schedule, Donovan said.