[getsmart-l] Big Pipe - Boring Machine trapped in sink hole

[Gloria Boxen]

http://www.thestar.com/article/432765

              
                        Boring machine stuck in Vaughan muck                  TheStar.com - GTA - Boring machine stuck in Vaughan muck             
                                                                     var imageL= '/images/60/44/73106dc5423b961242a6acb2ca6e.jpeg'                 if(imageL)                 {                 document.write('');                 }                 else{                  document.write('');                 }                                                                                RON BULL/TORONTO STAR                      
                                              Project manager Tomislav Hrkac stands near a sinkhole that caved in, trapping the boring machinery. (May 28, 2008)                                             
                 
                                                                                                                                                                            May 29, 2008      
                                                                Phinjo Gombu
                                                                              Urban Affairs Reporter
                                                                                                                                                                                                                                                         This is one boring tale that will be talked about in Vaughan for at least a year.
That's how long it will take to rescue a $5 million tunnelling machine touted as environmentally sound that now lies trapped in squishy muck 22 metres beneath the surface, not far from the front door of the Langstaff Gospel Hall.
Six workers for the joint McNally/Aecon venture digging a segment of York Region's controversial Big Pipe sewer line earlier this month were forced to run 1.8 kilometres to the entry point when 1,800 cubic metres of waterlogged soil suddenly came pouring into the tunnel they were boring below the local aquifer. 
No one was hurt. But the calamity is likely to set the sewer project back a year and may cost millions to fix. 
The rescue operation will involve building a 5-by-30-metre shaft down through the aquifer to pull out the 10-metre-long machine, plus trailing gear (hydraulic, electrical and ventilation equipment) that stretches about 50 metres behind, as well as suck out the mud that now fills 300 metres of pipeline laid deep under the neighbourhood, just east of Dufferin St. and north of Highway 407.
The project was designed to relieve pressure on existing sewer lines. It's unclear whether the delay will adversely affect development in the area.
When the muck started coming into the 3-metre-wide tunnel, "it poured," project manager Tomislav Hrkac said yesterday, adding he was thankful no one got hurt or trapped. "Quite a bit of ground came in very quickly."
Work on a bulkhead to seal off the pipe started right after the May 2 incident but it took until May 12 to make it airtight. News releases described a sinkhole and water main break associated with the tunnelling, but didn't mention that a boring machine was stuck below until the Star inquired this week.
The only indication of trouble on the surface today is a sign that says only local traffic is allowed on that stretch of Langstaff Rd.
 What exactly caused the soil to leak through a seal between rings of pre-cast concrete that are laid behind the machine as it moves forward – at about 7 to 8 metres a day – is still being investigated.
The borer, called an earth pressure balance tunnelling machine, uses an auger to transport dirt and rock via a conveyer belt onto a series of trucks that then take the slurry out of the tunnel, in this case to an entry point near Keele St.
"Stuff like this does not happen all the time," Hrkac said, pointing out that the crew didn't run into anything they hadn't anticipated in terms of soil conditions.
A news release the region put out a few years ago touting the machine said it could work through "almost all soil conditions, notably water-bearing soil." 
That's a huge advantage over conventional tunnelling methods, which may require expensive and environmentally damaging "dewatering" of soil before construction, a system that's been controversial in other instances in York Region.
It's also supposed to reduce the impact of tunnelling on the surface, especially when used in sensitive areas like the Oak Ridges Moraine, which covers much of the region.
The incident has caused a big piping headache for those running a $90 million, half-complete sewer project meant to accommodate the needs of a booming region.
 It's part of a network of sewers dubbed the Big Pipe, a contentious project begun in the 1970s that carries raw sewage from landlocked York Region to a treatment plant in Pickering, on Lake Ontario.
 At the time, it was determined that building more local sewage systems on the Rouge, Humber and Don rivers would threaten the environment. The Big Pipe was later handed over to York Region to build and administer. 
The $800 million system now consists of 14 separate links, all built in phases, with more to come as the region grows. The segment under construction is supposed to join up with a north-south pipe near Bathurst St. and Highway 407.
Who's going to pay for rescuing the boring machine and unclogging the pipeline will only be determined after the outcome of an insurance probe that will consider whether human error was involved.
Workers involved in the accident were not available for comment.
They will now have to resume digging at the opposite end of the route and tunnel back to the cave-in site, something they can do with great accuracy thanks to laser-guided equipment.

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