May 2nd marked both success and setback for McNally/Aecon JV’s two EPBM sewer projects, just north of Toronto, Canada. On the same day final breakthrough was successfully achieved on the 19th Avenue project, an incident occurred on the JV’s Langstaff Trunk Sewer Project, requiring evacuation of the tunnel and local road closures.
At the time of T&TNA’s last report, in March 2008 (p6), the 10.6ft (3.25m) diameter Lovat EPBM on the Langstaff drive had been progressing through the most difficult ground met so far on the two projects. Since then, conditions deteriorated further, with very fine silts and water pressures of up to 1.5 bar causing tail seal leaks.
“On May 2 a breach of the tail seals occurred, at ring 1450, approximately 150m west of the intermediate shaft,” said Laura McNally, Project Manager for the JV. “This resulted in a large inrush of material, which the crew was unable to control. The tunnel was evacuated and fortunately no one was injured.”
Crews responded quickly to secure the tunnel and surface, and work is now ongoing to further investigate the cause of the incident and recover the tunnel. “Several options are being considered to minimize schedule impacts, including launching a TBM from the east end of the tunnel drive,” McNally added.
On the remaining Bathurst Collector drive, a third Lovat EPBM has achieved record production rates for the JV, with a best shift of 17 rings and a best week of 129 rings. Final breakthrough on Bathurst is expected at the end of August, with just 900 rings remaining.
Following its successful final drive, 19th Avenue is due to be wrapped up next month.
