SURREY â€” Liquid nitrogen is to be used to freeze the ground beneath the Fraser River in order to repair a massive drill that’s been tunneling beneath the river for the past few months.
The drilling is part of a $240-million Metro Vancouver project to connect the Fraser Valley’s water supply with that north of the Fraser, in order to bring more consistent water access to those south of the Fraser.
According to Frank Huber, Metro Vancouver’s director of major projects, management systems and utility services, the tunnel is in response to an incident that occurred back in 1997.
"We’ve got an existing main under the Fraser River and it actually failed during 1997, and so there were severe water restrictions for all the municipalities south of the Fraser River for the whole summer," he recalled.
"So we patched up the pipe at that time and realized we had to build a more secure crossing. So after investigating which was the best way to go we concluded that a tunnel would meet all of our needs."
After years of concepts and designing the tunnel, a contract was awarded in 2011 to two companies and with the first few years spent on constructing the entry shaft, tunneling began at a depth of 68 metres below the surface of the Fraser River from the Surrey side last year.
In the time since, the tunneling machine has carved out 800 metres of the 1,000-metre tunnel, but just 200 metres short of the finish line tunneling has come to a halt.
"Basically, the conveyor got jammed and there was some damage to the parts of the conveyor so we need to get in there and make some repairs to it," explained Huber.
And with the machine so deep beneath the Fraser River, the challenge facing crews is how to get into the tunnel and repair the machine while dealing with 60 metres of water pressure in saturated ground.
Enter the liquid nitrogen.
Using a procedure that Huber says is sometimes used in situations like this, crews will use liquid nitrogen to freeze the earth surrounding the drill, holding back the pressure and allowing workers to go in and conduct the repairs.
To do that, Huber said a platform has been constructed in the middle of the Fraser River and crews have been drilling ‘freeze holes’ into the earth surrounding the drill, allowing them to inject liquid nitrogen and freeze the desired area.
According to Huber, the use of liquid nitrogen is completely safe as it’s an inert gas found in the air around us.
"We breathe this stuff in all the time." Currently crews are in the midst of completing the dozen or so ‘freeze holes’ and once workers have gone in to repair the drill, the tunnel is expected to be completed within two to three months.
Then, Huber explained, they will install the pipe and build a new chamber at the top of the shafts on the Surrey and Coquitlam sides with an expected completion in 2016.
As for the benefits to Surrey residents and beyond, Huber said the project, "will provide more resiliency to the system so if an earthquake happens this crossing will survive. We know populations are growing south of the Fraser so this will ensure that water remains secure."