So does this mean that Southern Ontario is more difficult than say? Greater Vancouver Region? Because i was always under the impression that the Vancouver region was very difficult to tunnel in...thus the reason for all its elevated transit routes (except the Canada Line)
I haven't worked with geotech data from BC that much, but in general they have two boring issues: fault lines and relatively high artesian pore pressure. There are generally three types of Tunnel Borers: Continous (CBM for hard rock), Earth Pressure Balance and Slurry Shields (for soft rock). For areas with soft ground and very high water pressure or large amounts of ground water, Slurry Shields are needed. Soils are mixed with bentonite slurry, which must be removed from the tunnel through a system of slurry tubes that exit the tunnel. Large slurry separation plants are needed on the surface for this process, which separate the dirt from the slurry so it can be recycled back into the tunnel.
Vancouver is in a basin area, but has two advantages over Toronto being a shallower frost depth and less glacial till, which kills the machines with the wide variety of large boulders to fine silts and sands. Vancouver is also more seismicly active than Toronto to decrease a tunnel's life-span, so it isn't like Vancouver is an easy dig.
As an example of tunnel conditions in Ontario, in 2008, a tunnel boring machine digging part of the York-Durham Langstaff trunk sewer, which they were excavating 22 metres below ground. About 1800 m³ of mud poured into the tunnel, leaving the 10-metre tunnel boring machine and 50 metres of trailing equipment stranded underground at a point east of Dufferin Street, north of Highway 407. The tunnel was sealed and delayed the project by a year. The TBM was later extracted.
Secondly, if Southern Ontario is so difficult to tunnel in, why don't consultants & the government push that point to the people so that we can stop tunneling?
As for why do it? Because consultants are paid to design what politicians want and don't mind getting paid to run around in circles. Politicians are elected on general sentiment rather than logic or technical understanding. It was the reason for TransitCity being 90% surface rail. It's also one of many reasons why Sheppard Subway P3 is lacking potential partners. I think that's one part where Miller failed to win public support for his plan, they didn't give sound bite explainations of the advantages in cost and impact. People don't want another 'Gardnier eye-sore' and there is not enough space for cars already at ground level, so that means people are in favour of trains where they can't see them. Most people don't every look at construction project costs beyond the total price tag.
