Quote:
Originally Posted by Metro-One
Interesting. Hmm, I wonder if in the long run they could build a short elevated section there? That is if a single span would we wide enough so that the pile driving wouldnt cause the same problem.
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Not likely. It would be unbelievably expensive and not as short as you think. The soil conditions in that area are extremely poor and as VanCvl pointed out, the Kinder Morgan line further punctuates the problems and potential solutions. It is built on a massive piled structure that does not move.
There's a significant peat (>10 m in some areas from what I remember) deposit that overlies channel cut from the more competent material left by the Fraser eons ago. The section that is slightly east cut into the hill is a completely different composition.
This area had some of the longest preload duration of the whole project, something in excess of 3 years. Unfortunately, the soils just never behaved the way they were supposed to.
At the end of the day, in an effort to get the road finally open, lightweight fill (pumice) was used to mitigate the weight of the new road on top of this area on either side of the KM line. It was always going to be a problem no matter unless you excavated the peat down all the way to till, which would have been a ludicrously expensive endeavor. Timber piles were considered, but they too were also quite expensive.
Also, the 'sewage main' in question is North Surrey Interceptor
Forced Main, which is a huge diameter, old concrete line. It actually zig zags across the SFPR alignment (Don't ask me why) and was another fixed point that couldn't be touched, despite the line itself having a history of settlement problems.