Quote:
Originally Posted by SFUVancouver
My suspicion is that following analysis of the original core samples they are going back to due further investigation of the areas that require more information (increased sample density, further depth, more angular sampling into surrounding strata, etc.)
It doesn't strike me as a worrisome development at all. Rather, it's a positive, because the money for further testing wouldn't be spent now if the project weren't active and the data this generates will help further refine the cost and schedule estimates for the project.
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This is pretty much the case. It is not indicative of them being worried about something problematic. It is normal engineering operations; acquiring more detailed information to move the engineering design forward.
As for the Evergreen sinkholes: this is not some scary and rare condition that is going to disturb experienced tunneling engineers. They understand the implications and potential difficulties. Sinkholes on one project are not going to 'freak out' the engineers on another. Tunneling is overwhelmingly determined on a case by case, project by project basis. The more information they gather, the lower becomes the risk of unforseen difficulties.
officedweller is correct: the less information, the less reliable the information, the higher the risk, and contractors must build that into their quotes - meaning higher estimated contingencies contributing to high priced bids. The catch being that they have to be aware of those facts. They were not on the Evergreen tunnel . . . something was not right in the bid process there.
WarrenC12: anything is possible, but no contractor will risk their profit margin in the manner you describe. They will only 'bid low' (a purely relative quantity) if they have a contractual loop-hole through which they know they can get extra money if something goes wrong. For them, this is just a different way of handling risk and contingency. In this situation, it is the client/government that is entering a higher risk contractual situation. That's how "we" always end up footing the bill. The contractors know what they are doing. They always use contracts to protect their interests across all foreseeable futures.
Just a little side note that never gets mentioned: tunnelling is typically complex and the design of the machine (or other method) depends upon the material it must tunnel through. That seems to be common knowledge. The routing of the tunnel is also partly due to these same conditions. But what gets forgotten is that the tunnel is like an above ground structure in that it weighs upon the earth below it. That earth/rock must also be capable of taking the live loads of full trains running over it. Just think of the above grade guideways. The tunnel must provide the same level of structuring of the same load determination + hold itself up against water pressure and the weight of the earth above. Of course, often the earth above holds itself up by transferring the load around the tunnel through the rock or other solid matter. The soils testing is also about the bearing capacity along the route.
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