Quote:
Originally Posted by denizen467
The (supposed) UP North viaduct project's work at Sunnyside and southbound Ravenswood (can we call it "West Ravenswood Ave" please?) has some gi-normous steel tubes maybe 50 feet long with highrise-caliber caisson-sleeve diameters and edge serrations. But there can't be any purpose to sinking highrise caissons there, so I wonder if these are just sewer pipes? Although they kind of seem outsized, and maybe of too thin a gauge, for ordinary neighborhood sewer piping. Maybe this is how storm sewer arterials look? I assume Deep Tunnel is too far away for these to be drop shafts. Or maybe there's something about rr viaducts or the earth-filled berms UP North runs upon that I'm unaware of. If anybody knows, or is in the neighborhood.
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If they look like caisson tubes, they probably are. It's common to use caissons to support bridge abutments in congested urban areas where they can't easily dig a pit due to utilities, and where pile driving would be unacceptable for noise/vibration reasons. This is part of the reason for the high cost of the project; digging a foundation pit with a backhoe is a pretty simple task, and pile driving is a little more complex but manageable. Drilling caissons requires a lot of specialized equipment and lots of highly skilled, experienced workers.
Sewers are usually built with precast concrete segments. A thin-walled tube would be too prone to corrosion. Whenever metal pipes are used underground, they are super-chunky and thick so they can tolerate a constant state of rust for many years before failure.
Plus, part of the rationale for the bridge replacement project is to gain clearance on the underpasses in one fell swoop without having to depress each roadway and rebuild all the utility lines that are currently close to the surface.