^
@BurlOak : Excellent points for discussion. No matter how outlandish some expressed ideas are, compared to the absolute vacuum of info from QP, and some of the wild ideas from "expert planners" (although it was Ford's concept, the bridge over the Don at Eastern in lieu of just tunnelling through with fully serviced and in-situ TBMs) these ideas are perfectly germane. I'd say we hit the mark pretty close with deducing 'metros' being the 'jaw dropping tech' albeit I defer from metros to a heavier and 'even more advanced' solution like London is using. (Thameslink, Great Northern, Crossrail, etc) which of course is virtually single deck RER EMU deluxe.
Some quick answers, some of your points require deeper digging to answer fairly later:
- A bridge with minimum clearance over DVP requires a height of 5m for clearance, plus the depth of the actual bridge girders, which for typical single span bridges would be somewhere between 18 to 24 times the span. If you want to span both lanes of DVP, plus have the abutments a safe distance back from the road, that span is likely over 60m length. That's a girder depth of 3m, and the overall embankment would be 9m - and more on the downhill side.
I checked both rail and US DOT highway specs to arrive at the figures I used. If it's out, it's only by degree for clearance. Your point on girder depth is well taken though. I'd say the cases for comparison already exist with the Pottery Rd and Bayview exists and embankments. So let me flip this over to state: "Built to the same elevation or perhaps a bit more than existing structures already extant in the Valley".
Single span bridges are less efficient than multi-span bridges (18 to 24 span to depth compared to 24 to 40) - meaning that the girders are deeper (almost up to twice as deep) and look clunkier. If the spans are less than 40 to 45m, then prestressed concrete girders can be used which would be less costly. As soon as you go above this, a different, more expensive structure type would be needed.
I got lucky getting two Google hits on this first try (Googling is an art and it's all down to the right 'tags'...and luck!)
chapter 8 precast pretensioned concrete girders - Caltrans
www.dot.ca.gov/des/techpubs/manuals/bridge-design-practice/page/bdp-8.pdf
PC
girders are a type of
prestressed concrete girder that facilitates rapid ... The
use of PC
girdersin California highway bridge system has increased rapidly .... used for
railway systems and relatively short span lengths ranging from 40 ft to 100.
[PDF]
Thirty Years of Prestressed Concrete Railroad Bridges
https://www.pci.org/.../Thirty%20Years%20of%20Prestressed%20Concrete%20Railroa...
by D Goldberg - 1983 -
Cited by 2 -
Related articles
Ref. 5 pro- vides more details of this structure. In 1966, the Frisco
Railway opened its third trestle
using prestressed con- crete box
girders with the ties resting.
- : Google
I have some reading to do there. Input from others most welcome. My concern was approval for pre-cast structures for rail use, but it's well established I see. To flip this over though, it appears to bolster the viability of three shorter bridges as much as a single one, but this will prove an interesting search.
I imagine the slope of the valley is steep than the proper grade for the "subway" to travel, so the embankment would be much taller for the span that crosses the actual Don River.
I presume you're referring to valley walls? I did some extensive viewing on Google Satellite 3D, and the valley floor is surprisingly flat, a virtual spillway, which does lend itself to powerful flood velocity if steps aren't taken to address that. But that being said, the flood concerns are only in the lower part of the Don it seems, or transportation infrastructure like the Bayview exit, Pottery Rd, and two...lol...*three* rail lines over the years have survived quite well in that part of the valley. The RH line flooding is to the south of there. I stand to be corrected, as it is a crucial point that *may* demand a bridge as you describe. What complicates a higher bridge is access to a yard and the RH line for operational and engineering needs. I'll do some more study on that and answer with reference later. (Edit to Add: Flood Control since Hurricane Hazel has inevitably reduced the flood risk factor substantially)
You're right about the flooding, but probably underestimating it. The design storm around here is Hurricane Hazel - which likely was closer to a 1000 year storm. It's something we haven't been close to seeing in the past 60 years. When the hydrology analysis is done, I am sure these embankments would be in the way.
It's a good point, and one I considered, until realizing that so much infrastructure is already in that area that doesn't meet that requirement. I suspect hardening of an embankment with lots of flow through culverts might address that. Perhaps not. It might take some digging to realize just what probability risk factor is at this time. That would certainly have impact further south on the Don, for all infrastructure.
Those embankments have weight - about 20 kPa per metre height. When you add this giant weight to the underlying soil, it will likely settle. Depending on the soil conditions, this settlement occurs over years. It means that the tracks over the embankment would also settle. It also could mean that the GO line also settles. (of course this depends on the compressibility of the soil, the depth of soil to bedrock, proximity of bridge abutment to GO tracks, and the embankment height).
This is interesting, especially as it relates to shale! With shale, the consideration is the opposite. It expands with time and released from geologic deposition/compression. That's discussed at length in the earliest link I posted from the US DOT Highway paper. It can swell so much so that it is deemed "light fill" along with styrofoam! I was pretty shocked by that, but it's actually an advantage in berm building, and can produce a valuable grade of 'light' gravel when crushed.
For the underlying soil weight bearing, the Millwood bridge seems to do very well with concrete pylons. I imagine bedrock is not that far down. It remains intriguing.
The other consequence of the settlement of the underlying soil is downdrag forces. Essentially, piles are driven into the ground to support the bridge abutments (they typically go to bedrock). The soils grab the piles to some degree and pull down on the pile as the embankment and underlying soil settle. This adds large forces to the piles, and it greatly increases the cost of the substructure.
Again, to gauge this in perspective without doing a specific reference, the nearby highway and arterial structures and bridges have already set a template. I'll try and find some engineering specs and dimensions on those structures and see if it could work. At the end of the day, for a variety of reasons you list, a single structure spanning the valley (or even partially to an embankment on the north side that allows ramps down to a yard and connection to the RH line for stock movement) might be the cheapest and most stable option. Something to consider is that the Prince Edward Viaduct west side lands on fill built from Sherbourne east to the beginning of the bridge proper.
I have to wonder if engineering students aren't already discussing what we are and it's a matter of time until we see some pretty good critiques published on this? That's worth a good Google in itself.
), or $115M per km (when converted to a 10m wide bridge). This really wasn't the best type of bridge for the location, so of course it cost more.