From south of the Fraser River the Delta Optimist reports that despite anything else you may have heard, the Provincial Liberal party want their overbuilt Massey Bridge despite financial, environmental, ecological and river impacts. Indeed former City Councillor of Delta and now MLA Ian Paton states that the bridge is the best option.
“The premier, I believe, recently had a meeting with Malcolm Brodie, the mayor of Richmond. Apparently they are a bit concerned with the design on the Richmond side of the bridge, the interchange and those things,” Paton explained.”
But here is where it gets a little strange. Why did the New Democratic Party and the Greens endorse the 10 year transportation plan by the Metro Vancouver Mayors’ Council? Why did the Liberals not endorse this? Could it be because the plan does not recognize the need for a replacement of the Massey Tunnel?
While Richmond Councillor Carol Day in a letter after the Throne Speech stated that the Premier was reconsidering the bridge, it appears that is not the case, and the Liberals are continuing their strange full throttle ahead with their overbuilt bridge located on top of the best farmland in Canada.
New MLA Paton gets the last word: “I can talk all day about some of the ridiculous ideas like submerging another tunnel… I’ve always contended that slapping a brand new concrete tunnel somehow next to an old beat-up tunnel that was built in 1958 doesn’t make any sense whatsoever…Also in 1958, there’s very little traffic on the Fraser River, now there’s tonnes of marine traffic. So how are you going to spend two years with barges out there trying to place a tunnel to the bottom of the river, which environmentally would be a nightmare for sturgeon and salmon and aquatic life.”
It is business as usual for the Provincial Liberal party.
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I know a lot of tunnelling experts, and I can pretty safely say that most of them aren’t keen to put another immersed tube tunnel on that site or in that area.
That says something significant, because why would you want to have work go outside of your technical discipline? People building tunnels aren’t the same people who build bridges for the most part.
So what is the answer if not a tunnel nor a bridge ?
Basically the bridge is the best. It’s not going to be simple, but from what I’ve read it’s reasonably doable.
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If I’m not mistaken, the so-called new tunnel would actually be box culvert sections joined together, no? Hence no actual tunnelling next to existing structures needed. Please clarify if you know differently.
Same idea, but it’s called an immersed tube tunnel.
The problem is that segments/culverts/boxes can float or settle in any seismic event. Since you join need the joints to stay together for the “tunnel” not to leak, you need to keep the relative motion between the segments down to a minimum.
Right now the earthquake that would be used to design a new bridge has the current “tunnel” moving by about 1m, when 30cm is the tolerance that is suggested. The last seismic report of the GMT was a treat to read.
Metro Vancouver is steadily replacing all it’s similar drinking and waste water infrastructure with deep bored tunnels which are better able to survive earthquakes and seismically induced landslides.
Instead of being just below the bottom of the river, the new tunnels are 40-60 metres below the river bottom.
So with the present Massey Tunnel at 22 metres below sea level, what you are saying is that the position of any new tunnel would need to be 40-60 metres below the present river bed. This would mean between 51 – 71 metres deep.
The river is said to be 11 metres deep. Any new tunnel would therefore be two to three times deeper than at present. This would necessitate a far longer entry and exit slope at both ends. This would be easier at the south side because there is more land before highway 17 and River Road. The north side would be far more complicated for connecting to Steveston Highway and require a long loop north, cutting across private land and the old Fantasy Gardens site, or a massive loop and bridge back over from the east.
A bored tunnel would have to be much deeper at Deas Island since it’s mud for a long way down. So much so, that it would likely be impossible without significant ground improvement.
The 40-60 metre deep tunnels are at around New Westminster or Port Mann.
Basically, the farther west you get, the finer and newer the soils get. So, their bearing capacity gets worse.
What I’m say is that for the most part a tunnel, bored or otherwise isn’t a great option. A bridge is probably going to be cheaper. It might got a ways to line my pockets building it, but it’s still not a good idea.
Every building above the low-rise level in Richmond, the tanks at the Annacis Island sewage treatment plant and a number of other huge structures built on the delta were designed with concrete raft foundations which spread the load. A box tunnel lays flat and does not create point loads like bridge foundations built on an array of deep piles. It seems reasonable that the bottom slab of the tunnel box could extend outwards to distribute the weight over a larger area, like a spread footing.
The geotechnical conditions would probably preclude deep bored tunnels because the soft soils extend too far downward in this location (in excess of 330 m / 1,100 ft) to gain adequate additional “traction” from more compact or solid soils, though this is not impossible as seen in much larger undersea tunnel projects around the world, though these projects would need to have similarly extremely deep soil conditions for a fair comparison. The key question is cost. A deep bored tunnel will extend several additional kilometres at both ends to maintain a reasonable slope. That will cost about $300M per km, but only for a narrow diameter tunnel. Even a 15 m diameter tunnel may be deemed inadequate. Seattle’s Bertha is 18 m for less than 50,000 vehicles a day, to some critics is THE definition of waste of public money. Increase the diameter to accommodate an adequate number of lanes and the cost escalates dramatically. How would a $5+B large diameter, deep bore tunnel over a longer length be justified for less than 80,000 vehicles and negligible transit? That’s $15+B with a 50-year debt amortization period and P3 profits.
Should a shallow tunnel flood, it can be pumped out a lot easier and quicker than a deep bored tunnel could. Geotech concerns were already expressed about the bridge foundations which, after all, have to support a 10-lane deck and two massive towers on two small points on the earth, but that info seems to have been suppressed, just like the cost of financing over 50 years (which was leaked to the Opposition by MoTI insiders after the Libs refused to release it). With geotech in mind, it is a sign of deep ignorance or possible negligence to portray the gargantuan bridge as a reinforced concrete structure instead of a much lighter (but likely more expensive) steel superstructure. Nonetheless, the thing could sink slowly over the years.
I don’t believe an experienced structural engineer would find it impossible to design fairly flexible waterproof joints between tunnel box segments reinforced with high-strength, non-corrodible steel cable bundles, seismic dampers, double or triple membranes, and other features. The Millennium Line, Evergreen Line and Canada line guideway segments are joined at several points with post-tensioned cable bundles pulled tight by a powerful electric winch then locked in place. The concrete joints are cast with precision and are very tight, giving a strong friction fit. The existing GM tunnel could be retrofitted further with some of these features.
Location is also important. The Alex Fraser bridge was built closer to the North Delta rise where the alluvial soils are shallower. Should the engineering challenges and expense of GM prove to be excessive, then twinning the AF may be a second choice while upgrading the existing GM tunnel. In my view the twin should be a two-lane rail transit-only bridge, or a four-lane rail + bus transit structure. The AF location is closer to the centres of population than GM, both north and south of the Fraser. The bridge deck is a bit more than 3 km to the 22nd Street Station, less than 5 km from Edmonds Station, and about 8 km to King George Station. It’s possible to conceive a large-scale SoF light rail network connecting to SkyTrain through several points on the south Burrard Peninsula rise (some tunnelling required) and extending southward with branches in all directions to Richmond, Tsawwassen, South Surrey / White Rock, North Delta and Surrey Centre. This would also be a great opportunity for North Delta to become a real city instead of remaining a mere bedroom community, and start generating its own town centres and concentrated employment corridors along new transit lines while gently infilling its land-hungry detached home subdivisions to do its share to accommodate the million+ people expected to arrive by mid-century.
This last concept illustrates how a relatively modest new bridge needn’t be considered only as a conduit for traffic and a generator of myths by being defined as a device to “relieve congestion.” These are not worthy city-building concepts because they are inhuman. However, as a more affordable piece of people-moving transit infrastructure, this alternative bridge idea will help to build a far more sustainable and humane Metro.
The problem is that all tunnels want to float. They’re basically an air bubble trapped in something much denser than water.
A single lane of traffic (4m wide, 5m tall, ~660m long) for the GMT is going to have about 30,000 tonnes buoyant force that needs to be held down. So, lets say we have 4 new lanes, probably about 100,000 tonnes needs to be holding the tunnel down.
Sure, concrete and steel is a bit denser than soil, but not enough to counteract the buoyancy. So it has to be anchored down.
The engineering challenge is making a structure that can withstand twisting and uplift without drowning the occupants. Then you have to ask will this be cheaper than building a new foundation, which can take place entirely on the foreshore.
LOOP skytrain from King George to 22nd via North Delta at a cost of about !/4 of a new massey bridge
Interesting deliberation. Thank you for sharing your considerable knowledge Alex. -deleted as per editorial policy-
A ‘floating’ tunnel. Interesting. I am no expert but it seems reasonable that a trench could be dredged across the channel and the precast tunnel segments assembled / attached on shore one by one then the tunnel floated across with sealed openings and sunk into the trench by letting some of the air out, and then covered over with gravel and sand or rip rap. There could be just enough cover to balance with the bouyancy, which in turn will keep the tunnel from sinking during seismic liquifaction.
Reblogged this on Sandy James Planner.
There is no money or need for a new crossing but there is a need to change the present method of rationing use of existing choke points by giving HOV priority access