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Note: this takes place in a world populated by humanoid bears, where the population density in Siberia is much higher. The northern part of Russia is taken up by a country called Medwedia.

As said before, Medwedia takes up the northern part of Russia in our universe; both countries span eastwards up to the Pacific coast (Alaska belongs to Medwedia, a hypothetical Bering bridge will be discussed in another question).

Now... Medwedia and Russia share Lake Baikal, with two cities, Truz and Ignaz, being located on the opposing shores of the northern, Medwedian part of the lake. Truz and Ignaz are both large cities; and if a bridge would be constructed between them, there would be a full motorway that connects Medwed and Ostby.

Fig.1. - the Map. Red line is the Medwedia-Russia border. Northern yellow line is the Medwedian motorway from the Capital of Medwedia (1000km northeast of Moscow) to the city of Ostby (Pacific coast, 400km north of Vladivostok), southern yellow line is the Russian motorway from Moscow to Vladivostok. Northern purple line is a hypothetical road which follows the Northern coast of the lake, southern purple lines are hypothetical roads that connect to the Russian motorway which will be used as a transit road in this case, the purple line between Truz and the peninsula near Ignaz is the hypothetical Baikal bridge.

Now, (mid-20th Century), we want to connect the growing cities of Truz and Ignaz with a bridge. The bridge should consist of a motorway and rail tracks and should be usable all during all times of the year.

Is something like this possible at Lake Baikal?

The following main problems would arise during planning, design and construction:

  • Depth of Lake Baikal - I have heard that Lake Baikal reaches depths of up to 1642 meters at some points. The depth map shows that the northern part of the lake usually has depths of no more than 700-800 meters, but it is still very deep! I know that most bridges are constructed in relatively shallow waters. A solution would be planning the bridge so that the ridge (middle part of the lake) which has smaller depths is used and to install floating supporting structures.

  • Climate - The lake freezes over completely in winter. This could damage the bridge due to temperature changes and also due to forces enacted on the supporting structures by the ice as it expands due to the density anomaly of water. This could be countered either by the usage of special materials or moving parts that take up the pressure or by heating elements that would at least prevent the ice from cooling down too strongly, minimizing the pressure effects enacted by the density anomaly.

    enter image description here

  • Length - The part of Lake Baikal where I want to build the bridge has a width of 60 to 70 kilometers. I know that bridges of this length exist, but could such a bridge be constructed if the depth and the climate is considered? And after all, did bridges of this length exist in the middle of the 20th century?

If a bridge can NOT be constructed under these circumstances, those alternatives which would allow for the connection of the cities of Truz and Ignaz as well as for travel between Medwed and Ostby:

  • Ferry in summer, ice in winter - Ferries are commonly used to shorten travel times and distances. However, this would be especially difficult in autumn and in spring: in Winter, the ice is strong enough so that heavy vehicles can cross the lake (the Transsib company used to place tracks on the ice in winter while using a ferry in summer), but in autumn and in spring when the ice is dense enough to disallow travel by ferry but not dense enough for driving or placing tracks, there would be a big problem.

  • Northern coast road - A road which follows the coast of the northern part of the lake would probably be less expensive than a bridge, but would mean that travel times are longer.

  • Transit road through Russian territory - This would again not need for bridges to be constructed and would allow for the infrastructure of the Russian motorway between Moscow and Vladivostok to be used; however, travel times would be increased, and most importantly, the crossing of the border into Russia and back again into Medwedia would be needed for a citizen of Medwedia to travel from Medwed to Ostby or from Truz to Ignaz. However, this should not be a big problem since the relations between Medwedia and Russia are good.

  • Tunnel - There could be good reasons why a tunnel is better than a bridge in this case; however, it would theoretically be even more expensive than a bridge or mean that the transport capacity would be even lower.

    enter image description here

Now, I am asking you the following questions:

  • Could a bridge like this be constructed with mid-20th century technology (before 1975)? If yes, what challenges would await the engineers of the bridge?
  • How would the bridge be designed? Should it be a rail-only bridge or should it be a motorway bridge? How to counter the main problems which I have named?
  • If such a bridge can NOT be constructed, why would it be the case? What alternatives would be the best ones?
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    $\begingroup$ I suggest you take a look at the Øresund Bridge between Sweden and Denmark. It seems like what you are aiming to do is very similar. $\endgroup$
    – user
    Commented Mar 12, 2016 at 13:37
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    $\begingroup$ Also the Honshū–Shikoku Bridge Project. $\endgroup$
    – CAgrippa
    Commented Mar 12, 2016 at 16:42
  • $\begingroup$ You can avoid damage from ice expansion by constructing all pier and base surfaces at an angle from the vertical. That is, the segment of the pier that penetrates the water surface should look like a truncated pyramid instead of a vertical tower. Surface ice that expands against the sloped side will be deflected upward instead of crushing the structure. $\endgroup$
    – A. I. Breveleri
    Commented Mar 13, 2016 at 17:49
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    $\begingroup$ Take a look at the Confederation Bridge between Prince Edward Island and New Brunswick here in Canada. Though it's only 13km long, it spans the Northumberland Straight, which experiences very harsh winters and freezes over, thick ice and high winds. $\endgroup$
    – DMfiend
    Commented Mar 13, 2016 at 22:40
  • $\begingroup$ All of the above suggested bridge span relatively shallow waters. The Øresund Bridge & Confederation Bridges only spans waters that are about 20 meters deep, while the Inland Sea never gets more than about 50 meters deep. Something more comparable to what's being proposed here is the never-built Georgia Strait bridge that would link Vancouver Island to the mainland. $\endgroup$
    – Michael Seifert
    Commented Apr 9, 2019 at 13:51

6 Answers 6

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Hovercraft can cross both water and ice (or, as this is Russia, Ekranoplanes). For a given weight of cargo, they're more expensive than boats but cheaper than aircraft.

Otherwise the ferry/ice road solution is workable if the ferries are ice breakers (and stay well clear of the road). An ice breaking ship can sail though ice that's thick enough to drive on, so instead of a period where you can't use either, both could be active. Perhaps heavy vehicles travel by ferry until the ice is thick enough for them to drive.

Ice roads can be thickened and strengthened by pumping water up through holes (on cold days) so that it freezes on the surface. These roads take longer to melt than the regular thinner, ice, which would also extend the season.

Bridges and tunnels are both not affordable, even with current day technology.

A possible near-future technology is a floating, underwater tunnel (as considered for crossing much narrower fjords in Norway). This is anchored to the seabed, but just deep enough that ships (and ice) can pass over it. No one has built one yet.

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    $\begingroup$ Upvote for Ekranoplan. The Hovercraft is probably a better solution for heavy cargo, but there's no reason not to use both depending on how much load you need to carry and how fast you need to get to the other side. $\endgroup$
    – Morris The Cat
    Commented Apr 9, 2019 at 14:27
  • $\begingroup$ Hovercraft is great solution alaskapublic.org/2020/01/08/… $\endgroup$
    – James K
    Commented Jul 19, 2022 at 8:46
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    $\begingroup$ Lest we forget, these will be bears riding the hovercraft. This is clearly a cooler answer than bears building a bridge. $\endgroup$
    – skeep
    Commented Jul 11, 2023 at 20:54
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The challenge of building such a bridge is beyond 20th century engineering.

There are some very big bridges: the bridge joining Honshu and Shikoku has a central span of 1991m But the bridge you are proposing must cross 30000m of deep water. All bridges of that length are multi-span bridges.

The water is really deep. It would be a considerable challenge to build pylons that are planted at the bottom of the lake. There was a proposal for an English Channel bridge, that would use multiple spans, in about 50m of water, it was rejected as too costly, and too disruptive for shipping. The ridge is still at a depth of about 400m, and if a bridge were to follow the ridge it would extend the length to nearer 90000m. For comparison, Lake Pontchartrain, which has a 30000m bridge over it, only has a depth of 5m.

The region is seismically active. Ensuring that the bridge can withstand Earthquakes adds to the difficulty and the cost.

A pontoon bridge might be possible. There are no floating bridges that come close to your 30000m length, but there is experience in the oil and gas industry in producing anchored floating platforms in deep water. However a floating bridge would prevent all North South shipping.

A tunnel is more realistic. But would be a massive engineering feat. The length would be greater than any existing tunnel (to allow for reasonable gradients the tunnel would need to be close to 100km long, the depth would be much greater. With enough will it could be made to happen, but the price tag would be huge. £50 billion could be a starting guess (compared with £12 for the channel tunnel) If you wanted it to be a road tunnel too, you can immediately start upping the price (rail tunnels can be narrower)

Given the difficulties the obvious solution is the road going round the lake, supplemented by ferries in summer, and possibly ice road in winter. The terrain is more manageable around the south of the lake, and the real road (P258) goes South.

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  • $\begingroup$ Floating bridges can have drawspans within them, but yes -- 30km of deepwater would require some serious engineering work to span (not saying you couldn't build pylons in 400m of water, but that'd be hard) $\endgroup$
    – Shalvenay
    Commented Mar 14, 2016 at 0:55
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    $\begingroup$ Remember that a tunnel would also have to be drilled in ~500m depth, which - while manageable - isn't helping either (most RL tunnels are basically level or merely have a slight incline.). 500+ m of height difference over a few kilometers is immense, the tunnel interior would be like a mountain road. $\endgroup$
    – Chieron
    Commented Oct 18, 2016 at 7:41
  • $\begingroup$ A pontoon bridge would be swept away when there are large amounts of ice moving around. $\endgroup$
    – Robin Bennett
    Commented Jul 11, 2023 at 14:17
  • $\begingroup$ A tunnel is impossibly, the lake is a tectonic spreading center, it is actively expanding, it is essentially a nascent ocean. you would be trying to build a tunnel through magma. $\endgroup$
    – John
    Commented Jul 13, 2023 at 12:56
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A floating bridge is doable.

Here in Seattle, we have the SR520 bridge: 520 bridge It's floating section is 2.4 km long and is supported on floating concrete pontoons far enough above the water, that storms aren't an issue: closeup We don't have ice, that could be an interesting engineering challenge, but extending it length wise, would be more of the same. The biggest reason why we don't have more floating bridges, is that they require a lot of maintenance, which is a pain in salt water and the list of lakes where it would be economically feasible to pay for one is pretty limited IRL.

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The likely single biggest obstacles would be cost and justification. Theoretically it is possible to build towers in very deep water. For instance the Troll A oil platform completed in the late 1990’s sits in 300m of water and variants on such a structure could be used. But the cost of providing many dozens of such structures to support a bridge is beyond all decent contemplation and simply could not be justified.

A floating tunnel might be used with buoyant tunnel sections tethered to the lake bed, but this would also be hugely and unjustifiably expensive.

A better bet would be to use a ferry in the summer, drive across the ice in the winter and drive around the lake between seasons. Any inconvenience would be dwarfed by the inconvenience of building a permanent structure (as in decades of toil and cost for no immediate gain).

In early winter and late spring it would be possible to break the ice with an ice breaker extending the ferry season (and ferries could have a limited ice breaking capability as well). Heavy icebreakers could probably clear a route even in winter if it was rely necessary https://www.marineinsight.com/types-of-ships/top-5-biggest-ice-breaker-ships-in-the-world-in-2011/

But at some point it would prove too costly to keep the ice at bay and at that point ice a few miles away could be used for the crossing. Fun feature for a fictional setting: liquid nitrogen might be used to freeze any soft spots or cracks on the ice road.

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Expansion of small scale.

A pontoon bridge has little environmental impact (historically) but can buffer in weather systems on large bodies of water. While I don't think it's practical, if you insist on a bridge, this would be a great alternative. There will be no disruption of major navigation, so why not?

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No

the lake is a rift valley it is actively expanding by 3-4 cm per year, and is full of seismic activity. this combines with its depth makes building a bridge over it impossible.

Tunnels are likewise impossible you would be digging through magma.

And as others have mentioned ice makes pontoon bridges impossible.

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