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> But any preventive measure will have limits as what and how serious an impact it can deal with. The recent grounding of a large container ship in Baltimore's

> But any preventive measure will have limits as what and how serious an impact it can deal with. The recent grounding of a large container ship in Baltimore's harbor channel demonstrates that a sufficiently massive berm will stop any ship. What's needed is the will to do something about low-probability but catastrophic events (though large-ship collisions, groundings and fortuitously harmless steering failures are frequent enough that this should not have been dismissed as a low-probability event.) https://www.cnn.com/2022/03/16/business/evergreen-container-ship-grounded/index.html https://www.cnn.com/2022/03/16/business/evergreen-container-... In this case, the nearby towers supporting transmission lines across the channel seem to be better-protected against ship collisions than the piers of the bridge. https://images.app.goo.gl/J6vTeDW5xjysbdjr9 https://images.app.goo.gl/J6vTeDW5xjysbdjr9

rkagerer 3y ago
What's needed is the will to do something about low-probability but catastrophic events In general I share your sentiment society could do more to insure itself against lower-probability catastrophes. But overbuilding every bridge would probably cost more than rebuilding the occasional one that's taken out when an unusual event like this occurs. Maybe in a different environment that would make sense, like a warzone (although I think even then there's more tendency to rely on redundant infrastructure and mobile, power-at-a-point defense).
deleted 3y ago
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throwaway48476 3y ago
The "berm" in this case happens to be the seabed of the earth. There's nothing bigger.
- mannykannot 3y ago
  Of course - but it doesn't take all of it...
bmelton 3y ago
Starting from xoa's calculations above, assuming you can pack a berm with well-compacted soil enough that it can absorb 1,000 joules per cubic meter, you'd need a buffer of something like 10 meters surrounding each piling with 3 meters of depth to keep it safe from this kind of impact. That's 10 meters in every direction from the center of the support -- let's assume the support has a thickness of 0 meters for the sake of the math, and acknowledging that the gaps between structural supports on the bridge is approximately 30 meters -- the only way to protect it with earth is to make the bridge impassable by water. Of course, this would protect it from ship strikes.
- SiempreViernes 3y ago
  You needn't stop the ship completely with the berm: just taking up enough energy that the bridge lives for 20 minutes after the impact would be useful.
- mannykannot 3y ago
  Even if it takes 10 meters to get the job done (in practice, ships will not be coming at the piers perpendicularly to the channel), that is far from rendering the channel impassable. Secondly, I believe riprap would be preferred to compacted soil (though compacted soil did a pretty good job stopping the Ever Given three years ago.) Thirdly (and rendering the above moot), what's been done around the replacement Sunshine Skyway bridge in Tampa bay (mentioned in other posts here) shows that protection is, in fact, practical. In view of these considerations, I'm not even going to check if, for example, xoa considered the energy absorbed by the ship (Update: in fairness, I did take a look at what xoa wrote, and I see that it is you who has introduced the figure of 1000 J/M^3.) For an introduction to a serious engineering approach to this problem, look here: https://onlinelibrary.wiley.com/doi/epdf/10.1002/stco.200910004 https://onlinelibrary.wiley.com/doi/epdf/10.1002/stco.200910...
  - bmelton 3y ago
    There are other issues with my work, namely that the central span is over 300m in width, not 30, as I had wrongly discovered, ergo the channel is passable even with my extremely half-baked solution. That said, the dolphin-bulwarks around the Tampa Skyway are interesting. I've sailed through similar and not known their purpose other than to observe that local waterfowl like to line up at them ahead of tidal shifts to catch the fish as they're encouraged by the currents through them.

rkagerer 3y ago

What's needed is the will to do something about low-probability but catastrophic events In general I share your sentiment society could do more to insure itself against lower-probability catastrophes. But overbuilding every bridge would probably cost more than rebuilding the occasional one that's taken out when an unusual event like this occurs. Maybe in a different environment that would make sense, like a warzone (although I think even then there's more tendency to rely on redundant infrastructure and mobile, power-at-a-point defense).

deleted 3y ago

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throwaway48476 3y ago

The "berm" in this case happens to be the seabed of the earth. There's nothing bigger.

mannykannot 3y ago
Of course - but it doesn't take all of it...

bmelton 3y ago

Starting from xoa's calculations above, assuming you can pack a berm with well-compacted soil enough that it can absorb 1,000 joules per cubic meter, you'd need a buffer of something like 10 meters surrounding each piling with 3 meters of depth to keep it safe from this kind of impact. That's 10 meters in every direction from the center of the support -- let's assume the support has a thickness of 0 meters for the sake of the math, and acknowledging that the gaps between structural supports on the bridge is approximately 30 meters -- the only way to protect it with earth is to make the bridge impassable by water. Of course, this would protect it from ship strikes.

SiempreViernes 3y ago
You needn't stop the ship completely with the berm: just taking up enough energy that the bridge lives for 20 minutes after the impact would be useful.
mannykannot 3y ago
Even if it takes 10 meters to get the job done (in practice, ships will not be coming at the piers perpendicularly to the channel), that is far from rendering the channel impassable. Secondly, I believe riprap would be preferred to compacted soil (though compacted soil did a pretty good job stopping the Ever Given three years ago.) Thirdly (and rendering the above moot), what's been done around the replacement Sunshine Skyway bridge in Tampa bay (mentioned in other posts here) shows that protection is, in fact, practical. In view of these considerations, I'm not even going to check if, for example, xoa considered the energy absorbed by the ship (Update: in fairness, I did take a look at what xoa wrote, and I see that it is you who has introduced the figure of 1000 J/M^3.) For an introduction to a serious engineering approach to this problem, look here: https://onlinelibrary.wiley.com/doi/epdf/10.1002/stco.200910004 https://onlinelibrary.wiley.com/doi/epdf/10.1002/stco.200910...
- bmelton 3y ago
  There are other issues with my work, namely that the central span is over 300m in width, not 30, as I had wrongly discovered, ergo the channel is passable even with my extremely half-baked solution. That said, the dolphin-bulwarks around the Tampa Skyway are interesting. I've sailed through similar and not known their purpose other than to observe that local waterfowl like to line up at them ahead of tidal shifts to catch the fish as they're encouraged by the currents through them.