Neutrally Buoyant Submerged Tunnel Bridges

This is an intriguing concept, somewhat resembling Seattle's floating bridges (hollow concrete pontoons) over Lake Washington. As heavy vehicles transit each pontoon, the variation in bouyancy perhaps corresponds to an inch of so difference in submergence (WAG). Thus there some flexure in the bridge, but not tremendously.

A fully submerged bridge doesn't have this differential submergence to respond to varying loads, and thus the flexure of such a bridge would likely be more--if relying only on neutral buoyancy. However, the bridge segments could be tension-anchored to the bottom, with net upward buoyancy always in excess of vehicle loadings. This strategy could essentially stabilize the structure, though still subject to currents.

Eliminating tunneling would be an advantage, and construction could be mostly modular, except for the sloped transitions at each end. It would be interesting to see some projected cost numbers.

Have you seen the documentary about the new road through Chicago in which they built a tunnel on dry land then floated it out & sank it into the bay, That worked! as for floating a tunnel on top of the sea or lake I think that the forces of nature would make short work of them.

Bazzer

????

I work in Chicago, and have heard NOTHING on a sunken tunnel in the Chicago bay. More details please!

"However, the bridge segments could be tension-anchored to the bottom, with net upward buoyancy always in excess of vehicle loadings. This strategy could essentially stabilize the structure, though still subject to currents."

The idea of tension anchoring the structure and maintaining a positive buoyancy in excess of any projected loading is a great idea.

Current is going to be a more difficult problem to solve. The hydraulic force on the structure in even very low water flow velocities is going to be quite large. The hydrodynamic shape of the structure a major factor. Perhaps this too could be approached by tension anchoring in the horizontal plane as well as the vertical.

For the intended use the structure may have to be almost rigid in order to maintain the tolerances required for high speed aerodynamic flight within the tunnel; using tension anchoring makes that possible.

http://cr4.globalspec.com/thread/51026/Electrically-Powered-Aerodynamic-Flight-in-an-Enclosed-Guide-Way

The processes and materials used in manufacturing and assembling the modules is quite interesting to me as well.

Gavilan

That must be some good stuff you're smoking, wanna share some?

There are so many low probability "maybes" in there. The chance of success goes down quickly when you multiply several one-chance-in-three maybes on the critical path.

The most immediate is that "neutrally buoyant submerged water tunnels" can only be statically set for one depth, send some big trucks through and the level of neutral buoyancy drops.

Then there are the ships that pass in the night...

I don't know...

One part of me wants to immediately dismiss this idea. Maintaining anything close to any level of buoyancy will certainly guarantee that the structure must flex and shift slightly as heavier and lighter loads travel through this tunnel. Certainly the most dangerous condition will happen when an accident happens inside the tunnel and traffic stalls making a true static condition. Being an underwater tunnel there will always be a concern of flooding.

Then again aren't these all just engineering obstacles to overcome and not impossibilities to the process. The tunnel sections can each be so massive that the weight difference between a convoy of cement mixers and an empty tunnel could in theory be made a negligible difference. As for the worry of escape paths and leaks, this is a problem that underwater tunnels must deal with now.

Possible? Yes.
Cost effective?.... _no?
Del
(You could just tie a bunch of RORO ferries in a line and drive over)

I really don't know this is practical, as there are several technical issues that could cause a failure if they're not entirely ironed out and made workable. First thing that comes to mind is the use of anchor cables, especially if they're steel. They'd be very susceptible to corrosion. Kevlar or some other composite-based cables may be workable sometime in the future, but I IMO I don't think the technology is mature enough yet, nor are all of the long-term environmental effect problems entirely understood regarding their use in sea water.

Another concern would be gaining a thorough knowledge base of underwater currents......it's going to be a very expensive undertaking doing such research, with no guarantees that we'll discover everything there is to know regarding current patterns, their velocities and resulting forces acting on any type of underwater structure. Then there are such things as underwater earthquake-induced wave oscillations and Tsunami to consider.

I'd be very worried about a submerged submarine cutting the anchoring cables by accident, or a surface ship dropping an anchor in the wrong spot. A whole host of undesirable accident factors, some unforeseen by designers, could destroy such a structure.

Ummmm BTW what is he smoking? Should I drag out my wife's ancient water pipe thingy? LOL

All true but isn't this the perennial problem when "thinking outside of the box". There are unknowns and hazards that have not been dealt with before. While I think your submerged submarine worry is a red herring, submerged debris taking out guy wires or impacting the tunnel are valid concerns. But shouldn't any safe design accept a certain number of failures and still remain safe. Then the problem changes to monitoring and maintaining problems.

What Gavilan is proposing in essence a submerged version of a pontoon bridge. Now the pontoon bridges that I know of are temporary constructions. Part of the reason that they must be temporary is that a pontoon bridge blocks surface vessels and debris from moving up or down stream. A pontoon tunnel concept removes this limitation.

Don't get me wrong. I'm not saying that this flight of fantasy should be immediately funded just because of the novelty of the approach. I'm just saying that a novel approach should not be dismissed for just being a novel approach.

Drag out the water pipe thingy, as this is a pipe dream.

To many joints, flex connections, ventilation issues, etc. There are big issues with standard tunnels to make them expensive propositions. This is a can of problems, that will begat new problems. If we cannot maintain the existing infrastructure, why invent new infrastructure designs that will not be maintained?

I concur with Reid, as this idea is fraught with technical and maintenance issues that would make it unsustainable....

Despite my apparent support for this pontoon tunnel, I agree that it is a completely impractical approach and riddled with too many complications for too few advantages. In fact it takes most of the advantages of a pontoon bridge (flexible assembly, replaceable sections, low mass, portability, few if any secure anchor points) and turns them into liabilities. In exchange this approach only offers the advantage that it will permit most surface vessels easy passage.

While I still believe that a pontoon tunnel is remotely possible, it is not worth the effort to even try to build.

Despite my apparent support for this pontoon tunnel...

Too late to back down now, you are on the board of directors and in it up to the hilt.
The heavy machinery arrives tomorrow, paid for on your credit card
Lyn & Doorman
(Joint CEOs of Lyndoor^TM industries)

It presents the possibility of spanning stretches of waterway many times the longest current spans and over depths that are impossible using any current method.

With longer tunnels there will be more complications with ventilation. Remember that unless you externally power the vehicles running through this tunnel, they will be consuming oxygen and producing poisonous fumes that must get removed. If you're going to ferry people through this tunnel, why not just ferry people on the surface in a ship.

Before you claim that this approach can span great distances, you must build one spanning a short distance.

Better yet, investigate the difficulties of installing and operating the Chunnel between England and France. Then add the difficulties of making it flexible, water tight, and idiot and terrorist proof. The Chunnel was expensive enough. We don't need more expensive infrastructure, we need to take care of the infrastructure that alreading exists and is falling apart. And we need inexpensive new infrastructure, not more expensive, unproven technologies.

Harry Harrison (I think) wrote a book titled "A Transatlantic Tunnel, Hurrah!" using this concept. It discusses some of the engineering challenges fairly well for a non-engineering reader and, as I recall, a non-engineering writer. An enjoyable Sci-Fi book, although probably not to become a classic.

WOW, How did I forget HH?

Thanks for the reminder

apparently much work has been done and some exist. Most listed here are just underwater for wartime protection - hard to see, they are a shallow ford in a river.

underwater tunnels

submerged bridges

Throughout the US involvement during the Viet Nam War, the NVA and VC typically crossed rivers with great efficiency using shallowly submerged wooden bridges. They were typically very difficult to spot, even from the air, due to the water usually being quite murky. It was an ingenious way to transport a great amount of weaponry and supplies across a watercourse during the night time hours and avoid US air attack! Of course this tactical advantage of the NVA/VC was almost entirely negated by the introduction of better and better NVG and scopes in US choppers and aircraft.

i have heard of this system being used, though i don't remember where. each section is floated into place then sunk by filling ballists with water. much like a submarine. drivers then bolt the sections together as the tunnel is extended.