The first is using the process to create solid sheets of calcium carbonate from 1/2 inch wire fencing or some similar frame. The sheets would then be used in construction of the polder and later shelters and other pieces of infrastructure.
Underwater construction of the polder then consists of building and anchoring a metal frame to the top of the seamount, and charging it with electricity. The electro-accretion then takes over and after a number of weeks a solid structure constructed of man-made limestone has replaced the flimsy wire frame. The best part of this is as long as the electrical charge is going into the frame the electro-accretion continues, making the structure stronger and stronger.
I think the polder construction could be completed in roughly this sequence.
- The top of the seamount where the polder is going to rest is cleared down to the bedrock. All the debris is piled toward the center of the seamount.
- Iron piles are driven into the top of the seamount - these piles will serve as anchors for the wire mesh and add to overall structural strength.
- Wire mesh frames are assembled in sections on board a barge or similarly open decked boat. They are built so that the end result is a 3 sided box with the future "land side" left open. These are lowered over the piles and attached (wired) together.
- The bottom of the wire structure is made to conform as tightly as possible to the seamount bedrock and is fastened to it on all 3 sides with metal fasteners, like cement nails driven directly into the rock. They are also wired to the piles.
- The entire structure is then electrified by the use of Swellfuel's ingenious ocean wave energy converter. I've chosen these wave power devices because of their small size, their portability and their autonomous operation.
- Once the process of electro-accretion has created a solid limestone structure out of the wire mesh frame a dredge is used to fill the 3 sided boxes. Seacrete sheets are attached to the piles on the land side as the frames are filled. Once the frames are filled up to sea level another layer of wire mesh is applied directly over the Seacrete sheets on the land side end. This too is electrified and soon becomes a solid sheet.
- With the box closed on all sides more debris is dredged and deposited into the frame from the top. This is done until the material in the frame is compacted and solid
More to follow...
I'm a bit confused. When you say build three sides of the mesh, is it three sides of the entire polder, or three sides of one section of the wall (in which case the process must be repeated a large number of times to create one polder)?
ReplyDeleteSorry, yes. Build 3 sided sections. This will make it easier for a small number of people to do the work.
ReplyDeleteWith regard to your other point about seepage and how some people wouldn't like a covenant that had a maintenance clause. I was thinking that the difference would be that the Dutch Polder are not designed to be water proof but this project could be.
I'm not sure how that would work yet, but I'm sure it could be done
Limestone does leak; that leads to the development of caves. Granted it's quite slow. However I imagine there would be ways of dealing with this.
ReplyDeleteOne other thing to consider, is how much silt is on top of the seamount? Surely enough to build this structure and the first polder, enough to build an arc of polders, perhaps; maybe even enough to build the entire ring of polders (including an embayment for a harbor)--but the interior might well end up being bare rock, once drained.
One possibility might be to continue running seacrete generators, but instead of letting a wall form, pull the grids up frequently and break the limestone off of them, to make a gravel or even sand. This would be useful for fill, underneath the soil obtained from the silt. I bring this up not because I imagine you'd be running hectares/acres of farmland (I know hydroponics is a part of the plan) but because people will want to landscape for esthetic reasons (and some garden as a hobby, too).
Overall the seacrete concept looks like a possible way to use indigenous materials (seawater, which would be in surplus here) rather than having to import millions of kilobuttloads of concrete (sorry for the excessively technical terminology) just to get started.
I am thinking an initial 100 x 100 meter (1 hectare, 2.5 acre) dry enclosure would be enough to serve as a useful logistical base for continuing expansion, allowing the builders to send home whatever permanently anchored boat they were working off of. However it'd be handy to have an airstrip, and for that we'd probably want something at least ten times as long. That'd be the next goal.
I read somewhere that the silt cover of most tabletop seamounts is quite shallow due to oceanic currents (estimates are 10 cm to 60 cm in most places. But I don't see that as a problem really.
ReplyDeleteI thought that once the seacrete generators were up and running we'd leave them running to continue the electro accretion process indefinitely. Once the initial outlay has been paid for the energy costs nothing and the benefits far outweigh any small gain in power production of shutting the thing off.
I do like the idea of creating rubble out of the accretion process and that fits in with the other part of the equation, that concrete is made from limestone and concrete would definitely be useful.
An airstrip would be a definite must but I don't think it is required immediately.
Something like this would be able to service the needs of the initial settlers. http://www.youtube.com/watch?v=R4EgOj0WKRA
The passenger configuration can carry 72 passengers http://en.wikipedia.org/wiki/Beriev_Be-200.
100m square polder would definitely be big enough to start,maybe even bigger than required.
Ach, how the hell did I forget about seaplanes?
ReplyDeleteThey could land whenever the seas are calm enough, and once a lagoon is enclosed (meaning no ocean waves), of course seaplanes should have no trouble and would have the advantage of being able to "land" in whatever direction the wind is blowing from, much like the circular grass aerodromes of yore. If the lagoon is drained, there is now a location big enough for an airstrip without having to create a ridiculously long polder first.
But I wasn't thinking of a 100x100m polder, really, I was thinking of the first block of a polder seawall--to eventually surround a 1km x 1 km or so (maybe a 2x 0.5) polder. This first segment of the polder wall would be a lot thicker than normal simply because it is the first--once people are able to work off a base on freshly dried land, they can make the newer wall sections by rowboating (if necessary) out from this base and building new wall sections perhaps only 10-20 meters thick by the process described above (surround two sides with mesh, the third side already built since we are building an extension off the already built wall segment, run the seacrete device, fill with rubble, build the fourth side, move on to the next section of wall.
I don't see being able to accrete seacrete indefinitely however--if nothing else one will have to move the device to new sections of seawall. Also as more and more seawall is built the current drain on our power system will go up. So at some point, it'd be necessary to disconnect some parts of the seawall from the device. (And the same consideration applies if there are multiple seacrete generators instead of just one). However there is no reason not to keep it (or them) running 24/7 somewhere, bulking up the thinnest part of seawall on whatever polder needs it the most, once there is no active construction going on.
The big problem, though, is one I just realized. This device won't build anything above the high tide line! What our intrepid builder would end up with is a reef touching sea level, and it would be necessary to build on top of that. A possible partial solution would be to accrete limestone blocks out at sea (held up how, though, as they get heavier and heavier?), then use a crane to lift and move the block into place. But then it becomes necessary to mortar the joints, and anchor the blocks, and fill (with limestone rubble) even more. (I want to use as little silt as possible for simple fill--there just isn't much of it and I think it will be much more valuable as topsoil. Remember the ultimate goal is an island as big as the top of the seamount, minus a harbor.)
Biggest imports during construction would be mortar and rebar for the mesh.
According to the linked site, 1kilowatthour produces 4.2 lbs of seacrete... figuring 2.8 grams/cubic centimeter, this is 680 cm^3 of seacrete. To make a cubic meter of the stuff, therefore, would require roughly 1500 kilowatthours.
To build a 100x100 meter base on a 2 meter below sealevel substrate (including rubble fill) would take 20,000 cubic meters of seacrete (either solid curtain or rubble) and require 30 million kilowatt hours of electricity. Divide that by the power supplied by your generator to find out the absolute bare minimum amount of time it will take to do this. Since I imagine you'd want the entire wall thickness to stick above sealevel at least two meters just to start with, you need to double *that* in order to include the added-on blocks.
On second thought: The initial seawall section, which would serve as an initial base, could simply be 20 meters thick by 500 meters long (or shorter if this amount of space is overkill for an initial base). for 20x500 the math is the same, but the electrical energy requirement just to get started can be reduced if you don't need that much room.
ReplyDeleteAssuming the entire 1km^2 polder is surrounded by a 4 meter tall (2 m above sea level), 10 meter thick seawall (which might not be adequate), you'd need a total run of 4,000 meters x 10 meter thickness x 4 meter height = 160,000 cubic meters of seawall; 240 million kilowatt hours total (and one absolute shitload of rebar and mortar). Double this for a 20 meter thick seawall, to make the thing stick 6 meters above sealevel instead of just 2, for a total constructed height of 8 meters, double it again.
Yup. It's one hell of a lot of material. However there is an alternative to building the seawall up. Here is my thought on it.
ReplyDeleteWe construct the initial polder with interior dimensions of however long and at least 50m wide though wider would be better. The length is unimportant because that is going to be added to with other polders as we go.
Then once the polder is constructed we use a variety of wave mitigation strategies to reduce the waves approaching the structure there are any of a number of designs of floating breakwaters http://tinyurl.com/3a263pw or perhaps we could incorporate something like this Wave Dragon technology to both produce power and reduce wave forces. http://tinyurl.com/2vp978v
We could also "build" some of the 3 sided polder sections that could then be craned onto the top of the others and filled to get us some height at least.
Once the polder is complete we continue building more polders, enclosing off an area (though not necessarily the entire seamount). These initial polders would be "sacrificial because once a suitable area is enclosed we fill them with the silt and whatever else is cheap (sand) ending up with a single large & permanent living space surrounded by a 50 to 100m wide seawall.
The reason I'd use the silt is that it is readily available and reclaiming it from the ocean and making it viable topsoil would be a long process. Dirt is dirt cheap ( :D ), and there is no need to wash it to get salt out or otherwise distract from the business of making land. You can also import as much or as little as you need.
The width of the seawall alone would take care of most waves, the only fear then being storm surges, but the area we are looking at (the Discovery seamount chain) is where hurricanes are spawned so I believe those situations will be rare.
Another thing, once the sacrificial polder are constructed we are going to have access to the Basalt bedrock (and hopefully other minerals) for building (mentioned in a previous post) this would allow for direct mining of stone for building with the accretion process creating limestone for cement. Basalt unlike Limestone is not as susceptible to water erosion.
Of course these mining operations would have to be enclosed in their own polder… We don’t want the excavation to hit an unknown fissure in the bedrock and flood the entire habitat.
I wonder if the water coming into the polder through seepage would be fresh/fresher and therefore a benefit rather than a nuisance?
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ReplyDeleteI would worry about tsunamis as well, yes even in the South Atlantic. Some are caused by landslides down the slopes of continental shelves and those tend to be worse than ones from earthquakes. Also I'd want to be sure the mount is *thoroughly* dead volcanically! (I think this is probably the case, it's not part of the Mid Atlantic ridge.)
ReplyDeleteI suspect we are talking past each other with regard to the construction sequencing. The idea of enclosing a polder for the purposes of digging out basalt had occurred to me but I didn't expect it this early in the construction sequence. It'd have to be a quarry, though, cutting shaped blocks to be mortared together. (In fact, that's a consideration with my idea of making blocks of seacrete and craning them above sea level, too--the blocks would have to have their sides planed in order to minimize mortar use, but the waste can be used as fill).
I'm now thinking in terms of limestone for most of the structure, at least for thickness, sheathed with basalt for erosion resistance. Once we get past a "sacrificial" phase, to build a polder, we'd build the basalt sheath first then back it with limestone, then pump out the polder.
Important skill here--scubadiving!!
I didn't realize silt would be that hard to process to usefulness--if that's the case it'd probably be faster for use as fill than running a seacrete grid and crumbling limestone off of it. Still I cringe at the thought of paying to ship dirt in the quantities we'd really need.
With regard to volcanism as far as I have read the Discovery Seamount chain was formed over a "hot spot" but has since "drifted" away from the hot spot and is no longer active.
ReplyDeleteHere is the Dutch Polder reclamation process in simple terms. This PPT says it takes 15 years before the soil can be used for crops (Pg 6)