Building Tunnels, anyone?

[LaurieAG]

Originally Posted by Ganoderma

bummer....i am wanting to avoid any water coming in in the first place....even if one does pump it out fast, its still going to be humid and feeling kinda fungi....

A friend of mine once told me about 4 very large concrete water tanks that he helped build that were incorporated into the foundations of a house that was then built above the tanks. Ferro cement construction is cheap , lightweight, strong and watertight when finished correctly.

[JMJones0424]

Originally Posted by Boerseun

Well, you're planning to build something big that can hold water out...


...lemme think...

Yep - you're planning on building an underground boat!

So, whatever you'd do to keep a boat afloat, should work for your tunnel system.

For instance, you can do the structure with brick, and have your tunnels be arched brickwork, and then just paste the entire inside with fibreglass. Same as a cheap boat. And you have to apply only a thin layer of fibreglass, seeing as it won't be structural and won't take any stress. That's what the bricks on the outside is for.

Underground structures have absolutely nothing in common with boats. The more appropriate analogy would be a submarine. If you were to follow Boerseun's advice, I can GUARANTEE absolute structural failure. You NEVER waterproof the inside of the structure, especially if you were planning to use brick, which is a very porous medium and mortar which would rapidly deteriorate underground anyway. Hydraulic pressures on the inner fiberglass shell would rapidly overload the fiberglass and cause failure, unless it was thick enough for it to be structural itself, and then there would be no need for the brick.

Ganoderma, it sounds like you have at least a passing knowledge of basement waterproofing, but the important part you left out, especially in slow draining soils, is adequate slope above ground so that rainfall will drain away from the structure rather than towards it. Extra insurance can be had if you were to use thick pond liner or some other extremely durable membrane and bury it 8 inches or so under the surface extending at least 20 feet beyond the dimensions of your cave, once again taking care to make sure slope ensures that rainfall drains away and does not pool over your cave. Imagine this being an umbrella for your cave. As long as you do not have a really high water table, this will absolutely negate the need for french drains and sump pumps.

A day or two of research on the internet can give you enough info to help you decide if you want to go through with this, but unless you have some experience in either engineering or construction, I would recommend having someone design this for you. Or perhaps convert some old fallout shelter plans to fit your needs if you can find anything like that. Waterproofing is easy compared to structural load from above and from the sides, and you certainly don't want to literally be digging your own grave.

Ferrocement is no different than regular cement when it comes to waterproofing (it isn't waterproof). Ferrocement is different from conventionally reinforced concrete in that it uses fine mesh wire like chicken wire rather than rebar. It is in no way whatsoever waterproof, and if you choose to go that route, then it should be waterproofed the same way as conventional concrete construction.

[Ganoderma]

never heard of Ferro cement...if its just mesh instead of rebar, is that really that structural? we used to build fake rock/waterfalls/landscapes in the zoo using very spread out rebar with mesh wired on with XXXXX brand cement and sand. we could walk on it and it was great for animals, but nothing i would trust with 20 feet of dirt and some water pushing in on it....for that i am a rebar guy...mesh seems more cosmetic, or am i missing the point here?

the thing i am having difficulty with is with say a foundation and concrete basement. usually the area directly around the walls is dug out and there is some walking room to apply tar and plastic (at least by BC, canadas current code)....with a tunnel, one only has access to the outside of the wall *before* the wall is built.....once the wall is built, there is no more access....unless there is a lot more digging involved...i am not thinking having a chunk of land and digging a big hole then filling it later when done, i am talking more about digging a tunnel through the ground underneath stuff. Vietnam style, but safer.


we buy our house this new year sometime, but tunnel construction wont start until everything else is all settled in (ie. insurance company is happy and not looking)

[JMJones0424]

Ferrocement, when compared to a same thickness of standard rebar reinforced concrete, is actually better. Remember, concrete is incredibly strong against compression, but incredibly weak against flexing. It is the steel that provides the rigidity against flexing. And in your application, we aren't just talking one layer of chicken wire, but rather many overlapping layers with concrete in between, somewhat resembling a cross section of plywood. It is most often used for free form flowing structures that can not be easily formed up, as it is far more labor intensive than standard rebar at say 6 or more inches thick.

I did not have in my minds eye a correct picture of what you want. What you need to look into is mining techniques and shot-crete, two subjects with which I am utterly unfamiliar with.

Waterproofing is still going to be the easiest part though, if done correctly. As long as the water table is below the maximum depth dug, and you prevent water infiltration from above by using correct grading and either waterproof membranes just under the surface or additives to truly waterproof the cement (I'm sure they exist, there are underwater tunnels lined in concrete).

However, I am of the un-educated opinion that it is far easier, cheaper, and SAFER, to dig a huge hole, build a structure, and then bury it, rather than to dig out a tunnel and line it. Whatever you do, talk to someone who actually knows what they are talking about first

[LaurieAG]

Hi Ganoderma,

Originally Posted by Ganoderma

never heard of Ferro cement...if its just mesh instead of rebar, is that really that structural?

More like 2-4 layers of chicken wire surrounding 2 inch mesh, a bit of reo and a soft steel tie on every intersection of the mesh in the entire boat/tank that ends up about 3/4-1 inch thick after plastering and finishing.

I've helped build 3 ferro cement boats, 18ft, 26ft and a 52ft trawler built under survey. We have a major seaway entrance near where I live. Wooden, steel and aluminium boats tend to break up very quickly in big surf, the ferro cement wrecks have to be dynamited because they don't break up in the same situations and become a real hazard.

Have you noticed how some concrete floor slabs are very shiny, slippery when wet and water pools on them while other ones seem to soak up any water that falls on them? When a cement surface is finished, i.e. smoothed multiple times with a steel trowel or mechanised trowling machine, as the main body of the cement starts to harden the trowelled edge becomes less porous as water and air voids are pushed out, creating a dense layer. If you finish concrete with a wooden float/trowel or broom, it will be very porus, soaks up heaps of water but will be a very non slip surface.

So correctly finished ferro cement is not only very strong, 1 thin external epoxy seal coat will make it extremely watertight and, as long as you don't use too many straight lines (round water tanks excepted), many different shapes and designs are possible.