Granite Tunnels

Hi folks,

I have a somewhat unique building site opportunity that has the house attached to a large granite ridge around 25 meters across and 60 meters or so long (and longer as it blends back into the main underlying granite hillside). Part of the house design will have access to a walled off section of the face of the granite base.

I had always intended to create a root cellar type environment there but as I did my reading, it soon seemed that some tunnels may also be in order.

The usual logical constraints exist, such as:
1) Silicosis prevention - appropriately rated breathing gear, washing, dust disposal, etc
2) Radon detection, monitoring and wall sealing
3) Positive air flow and ventilation requirements
4) Appropriate power tools and techniques (e.g. impact drilling and fracturing and blade cutting for certain surfaces)
5) Debris removal and tunnel angle logic versus sliding blocks / pulley systems

Beyond these though, I am interested in optimal roof curvatures versus span widths for greatest strength.
I wasn't able to find a decent simple book on what the curves should be set at and what the logical maximum room widths you could strive for.

The entrance will unfortunately (for debris removal) be a square cut set of stairs downwards to reach a suitable below foundation depth.

If anyone has any internet links or book references for this topic, that would be great. The ones I seem to find tend to focus on large grade commercial tunneling which isn't exactly viable for this project.

Or,m if anyone has done any actual tunneling in solid granite, I'd love to hear your experiences too.

Hi Richard, Welcome to Permies!!!

I have to ask before getting to excited for you...

Have you ever done any stone carving or extreme quarrying of stone?

These are massive skills with very expensive tools...and...work that takes a lot of time and/or money.

Most books that you need are very technical and aimed at Mining Engineers, and the related fields.

"Mine timber craft" is more germane than "arch carving a ceiling." There is huge PE assessment needs for such a project.

Give me specifics and I will do what I can. Bullet questions are easier for me to answer.

Regards,

j

Better to move the house to where an existing hole is
Here in Anjou there are lots of houses built into limestone cliffs and as far as I am aware, zero built into granite and we have that too
http://www.anjou-tourisme.com/preparez-votre-sejour/carte-anjou/visites/rochemenier-village-troglodytique-louresse-rochemenier

David

Jay C. White Cloud wrote:Hi Richard, Welcome to Permies!!!
I have to ask before getting to excited for you...
Have you ever done any stone carving or extreme quarrying of stone?
These are massive skills with very expensive tools...and...work that takes a lot of time and/or money.
Most books that you need are very technical and aimed at Mining Engineers, and the related fields.
"Mine timber craft" is more germane than "arch carving a ceiling." There is huge PE assessment needs for such a project.
Give me specifics and I will do what I can. Bullet questions are easier for me to answer.
Regards,
j

Hi Jay,

Thanks for the vote of potential excitement and the welcome to permies.

I've done some limited stone carving but small shaping works feel rather different in my mind to intents to excavate human sized areas. The general concept of using holes to wedge fracture the rock is familiar to me but for mostly external sorts of works. The tunnel concept introduces shapes for strength which I have not had to deal with before.

I'm not particularly worried about buying the right tools or having the project take years. I'm not an instant gratification kind of guy. My primary concern is doing it right and avoiding being inadvertently killed.


Because the site has such a massive area of granite, there are various exterior opportunities to further practice some techniques on too. For example, there is a cascading set of levels down one side into which a set of stairs could be cut without actually having to remove all that much rock.

Secondly, I had intended on using the walled off space under the house as an easy spot to further test the various techniques before committing to anything else. Essentially it would be an square spiral pit with recessed arched areas deep enough for wine (for example). Conceptually simple enough to practice some basic approaches while still yielding a useful final product if that is as far as it goes. Also, I can try a fair amount of the cut before the floor gets placed on.


I find it difficult to ask short bullet point questions as it feels like a set of scenarios, but here goes (actually a series of small diagrams might be easier to convey things so I'll create those when I get a chance):
1) From my reading, it appeared that drilling a series of holes and wedge fracturing the pieces out seemed like the easiest way to begin and extend a specific shape as well as ultimately achieving the curve. Is that correct?

2) I had wondered though, if a series of horizontal blade cuts across an area to be removed and then hitting them from above (or wedging them from below) once a sufficient hole existed would be more or less efficient. It seemed like an easy method to try anywhere on the site though. Does that seem reasonable?


As for moving to a different site that already has caves, that is not as easily done as said unfortunately. This location has a 3 story near vertical drop off on 3 sides with extensive views out to sea, along a coast, across a forested valley, can't be built out, won't have neighbours etc. To try and find that with a natural cave too might take me longer than just making one. Maybe

So, Jay, I haven't yet done any extreme quarrying of stone but I'll happily reiterate that speed is not my main concern here. Precision and having a good safe outcome is. The right tools, approach and technique should make all the difference. Personally, I think this will be a truly amazing project opportunity in a location that has an incredible amount going for it.

Tell me more about the PE assessments. I'm happy to spend a long time planning before going near the rock as I won't really get a second chance with a location like this and want to do it right.

Conceptually simple enough to practice some basic approaches while still yielding a useful final product if that is as far as it goes.

Yes...conceptually...much work I do in stone is basic and even easy depending on the heavy equipment at had...but very slow and time consuming. When you add "confined space" safety issues and logistics...even harder than before by a minimum factor of 2.

1) From my reading, it appeared that drilling a series of holes and wedge fracturing the pieces out seemed like the easiest way to begin and extend a specific shape as well as ultimately achieving the curve. Is that correct?

Drilling "feather and wedge" holes for a quarrying and/or mining operation is not the same as even splitting a large glacial erratic. You need huge air compressors and or diesel operated 30 mm to 50 mm drill bits that can coast up to a thousand dollars or more each. Most operations now use dimon saws, cables saws, and related tools for projects such as yours. These start at $80K and go up.

For house scale work you can get by with "kerfing and wedging" with a 400 mm to 500 mm hand held diamond chop saw. This is fastly quicker and more efficient than "feather and wedge" methods.

2) I had wondered though, if a series of horizontal blade cuts across an area to be removed and then hitting them from above (or wedging them from below) once a sufficient hole existed would be more or less efficient. It seemed like an easy method to try anywhere on the site though. Does that seem reasonable?

Kind of...see above answer. Remember...many operations like this start with "blasting" and "mine timber framing methods." Your project is actually attempting to not fracture the rock but keep in whole and intact for structural purposes...much hard and slower work.

As for moving to a different site that already has caves, that is not as easily done as said unfortunately. This location has a 3 story near vertical drop off on 3 sides with extensive views out to sea, along a coast, across a forested valley, can't be built out, won't have neighbours etc. To try and find that with a natural cave too might take me longer than just making one. Maybe

I agree...that area sound great...but..."shafting" into solid granite is probably not the best use of your labor to build a natural house...nevertheless, if I had the time and fiscal resources...plus the kind of rock you mention...I would attempt at least a small scale project of some type under or near the permanent house.

So, Jay, I haven't yet done any extreme quarrying of stone but I'll happily reiterate that speed is not my main concern here. Precision and having a good safe outcome is. The right tools, approach and technique should make all the difference. Personally, I think this will be a truly amazing project opportunity in a location that has an incredible amount going for it.

I can take you through all of this and what I don't know of the top of my head...I can point you in the correct direction...You project sound like dream...doable...and will look magical in the end...but the road is a long and expensive one...

Tell me more about the PE assessments. I'm happy to spend a long time planning before going near the rock as I won't really get a second chance with a location like this and want to do it right.

Well first you really have to "cut in" and start before actually getting an assessment from a PE (my Brother in Law's father is a Mining Engineer and I know several more.) A design with blue prints of the architecture in and above ground is also going to need to be created.

Regards,

j

Many thanks for the detailed response Jay. I'm glad to see that at least some of what I have described about the site has been inspiring.

Jay C. White Cloud wrote:
Drilling "feather and wedge" holes for a quarrying and/or mining operation is not the same as even splitting a large glacial erratic. You need huge air compressors and or diesel operated 30 mm to 50 mm drill bits that can coast up to a thousand dollars or more each. Most operations now use dimon saws, cables saws, and related tools for projects such as yours. These start at $80K and go up.

I think my use of the term fracturing was a poor one.

When I had read up about the diamond blades, it made sense, but I couldn't picture how you would work with that device at the edges of the cut.

For example, (I'm picturing facing an arched recess), how to cut the next 400-500mm of recess (i.e. extend the tunnel)? I picture the bladed device being unable to be moved into the corners so I had imagined cutting the easy surface, hollowing that area and then using the drill/wedge method to take out the final edges to the width of the recess (then repeat). Again, a diagram would explain things far more effectively than my choice of words I suspect. That approach seemed to minimise the area of unsupported shape (to the depth of the new cut) while then allowing you to complete the right curves to continue the correct shape of the tunnel. Marking a larger width tunnel appeared a factor of curve versus height. Maximum height with maximum curve.

Jay C. White Cloud wrote:
For house scale work you can get by with "kerfing and wedging" with a 400 mm to 500 mm hand held diamond chop saw. This is fastly quicker and more efficient than "feather and wedge" methods.

I agree here. The prospect of individual holes versus a straight thin progressive cut just makes a lot of sense. It was only the corner edges of a new recess that were unclear.

Jay C. White Cloud wrote:
Kind of...see above answer. Remember...many operations like this start with "blasting" and "mine timber framing methods." Your project is actually attempting to not fracture the rock but keep in whole and intact for structural purposes...much hard and slower work.

Agreed. Blasting isn't exactly on the cards given the rather precise dimensions of the access point and that I want the house sitting on top of it to remain stable and standing (call me old fashioned).

However, the blade cutting was definitely on list although I had been unsure which was the better way to start (surrounding edge of the recess or the middle main area and work outwards).

Jay C. White Cloud wrote:
I agree...that area sound great...but..."shafting" into solid granite is probably not the best use of your labor to build a natural house...nevertheless, if I had the time and fiscal resources...plus the kind of rock you mention...I would attempt at least a small scale project of some type under or near the permanent house.

I find it very hard to be on the site without my mind just naturally gravitating towards the concept. The main part of the house will straddle the ridge from edge to edge while providing a natural secure/enclosed area to work with for the root/wine cellar concept. While the shafting approach is not ideal, it represents what seems to be the best option in the limited space.

Actually, it gets worse. Imagine that about 20 meters in one direction from the access point under the house is a 40-50 foot vertical granite cliff into a ravine. In an ideal outcome, you could cut across to that face and create operable windowed terraces. Natural light and ventilation bonus. Or, you could gently go down and come out at the base to the cliffs, or both. The site just has too many opportunities.

However, all that being said, I would be perfectly happy with a squared spiral cut stairs with recessed sections for wine and other bits and pieces and consider that a huge success. That project alone should yield a structurally safe, easy access project while still presenting a number of the initial challenges in a relatively friendly manner. I wouldn't even begin that until I had spent some time externally in the area cutting some of the easily accessed rock for stairs etc.

Jay C. White Cloud wrote:
I can take you through all of this and what I don't know of the top of my head...I can point you in the correct direction...You project sound like dream...doable...and will look magical in the end...but the road is a long and expensive one...

Long roads are fine. A little bit of OCD can go a long way. Expensive is a relative term as well and I don't like cutting corners (no puns intended). I'd like to do it safely and correctly and use tools appropriate to the job. Of course, I don't need to create a structure big enough to park an aircraft carrier in, rather, I want something that will ultimately yield an amazing outcome that can be progressively accomplished over time.

Jay C. White Cloud wrote:
Well first you really have to "cut in" and start before actually getting an assessment from a PE (my Brother in Law's father is a Mining Engineer and I know several more.) A design with blue prints of the architecture in and above ground is also going to need to be created.

So far I have a good coverage of survey points over the ridge to the purposes of anchoring and building the house structure. The house design is also completed and 3D modelled on the site. The exact points in and around the ravine and other cliff edges are not yet taken though as they were not key to the house plans. From here, I was going to extend the survey and 3D model to include the potential below ground cuts.

Cheers,
R

I've never tunneled through granite, but I have removed it from trenches and a basement. It recently cost my customer $1500 to remove about half a yard of granite from a narrow trench. It took 5 days. We broke 2 tips and dulled 20 others. Equipment costs ran around $400.

A few years ago, my friends were about to spend $700 more on a low profile oil furnace than it cost to get a similar upright model. It was to go into a tight crawl space. The house sat on soft shale. I was able to excavate space for the furnace and a root cellar for $300, using a 3 man crew. It took 8 hours. We saved $400 and created more room under the house.

Some rock is incredibly hard and difficult to remove. Other rock can be removed using pick, shovel and sledgehammer.

Dale Hodgins wrote:I've never tunneled through granite, but I have removed it from trenches and a basement. It recently cost my customer $1500 to remove about half a yard of granite from a narrow trench. It took 5 days. We broke 2 tips and dulled 20 others. Equipment costs ran around $400.

A few years ago, my friends were about to spend $700 more on a low profile oil furnace than it cost to get a similar upright model. It was to go into a tight crawl space. The house sat on soft shale. I was able to excavate space for the furnace and a root cellar for $300, using a 3 man crew. It took 8 hours. We saved $400 and created more room under the house.

Some rock is incredibly hard and difficult to remove. Other rock can be removed using pick, shovel and sledgehammer.

Thanks for the story. It's always interesting to hear about the varying circumstances.

I will have to get some analysis done on the granite that we have in terms of what will work best on it. It certainly seems a bit different to the classic sort of (no pun intended) rock hard granite for bench tops etc. Because of how common it is at this location, many of the houses are anchored to it for foundations. Naturally, our location never freezes so you don't get that sort of progressive water based damage to the rock that can occur elsewhere. It will be an interesting experiment but I will ask the builders what sort of experience they have with the anchoring and shaving processes to get their thoughts as well.

For anyone who simply needs to remove a ridge or hump of granite, heat shock can work wonders. I once used a propane tiger torch to heat the rock and then I doused it with ice cold water. When my dad's barn burnt, I used my hammer to bust up formerly hard foundation rocks. I got a pound of fools gold and I didn't welcome the name that my mother assigned to my treasure.

If a granite ridge obstructs a driveway, a brush pile fire can soften the rock considerably.

I once quarried a sandstone face by accident. A fire against it caused fracturing and a steam explosion. About 2 yards of rock came down. Oops.

I dont have any direct experience to share but I do have a suggestion of a research angle. Look out up mining on dartmoor. Dartmoor is granite and has been mined for hundreds of years, if not thousands.
And think about the radon testing whilst doing your test pits. You dont want to put massive amounts of work in and then find that you cant use it because of the radioactivity of the rock.

Richard Broome : If you are still a young man you can try to get some hard rock mining experience on someone else's dime ! Often, to make large road cuts
for say new interchanges or straighten out a curve in a road, " long hole drillers'' are called in to get core samples for the work ahead ! Most but not all of these
jobs are Union jobs, but not all as it varies from region to region !

With todays web-connected-everything you can search 1 or more data bases for every jog that wants a Hard Rock Miner or ''Long hole driller'' crew members!

A little practical experience, and you to can have a blasters license, and be an entry in Homeland securities data Banks ! For the Craft! Big AL !

late note : my distant neighbors started outdoor trash fires as a way to deal with trash , built it up against the rock face of a ''hanging Tor'' and fractured off a
whole lot of rock, now they haul in trash to burn to increase the size of their parking lot !

You want to tunnel through one of the hardest rocks on earth for what now?

The guy's from Hogan's Heros were awesome tunnelers. I watched them tunnel under Stalag 13 when I was a kid. It looked pretty easy. If you get started and attract unwanted officials in uniform, tell them "I know nothing!" "I see nothing". You don't want to get thrown into the klink.

Thank you everyone, for the various combinations of serious and amusing responses.

There is a lot of information on the Internet, that's for sure and I have been happily reading up on it to compliment my limited rock carving experience.

Some of the side bar discussions have been very interesting as well and I thank the members for those too.

Thankfully, there are different grades of granite from what appears to be 'soul destroyingly hard' to 'not as bad as you might think'. From what I can read about where we are, it looks like the slightly more enjoyable kind. I'll know pretty soon anyway when I try a few things around the property with the exposed granite.

Henry - we will definitely be doing that. That would be a horrible outcome to have though...

As for the 'why' question, there are many reasons but partly because it is there and that some amazing possibilities exist.