Random rubble mortar cellar construction

[BjornM]

I'm planning to build an underground cellar using the random rubble masonry construction method. I've decided on this method to save cost on construction materials, because I have access to a lot of natural stones on my property, and I also have a lot of spare time. The stones are a mix, but mostly granite 10-40 cm / 4-16 inches.

The cellar will be dug into the side of a tall hill with steep slopes. The cavity will be on ground level. The ground is densely packed gravel/silt that is hard to break. If I excavate from above, that would be a lot of material, so instead I plan to dig it out from the side, like a horizontal shaft. The structure will have vertical walls and a circular arched ceiling, to take the load from above. Temporarily supported by wooden beams while I dig and do the masonry.

Please give me some pointers and best practices.

- Strength. What is a suitable wall thickness to make it strong enough to prevent collapse? I'm thinking that I don't need rebar (which is hard together with RRM), because there will be no tension loads. The vertical walls will have almost entirely compression loads. Same for the arched ceiling, the same way an arched bridge works.

- Moisture. What is a suitable type of mortar for strength and to prevent moisture penetration? This is above the water table and in dense ground, but do I still need a liner? Perhaps a French drain (loose gravel around the structure) might be good enough to lead the water away.

- Technique. Either standard stone laying with mortar using a trowel. Or creating wooden forms and stacking stones while pouring concrete.

 

[Harbringer]

If you don't have experience designing and constructing underground structure find someone that does. This sounds like a good way to end up dead.

 

[SWComposites]

yeah, find someone locally that has done it before.

 

[WesternJeb]

Just wanting to reiterate the points above.

 

[BjornM]

Fellows, I didn't ask whether I should do it. Would appreciate if someone had something useful to contribute.

 

[Enable]

BjornM: this site is intended for professionals to help other professionals in their usual line of work. It's apparent that you are not a structural engineer and unfortunately to suggest any course of action other than you should hire one, would A) be poor form on our part and B) dangerous to you as it might give you false confidence.

 

[Harbringer]

Fellows, I didn't ask whether I should do it. Would appreciate if someone had something useful to contribute.

I thought my contribution was very useful. Your questions are very basic and non-technical indicating you have limited knowledge of the construction method and the design method. I didn't say it can't be done just that you are probably out of your area of expertise and should seek the advice of a local expert before you get yourself or someone else injured or worse. Underground excavation is potentially dangerous work.

 

[RPGs]

I'd be surprised if anyone here will help you the way you need it because the forum is against DIY stuff for the reasons mentioned above, but I'm sure you could learn a lot with just some google searching. I found some youtube videos and this blog for one people built by hand (which I actually found pretty interesting)

https://smallfarmersjournal.com/building-a-root-cellar/

 

[Luceid]

If your walls are retaining soil/below GW table - there could be tension from bending. Not sure if you want to wing this one.

 

[Greenalleycat]

Best practice would be to get professionals to at least do the design, if not the construction too
It's not within our best interest, ethical obligations, or indemnity cover to tell you to anything other than this
Digging effectively a mine shaft into a hill is a serious undertaking, not a weekend DIYer

 

[BjornM]

Thanks RPGs, interesting project you linked to.

 

[phamENG]

Neat project, yes, but also dangerous. Lots of places where those soils wouldn't remain stable. More than a few people have been killed in excavations of that size.