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Fix-It Chick 09-11-2006 03:42 PM

Reinforcing dirt walls in crawlspace
How do you keep dirt walls from crumbling? I began to deepen the crawlspace under my cabin (which contains the water pipes and pressure tank) in order to replace the worn out pressure tank with a larger model. Soil is a mixture of dirt and pea-sized gravel - 10" rocks - even a sneeze will start an avalanche! There is little room to maneuver and nothing solid to brace against. I thought there might be a type of product I can spray on to stabilize the dirt so that I can work on a proper retaining system. Has anyone heard of something like this and/or have any other suggestions?

I need some advice ASAP - before my basement walls crumble beyond the foundation :(

billinak 09-11-2006 03:51 PM

Perhaps some more information might make this easier to visualize. Is the cabin built on pilings? Is there a cinder block footer of some kind? I'm not sure how you can have dirt walls and a foundation at the same time. As far as I know there are no products to stabilize dirt walls, per se, without building some kind of brace or something, still it's hard to visualize your problem.

Fix-It Chick 09-11-2006 04:22 PM

Wow! Thanks for the quick reply.

The cabin was originally set on an above ground cement foundation (I guess it's probably more of a "footing") 6" thick and 6" deep. The cabin sits on this foundation over unbroken ground. When the well was drilled several years later, the crawspace for the piping and pressure sytem was dug out though an access panel cut into the floor. It was so tight, you had to slither down and shimmy along the pipes on your back for several feet until you reached a space about 4'x6'x4' high, where the pressure tank sits. Needless to say this is a pain to work in (especially when the pipes freeze and burst).

The new pressure tank wouldn't even fit through the access panel, so I dug under the foundation from outside (supporting it with brick set on a cement pad) to gain access. There has always been some shifting and crumbling in the walls, but now it is getting close to the edge of the cement. It would be nice to have enough room to work and to properly insulate down there.

billinak 09-11-2006 04:59 PM

I'm not a professional, so I'm not the best one to give advice on this topic. If it were me, I could see myself removing dirt up to the footer, then permanently shoring up the footer with a sonotube or pier block or something like that to expand the crawlspace, while leaving the rest of the footer undisturbed. You could then add plywood/insulation or something on the crawlspace side to keep out the cold.

You really (!) don't want to mess it up though, so I would wait for someone who has more experience than me to weigh in, or even get someone to take a look at it.

Fix-It Chick 09-11-2006 07:21 PM

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Thanks for your advice. That's EXACTLY why I made this post. I did pour a cement pad and build two brick pillars to support the foundation where I excavated from the outside; however, ALL of the walls that are within the perimeter of the foundation continue to collapse.

If you look at the attachment (my great artwork), you'll see the light and dark grey areas that mark the original crawlspace and the newly excavated portion. My concern is that these walls will continue to collapse from under the foundation and that I will have to dig out and reinforce the whole thing - a situation I really want to avoid... especially at my age!

billinak 09-12-2006 11:59 AM

I see from your drawing (very good by the way) that your new excavation is getting dangerously close to the upper right corner of your footer (plan view). You say you've already shored up the breach from where the tank was moved in, which is what you will have to do if you undercut the rest of it any further. Because it is a corner, I would try to avoid this if possible because shoring up a large part of your footer is a difficult DIY project with big consequences if it is not sufficient to support the structure, not to mention a lot of work.

I guess I still don't have a good answer for the crumbling soil problem. Maybe after your done digging you could line the walls with plastic, but that's more housekeeping than anything else. Good Luck!

Fix-It Chick 09-13-2006 08:05 PM

Thanks. I think I'll sit and ponder my choices for a few days... maybe I'll wait a week or two then soak the whole thing down and let it freeze (igloo style) haha

Tscarborough 09-13-2006 09:20 PM

The angle of repose for your soil is probably close to a 45 degree angle. If you have the space to slope the dirt to that angle, it will probably be OK. If not, you would probably be best served by using a segmental retaining wall system to line the walls, as you could use small individual units and the setback would be relatively small.

dearyl 01-13-2008 11:57 AM

Your original post mentions pea gravel.

Pea gravel has a very low angle of repose. My experience is that it is lower than 45 degrees. Sooo, to dig a 1 foot deep hole near a footing you may have to be 2 feet or more away from the footing.

We added pea gravel to some areas under my foundation several years ago when we were doing some repairs. Seemed like a good idea at the time because pea gravel compacts wonderfully when contained. Later, however, I had to excavate adjacent to this area. It is almost impossible to contain the pea gravel when excavating adjacent to it. (Think marbles.)

If you do accidentally create some voids under a footing I suggest you put in some forms and pour concrete in to fill the void. Vibrating the concrete or giving it some good action with a stick should allow it to fill the entire void.

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