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carbonebria 06-01-2015 08:34 AM

Yurt platform post holes
Hi all,

I just kicked off construction this past weekend on a 25' yurt platform in Rochester, VT!

The location is on a piece of land that is about 1200 feet in elevation with a fairly steady pitch to it (~25 degrees). This weekend we marked off all of the post holes (which in this case there are 20 as I am following a Pacific Yurt platform design which calls for laying 2x6 tongue and groove directly onto the beams and avoids any joists).

For about 4 of the post holes, there was a significant amount of water coming in (on in particular had water almost to the top of the hole), but strangely enough 5 feet in a different direction the post holes did not fill up with any water at all.

My plans is to go down 48 inches with 8 inch sono tubes. Has anyone run into similar issues with water coming into post holes?

Does anyone have any recommended solutions for this so that when adding concrete, the cement with cure appropriately and not wash away by the water?


Bob Rowlands 06-01-2015 09:07 AM

Re: Yurt platform post holes
Two come to mind. Attach a snorkel to a sump pump and run it to the base of the hole. Second is dig a trench and let gravity drain the hole. I'd likely go with trench and then daylight that footing with corrugated pipe. Also, if those were my piers I'd put a stick of rebar in each of them. Good luck on your project.

hierony 06-01-2015 10:05 AM

Re: Yurt platform post holes
What's the soil type there? A number of places around here have basement problems due to the low water permeability of the clay soils, especially during spring.

Are you sure you haven't found a natural spring you could use as a water source?

Are the watery holes all clustered together, sporadic, or just on the edge of your platform? If the watery holes are all together or on the edge, I might be tempted to shift the platform so as to avoid them--a bit more work but maybe avoids the problem.

carbonebria 06-01-2015 10:43 AM

Re: Yurt platform post holes
Thanks for the responses. The soil is clay after you get down about 18 inches. The watery holes are sporadic so my concern is shifting the platform will uncover some more watery holes.

Bob - I like your thoughts on adding a trench and drainage to the watery holes and then also add in some rebar to those holes as well.

My hope is as long as I can keep the holes dry enough for concrete to set, I should be ok structurally.

Bob Rowlands 06-01-2015 10:04 PM

Re: Yurt platform post holes
I 'wikied' concrete :D and FWIW it can cure in water. However I wouldn't place the fresh mud in an 8" dia. sonotube filled with water. I'd go with the extra expense of six bag mix as well since the columns are narrow. I'm guessing the column dia isn't engineered for that kind of slope. Just a guess though. I'd talk with the concrete guys and tell them the tubes are 8". Gotta say I'm a bit skeptical 8" is appropriate for an extreme slope like 25 degrees. Good luck.

Bob Rowlands 06-01-2015 10:06 PM

Re: Yurt platform post holes
I'm a carpenter. Deck piers here in hilly Colorado are usually 12" sonotube. Just thought I'd toss that in here.

carbonebria 06-02-2015 08:35 AM

Re: Yurt platform post holes
The general slope of the land is around 25 degrees but the site of the yurt is probably around 15 degrees.....its one of the more flat sections on the land.

There is a fairly prominent stream about 50 feet from the yurt that one thought we had was to dig a drainage trench at an angle and try to divert water away from the post holes.

Another options after talking to some contractors is if we wrapped the sonotubes in plastic for the holes that were filling in water to allow the concrete to cure property....and pump out the water first.

Has anyone heard of something like this? I also read somewhere about using hydraulic cement for the initial few inches of the sonotube but I am not familiar with this.

Bob Rowlands 06-02-2015 09:33 AM

Re: Yurt platform post holes
I'm no concrete pro. My comments are based on my limited personal experience digging piers and postholes at work for decks, fencing and my own yurt. Furthur, I'm not a soils engineer. And I'm not there to see your project.

The sontube I'm familiar with is wax coated on the inside. If concrete can cure in water, I'm thinking that after the initial set in ~ one day I'm -guessing- there won't be a problem with just placed mud eroding away. I don't think a sonotube would degrade to point of exposing contents to ground water in a days time. It's all a guess. We have a dry climate here and I've never dealt with any real water problem when digging piers.

I've heard of hydraulic cement, but that's it. I know absolutely nothing about it.

Water at foundation is definitely problematic. If you have a hole or holes that are rapidly filling with water, try ditching and daylighting, or pumping it out. If there is ground water flowing towards the pier holes, try diverting it.

Quick story about this issue. Martina Navratilova built a mansion up near Aspen CO in the early 90s. A couple friends and I were camping up by Maroon Bells and we went by to see it. It was under construction, but the place had a 'stop work' order. The foundation was completed. The ~15K foot home was framed and the mechanicals were well underway.

A lawsuit was in progress. Why? Well the architect had deliberately sited the residence in the direct path of a natural mountain stream, so as to use the stream for landscaping around the back and side of the house! Basically the stream pointed at the center of the foundation on the uphill side. They had diverted it for construction. IMO this was really foolish. The concrete foundation had bowed in so badly on the side facing the stream it had caved in and developed cracks you could stuff a cat into. Construction came to an abrupt halt.

Just sayin. Best to give your yurt site serious consideration before spending hard earned money. I'd absolutely get the opinion of some concrete pros in there, and any friends that are in construction trades as well. Good luck.

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