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horsechick
Feb. 29, 2012, 08:28 AM
We are going to be doing an outdoor this year. The area is unfortunately in a low lying spot, so I was thinking to not disturb the topsoil and just build up the base on top of the existing ground. What are your thoughts? Excavate first or just develop the base on top of what's there now?

And favorite recipe for a good base? (We're in Pittsburgh so good drainage is key)

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JB
Feb. 29, 2012, 08:42 AM
SO much depends on what the soil is already like and whether it already drains well, low-lying or not.

Unless you're just going to ride on the footing that's already there, it's usually a really bad idea to just build right on top of the existing stuff. It may look flat/level, but it's not, and you'll end up with an uneven top footing, which means you'll get puddles, which means the area will compact some more, which means bigger puddles, etc.

So at the very least, you need to grade and compact the soil already there. But what's there may not take compaction very well.

Find other barns in your immediate area with rings you like and talk to them about what they did :)

Gloria
Feb. 29, 2012, 10:10 AM
Remove vegetation first, and if your soil is stable, build your base on top of it. An undisturbed earth is many times more stable than man-made subbase.

JB
Feb. 29, 2012, 10:12 AM
That entirely depends on what the soil IS

Undisturbed sand is not more stable than compacted rolled vibrated clay :)

And because the area is already in a low-lying spot, stability won't mean anything if it doesn't drain

horsechick
Feb. 29, 2012, 11:00 AM
It doesn't drain at all right now! It's awful...all the water on our property runs down to this spot, so we will be redirecting the flow with french drains around the perimeter of the ring. Once we build up above the level it's on now, we should be ok. Thanks for the advice so far, taking it all in :)

JB
Feb. 29, 2012, 11:15 AM
yes, regardless of whether the area currently drains or not, you will absolutely need that uphill redirection of water :)

Since it doesn't drain now, which is probably independent of being in a lower spot, I would absolutely scrap off the topsoil (which is not all that stable), as far down as you need to reach more stable ground, then build up from there.

if your topsoil and what's under it are all the same (meaning there really isn't any "topsoil) then it should still be "scraped" to whatever degree is necessary to properly grade it, which means some degree of slope to the downhill side. You don't want anything to slope to the uphill side at all :no:

My ring is on the side of a "hill". It's the lowest spot, but it borders my fenceline and the other side of that continues downhill as well. So, my grade/slope of the ring goes entirely from the high side to the low side, with each of those being the long sides, with water draining across the short length.

I would NOT have an entire slope/grade going from one short side to the other - far too long for the water to travel.

You want your sub-based to be hard and level and impermeable on that graded slope. You want that to catch the water coming from the above layer(s) and to direct it out of the ring.

Ideally you'd then have a base on top of that - something equally hard, equally graded, but permeable. On top of THAT is what you ride on.

Your footing should drain to the base. The base keeps your footing from sinking into anything and disappearing, but allows the water to drain through to the sub-base.

You CAN do your footing right on top of the sub-base, no real base in the middle, but that footing needs to be deeper, the sub-base has to be very, very solid, or you will end up punching through the footing, to the base, creating little pockets which will hold water a little longer, get deeper, and make a nasty cycle

BeeHoney
Feb. 29, 2012, 09:16 PM
I agree. You need to remove topsoil, then level and compact the soil underneath, then add 4-6 inches (or more) of crushed stone (3/8 minus) and then level and compact that. For a great base, make sure that your crushed stone contains a nice mix of particle sizes (from 3/8" down), especially including fines. This will help your base material compact better. Do not use any type of crushed stone that includes actual rock sized pieces (at least for a traditional arena design).

If you need to raise up the area where the arena will be you still need to remove any topsoil and then you could have clay brought in by the truckload to raise your arena area up. Or you could go with a deeper base of crushed stone. Probably the clay is cheaper, but truly your main cost in doing that will be the trucking.

A key to good drainage is that your arena will need to have a small amount of slope to the base. For example, a 1% grade all in one direction, or "crowned" in the middle with a 1% grade heading down each side.

Then, once the water flows off the sides of your arena it will need somewhere to go, and it sounds like you might need drains for that.

keatssu
Mar. 1, 2012, 11:02 AM
Are you building the arena yourselves? We are having ours professionally built. We thought our flat, low lying area would be perfect, but the expert came in and dashed that idea! He said the composition of the soil in low lying areas is loose and very hard to get compacted. Not to mention all of the fancy drainage work it would entail.
The USDF publication Under foot is worth getting if you haven't already. The base has to be packed hard enough for big trucks to drive on without disturbing it. Otherwise you will run into problems that are costly to fix. The base material would depend on your area, what is locally available. Transporting materials adds to the cost A LOT.

Watermark Farm
Mar. 1, 2012, 04:37 PM
A lot depends on the existing soil. My all weather outdoor was built in a low lying area. I had a soil engineer look at it. We built the 12" (yes, 12"!) tall base pad over existing sandy loam --- engineer said heavy clay would have been an issue as it expands. There is soil stabilization fabric under the base. They removed the vegetation prior.

With your base, COMPACTION COMPACTION COMPACTION. That is key. Compaction rates of base should be 95%+. Make sure contractor actually does compaction tests. And compacts the native soil prior to starting to build the pad.

Due to our low lying area, I had to spend bucks to install the base pad, which is 12" high. A ton of materials. Were I to do it again, I'd look for a quality source of fill that's cheaper than base rock to build up the pad area first. I actually vomited when the 100th transfer load drove onto my property. Make sure your contractor shoots the existing grade with a laser and knows EXACTLY how much fill/baserock you will need to build the pad. Mine didn't --- and our base costs were over by 25%, which was about $12,000!

We have a simple drainage swale all around the arena, and that has worked well for 6 years. The contractor steered us away from french drains as he said they tended to clog up over time. You can always tweak a swale. Use a contractor that has built many arenas that you can go see, ones that are still functioning well after a number of years!

JB
Mar. 1, 2012, 08:49 PM
I have a swale around my ring too, and it works very, very well in all but the heaviest of rains.

Rabtfarm
Mar. 1, 2012, 11:37 PM
Dear Horsechick:

The USDF has an excellent booklet called Underfoot which they sell off their website for something like $15. It will answer 99% of your questions regarding arena design and footing, along with materials and drainage elevations. Excellent resource to have before spending upwards of $20,000 on a standard sized arena. I am glad I did.

https://www.usdf.org/cgi-bin/commerce.exe?preadd=action&key=UNDERFOOT&reference=/cgi-bin/commerce.exe%3Fsearch%3Daction%26keywords%3DUSDF%2 0lun%26searchstart%3D20%26template%3DPDGCommTempla tes/FullNav/SearchResult.html

George