What if it is indoors?
Yes, that base (right below the top footing) needs to be able to have a truck drive across it and not leave tire tracks, AND it needs to drain well.
Why? It needs to support, not eat, your footing, and it needs to get that water away from the footing as fast as possible.
If it’s not flat, water will pool and eventually you’ll get “waves” in your ring.
The compacted sub-base should (ideally) not drain, but water should run across it and get out of your arena
My understanding and open to correction - putting in an indoor currently. Yes, an indoor needs a proper base. It provides a surface UNDER your footing for support and a bit of traction. If a hoof goes through the footing TO the base, they push off versus slip. And a proper base definition is compacted to 95% and tested.
JB, are you saying that the sub base under an indoor would somehow take on water? Like from under the ground or around the building?
Uh, what? LOL! Not at all. Water needs to go through the loose and permeable top footing.
It needs to go through the “solid” and permeable base.
It needs to hit the solid sub-base and exit the ring.
It should definitely not allow a horse to sink several inches like that :eek: YI’m not even sure how he thinks he can back a truck on that to even dump the footing.
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So it was right after a hard heavy rain but I still think the hooves shouldn’t have sunk in like that. Two days later, hard as a rock.
I think I have two options at this point. Let him try and further compact this base or have him add a few inches of compacted stone dust. One or the other before adding sand.
I feel like this is the most expensive sand arena in history 🤦”♀ï¸
No, feet shouldn’t have sunk, as the whole point of compacting this sub-base is to have water run OFF it, not into it
I think I have two options at this point. Let him try and further compact this base
What is this sub-base?
or have him add a few inches of compacted stone dust.
Nope, because anything that can be sunk into after a good rain, is going to eat whatever material is on top of it, eventually
I feel like this is the most expensive sand arena in history 🤦”♀ï¸
I feel your pain :\
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Having a proper underlayment to it is important. This is where your local sand and gravel contractor comes in as hey know the ground you are dealing with, as well as the materials available.
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Sub base is crushed shale. They use it to build roads and building pads. Im not familiar with it but I told him a hundred times, it needs to be hard and smooth like concrete before any sand goes on it.
I think adding a few inches of compacted bluestone might be the only option. It rained again hard last night. I can leave footprints in it this morning ðŸ˜
After you have stripped down to the clay and leveled, four inches of street compacted screenings is recommended- and let it sit and bake in the sun for at least 30 days. THEN you can add your sand and rubber or whatever.
Weve already got about 9 inches of this compacted shale on top of clay. We had to raise one end of the surface up to make it level.
I don’t know enough about shale to know how hard it can compact, given a fine enough particle size - I’d guess pretty hard IF you’ve got the particles small enough, just like anything else
I think adding a few inches of compacted bluestone might be the only option. It rained again hard last night. I can leave footprints in it this morning ðŸ˜
I think that’s throwing a problem on top of a problem. If that base does not get compacted properly, you will have problems working their way up sooner or later.
what exactly did he do to attempt to compact this? It’s got to be a vibrating roller.
That’s about how mine was, with screened sandrock as the base on top of compacted red clay as the sub-base, with one end a lot deeper than the other to raise it to “level”.
Knowing (or realizing, maybe I’ve totally missed this the whole time), this shale is your base, then the water shouldn’t run off it like the sub-based, but it does need to go through it. However, you still shouldn’t be able to make footprints of any sort. And definitely do not add your top footing to this, or any other attempt at a base, if the shale is that soft 
Water needs to flow quickly through the top footing.
It then needs to filter through the base.
It then needs to run out of the area across the sub-base
Your bottom-most layer needs to get the water out of the way as fast as possible. That means it needs to be impermeable, and “as fast as possible” is determined by the grade of slope you have, which is determined by how the ring sits in the surrounding area. Mine is basically cut into a slope, so it didn’t make sense to crown it in the middle and have short half-arena lengths to eliminate water, so it slopes from the long side on the high end, to the long side on the low end, a roughly 2* slope across.
I am in the process of designing an outdoor ring. 150’ x 220’ for hunters. Have read everything I can find. I hate to repeat a question, but there seems to be a ton of knowledgeable people on this topic and I am terrified of screwing this up. I’ve heard nightmare stories… Any advice would be greatly appreciated.
I’m most concerned about the base at the moment. I am thinking that on top of the sub-base, I’d do an aggregate (large aggregate stone) layer 2"-3" think. But, I’ve seen other recommendations that say 4"-6" is required. That would be covered by a geotextile liner. On top of the liner, would do compacted stone dust, 2"-3" deep. And then 3" of footing on top. Planning to crown it and put a perimeter drain around it.
My main questions are: is it necessary to do both the aggregate base and the compacted stone dust (I feel like it probably is)? How big should the aggregate stones be? I’ve seen varying recommendations on that, too. Also, I’ve seen people say you need to compact with a 10-ton roller. I get that.
No clay in the soil. Believe it’s probably good draining from everything I’ve heard. It can be very dry in the summer.
Sorry if I’m rehashing, but feel like every situation is unique and haven’t seen the answers to these specific question yet. TIA!!
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What is your sub-base? Is it rock hard such that a truck won’t leave tracks?
What’s the thinking behind doing both a larger aggregate, then fabric, then smaller stone dust?
This is going to sound totally ignorant… because I am. Regarding the sub-base, we have not started digging yet. I have read a couple of things that said to create the sub-base that you dig down deep enough to get to the compacted natural soil. Then thoroughly compact and crown that. I’m gathering that whatever is done MUST be rock-hard such that a truck won’t leave tracks. Please feel free to tell me if this is not the correct way to do a sub-base.
As for the rest of the plan, I can’t really call the design “my” thinking. I’ve just seen a couple of articles online that suggest designing in this manner. I suspect the idea is that you have the stone dust to have a compacted layer beneath the footing itself but the larger aggregate stone to allow drainage. I know the geotextile is to prevent the compacted stone dust from becoming mixed with the larger aggregate stone layer and also to collect fines that could clog the perimeter drains. But, all in all, to be honest, I’m not 100% sure. I got this info from a couple of sources. One is the “Ultimate Arena Guide”. Here’s the link http://ultimatearenaguide.com/horse-arena/base-information/
The other reference is Avoid Common Mistakes When Building an Outdoor Arena. https://thehorse.com/149152/avoid-common-mistakes-when-building-an-outdoor-arena/
JB, you seem to have a lot of experience with arena design. I would completely value your input. I have no clue whether or not the things I found online are accurate. Hence, my original post. 
Thanks so much for your input.
I am in the middle of constructing an outdoor arena. I agree cabbru, it can be really confusing. It seems like many of the resources that come from the UK and Ireland include an aggregate stone layer underneath the base, often with drains that run underneath the arena. The American resources like the USDF Underfoot book and PennState Extension focus more on a compacted natural soil subbase and then the base layer, with perimeter French drains as needed. I am guessing, but I think this has to do with the properties of the sub-base soil. I have seen the aggregate drainage layer recommended specifically for poorly drained subsoil or for areas with a high water table (Eileen Fabian Wheeler book). These properties are highly regional. I used the USDA Soil Survey to help me understand the soil where I built my arena. My soil is naturally well draining and I have a well compacted clay sub-base. I am not doing an aggregate layer even though I am in an area with high rainfall. We will see how it holds up!
Ok, that makes more sense. I’m definitely not an expert though! I can only tell you what I learned from researching mine, and getting mine done.
We have red clay, top to bottom, so we only had to dig enough to create a flat ring on the side of the hill - very little at the low end, almost 6’ at the high end. But even that was compacted with a vibrating roller after it was graded for a 2* slope from the high side to the low side - no crowning here because of the slope.
If that is rock hard, there’s no need for any larger aggregate and fabric then smaller bluestone, not maybe unless you’re building a large commercial ring.
Add enough of your base - bluestone for example - so that it compacts to 6-8" (a bit more IS better here, allows more water to drain through to then run off across the sub-base), and I think I ended up with 8" after compaction because remember, it’s on a hill so even though there’s a swale on the high side, there’s still water running into the ring.
That base material should also be compacted to be rock-hard, truck drive across no tracks, but because of what it is, it still drains. You just gotta use a vibrating roller and wet material to get it compacted properly, unless there’s another method I’m not aware of
Then add your footing - how much depends on what it is - 2" max to start with sand, 3 to maybe 4 if it’s screenings/bluestone/etc.
I know people in the southern part of my county whose soil is sandier/loamier, who only leveled and rolled their native soil, then added their footing on top of that. Everything drains much more naturally as they don’t have clay to contend with.
So it really depends what your native soil is. I found a guy whose day job was grading roads, so he was 100% aware of the need for compaction and drainage, but who also did rings on the side, so he understood that aspect of it too
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mbv the USDA soil survey is a wonderful idea!! Thanks. And your comments about the aggregate layer are probably right on with respect to it being a design used in Europe. I actually had an interesting phone conversation today with a guy who goes around the country building (and fixing) rings. He said that the concept of having aggregate rock below your stone dust base layer is really silly, as the stone dust is supposed to be compacted to the point where water will not get through it. So you’re setting up a drainage area below a layer that will not drain. What he said made sense to me. So I think the new plan will be simply to do a sub-base layer of compacted soil, followed by 6" of compacted stone dust, and with a 3" layer of footing on top. He also said that he puts a wood border around the base of the ring to prevent the base from shifting or being carried away with water. He then puts a french drain, that runs down both long side of the ring within that wood border.
JB, does that sound like a reasonable plan to you?
Again, thanks to everyone who’s contributed to this discussion. Enormously helpful.
