Building Dirt Jumps

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Building Dirt Jumps
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flag smoovebmx
Posted: Aug 19, 2017 at 10:51 Quote
Hello Everyone. I live in beautiful Wilmington, North Carolina about 10 minutes from the beach. The area is great. I love it! What I don't love is the soil around the area. I just built a new house on an acre of land. I have 1/2 acre to build dirt jumps on. The problems is...all the dirt around me is sand. Every bit of it. You dig down deeper and the sand gets finer...like sand box sand. Its a big issue when you are trying to build dirt jumps.

So, my question to all is: Does anyone have any good recommendations for building dirt jumps on sandy ground?

Here is what I have done so far. I have hauled in 20 tons of clay that I had to get brought in from outside of the area. I also had 20 tons of crushed asphalt brought in to lay down on the surface of the sand to form a riding surface. I've used different pathway stabilizers and tamped down the riding surface. My thoughts are if I can get a good solid riding surface, I can start to build the lips and landings out of the clay I had brought in. 20 tons of clay sounds like a lot, but it really isn't. I have enough for about 3 lips and 3 landings.

What if I dug down into the ground, took the sand and built that up for my lips and landings, and then capped off the piles of sand with clay...would that work? Has anyone ever rand into this issue before?

I can't do carpet over the jumps because my property is right off of a golf course and my home owners association won't allow a bunch of carpet and stuff like that to be view-able from the road or the golf course.
flag Luneec
Posted: Aug 19, 2017 at 14:28 Quote
As you seem willing to spend some money look into mechanically stabilized earth. It works even with the crappiest Sands around and creates great loadbearing surfaces.
You would place layers of fabric in between layers of sand. The textiles will take up the shear forces in the soil. You would still need a faceing material, but you could use wood for that. However this kind of building is very inflexible.
You could add a hydraulic binding agent, ie cement. This could be cheaper and more durable but you would have to play around with the ratios in order to not create concrete but have the mixture tough enough for your needs.
In the end sand is pure shit for building… wooden kickers would be more viable, then having mechanically stabilized earth for the landings.
flag adrennan
O+ FL
Posted: Aug 31, 2017 at 7:35 Quote
Luneec wrote:
As you seem willing to spend some money look into mechanically stabilized earth. It works even with the crappiest Sands around and creates great loadbearing surfaces.
You would place layers of fabric in between layers of sand. The textiles will take up the shear forces in the soil. You would still need a faceing material, but you could use wood for that. However this kind of building is very inflexible.
You could add a hydraulic binding agent, ie cement. This could be cheaper and more durable but you would have to play around with the ratios in order to not create concrete but have the mixture tough enough for your needs.
In the end sand is pure shit for building… wooden kickers would be more viable, then having mechanically stabilized earth for the landings.

as a retaining wall engineer, it makes me smile seeing mechanically stabilized earth being brought up in the forums.
flag Luneec
Posted: Aug 31, 2017 at 10:05 Quote
Well, you beeing a professional, do you think it would make sense in this application?
flag adrennan
O+ FL
Posted: Aug 31, 2017 at 10:18 Quote
i mean it will help build a taller mound but it wont necessarily help a smooth landing. the sand will still be susceptible to ruts and like you suggest, you would still need a surfacing material. i like your idea of mixing some cement in. i would assume a 6 inch thick layer of well compacted clay on top of a sand mound will hold up pretty well.
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