# wooden structure ground anchoring



## snug dug (Jul 7, 2012)

Curious what y'all do to anchor your wooden structures to the ground. I'm talking mainly about wooden berms and wall ride type things, things that may have outward force applied to them. 
I've had some advice not to set posts in the ground as they will rot eventually and be a ***** to replace, just set them on the ground and brace the hell out of it. On the other hand, more wood is required for bracing, and I'm still afraid if not anchored, the thing may topple over.

Thoughts and opinions? Thanks


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## Trail Ninja (Sep 25, 2008)

I have built stand alone wooden structure but nothing that would be taking any lateral force like a berm or wall ride. Whoever gave you your advice shouldn't be giving advice. 

Yes, wood rots. If you use rot resistant wood or treated wood, it will last longer. Steel and concrete last longer still. Most structure like you are talking about is made with wooden posts sunk into the ground.

Wood placed ON the ground and braced will still rot.

My advice is to use the biggest rot resistant wood you can get, sink it deep and be prepared to replace it in about 10 years. Meanwhile, enjoy your safe and strong wall ride or berm.


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## aero901 (Apr 11, 2012)

I would use at least 4x4 treated posts for a small wooden berm. Upgrade to 6x6 (or greater) posts if you are talking about a wallride of significant height.

On the issue of wood rot, there are different grades of treated posts available. You will want to use the ones rated for direct ground contact or burial. If you live in an area where climate conditions cause wood to rot unusually fast, you may want to consider steel tube or plastic/wood composite posts for the ground contact areas. Maybe even concrete footings depending on your budget and the desired lifespan and load requirements of the structure.

Any structure that has lateral forces applied to it needs to be securely anchored to the ground and one of the easiest ways of doing that is using buried posts. Making the structure rigid is going to be a priority anyways because significant movement between structural members when loaded will lead to accelerated fastener/structure failure.

Overbuilding trail structures usually saves time and money in the long run and will give you peace of mind that it won't fail.


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## Cotharyus (Jun 21, 2012)

Alternatively, using local woods you can harvest easily is also an option for sinking poles to keep structures in place. But you absolutely want to put something in the ground. Locally, we find fallen Cedar or Locust trees and cut posts out of them. We also use them for bridge stringers. They last quite a long time.


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## Maday (Aug 21, 2008)

Don't guess at your design. You need to work to a set of plans that are rated to the loads that your berm will likely see. If you guess that a 4x4 is needed for a post and you need something much stronger, you are going to hurt someone.


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## snug dug (Jul 7, 2012)

Maday said:


> Don't guess at your design. You need to work to a set of plans that are rated to the loads that your berm will likely see. If you guess that a 4x4 is needed for a post and you need something much stronger, you are going to hurt someone.


And those plans are available at ....Lowes?

I have a solid design, using 6x6 for support structure, etc. Intent was to see how folks anchored their structures to the ground.

Anyone using helical piles or pier pin foundations for these structures? Main thing I like with those is that the lumber is off the ground, but solidly anchored to it. I dislike the expense, though.


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## JustMtnB44 (Nov 8, 2004)

All structures we have built in a local county park near Pittsburgh, PA for a DH/freeride trail were designed to last roughly 20 years with no maintenance. That means pressure treated lumber (we don't have wood like cedar around here) with vertical support posts sunk in the ground 20-24" in a hole filled with concrete. We just mix the concrete in the hole as we go.


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## snug dug (Jul 7, 2012)

JustMtnB44 said:


> All structures we have built in a local county park near Pittsburgh, PA for a DH/freeride trail were designed to last roughly 20 years with no maintenance. That means pressure treated lumber (we don't have wood like cedar around here) with vertical support posts sunk in the ground 20-24" in a hole filled with concrete. We just mix the concrete in the hole as we go.


Thanks...that is some nicely done structure you have there in PA. My build is going to be just a bit beefier than what you have pictured.


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## Maday (Aug 21, 2008)

snug dug said:


> And those plans are available at ....Lowes?
> 
> I have a solid design, using 6x6 for support structure, etc. Intent was to see how folks anchored their structures to the ground.
> 
> Anyone using helical piles or pier pin foundations for these structures? Main thing I like with those is that the lumber is off the ground, but solidly anchored to it. I dislike the expense, though.


Those plans are available by getting out a pencil and paper, and crunching some numbers (or a spreadsheet). Just don't leave any loads out like Mr. Trotter did on this bridge jump at the 8:25 min mark.

Steve Trotter Tampa bridge swing from ON the bridge & rescue 4/27/97 - YouTube


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## snug dug (Jul 7, 2012)

Maday said:


> Those plans are available by getting out a pencil and paper, and crunching some numbers (or a spreadsheet). Just don't leave any loads out like Mr. Trotter did on this bridge jump at the 8:25 min mark.
> 
> Steve Trotter Tampa bridge swing from ON the bridge & rescue 4/27/97 - YouTube


I've put pencil to paper, but the point of this topic is not how to design/build them, but how best to anchor them, so holes and concrete it is!


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## thickfog (Oct 29, 2010)

JustMtnB44 said:


> All structures we have built in a local county park near Pittsburgh, PA for a DH/freeride trail were designed to last roughly 20 years with no maintenance. That means pressure treated lumber (we don't have wood like cedar around here) with vertical support posts sunk in the ground 20-24" in a hole filled with concrete. We just mix the concrete in the hole as we go.


Isn't the frost line 36-44 inches in pa? Do your posts ever heave?


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## cmc4130 (Jan 30, 2008)

building for the long term is great and all. but sometimes a lot of fun can be had on something _not_ intended to last long. like this . . . . just sayin' 










https://forums.mtbr.com/trail-building-advocacy/looking-info-wooden-berms-walls-824784.html


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## JustMtnB44 (Nov 8, 2004)

snug dug said:


> Thanks...that is some nicely done structure you have there in PA. My build is going to be just a bit beefier than what you have pictured.


How beefy? For reference, the vertical posts are 4x6, the stringers are 2x8, and the decking is 2x6 and some 2x8. Lots of bolts and lag screws and metal brackets holding things together as well.



thickfog said:


> Isn't the frost line 36-44 inches in pa? Do your posts ever heave?


Probably, but who is going to dig a post hole that deep in the woods by hand? It can be hard enough getting to 20 inches deep sometimes, and we might dig up to 20 holes in one day if there are enough people. We haven't had any issues with heaving yet, but the oldest structures built this way are only about 4 years old.

Picture of completed structure:


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## snug dug (Jul 7, 2012)

JustMtnB44 said:


> How beefy? For reference, the vertical posts are 4x6, the stringers are 2x8, and the decking is 2x6 and some 2x8. Lots of bolts and lag screws and metal brackets holding things together as well.


6x6 posts, 2x10 cross members, 2x8 joists, joists will be blocked between, real 2x6 rough cut deck boards, plus 5/8" diameter bolts and screws.

In that first pic of yours, it looks like the posts are angled in, rather than at 90 (plumb). Are they, or is it an illusion?


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## JustMtnB44 (Nov 8, 2004)

snug dug said:


> In that first pic of yours, it looks like the posts are angled in, rather than at 90 (plumb). Are they, or is it an illusion?


It is an illusion, we set the upright posts vertical (plumb in both directions).


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## bitflogger (Jan 12, 2004)

We take rebar and weld fender washers for massive home made TTF anchoring nails.

22 seconds into this video shows them being driven through the bunks.


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