Setting fence posts in saturated soil

15 years ago

Has anyone experience with how to set a 4X4 PT 8-foot tall wood fence post into wetlands soil?

I need to fence off a wetlands from marauding ATV's that ran down by wetlands. I want to use a post and 3 rail horse fence as a visbile and physical barrier.

In the post holes, groundwater is encountered about 1-foot below groundsurface.

Any suggestions are welcome!

TIA

Isabella_ma

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Comments (8)

deep_roots
15 years ago
isabella_ma,
I have rounded wooden fence posts that have lasted several years submerged in water. However, eventually wood rots. Even treated lumber will not sustain submerged conditions. Aluminum poles with pier augers are longer lasting. If you are bent on using wood, I would suggest reading up on how quick set concrete can be used for the base of your posts, as is done with building docks in lakes for boats.
isabella__MA
Original Author
15 years ago
Thanks deep roots,

I'll be using wood as it's in the upland portion of a wetlands, and retaining the natural feeling is a desired goal. I have gotten some furhter advice from my construction friends that concrete actually cures very well in saturated soils/groundwater. So I'll be putting in concrete piers with 4X4 metal post attachements on the top. The piers will be made using a sono-tube concrete form to prevent hole collapse in the saturated soils and to prevent phase separation of the cement components which may be caused by pouring them into standing water. The peirs will be constructed to be a few inches above ground level (in case of seasonal flooding), which will keep the post dry. These posts may actually last longer then the other posts installed above the groundwater level!!
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What you are suggesting sounds good. When using wood posts, even the pressure treated ones will rot sooner in wet ground, so if you pour a cement footer and attach the post where it will be above the moisture, it will last a full life. Other alternatives are to use steel posts which will take much longer to rust away than wood posts will take to rot, or use cedar posts. Cedar lasts almost forever in difficult conditions, is nearly indestructible (and difficult to hammer staples into).
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The bar they mentioned is called a "San Angelo bar" around here, at least - that may help you locate one. HOWEVER, I still don't find them very useful for seriously rocky ground. (They are good for hardpan.) If you can't find a San Angelo bar as such, you may be able to find a six foot straight pry bar, used by riggers for loading heavy stuff - it's better steel and will cost more, but works just as well. I've tried using a bulb-planter auger in a large electric drill, and you'll spin, pretzel or break it in this kind of soil. However, one thing to try would be the smallest possible auger size in a large gasoline-powered auger. Another trick is to use an SDS-Max masonry bit in a rotary hammer. And I just saw a manual rotary post-hole digger, of the manual kind, with a very small but heavy set of blades - will cut a three inch bore or so. However, the one I saw was priced at 95 dollars!
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Hi, I'm building a fence here in sunny southern California. I'm using con heart redwood 4x4 posts. I've found some conflicting theories about how to set the posts. Some say concrete, some say gravel... and I'm looking for some advice on what wood protector to use for the base of the posts. Because my soil is heavy clay and the drainage is poor, I don't think gravel is a good idea, it'll just create a cauldron of water for the post to soak in after it rains. Even though concrete doesn't seem much better, I think that's the way I'm going to go. I'm definitely going to use about 6" of gravel at the bottom of the hole, and make sure the base of the post is set in an inch or two of said gravel before the concrete goes in. Since the fence is going to be unpainted and I want the natural look of the wood, I'm avoiding using PT wood for the posts, and I've had recommendations to use either asphalt emulsion (Henry 107) or Woodlife Copper Coat green to coat the part of the post that's going into the concrete. The Henry seems like a waterproof coating, while the copper is more of a wood preservative. It doesn't rain very often here, but when it does the posts will get a good soaking, and the ground will take a while to dry out due to the poor drainage. Some say that the Henry 107 will cause water to get trapped inside the wood below ground, accelerating rot. The copper coat would at least allow the wood to "breath" a little and allow it to dry out during our long periods of no rain. I know no matter what I do these posts may only last 10 years or so, but I'm looking to give them the best protection to start with, so they'll last as long as possible. Thanks for any input!
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The 3 to 4 foot depth may be needed for corner posts or those on either side of a gate, especially in an extremely windy location, but is excessive for the line posts. Two feet in the ground is enough. The usual recommendation is to tamp the bottom of the holes well, then add a minimum of six inches of gravel to the bottom for drainage. Concrete is then poured into the hole, tamped and the top sloped away from the posts to shed water. You could, if you're really ambitious and love to dig holes, install Sonotubes and above ground hardware to hold the posts. This would give as close to a rot-proof installation as possible, but would require a lot of concrete and a huge excavation project. Otherwise, Sonotubes are not needed at all. Pressure treated posts listed for ground contact and installed as indicated in the first paragraph above will last for a very long time.
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charlie1949
15 years ago
What about using the metal bases that are pounded into the ground and then the post is attached on top. I have seen these at Lowe's. These are most often used for mail box posts, but may work for you.
isabella__MA
Original Author
15 years ago
I was looking at that set up, but I was concerned about the metal rusting out over the years. These fence is in an uplands area and depth to groundwater is only about I want to minimize the amount of disturbance to this environment, and to keep the ATVs from doing the same.

The engineer types at my office have said that concrete cures better in saturated soils than in dry soils.

A bit more expensive and time consuming, but within my skill-set.
wally_1936
15 years ago
Swamp cedar will last a little longer.
nornster
15 years ago
We have wood posts driven into the ground with metal spikes into our very wet yard, and I can confirm that they've been there for eight years or so, and they have really started to rust - some are almost completely rusted out. We thinking of redoing with concrete, too.
PRO
Central Valley Fence
7 years ago
With a water table/marshy soil concrete is

an absolute and watch this video!
ken_mcdonnell
5 years ago
Here's a way to prevent decay for your fence, deck, pole barn, etc.

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Setting fence posts in saturated soil

Comments (8)

deep_roots

isabella__MA
Original Author

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charlie1949

isabella__MA
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nornster

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Setting fence posts in saturated soil

Comments (8)

deep_roots

isabella__MAOriginal Author

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charlie1949

isabella__MAOriginal Author

wally_1936

nornster

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ken_mcdonnell

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isabella__MA
Original Author

isabella__MA
Original Author