The number one question we receive about our no-dig fence installation system is "How strong is it?". We understand the concern as traditionally posts are set in holes dug to a specific depth and then filled with concrete. If any one has ever removed an old fence post set in the proper amount of concrete, it leaves a lasting impression as to the weight and strength it provides.'
The synonymous relationship between fences and concrete.
Concrete is, and has, always been assumed that it is used to anchor the post into the ground. It is what gives the post it's strength. I imagine Tim "The Tool Man" Taylor, from the old sitcom Home Improvement, making his manly grunting laugh as he imagines the perfect, 30" deep, 12" round slug of concrete that a traditional 4x4 post would be set in.
Concrete was not intended to be used to add weight to a fence post, anchoring the post into the ground.
The Real Reason We Used Concrete
When a hole is dug, whether using post hole diggers, a spade bar, shovel, auger, or even your hands, the soil is disrupted around the outside diameter of the whole. You will not be able to compact the soil enough to achieve true compaction with soil alone. Hence the reason homes settle.
What will compact is concrete. Concrete being a mix of cement, sand, and agregate (stone/rock), is able to be compacted back into a hard surface. These materials are able to essentially "lock" themselves into each other. After we have dug the hole, we then add the concrete to replace the disturbed soil to prevent settling as much as posssible.
When we drive a post directly into the ground, that post is being forced into the soil. Imagine filling a bucket full of sand and attempting to stick your finger into the middle. As you force your finger in, the sand is being compressed and compacted into the sand around it. In the same way, as we drive our posts into the ground, the soil's compaction is being increased.
With our Ga Red Clay, we have driven i-posts as little as 12 inches when we first started testing the system. When we attempted to remove those posts, we ultimately damaged the post prior to it being removed, and that was with the intention of working out spacing with our jig, not setting posts for strength. Now, with our fence installations, we always drive a minimum of 30" in hard, established, compacted soil. If we find ourselves working in backfill conditions, or areas that may have a lot of gravel, such as against retaining walls, we will increase the length of our posts therefore increasing the depth they can be driven.
Take a look for yourself!
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