In-ground anchor

[lumberjackson]

Does anyone have any experience, concerns, or thoughts regarding an anchor made from concrete? I want to make an anchor by digging a hole and filling it with about 500 pounds of concrete and setting a piece of hardware in it to use as an anchor for a rope swing I set up in the summer.

I know that life support gear needs to have a minimum breaking strength of 5300 lbs, and I know that 500 pounds of concrete would definitely be pulled out of the ground before 5300 pounds of force would be exerted.

Attached is a drawing of the life-support portion of the swing. Anchoring the 2:1 MA system to the tree that the pulley is in is what has been done in the past, but because of lean, the rope rubs on the tree and I am concerned about abrasion because of the high use the swing gets.

I (probably ignorantly, which is why I am posting) think that it would be safe to use a concrete anchor here as long as the hardware is well embedded in the cement, which I plan on doing by using rebar that is welded together, because nobody will be generating near enough force on this swing to pull up 500 pounds of concrete.

What do you guys think?

 

[Tom Dunlap]

check out Duckbill Earth Anchors. They're inexpensive and easy to install. I'm sure that the engineers can tell you how much load they can handle if they know your soils.

YOu could setup two or three anchors and join them to get enough strength.

Google: US Army Rigging Manual FM 5-125

This is a good intro to all sorts of rigging.

Is there some reason you can't attach the anchor to one of the trees?

 

[moss]

Would be an interesting experiment to anchor to a 500 lb. weight NOT buried in the ground. Bounce the hell out of it and see what happens. Assuming the attachment to the anchor is life-support rated I don't think you'll be moving it much. -AJ

 

[Tom Dunlap]

500# of water is only about 60 gallons. Not too hard to find a dozen 5 gallon buckets and do some rough tests.

 

[southsoundtree]

Only half the participant weight will be on your counterweight/ concrete anchor.

The life support requirement is for employees at work at a company.

Solid hardware in heavy concrete would be fine, IMO.

Even if it starts to move, it isn't going to break. You'll be dragging feet, maybe.

 

[lumberjackson]

Thanks for your thoughts, guys. I just wanted to make sure I wasn't overseeing something dangerous. I'll let you know how it works out.

 

[Norm_Hall]

In the sandy soil of Lake Michigan, in Northeast IL, we would dig "bell" shaped holes and fill with concrete as an anchor for stabilizing trees.
Our best was a 25" linden that was uprooting and at about a 15* angle. Using the bell shaped holes, with 1" threaded rod and amon eyes, it was pulled vertical and anchored.
See attachment.