*Tower Base & Anchors*
This base and anchor is designed to support 130' of Rohn 45 tower. It has been *slightly* over engineered.
A hole was dug five feet deep with a backhoe and ledge was found. Ledge is good as it doesn't move. The tower won't sink. Due to heavy rains the hole filled up with water and had to be pumped out before I could put the sono-tube in for the cement. The tube is 30 inches diameter and 4 feet tall.
Once the hole was empty I put the tube in and started backfilling it. The tube is higher out of the ground than I wanted because some of the dirt fell back in the hole. It's not a big deal. This tower might sink a few inches, but will stop when it hits the ledge.
After backfilling the tube I inserted the rebar cage. The center pin and lift pin were wired to the top of the rebar before pouring cement. Both are secured to rebar and angle iron so that they can't be pulled out of the concrete.
The rebar was slightly taller than the tube because of the hole filling itself. If I wasn't in a crunch mode with the cement truck I would have cut them down before pouring, but that's all right. They make sawz-all blades every day. After the cement dries just cut them off and if you're fussy, slap some concrete patch on top of them.
Now this is how to pour cement!
The center pin keeps the tower base from being able to kick to the side. The lift pin can be seen on the left side of the left picture, it has an eye in it. This is to attach a block (pulley) to for hoisting tower sections so we don't have to be putting a sideways strain on the tower base.
When the concrete dried I peeled the sono-tube down to the ground and then finished backfilling.
One concrete anchor had to be used. Two anchor points are done with rock anchors because the ledge was so close to the surface. (Drilling ledge and inserting rock anchors is covered in an article inside the Rubicon.) The third is six feet deep to ledge.
Installing a rock anchor
A rebar cage approximately 4x3x3 feet cage was built and we used two concrete anchor rods.
Anchor rods in cage ------------------Pointed toward new tower location
Before pouring concrete I pumped out the anchor hole. Then we emptied the cement truck on top of the cage. After it hardens up simply backfill the hole. That puppy ain't goin' nowhere.
Two anchor rods
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