Sorry for the long post, but here it goes: I constructed an 18'x18' shade sail in my back yard a few years ago. One side is anchored into the rear of the house, and the other extends over the patio to two steel poles anchored 4' into the ground with 300+ lbs of concrete each. Tensioning the sail puts a lot of force on the anchor points and poles, of course. Everything was okay until a freak hail storm deposited several hundred lbs of ice on the sail. When I got home, the sail was sagging under the weight of the ice and nearly touching the ground! Needless to say the poles were pulled inward toward the house (the steel within the concrete footings was fine, but both the steel and concrete was pulled inward in the soil like a popsicle stick in the ground). Whereas previously the poles were angled out 5 degrees, they are now vertical, if not angled in a degree or two. They now have play in the ground, and I cannot tension properly anymore. The only thing I can think of is to put countertension on the poles in the opposite direction of the sail by driving earth anchors into the ground and attaching them to the poles with wire cable. I don't want to do this for cosmetic and safety reasons (someone could trip over the wire going from the pole into the lawn). Any other thoughts??? Thanks
I have not studied your site and I am not an expert in this field. These are just the rantings of a lunatic mind.
The footers for your poles are way too small as you already know. How tall are your poles above ground, and how much pole is buried in the footer? What size are your posts (dimensions)?
I'm assuming you used 4 diameter schedule 40 steel tubing. A general rule of thumb is 2/3 of the post is above ground and 1/3 below. So, if your sails attach to the poles 10ft above ground there should be 5ft of pole underground. You could dig around your existing footing creating a new larger hole of a more proper sized footer. Brace your posts in the proper position and pour new concrete around your old footers. As a minimum I would go for about 9 cubic feet of concrete (1'350 pounds) per post in a hole about 18 square by 48 deep. The depth is important. If yours are shallower or don't meet the 2/3 above, 1/3 below guideline I'd go bigger on the concrete to provide a broader footprint.
Just a jump in, but you do have a method of removal of this sail, right? I mean, Colorado....snow.....heavy. I know you said it was a freak hail storm, so that may explain it, but I was just curious. PD has good ideas rectify what you have, aside from starting over, which I know you don't want to do. I agree with not having the tether lines.
Oh, welcome to the forums!!
Thanks for the replies. A little background: I used steel posts, not poles actually, and I had them custom weld rebar at right angles at the base to grab into the concrete. I have 4' underground and 12' above. The steel and concrete are very solid. I think the main reason it failed is that I didn't auger the holes for the footers, but dug by hand. As you can imagine, I had to dig an ice-cream-cone-shaped hole in order to reach 4' deep (hole is wider at top then base). I then put the steel in a cardboard cylinder footing and then the concrete. Had I used an auger to reach 4', the soil around it would be firm. Therefore, I am reluctant to dig it out again and decompact the soil even more (it has compacted, but shifted with the weight of the ice). Yes, I remove in winter and put back up in spring--this was a summer hailstorm, so impossible to predict before going to work.
I think you may have been fine if you had not used the tube as a form around the posts. It severely limited amount of concrete and has it bearing on soft soil. It sounds like you have good depth on the poles. Is the site accessible to a ready mix concrete truck? How much work money are you willing to put into the repair?
The proper repair would be to remove the poles, re-dig the footer holes and hold the posts in position while you completely back fill the hole with concrete. It would some machinery to get the old poles out. Then hand dig or use a large machine mounted auger to dig the new footer hole. Place your old pole back in the hole and brace it in position and fill the hole with concrete with no back filling except for a layer at the surface for your lawn or landscaping.
A 2nd choice is you could dig around the posts as deep as your willing. Wiggle pull the poles to the correct position and brace them and fill the hole with concrete. Again with no back filling of dirt except at the surface. The level of success will vary with the amount of digging and concrete you are willing to invest.
Another option depending on where you live is to look into grout injection like is used for foundation repairs. It would only be an option price wise if there is someone close by otherwise I think the cost could skyrocket for such a small job. Get the posts in the proper position and give them plenty of time to work your little job in as fill work on a slow day and you might get the price down some.
thanks for the input, will keep you posted on the fix.
I'm on the opposite end of the situation. I have a couple shade sails at my place and I engineered the footers to commercial standards for a hundred year storm so there is an obscene amount of concrete in my back yard. The sails will fail long before the poles or their foundation. At least I tried to think of future owners a little bit. The concrete is 6 below grade so they can cut the poles off flush with the concrete and landscape over them. I know there is no way anyone will be willing to remove the footers. If there is a tornado we are going to leave the basement and chain ourselves to the poles. Aliens, thousands of years from now will excavate my back yard and wonder what those blocks of concrete were for.
Ha! That's great!
Do you have any pics of your project, specifically the footers? I'd like to see them. I don't know many people who have done this project. I'm still thinking of anchoring tethering lines (like you see on power lines). May also order a smaller sail so less tension is needed to pull it flat, but will lose shade acreage under the sail if I do that.
Not sure on best solution.
catalpa,
See PD's thread Need mat'l ideas for pics of his back yard with the shade sails in place. Might be worth a PM to Pilot Dane to get the details.
catalpa,
Maybe a horizontal support off the back side the pole (opposite the sail maybe a foot or 2 below the top) and a wire going straight up from the ground to the support then angled up to the top of the pole would work. The utilities do that out here when the support wire crosses over a sidewalk. This will reduce the clothesline effect and you could put a planter of something around the wire where it enters the ground so it is more visually appealing.
Boy am I glad I went ahead and did full, proper footers for my shade sail posts. I left the sails up for Hurricane Irene since we are well inland. Several times I looked outside and was surprised to see the 4 schedule 40 posts flexing so much. They sprung back straight but it's just funny seeing something so strong flexing like that and my sails are not that big. Now I know why they use such massive steel and fittings on the larger commercial installations.
Tags: shade, sail, poles, with concrete, back yard, above ground, fill hole, fill hole with, fill hole with concrete, hole with, hole with concrete, amount concrete, anchored into, around posts
