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Author Topic: 1kw foundations size  (Read 2076 times)
mhes
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« on: August 21, 2006, 09:51:50 AM »

Hi

I am setting up a 1kw turbine on a remote Scottish island. Thus, getting sand and cement plus cement mixer is a problem as access is via a small boat. How big does the foundation really need to be? I have dug a cubic metre hole for the mast and 4 1/2 cubic metre holes for the pegs but now am faced with the huge task of filling these with cement...... any advice on the minimal amount required could save a lot of effort!

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martin
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« Reply #1 on: August 21, 2006, 10:16:28 AM »

you could try these people - they make a patented ground screw - it can be used "as is", or can be used with concrete to improve the strength - there is one British turbine manufacturer who is offering them as part of their fitting kit! Wink
http://terralock.co.uk/ Cool
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Unpaid volunteer administrator and moderator (not employed by Navitron) - Views expressed are my own - curmudgeonly babyboomer! - http://www.farmco.co.uk
Ian
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« Reply #2 on: August 21, 2006, 04:11:07 PM »

mhes - Automatic logic suggests you will need a bigger boat!

But, sinking a few blocks of concrete is the "normal" way because it is (usually) easy to get an RMC delivery and do a one-day-pour. Can I suggest an alternative (which is also cheaper)?

Try to undercut the base of the holes you have dug for the ground anchors and set your anchors in place and the more you can do in undercutting the less concrete you will need. Make sure the anchors are long enough to come to at least ground level and try to "sheath" them in something that will reduce the likelihood of chemical reaction and set them in place in the pit. Now put some rebar in (reinforcing bar) and make sure that it is not all parallel (ie 3 dimensional) and covers a good area but rises vertically so it can later be bent over and tied. Now pour a concrete base in the pit - about 4 -6 inches should be enough and allow a few days for it to cure and hold the rebar in place. Work the concrete around the rebar to make sure there are no voids. Now tie the rebar together above the base by bending and twisting it. This is hard work. Now top off with concrete so you fully cover the rebar and only have the ground anchor sticking out the top. Once hard, back fill the hole with all the earth you took out when you dug the hole and compact very well. Heavy stones are good to go back in too. Water is good at helping to compact earth (if you have it available).

What you have done is make a very strong "raft" of concrete which in itself is heavy and stable but it is actually held in place by the earth piled on top of it. You will have used only about 1/4 to 1/3 the amount of concrete you would have used otherwise.

I still think you will need a concrete mixer as this is really back breaking to be done by hand.

In reality you need to have very little support for the mast as it carries very few forces; only the weight of the generator and mast - which are not great. All you really need is a little bit of concrete to form a good base for the pivot. The "weight" is needed at the guy bases.

A 1 kW turbine is not very big really. You could probably get away with, say, 200 Kg of wet concrete at the base and a max of 500 Kg at the bases of the guys (less if you have rafted them).

I hope this helps.

Regards,
Ian
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mhes
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« Reply #3 on: August 21, 2006, 07:28:45 PM »

Ian - Fantastic reply and many many thanks. I shall follow your instructions to the letter.
If it falls down, it will probably fall onto my boat, which will serve me right  Shocked

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