DIY Doctor

Laying a solid block of concrete for ground anchor

Postby RobJ » Sun Apr 06, 2008 2:35 pm

I am hoping someone can help me with this.

I need to put a ground anchor in my shed to lock my motorbike to.

The flooring in my garage is a simple screed layer no more than a few mm thick. I want to dig out a section 0.5mx0.5mx0.5m and fill it with a dense block of concrete mix (with gravel presumably?) that will give a really dense block into which I can fit the ground anchor.

I am no good at DIY and have never done anything like this before.

Could someone please tell me in simple terms what I need to do? I am obviously wary of a finish that will crack and be useless. It's got to give a REALLY strong grounding for the anchor.

Your help would be very much appreciated.
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Simply Build It

Postby thedoctor » Sun Apr 06, 2008 3:20 pm

See the projects section for concreting a fence post and cut the post off about 600mm above ground level With the concrete holding the post in you can bolt a very strong staple (follow link below) to the post which will allow you to chain the bike with ease.
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Postby RobJ » Sun Apr 06, 2008 5:28 pm

Thanks for the response.

I have looked at the project as you suggested and am unsure it's what I need.

This is the ground anchor I need to set
From looking at the concrete mixing page it looks like I need a C35P mix? I think that's 1 cement -1 stone -2 sand?

I think .5mx.5mx.5m should be sufficient so that gives me 0.13m3

What I can't figure out is how to distribute those elemtent into an overall amount I need?

2 bags cement, 2 bags stone, 4 bags sand? How much water? I can't find a calculator on the net which will tell me how much I need altogether to fill this space with C35P mix, or if that is even the right mix to use.
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Postby chris_on_tour2002 » Tue Apr 08, 2008 9:01 am

the quantities you suggest sound about right - better to have too much, you want to make it in one batch. if you have to add another batch you could weaken the end result. with regard to the amount of water, the less water the stronger the mix. i would add just enough water so that it looks dark but not so it has the consistency of mud. so it looks quite dry but will stick together in a tight ball if you squeeze it in your hand.
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Postby yappaty » Tue Apr 08, 2008 9:12 pm

I did a similar thing a couple of years ago, using an Oxford TerraForce anchor. My bike was parked on a strip of land beside my house, which I had laid paving slabs on.
I moved one pair of adjacent slabs about the same width apart as the eye of the anchor, then dug a large hole underneath the slabs, filled it with several bags of ready mixed fence post mix (the stuff with aggregate) and stuck the anchor into it.
To make it harder for someone to attack it directly or break it out I recessed the eye so that the top was level with the top of the slabs, smoothing the concrete into a gentle slope from the edges of the slabs down to the eye of the anchor (and including a hole for rudimentary drainage). This had the added benefit of making it much easier to feed the chain into the eye of the anchor.

On a side note, I had a couple of expensive mountain bikes in a shed that I needed to secure, so I filled a tall plastic bin with concrete (reinforced with chicken wire) and put an anchor in the top of that. I think it weighed about 75kg. On the advice of my insurers I then got 4 hefty L brackets, screwed them into each side at the base and then screwed them into a thick piece of plywood that was wider than the door to the shed (so it couldn't be slid out of the door). And just to be safe I drilled out the screw heads. It survived one attempted theft (they went for the lock instead of the anchor and failed miserably) and took me about 2 hours to take apart when I moved house.

Have fun :)
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