Railway sleeper primary school dipping pond project

Got a project coming up where I need to build a dipping pond from sleepers for a primary school

Luckily they’ll be new softwood sleepers…so relatively easy to work (stored outside of course, so moisture content unpredictable)

So I thought of a large biscuit joint in a routed slot to aid lining up and construction, especially to get the neat faceted top, but it could also potentially work for the sides: leaving a nice mitred joint effect with no cut end grain exposed. Will aim also to have no visible fixings on the top as children will use this to lean on and dip the pond for wildlife

Construction is 200x100 softwood sleepers in different configs: sides are largely 100x200, top is 200x100, rough overall dimensions: 4000 x 2400 x 600mm

I’ll be building this with volunteers so like the idea that I can get them cutting batches of identical parts to construct the outer frame

There will be long screws as mechanical fixings, but I’d like the timber joints to be serving a mechanical purpose containing the 5 tonnes of water (it works fine when you overlap sleepers in a rectangular brickwork construction with bolts through overlapping sleepers)

Thoughts?

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I havent done this before but am doubtful and I would not trust biscuits for a permanent installation

I assume you want a wood exterior ? if that can be compromised - you could put internal steel brackets in and use coach bolts all the way through

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I’ve had a go at something (alot less elaborate) before Dermot. I put rebar through the whole thing…
As you want an unmarked top, you could cut off the rebar and slot the top layer, with holes therein, ontop of the bars.
Good luck with that venture. Ive never seen a straight sleeper yet…

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I’m going for something very similar!

Even if they arrive straight… they’ll probably twist a fair bit in the drying?

EDIT: P.S. in the name of practicality (bring able to build it in a weekend with volunteers) I’ve sacrificed the dream of mitred corners with no exposed grain…it’s doable but about double the work…the coping layer will probably be biscuit jointed though

Starting to take shape now…

A.weekend working with primary school parents was pretty productive…in spite of the showers

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Nice! Great work!

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It’s about 1/3rd bolted together (parent turnout was very low on a wet Sunday afternoon)

Some finishing details…

Couple more hours bolting together, then cut the coping, final levelling (anyone got a laser level I can borrow?), then line and fill it with water and fit the coping, and then build up an island with a ‘beach’ using local soil (for the crawling/hopping things to use), create a slope down to a bog garden on the left side…add some plants and see what wildlife appears!

My laser level was somewhere in the space. I lent it for arch works and didn’t recover it. If it’s still around of course you can borrow it!

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That’s about where I got to before I found out it was isolation time. Top is glued on with PU glue, although it was pretty impressiven when just held on by the studding ends friction fitted in to the coping by 50mm. Had to belt them with a hammer to free them!

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