Home made concrete slab bridge across stream

AilbeL200 · 29-01-2015 10:25PM #1

I am considering building a small bridge across a small narrow stream using a single slab of concrete. The slab will be about 8ft long to span from bank to bank, the width 10ft and thickness 6in. I will need to drive a small tractor and trailer across. I was curious if I could build a form out of plywood on level soil and lay rebar mesh inside it and then fill it with concrete, and when cured drag it into place with tractor. My question is would this hold or would a reinforced slab like this break in the middle without major beams supporting it like the usual bridges you see? The base of slab would be approx 2ft off the top of stream. Thanks for any opinions.

mayota · 29-01-2015 10:33PM

AilbeL200 wrote: »

I am considering building a small bridge across a small narrow stream using a single slab of concrete. The slab will be about 8ft long to span from bank to bank, the width 10ft and thickness 6in. I will need to drive a small tractor and trailer across. I was curious if I could build a form out of plywood on level soil and lay rebar mesh inside it and then fill it with concrete, and when cured drag it into place with tractor. My question is would this hold or would a reinforced slab like this break in the middle without major beams supporting it like the usual bridges you see? The base of slab would be approx 2ft off the top of stream. Thanks for any opinions.

Safer to use a couple of tractor gang slats.

_Brian · 29-01-2015 10:59PM

Big difference in what your describing and a pre stressed cast slab.

I'd say buy some pro made as suggested above as it will be stronger and last longer.

Reminds me if a river crossing I saw on a farm in France. 20ft steel container, door off one side and the other end cut open. Spanning 10-12 ft small river.
Seemed to just be for stock and a quad though.

Username John · 29-01-2015 11:01PM

What about the bank? If you had big weight on it, wouldnt it collapse?

Milked out · 29-01-2015 11:13PM

Could you get a number of large concrete pipes and sit them into the stream then fire up shuttering over them and pour the concrete on top of the pipes. Could sit a few posts along the side then as well to allow cattle over it without fear of them jumping of the side

Genghis Cant · 30-01-2015 12:02AM

Milked out wrote: »

Could you get a number of large concrete pipes and sit them into the stream then fire up shuttering over them and pour the concrete on top of the pipes. Could sit a few posts along the side then as well to allow cattle over it without fear of them jumping of the side

Careful with instream works. It could fall foul of Fisheries legislation. Or it may not. One way or another you need to be sure of the answer before you proceed.

ford 5600 · 30-01-2015 12:18AM

Could you get an old lorry body and use it as the bridge? I have seen it done several times for that purpose, but on a wider span than you are talking about.

Another option is shutter the two banks , and backfill it with mass concrete, then put ply across the top,acrow it for support, throw a bit of rebar in , and pour the top then.

Farmer Pudsey · 30-01-2015 05:20AM

You can get Corri-pipe now in diametre's up to 2'. I would consider a length or two of this. I imagine if as you say it is a small streme the bank slopes down to it.. If the pipes are suitable no need for concrete just fill up with stone and earth to make bridge. Use a bit of concrete at the sides to make ends stables. If stremem is 8' wide this may not be suitable. However it is not cheap

http://www.jfc.ie/CorriPipe&Fittings.html

Victor · 30-01-2015 07:28AM

And then we wonder about things like this: http://www.irishtimes.com/business/agribusiness-and-food/farm-fatalities-far-more-likely-than-in-other-jobs-committee-told-1.2084574

Genghis Cant wrote: »

Careful with instream works. It could fall foul of Fisheries legislation. Or it may not. One way or another you need to be sure of the answer before you proceed.

Also rules on drainage and you just might need planning permission.

You can get culvert units from most pre-cast concrete suppliers.

onyerbikepat · 30-01-2015 09:12AM

You'd far better off buying something designed and fit for this purpose. Culverts are ideal. So what if you have to dig back the bank a bit to fit it in. The culvert should be load rated aswell.

If you do decide to make a slab yourself, remember that the rebar will be needed most lengthwise, across the bridge as this is the direction of the greatest load. Also keep the rebar down low. Rebar say 3 inches down in 6 inches will be useless as the stresses here are near zero.
How much rebar you need, what size, what depth of concrete, how to cure etc etc. That's a job for a civil engineer.

I've seen concrete pillars put down across a trench like this in soft land. A few years down the road, the pillars had sunk and when cleaning the trench, the digger couldn't get in under it to clean it.

Farmer Pudsey · 30-01-2015 09:18AM

This is not a huge engineering job TBH depending on stream. If stream is 8' wide at the bottom then yes it is a fairy big job. However if stream is narrower at the bottom. OP said slab is 8' therefore I imagine stream is 4-5' wide at top of bank and is more than likly narrower at bottom. Bigges issue is to allow water through at times of flood. However I imagine that planned crossing point is on a flatish bit of ground.

I be slow goung for a slab or cattle slats to do this. A small crossing point is unlikly to effect fish life and is unlikly to require planninf. I presume that OP is not goind digging or deeping stream. Corripipe is best option 1-2 withs should be adequate and case side. I would go 12+ feet of pipe and build sides with stone if not deep (1-2') or case with concrete if deeper than this and then fill with stone. Ideally you do not want this to have a dam effect at times of flood so look at volume taht is normal during flood and choose pipe size to suit.

frazzledhome · 30-01-2015 10:18AM

Fire a length or two of Jfc into stream, if stream is bigger 4*1m concrete liners then tip 1-2 lorry loads on top job done. No retaining walls, have some here cows cross twice daily as well as some big machines

I often marvel at people's ability to complicate the shyte out of life.

foxy farmer · 30-01-2015 12:04PM

Pour a decent concrete footing back from the edge on both banks. Lob in a few second hand hollow core slabs cut to length on the footings.
100mm Screed of concrete on top.
No obstruction to water flow.
No pollution issues.
Homemade slab could be done but would need ribs underneath for strength. Concrete strength and rebar would be important.

onyerbikepat · 30-01-2015 01:26PM

We have low lying corcas type land and have bridges like these. They were all done maybe 15~20 years ago. All the neighbours have the same. Trench dug, concrete pipes maybe 3 or so placed end to end. Filled on top with stone. Years later and a lot have side walls falling in. Pipes also loose alignment as they sink over the years. In reality most of them are holding back water. With a little bit more effort and cost at the time, they would still be fine today.
Do the job right and do it once!

severeoversteer · 30-01-2015 07:06PM

i think you should ring someone like oran precast, moylough concrete, and get a few slabs of hollowcore

they are 1.2m wide so for your case you would need 3 of them to give you 3.6m width

if the stream is say 10 foot wide and to be safe id get 18 foot long slabs

this would mean they are sitting on 4 foot ledge each side to help insure against the bank being eroded and the bridge falling in.

you could get them delivered and lift into place with a teleporter or digger, if the river is in a way a lorry can drive beside you could even crane them off the lorry with a hiab

this would mean you are not pouring concrete over the river which is a big no no, you could get a big fine if caught

mf240 · 30-01-2015 10:30PM

frazzledhome wrote: »

Fire a length or two of Jfc into stream, if stream is bigger 4*1m concrete liners then tip 1-2 lorry loads on top job done. No retaining walls, have some here cows cross twice daily as well as some big machines

I often marvel at people's ability to complicate the shyte out of life.

No no no. You need an engineers report. An envoiremental report. A fish census . And then a tribunal.

Youll have to block all trafic within one mile of the project while its ongoin and will have to wear a hard hat and a hi vis jacket at all times.

foxy farmer · 30-01-2015 10:34PM

mf240 wrote: »

No no no. You need an engineers report. An envoiremental report. A fish census . And then a tribunal.

Youll have to block all trafic within one mile of the project while its ongoin and will have to wear a hard hat and a hi vis jacket at all times.

And if the botanists find a rare snail worm or beetle you can kiss your river crossing goodbye. It'll become an SAC.!

Genghis Cant · 30-01-2015 10:42PM

foxy farmer wrote: »

It'll become an SAC.![/qwote]

For all we know it could be one already. I don't want to sound like a broken record, but be absolutely sure before you wet a bucket where you stand legally. I've seen situations like this get very messy.
On the other hand, handled correctly I've seen them carried out seamlessly.

Nekarsulm · 30-01-2015 10:53PM

or have a look and see if this lad has anything that might suit.....

http://www.donedeal.ie/farmsheds-for-sale/precast-for-sale/8534889?offset=8

Miname · 31-01-2015 08:17AM

Two of those beams in the last pic and a few slabs and Roberts your mothers brother.

onyerbikepat · 31-01-2015 09:04AM

There was an estate Waterways Estate Sallins, Co. Kildare, that flooded from 'An inadequate and partly blocked Culvert'.

"The Waterways flooding has notable aspects, one being that it was entirely avoidable. The flood was not caused by a large river breaking its banks or by virtue of the estate being built on a flood plain. It was caused by an inadequate and partly blocked culvert. The flooding of houses up to a depth of 4 ft. lasted from the morning of Sunday, 21 November until the evening of Tuesday, 1 December. A blocked culvert under the road was identified as the cause."

http://debates.oireachtas.ie/dail/2010/02/04/00023.asp

Nekarsulm · 31-01-2015 09:25AM

onyerbikepat wrote: »

There was an estate Waterways Estate Sallins, Co. Kildare, that flooded from 'An inadequate and partly blocked Culvert'.

"The Waterways flooding has notable aspects, one being that it was entirely avoidable. The flood was not caused by a large river breaking its banks or by virtue of the estate being built on a flood plain. It was caused by an inadequate and partly blocked culvert. The flooding of houses up to a depth of 4 ft. lasted from the morning of Sunday, 21 November until the evening of Tuesday, 1 December. A blocked culvert under the road was identified as the cause."

http://debates.oireachtas.ie/dail/2010/02/04/00023.asp

If a farmer had built that culvert, it would have been done right!:D
Instead you had Co.Council's, Engineer's, Architect's, Developers, Plant Hire firms and Sub Contractors involved, and it floods!

Victor · 31-01-2015 09:38AM

foxy farmer wrote: »

No pollution issues.

Not necessarily. Both soil and concrete entering the water can cause pollution.

foxy farmer · 31-01-2015 01:10PM

Victor wrote: »

Not necessarily. Both soil and concrete entering the water can cause pollution.

My suggestion didn't involve interfering with stream bed or the banks so pollution would be minimal. Certainly less than pipes and filling.Footings on hard ground back from the banks.
If the stream is marked on a map don't interfere with it by putting objects in the water.

milkprofit · 31-01-2015 06:04PM

AilbeL200 wrote: »

I am considering building a small bridge across a small narrow stream using a single slab of concrete. The slab will be about 8ft long to span from bank to bank, the width 10ft and thickness 6in. I will need to drive a small tractor and trailer across. I was curious if I could build a form out of plywood on level soil and lay rebar mesh inside it and then fill it with concrete, and when cured drag it into place with tractor. My question is would this hold or would a reinforced slab like this break in the middle without major beams supporting it like the usual bridges you see? The base of slab would be approx 2ft off the top of stream. Thanks for any opinions.

If river small -like 2 ft deep slope banks and drive through water

AilbeL200 · 03-02-2015 09:24PM

Thanks for the advice received so far. At this point in time, I am thinking of going with building a 'wall' foundation in each bank , about 2400mm long, 600mm deep and 125mm wide. I will put rebar into these walls. I will then put three concrete lintels across the stream, resting and recessed into the walls. Each lintel will have two strands of rebar, and will be 2400mm long, 200mm wide and 65mm deep. I will put up formwork across the stream and build a slab 2400mm wide and 2400mm long from wall to wall across the stream. I will mix the concrete on site and lay it on the rebar mesh. The slab will be approx 150mm deep. The mesh will be 50mm from bottom of slab. It is a job for the summer, as the land is too wet until then.
I estimate the costs as follows:
I will need approx 1m3 of concrete which equates to 2ton of gravel and 10x25kg bags of cement.
2 tonnes of gravel = €35
10*25kg of cement =10*5=€50
Sheet of 2440mmx2440mm mesh =€40
Buy 3 lintels =3x20 =€60
Shuttering ply, 3 sheets of 2440mm x 1200mm x15mm = 3*25=€75
2 lenghts of 6mx12mm rebar =€16
Hire of cement mixer for a day (maybe 2 days!) €50
4 lengths of 4.8m x100mmx50mm of rough timber =€30

Total approx €400
I can't post photo of stream (need 50 posts)

Home made concrete slab bridge across stream

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