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MJCM

Concrete slab (supporting Water Tanks) on new landfill.

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Need your advice please.

 

We are thinking of building a concrete slab (1,40 width and up to 20-30 meters in length) to put water tanks (each are 2500 Liters) on (rain water collection). The main problem, why I need your advice, is that land has just been raised (1-1,5 months ago) up 1,2m so the slab will sit on this new land fill.

 

As it's new land fill, we are afraid the whole slab will sink when the land fill settles.

 

Is there a way to prevent this?

 

Any thoughts?

 

Thanks in advance.

Edited by MJCM

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Compress it the best you can, if you got time you can use water to help. Then dig a trench lengthwise down the middle and pour a beam down the with some rebar in it A 15x15 cm beam beneath another 10 cm thick pad with mesh in it should be fine. If you want to be extra sure make two beams under the long sides instead of one down the middle.

Edited by canuckamuck
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My advice would be get a civil engineer to look at it and advise accordingly. 

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Any hire places around you with a vibrating roller,you will soon seen if land starts to slump as normally you would build up and compact in several layers.

If not a roller available,see if you can get an excavator to walk back and forwards.

Edited by farmerjo
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thx @canuckamuck and @farmerjo

 

Vibrating Roller I know where to get, will go there tomorrow to rent one.

 

@canuckamuck

 

How deep should the trench down the middle be approx? Just under the intended slab or ...?

 

Thought of pouring around 20-30cm thick concrete for the slab. CPAC is not that far away so very easy to get their trucks in.

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21 minutes ago, MJCM said:

thx @canuckamuck and @farmerjo

 

Vibrating Roller I know where to get, will go there tomorrow to rent one.

 

@canuckamuck

 

How deep should the trench down the middle be approx? Just under the intended slab or ...?

 

Thought of pouring around 20-30cm thick concrete for the slab. CPAC is not that far away so very easy to get their trucks in.

You could land a jet liner on 30 cm. 15 would be sufficient especially if you make the foundation I suggested. The trench will be the size of the concrete beam you pour, so 15 deep and 15 wide would do it, but if money's no object you can go as big as you like.

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1 hour ago, MJCM said:

We are thinking of building a concrete slab (1,40 width and up to 20-30 meters in length) to put water tanks (each are 2500 Liters) on (rain water collection). The main problem, why I need your advice, is that land has just been raised (1-1,5 months ago) up 1,2m so the slab will sit on this new land fill.

 

As it's new land fill, we are afraid the whole slab will sink when the land fill settles.

Your current landfill is at least 30% air so yes a slab that is built on that without supports down to the original level will sink. Each 2500 litre tank will weigh 2.5 tonnes when full that may mean that you could get a differential settlement and if the slab isn’t thick enough it could crack.

 

A vibrating plate will do a little to compact the fill but not very much.

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18 minutes ago, sometimewoodworker said:

Your current landfill is at least 30% air so yes a slab that is built on that without supports down to the original level will sink. Each 2500 litre tank will weigh 2.5 tonnes when full that may mean that you could get a differential settlement and if the slab isn’t thick enough it could crack.

 

A vibrating plate will do a little to compact the fill but not very much.

Correct, as my suggestion for someone qualified to sort it out. 

It will probably need deep footings of appropriate area to support the load and not rely on a poured slag sitting on unconsolidated fill.

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26 minutes ago, sometimewoodworker said:

A vibrating plate will do a little to compact the fill but not very much.

That's why i suggested a big roller,you will see on 1st pass if dirt goes like jelly underneath it's a no go unless you dig out and start again.

No jelly happy days.

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Thx Guys for the advice given so far. :wai:

 

I should have attached a Poll to this Topic 😉

 

a- Possible

b- Possible but with troubles

c- Impossible

d- Are you mad?

 

😀

 

 

  • Haha 1

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14 hours ago, farmerjo said:

vibrating roller...excavator to walk back and forwards.

Amateur mistake. These things won't compact 1.2 meters. Waste of time and money and project will be a failure. The OP has already received the best advice, get a civil engineer. Interesting the OP gave a like to various faulty/suspect advice and the engineer advice seemed to be discarded. It's just the blind leading the blind and you know what happens, you end up in the ditch. Too bad you can't see that. So even though I am just reiterating what two people already said I think you need to hear it again. Get an engineer!

 

Stepping back though that many water tanks sitting around is going to be ugly, take up a lot of useful space, impacts view, huge number of plumbing fittings, and expensive. You should strongly consider drilling a well for unlimited year round water that also resolves these issues. You haven't said if you are going to use this for household use. If so, the problem with rainwater catchment is all those contaminants Thai's love to use all around you go airborne and will settle on the roof and go right in your tank. Think of all the paraquat, all the nasty poisons. Then there is the bird poop, the dead bugs, dust and such. What are you going to do about these things?

 

Also note there are free plans on the net for making rainwater catchment ferrocement tanks of any size all the way up to 100 cubic meters. The instructions are designed for unskilled persons with limited materials and equipment (i.e. the developing world). This would be really cheap and take a really compact space. If you have more money a swimming pool installer is another option. Your catchment tank is basically a swimming pool with a lid. This would sit deep enough to sit on undisturbed earth and with a strong lid you could drive on it or plant grass over it. Again, an engineer would be valuable to set it up with a few chambers and so on. Doesn't sound like you want expert advice but maybe someone else will find this useful.

 

Edited by canopy
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If the land has being raised 1.2 M then simply dig  holes  1,2M deep every 4m  so you will need 10 holes . 

5 for the front and 5 for the back . Pour piers in the holes and then pour the slab on top of the piers, transferring the load  to virgin  compacted substrate.  

As said by other , it will be impossible to compact 1,2 m of dirt sufficiently unless you did it in layers. 

and water tanks are very heavy, It will be impossible  for the whole 20m length of slab to settle uniformly  and I can guarantee you it will crack unless you have piers transferring the load to stable ground. 

PS: a beam  running the whole length on top of the piers will make it even stronger

Edited by sirineou
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23 minutes ago, canopy said:

  

 Doesn't sound like you want expert advice but maybe someone else will find this useful.

 

Where did I say I don't want expert advice, because I didn't give a like?

 

I just asked for opinions, IMHO the general consensus here is that it would be hard to do, and that is why I asked the question.

 

We have a meeting with our architect next week on other matters, but we will discuss this with him. I believe he or has someone on his team who is a structural engineer. But if it is to difficult or too costly then we will scrap the idea.

 

Thx again to all who replied (the ones with likes or without 😉 )

Edited by MJCM

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23 minutes ago, MJCM said:

Where did I say I don't want expert advice, because I didn't give a like?

 

I just asked for opinions, IMHO the general consensus here is that it would be hard to do, and that is why I asked the question.

 

We have a meeting with our architect next week on other matters, but we will discuss this with him. I believe he or has someone on his team who is a structural engineer. But if it is to difficult or too costly then we will scrap the idea.

 

Thx again to all who replied (the ones with likes or without 😉 )

How was the pad filled.

Trucks backing over the dumped fill after tractor to level.

 

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