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MJCM

Concrete slab (supporting Water Tanks) on new landfill.

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21 minutes ago, MJCM said:

It could be but I can't do anything yet till end of next month. So I am just gathering suggestions/idea's/comments/remarks/criticism 😉 

Point 1 for your review:

Unconsolidated filled land is not load bearing. 

Point 2 placing an unsupported slab onto unconsolidated fill will result in uneven settlement and probable   slab failure. 

 

That is all you need to understand initially.

 

Once understood you can take the next step:

 

Design and build a structure  that isn't supported on unconsolidated fill. 

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1 minute ago, Artisi said:

Point 1 for your review:

Unconsolidated filled land is not load bearing. 

Point 2 placing an unsupported slab onto unconsolidated fill will result in uneven settlement and probable   slab failure. 

 

That is all you need to understand initially.

 

Once understood you can take the next step:

 

Design and build a structure  that isn't supported on unconsolidated fill. 

What @sometimewoodworker is suggesting is dig all the way down to the OLD soil and pour the slab on that and then put the tanks on that slab. That's why the BIG hole.

 

 

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1 minute ago, MJCM said:

What @sometimewoodworker is suggesting is dig all the way down to the OLD soil and pour the slab on that and then put the tanks on that slab. That's why the BIG hole.

 

That will fill with water during the wet session and hydraulically lift any tank that is empty enough to become buoyant. 

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5 minutes ago, Artisi said:

That will fill with water during the wet session and hydraulically lift any tank that is empty enough to become buoyant. 

Drainage pipes? Or a simple bilge pump?

 

Edit: And during the rainy season I am not worried that the tanks will be empty, but I see your concern.

Edited by MJCM

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@sirineou Has the right idea, Put in support columns down past the fill. Build it like a pillar and beam construction.

 

 

Sorry for my original advice, I had missed that the fill was 1.2 meters, I was thinking it was much less than that.

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Make your slab about 1 meter wider than the tanks and at least 20 cm of Concrete. also double mesh the slab with good rebar grid wire.

If the slab moves it will do so unevenly, and at least with this you stand a chance that the slab will not break / crack

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  • Calculate the maximum stationary live load that concrete slab-on-grade floor can support.
 
 
  • Calculate the minimum thickness required for a concrete slab-on-grade floor to support a stationary live load.
 
  • Calculate the required concrete slab-on-grade floor thickness required to support traffic loads.
 
  • Calculate the required floor thickness for a concrete slab-on-grade floor supported by a stabilized/modified soil subgrade.
 
  • Calculate the maximum length of steel reinforced slab-on-grade floors.
 

 

 
  • Calculate the approximate flexural strength of concrete (S'c) from the 28 day compressive strength (f'c).
 
  • Calculate the approximate 28 day compressive strength of concrete (f'c) from the 28 day flexural strength (S'c).
 
  • Calculate the California Bearing Ratio, CBR, from the Modulus of Soil Reaction, k.
 
  • Calculate the Modulus of Soil Reaction,

 

Those are the calculations an engineer would have to do to construct a slab in the west. But hey this is Thailand.

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1 hour ago, MJCM said:

What @sometimewoodworker is suggesting is dig all the way down to the OLD soil and pour the slab on that and then put the tanks on that slab. That's why the BIG hole.

Absolutely.

 

57 minutes ago, Artisi said:

That will fill with water during the wet session and hydraulically lift any tank that is empty enough to become buoyant. 

That is why I said the first thing to do is fill with water to ground level, as soon as the tanks go in, though depending on the exact layout drainage could avoid having to do that.

 

27 minutes ago, Cake Monster said:

Make your slab about 1 meter wider than the tanks and at least 20 cm of Concrete. also double mesh the slab with good rebar grid wire.

If the slab moves it will do so unevenly, and at least with this you stand a chance that the slab will not break / crack

It’s going to be on the old compacted soil so that should not be needed.


 

 

The fill level is why going back down to the original level is probably going to be the best, fastest, cheapest option, not to mention that having different levels in the garden makes it much more interesting for SWMBO, my own boss told me exactly that 

38 minutes ago, canuckamuck said:

sirineou Has the right idea, Put in support columns down past the fill. Build it like a pillar and beam construction.

38 minutes ago, canuckamuck said:

Sorry for my original advice, I had missed that the fill was 1.2 meters, I was thinking it was much less than that

 

Edited by sometimewoodworker

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MJCM

While I am an Engineer this is not exactly my area of expertise but I will give you my opinion anyway because that what forum's are for people to express opinions not necessarily to provide expert advice.

 

Anyway I think you best option would be to do as you have suggested and that is dig a hole down to the original soil surface and place your slab on top of that soil. As Cake Monster has just suggested make you slab 1m wider than your tanks to allow access all around. When making the slab use good rebar, I would suggest at least 10mm, reinforcing not the <deleted> wire mesh that they usually use this will ensure that even if the slab does develop minor cracks it will not break up.  If possible arrange your trench so the longest dimension is going downhill (based on the original ground surface) that way you should be able to install some simple drainage to ensure it doesn't fill up. A point to be aware of is how are you going to maintain the sidewalls of the "trench". I personally would build a retaining wall along the sides at least 800mm high if the trench is going to be 1.2m deep.

 

Now having said all that I personally would build the slab on top of the uncompacted (because it would be cheaper) fill you have placed BUT with the following proviso's.

  • Make the slab at least 150mm thick.
  • use strong rebar (20mm dia.) which is closely spaced (no more than 300mm apart) and located nor more than 50mm from the bottom of the slab so that would mean it would have 30mm of concrete under it. This should provide sufficient tensile strength to the slab to stop any buckling which may want to occur if the soil settles unevenly. 
  • the tanks are all connected before any water is added to enable them to fill evenly so the load from the slab is evenly placed onto the fill.

The reason I have said that the first is perhaps the best solution is that as your wife says it allows you to somewhat hide the tanks if you think that would be a good idea.

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9 minutes ago, sometimewoodworker said:

Absolutely.

 

That is why I said the first thing to do is fill with water to ground level, as soon as the tanks go in.

 

It’s going to be on the old compacted soil so that should not be needed.


 

 

The fill level is why going back down to the original level is probably going to be the best, fastest, cheapest option, not to mention that having different levels in the garden makes it much more interesting for SWMBO 

I wasn't talking about initial installation, it was about a flooded ground condition and 1 or more tanks becoming buoyant for what ever reason. 

You understand Murphy's law. 

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9 minutes ago, sometimewoodworker said:

Absolutely.

 

That is why I said the first thing to do is fill with water to ground level, as soon as the tanks go in, though depending on the exact layout drainage could avoid having to do that.

 

It’s going to be on the old compacted soil so that should not be needed.


 

 

The fill level is why going back down to the original level is probably going to be the best, fastest, cheapest option, not to mention that having different levels in the garden makes it much more interesting for SWMBO, my own boss told me exactly that 

Digging a hole comes with it's own problems, drainage and tank cleaning for one. And floating tanks for another.

 

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7 minutes ago, canuckamuck said:

Digging a hole comes with it's own problems, drainage and tank cleaning for one. And floating tanks for another.

 

Valid points.

 

For drainage, I could have PVC pipes on the sides of the hole that run all the way to an overflow area and also a simple BILGE Pump, or a Submersible Pump with a Float valve, something like this: Submers

 

Floating tanks, I understand the point and the issue, but during the rainy season the tanks will be filled constantly because of the supply from the Rain gutters, but we will initially fill them with a Water truck that comes by when we call them (4800 liters for 500 THB, NO mains water unfortunately)

 

At the moment we are hesitant to the idea of filling the hole with sand, and we are thinking of just leaving an "open" hole. (cordoned off of course)

 

In our current house we have an underground water tank, that sits on a concrete slab with sand all around that, but that is just 1 tank (1000 Liters), but in the new house we are talking 10-12 (maybe even 15) tanks.

 

Thanks you guys, you have given us lots and lots to think about, and we need some time to let it settle in (pun intended 😉 ) and will keep you informed. Maybe even going with just 2-3 tanks at first in the big hole (easy for the workers to dig that hole) and see how that goes.

 

Thx again, really really appreciated

 

:wai:

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Just curious, what is the advantage of this system over drilling a well?

 

And you say you won't drink it, but still why would you use pvc in the sun? pvc rots and leaches toxins into the water. Deliberately increasing contaminants and using a material that will decay and need replaced and redone in time seems an odd choice.

 

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57 minutes ago, canopy said:

Just curious, what is the advantage of this system over drilling a well?

 

And you say you won't drink it, but still why would you use pvc in the sun? pvc rots and leaches toxins into the water. Deliberately increasing contaminants and using a material that will decay and need replaced and redone in time seems an odd choice.

 

A properly installed and equipped well might be cheaper than the system currently being considered. 

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12 hours ago, canopy said:

Just curious, what is the advantage of this system over drilling a well?

 

And you say you won't drink it, but still why would you use pvc in the sun? pvc rots and leaches toxins into the water. Deliberately increasing contaminants and using a material that will decay and need replaced and redone in time seems an odd choice.

 

Well? Well we thought about it and asked around about it and first we need a permit, which takes weeks to get around here then the costs including a Submersible pump we were quoted 35K UP.

 

So we are just looking for alternatives. No Mains water around there.

 

And leaving PVC in the SUN? We are going to use HDPE Blue buried under ground from the tanks to the underground tank, but only use PVC to interconnect the tanks.

 

 

Edited by MJCM

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