Concrete slab (supporting Water Tanks) on new landfill.

[Artisi]

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. 

[MJCM]

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.

 

 

[Artisi]

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. 

[MJCM]

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 February 26, 2020 by MJCM

[canuckamuck]

@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.

[Cake Monster]

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

[Toosetinmyways]

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.

[sometimewoodworker]

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 February 26, 2020 by sometimewoodworker

[OOTAI]

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.

[Artisi]

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. 

[canuckamuck]

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.

 

[MJCM]

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

 

[canopy]

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.

 

[Artisi]

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. 

[MJCM]

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 February 27, 2020 by MJCM

[saengd]

8 minutes ago, MJCM said:

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.

 

 

We have a fairly complex sprinkler system in our garden which measures about one rai, you may find some of the following useful:

 

A klong runs through our garden so we feed water from that into the sprinkler system pipework using a conventional centrifugal pump. Next to the pump is a fifteen meter well and the pump is set up to be manually switched between the klong and the well because the klong is dry outside the rice planting season. The well taps into ground water which is about three metres down at the end of the rainy season, during the dry season it will fall to below nine metres which is about the maximum depth of a centrifugal pump. We didn't think it was worth the expense and effort of upgrading the pump to a jet pump which would let us get to the remaining six meters of water in the well so we added a second well.

 

The second well goes down 35 meters and houses a submersible deep well pump which pumps to a 2,000 litre storage tank, a second pump nearby pumps from the tank to the sprinkler network. That configuration gives us the choice of which water supply and pump to use, the klong, the shallow well or the stored water from the deeper well.

 

The pipe network that connects everything is PVC which is heavily painted with household paint, that protects against sunlight damage. The pipe is fastened to the wall and comprises one big loop to which everything is connected and feeds 13 sprinkler heads. Initially we used 1 inch PVC pipe which is not good for longer runs because of friction loss so we upgraded to 1.5 inch PVC pipe and that works just fine. PVC pipe is cheap, easy to work with and in my experience quite sturdy, ours in in its sixth year without a problem. I've installed to shut off valves in the pipework loop which means I can operate to separate sprinkler systems at the same time if I wish.

 

The two centrifugal pumps cost about 4.5k each and they last around seven or eight years before they degrade. The deep well submersible pump cost 15K but with the electrics to automate the tank refill process the price became 20k. The 2k litre tank is a green DOS tank and cost 4.5k.

 

 

 

 

 

 

 

 

 

 

[Thailand J]

The slab will settle evenly under an evenly applied load. But nothing in real life is ideal. I would suggest running finger size steel rebars longitudinally at about 12" o/c to create a monolithic slab. Allow 48" overlaps at the splices. Don't forget wire mesh and expansion joints to reduce hairline cracks. The slab should be 5" min thickness. 

 

My license to practice structural engineering in the state of Florida expired in 2008. This is a low risk project does not need an engineer.

 

 

 

[sometimewoodworker]

One further point to consider is using GRP tanks as you can easily get 4kl tanks and of course they are more UV Resistant than PVC or plastic tanks they may be slightly more expensive per litre but not by very much. We used the very wide toped tanks because we had limited hight under our paint room these are 2.5kl tanks 

 

 

[OOTAI]

3 hours ago, Thailand J said:

The slab will settle evenly under an evenly applied load. But nothing in real life is ideal. I would suggest running finger size steel rebars longitudinally at about 12" o/c to create a monolithic slab. Allow 48" overlaps at the splices. Don't forget wire mesh and expansion joints to reduce hairline cracks. The slab should be 5" min thickness. 

 

My license to practice structural engineering in the state of Florida expired in 2008. This is a low risk project does not need an engineer.

 

 

 

Here's what I said in post#39 with Thailand J's recommendations in RED

 

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 5" min(125mm) thick.

use strong rebar (20mm dia. finger size) which is closely spaced (no more than 300mm apart 12" o/c) 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.

 

So there you have the opinions of 2 Engineers saying almost the same thing. The main thing to take out of Thailand J's reply is the comment at the end that this is a low risk project and does not need an Engineer.

[moe666]

You can compress and tamp all you want, it will help but it will still subside more. Tie in your pad with plenty of support from below. You are talking a lot of weight concentrated in a small area.

[MikeN]

If you are going to dig the hole as suggested but worry about flooding inside it, why not  add a roof over it ? That could be connected to the rainwater collection, adding more surface area, it would also give some UV protection. 

But personally I would just treat it as a house slab....dig down to undisturbed soil, use footings, piers, a beam around the side and the slab on top.

Edited February 27, 2020 by MikeN

[MJCM]

2 minutes ago, MikeN said:

If you are going to dig the hole as suggested but worry about flooding inside it, why not  add a roof over it ? That could be connected to the rainwater collection, adding more surface area, it would also give some UV protection. 

5555555555555. Wow Top Tip Thx!!!

 

Something very obvious but easily overlooked! thx again

 

Edited February 27, 2020 by MJCM

[MJCM]

We really like the idea of the "Big Hole" in the ground and especially with the roof over it's "head". And it's also easy to hide because it will only be sticking out approx 1-1.5 meters above ground and with the use of plants on either side (SWMBO's hobby) no one would expect that there is a big hole with tanks in it ???? 

 

(I am thinking of doing that big hole all around the property and raise some alligators in it, great theft deterrent (just kidding ????) )

 

The Slab idea (above ground) is also good, but what will happen to the connections PVC/HDPE (from outside to inside) when the ground starts to settle in? The slab will be stable (hopefully ???? ) but the ground surrounding it NOT.

 

Thx again for all your comments/remarks/suggestions/etc, will keep you updated.