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MJCM

Concrete slab (supporting Water Tanks) on new landfill.

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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.

 

 

 

 

 

 

 

 

 

 

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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.

 

 

 

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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 

 

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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.

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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.

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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 by MikeN

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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

 

:wai:

Edited by MJCM

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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.

 

:wai:

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