Concrete slab (supporting Water Tanks) on new landfill.

[MJCM]

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 February 25, 2020 by MJCM

[canuckamuck]

 

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 February 25, 2020 by canuckamuck

[Artisi]

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

[farmerjo]

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 February 25, 2020 by farmerjo

[MJCM]

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.

[canuckamuck]

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.

[sometimewoodworker]

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.

[Artisi]

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.

[farmerjo]

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.

[sometimewoodworker]

4 hours ago, farmerjo said:

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.

It’s extremely unlikely that you will be able to compact a 1.2 metre fill in the time required. The only way to compact that much would be to put it down in thin layers and compact each layer. 

 

Even with large scale equipment (that would be totally ridiculous to use) you would have significant difficulty, if it were even possible.

[MJCM]

Thx Guys for the advice given so far.

 

I should have attached a Poll to this Topic ????

 

a- Possible

b- Possible but with troubles

c- Impossible

d- Are you mad?

 

????

 

 

[canopy]

  

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 February 26, 2020 by canopy

[sirineou]

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 February 26, 2020 by sirineou

[MJCM]

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 February 26, 2020 by MJCM

[farmerjo]

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.

 

[MJCM]

5 minutes ago, farmerjo said:

How was the pad filled.

Trucks backing over the dumped fill after tractor to level.

 

 

trucks dumping the fill, tractor leveled it, then trucks, both dump trucks and delivery trucks ran over it, many times already in those 1-1,5 months.

[sometimewoodworker]

2 hours ago, MJCM said:

 

trucks dumping the fill, tractor leveled it, then trucks, both dump trucks and delivery trucks ran over it, many times already in those 1-1,5 months.

That will have done a little but not  very much to compact the fill, what ever you do its still going to sink 200mm to 300mm over time. We had a similar amount of fill with a similar kind of traffic over it so I am talking from experience, we left ours to natural compaction for a few years and that was what happened.

 

So short answer, the fill can not support the water tanks, it will compress.

 

You can create a concrete raft either floating on the fill or supported by foundations that go down to the original surface. Probably not value for money unless combined with something else

 

You can also dig holes in the fill to put your tanks in, the base layer would need much less preparation.

[MJCM]

2 hours ago, sometimewoodworker said:

 

You can also dig holes in the fill to put your tanks in, the base layer would need much less preparation.

Thx for the advice.

 

Dig holes to put the tanks in, is IMHO not an option because we want the tanks to be connected to each other via 2" PVC. There will be rain water flowing into 2 tanks (one on each side of the rain gutters) and all the other tanks (I estimated we need approx 10-12 tanks (maybe even more depending on the length of the dry season)) will be connected to those 2 tanks.

 

That water then goes through a Sediment, Carbon and Resin filter to a underground water tank (2000 Liters) to supply the house. That water is ONLY used for showers and dishes and washing).

 

But will give your idea some thought and discuss this with the SWMBO.

[MJCM]

Discussed this with the SWMBO and she thinks it's a good idea, but will look weird as the hole will be 1.2+ deep and the tanks are approx 1.9m high so they will only show 60-70cm above ground. A good way to hide your tanks she said 5555555555

[sometimewoodworker]

25 minutes ago, MJCM said:

Dig holes to put the tanks in, is IMHO not an option because we want the tanks to be connected to each other via 2" PVC. There will be rain water flowing into 2 tanks (one on each side of the rain gutters) and all the other tanks (I estimated we need approx 10-12 tanks (maybe even more depending on the length of the dry season)) will be connected to those 2 tanks.

There would be no problem in connecting the tanks just a little more digging, to put the connections in then 6” pipe risers to allow the stopcocks to be turned on and off

 

You should allow 200 litres per person per day consumption possibly a bit more for washing

Edited February 26, 2020 by sometimewoodworker

[sometimewoodworker]

If you arrange for the water to feed from the last tanks in line you can use the first ones as settlement tanks so getting absolutely clear water from the series. 

[sometimewoodworker]

16 minutes ago, MJCM said:

Discussed this with the SWMBO and she thinks it's a good idea, but will look weird as the hole will be 1.2+ deep and the tanks are approx 1.9m high so they will only show 60-70cm above ground. A good way to hide your tanks she said 5555555555

Probably a little better looking than 

[MJCM]

I made this "simple" drawing.

 

 

It then will go from the "connected tanks" to filters to an underground tank near the house.

 

The 1st holding tank is situated right at the back of the house, the connected tanks will be approx 10-20 meters away from the house and it will be then pumped from the "connected" tanks on a timer to the underground water tank which is again near the house.

 

The only point my wife made was will not the "hole" with the connected tanks not fill up with water when it rains heavily,

Edited February 26, 2020 by MJCM

[sometimewoodworker]

26 minutes ago, MJCM said:

The only point my wife made was will not the "hole" with the connected tanks not fill up with water when it rains heavily,

Yes it will but since the tanks will be ⅔ in the ground and back filled (don’t forget to use sand not the  Excavated earth to backfill beside the tank) they won’t be a problem. The only thing that could fill with water would be the riser pipes that allow access to the tank isolation stopcocks but they would drain after.

 

 

Of course once you have put the tanks in you MUST immediately fill them up to ground level with water.

 

I would take the feed from the 1st holding tank from the top to allow settlement, eliminate the ballcock in the in ground tanks and instead put in an overflow pipe from the last one. Otherwise all the excess water is going to dump beside the house.

Edited February 26, 2020 by sometimewoodworker

[MJCM]

You make some really good points, but I am thinking of leaving the tanks exposed (so no back fill) but then need to think of sufficient drainage for the "hole".

 

Will run pipes from almost at the bottom of the "hole" to a drainage area.

 

What do you think about that?

[Artisi]

You are turning what is a simple project into a major complex problem. 

With the money you about to invest, hire a civil engineering to design a proper slab to support the tanks that's not going to settle, crack or break its back, probably an hour or so's work.

Edited February 26, 2020 by Artisi

[MJCM]

Just now, Artisi said:

You are turning what is a simple project into a major complex problem. 

With the money you about to invest, hire a civil engineering to design a proper slab to support the tanks that's not going to settle, crack or break its back. 

IMHO what @sometimewoodworker is suggesting is not a major complex problem. His suggestion eliminates a lot of problems but I just have a big hole with tanks in it. But that big hole is not a major issue as we have 3,5 Rai to play with.

[Artisi]

2 minutes ago, MJCM said:

IMHO what @sometimewoodworker is suggesting is not a major complex problem. His suggestion eliminates a lot of problems but I just have a big hole with tanks in it. But that big hole is not a major issue as we have 3,5 Rai to play with.

Round and round in circles chasing your tail. 

 

 

[MJCM]

Just now, Artisi said:

Round and round in circles chasing your tail. 

 

 

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 ???? 

[MJCM]

I think the suggestion @sometimewoodworker only costs approx 1-2 day of digger hire (4k THB per day) to dig a hole approx 1,2m deep and 20meters long and then pour a slap of 1,4m width and 20 meters long and 15cm thick would cost approx 10KTHB for 5m³ of Cpac concrete. (excluding the workers and the rebar of course)

 

Concrete calculation from here: https://www.calculator.net/concrete-calculator.html?slablength=20&slablengthunit=meter&slabwidth=1.4&slabwidthunit=meter&slabthick=15&slabthickunit=centimeter&slabquantity=1&slabcal=Calculate

 

Don't forget it's fresh land fill (and only slightly compacted ???? )

Edited February 26, 2020 by MJCM