Slab(s) For 2500l Water Tanks

CowboyDan

Hi guys, new member here. I install kerb and gutter and I've been asked by a mate to put in a slab for them to install 2x 2500l water tanks on... I haven't done much in the way of slabs (then again I've done a fair few footpaths) and have only been doing concrete for a while so I just wanted an opinion or two.

I was going to put in two slabs, one for each tank. If the tanks aren't installed dead centre on the slabs is there more of a chance of the slab tipping over time or anything, particularly if the compaction is bad? They're saying the site is prepped already so it sounds like I won't be able to control the fill or compaction... looking at it tomorrow though so I'll know more then. The reason I ask is that they want an extra 500mm or so on each slab to install pumps but instead I was thinking of building two thick square slabs for the tanks and a thinner one in the middle for the pumps.

I was planning on building the slabs 150mm thick (6") and reinforcing with mesh on 75mm chairs. Will this be sufficient for a 2500kg+ load?

I've seen a couple of mentions of cutting a trench roughly 150x150 around the perimeter. We've never done this for vehicle crossings or footpaths but then again they don't hold big loads for long periods. Is this necessary?

thanks

SLSTech

For us Americans - 660.4 Gallons each @ 8.3452641 #'s per gallon = 5512 lbs. How big are the tanks? Round, square, rectangular? Are the tanks resting directly on the concrete or on stands - 3000 PSI concrete @ 6" should support it - if they are narrow supports you may want to put footings underneath them or increase the PSI strength

As for the slab tipping over - is it on a hill or is there a sink hole problem? I would probably make sure that you had your 1.5 Foot clearance (500 MM) all the way around including around the pumps for ease of maintenance, etc...

I am not an engineer & if in doubt I would call an engineer

FYI - what is a kerbie???

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CowboyDan

Thanks Sean, sorry I forgot to convert to lb's. The tanks are round and will rest directly on the concrete slabs.

As for the site I don't know yet - I'll be visiting this afternoon to have a look so I'll have a better idea then. I'll make sure to ask if they've had any other sinking problems.

Giving them enough clearance for the pumps all the way around is a good idea, gives them options and still keeps the tank in the centre of the slab. The way they were talking on the phone though it sounds like space might be a bit limited but again I won't know til I see the site this afternoon.

Our driveway mix is rated at around 4000psi (28mpa) so it sounds like it'll be fine. I'll have a talk to the supplier anyway just to be safe.

And a 'kerbie' is a kerb and gutter bloke We do mainly roadside kerb/gutter (pumped from a machine) and some driveways and footpaths.

CowboyDan

Righto I went and had a poke around the site this afternoon, I've attached a rough drawing.

The house is on the left and a rock retaining wall on the right. There's a fence between the slabs. They're talking about square front slabs running all the way back to the wall, which I don't really see too much of a problem with. It would take the load off the centre slightly though and if the slabs decide to tip, they're going to tip towards the house.

Which brings me to the ground...... the soil is ****. It's a mulch-filled topsoil which is not going to compact at all. The bloke was talking about not excavating at all and just dropping the slabs on top of the soil but I told him he's going to need to at least go down some, plus I managed to convince him that it'll come up much tidier if tops of the slabs are level (or just under) the bottom of the fence too so we should be on half decent soil.

Oh by the way in Canberra we experience temps from -8deg to 40degC, although those extremes usually only come around for a couple of weeks a year. We get probably 3 weeks worth of frost in the year. We don't use anything to help with the frost in our mixes, so I doubt I'll need anything for this job.

Comments, suggestions?

thanks!

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Hoven

Bring in good fill and compact. Pin the slab. Pour 4000lb its only a couple of bucks more a yard but there is a significant increase in the amount of concrete dust per yard. Haunch perimeter and also where tanks will rest. Reinforcement is key and don't pour crazy wet. 4 inch slump is good.