ᐅ Small foundation 1.30m x 1.10m – any experiences?

Created on: 3 Feb 2023 19:49
R
rennschnecke
Hello,

I need a small foundation, about 1.30 x 1.10 m (4.3 x 3.6 ft).
A device (weighing approximately 400 kg (880 lbs)) will be placed on it and fixed to the ground with four bolts. That’s why the foundation is necessary.
Both the device and the foundation will be exposed to weather conditions, and the device may get completely wet.

My current plan is to excavate the area, lay about 10 cm (4 inches) of gravel, and then pour around 15 cm (6 inches) of concrete. I was planning to skip the steel reinforcement mesh.
The whole thing would be formed with wooden shuttering, using a release agent for the formwork.

Are 10 cm (4 inches) of gravel and 15 cm (6 inches) of concrete sufficient? Or is that too much for the intended use?
Do I need to compact the gravel layer? I don’t really have access to a plate compactor.
For the concrete, I was going to use a 40 kg (88 lbs) bag of ready-mix concrete screed from a hardware store.

What are your thoughts on this plan?

Best regards
W
WilderSueden
4 Feb 2023 18:38
I also see ground anchors or fastening to isolated footings as effective. Under the machine, a minimal paving is sufficient; 15cm (6 inches) of crushed stone and 4cm (1.5 inches) of paving slabs should be enough.
O
Oberhäslich
4 Feb 2023 21:51
So, 400 kg is not that heavy. Four pad footings should be sufficient, 80 cm (31.5 inches) deep and around 30x30 cm (12x12 inches) or preferably 40x40 cm (16x16 inches) in size.
R
rennschnecke
5 Feb 2023 11:09
I just thought that a 1.30x1.10m (4.3x3.6 ft) foundation, with say 40-50cm (16-20 inches) depth, would be easier to implement than four 40x40cm (16x16 inches) pier footings with 80cm (31 inches) depth.
O
Oberhäslich
5 Feb 2023 12:08
Why. With an earth auger, it’s done in no time. It takes less than 5 minutes per hole. Using a shovel, digging a 1.10 x 1.30 x 0.60 meter (3.6 x 4.3 x 2 feet) hole takes quite a while... unless a digger is used. For a larger area, obviously more soil has to be removed and more crushed stone (or gravel) is needed for the foundation as well. For smaller structures like garden houses, sheds, or patios, I would recommend using isolated footings.
R
rennschnecke
5 Feb 2023 13:04
@Oberhäslich

Thank you. Earth augers with a diameter of 150-200mm (6-8 inches) and a tamper foot are available for rent nearby.

So, drill four holes with the 150-200mm (6-8 inch) auger and try to widen them to about 40x40cm (16x16 inches), 80cm (31.5 inches) deep.

Is it still necessary to use coarse lime gravel and a polyethylene (PE) sheet? If yes, what thickness should the lime gravel and concrete have at an 80cm (31.5 inch) depth? Is steel reinforcement needed for the pier foundations as well?

Can I use regular screed concrete, or is it also possible to use ready-mix fast-setting concrete, which is available at hardware stores?

There won’t be much space left between the pier foundations. I would just remove 10-15cm (4-6 inches) of turf and spread gravel. I don't want to lay stones there, especially since I probably wouldn’t get it perfectly even. ;-)
H
hanghaus2023
5 Feb 2023 13:23
rennschnecke schrieb:

@Oberhäslich
I didn’t want to lay stones there specifically, especially since I probably wouldn’t manage to do it neatly ;-)

Anyone who can manage the foundation shouldn’t have a problem with a few paving stones. 😉