ᐅ Setting formwork blocks on a foundation or into concrete

Hello everyone,

The excavation for a pool is currently underway. The pool will be built with 17.5cm (7 inches) formwork blocks. One long side and one short side of the pool are buried up to the top edge in the ground, while the other two walls extend about two-thirds above the ground.

I will not pour a full concrete slab but will pour the base slab inside the pool later once the walls are in place.

Do I need to create a reinforced concrete foundation with rebar and rebar connections on top of my gravel bed for the exterior walls and then set the blocks on that, or would it be sufficient to set the first row of formwork blocks directly on the gravel bed in concrete and then reinforce the blocks accordingly?

Is there a structural difference in this case between having a foundation or not? I assume it should hold against the pressure, but what is the difference between having a foundation to build on or setting the first block row directly in concrete?

Thanks for your answers.

well then.... DIY pool construction....

how big will the pool be?

6 by 6 meters (20 by 20 feet)? then the walls will be under considerable pressure

We also have a pool. In our case, a concrete slab was poured, just like for our house. I’m not an expert, but how are the exterior walls supposed to withstand earth and water pressure if you simply place them on gravel? I wouldn’t just start building without proper foundations, or all the work might be wasted later on. Couldn’t you check with a pool contractor?

Best regards,
Sabine

The pool will be 9x4 meters (30x13 feet).

It will be filled with water from the inside and subject to pressure from the surrounding soil on the outside... I was thinking that the walls shouldn’t be able to move or shift anywhere, especially at the lower section.

abc12345 schrieb:

Filled with water on the inside and pressure from the surrounding soil on the outside... I thought the walls couldn’t really move or shift at the bottom.

That's correct! Your only issue is that it will take quite some time before the pool is finished. Until then, the external pressure can act continuously, especially if the walls are just loosely resting on the ground.

But where exactly does it make a difference whether the walls simply rest on the gravel base and are enclosed on the sides with concrete, or whether they stand on a concrete foundation?
That is not entirely clear to me.

Shouldn't the version without a concrete foundation actually be more stable?