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.
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.
abc12345 schrieb:
Filled with water from the inside and under external pressure from the surrounding soil... I thought the walls wouldn't be able to shift anywhere at the lower part. The pool is also empty sometimes when the water is replaced and the pool is cleaned.
Regards
Sabine
Hello abc
Hollow blocks actually serve only as "formwork." The reinforcement and concrete provide the stability.
I consider 17.5cm (7 inches) blocks to be undersized. If you subtract the thickness of the blocks, there won’t be much concrete left.
I would also recommend first constructing a proper foundation. It is something like a ring beam. The foundation rests on a large surface area, so nothing can shift. After that, place the first row of hollow blocks leveled, drill 16mm (5/8 inch) holes into the foundation, insert 16mm (5/8 inch) rebar, leaving 30 to 40cm (12 to 16 inches) sticking out. Place two horizontal rebar rods each time, then pour concrete. Extend the vertical rods up to 5cm (2 inches) below the top edge. That way, you will have long-lasting stability.
And reconsider the 17.5cm (7 inches) blocks.
Steven
Hollow blocks actually serve only as "formwork." The reinforcement and concrete provide the stability.
I consider 17.5cm (7 inches) blocks to be undersized. If you subtract the thickness of the blocks, there won’t be much concrete left.
I would also recommend first constructing a proper foundation. It is something like a ring beam. The foundation rests on a large surface area, so nothing can shift. After that, place the first row of hollow blocks leveled, drill 16mm (5/8 inch) holes into the foundation, insert 16mm (5/8 inch) rebar, leaving 30 to 40cm (12 to 16 inches) sticking out. Place two horizontal rebar rods each time, then pour concrete. Extend the vertical rods up to 5cm (2 inches) below the top edge. That way, you will have long-lasting stability.
And reconsider the 17.5cm (7 inches) blocks.
Steven
K
knalltüte26 May 2020 11:43Water exerts its force downward differently than it does on walls.
My civil engineering studies were about 30 years ago, but I would bet that the ground would "give way" if there is no continuous slab foundation of sufficient thickness and with proper reinforcement.
Just make a sketch and mark the forces (downward, lateral).
The wall is subjected to forces from above due to its own weight. Soil "pushes" from the outside, water "pushes" from the inside.
However, the floor experiences the full weight of the water (36 tons at 1m (3.3 ft) fill height). That is significant...
My civil engineering studies were about 30 years ago, but I would bet that the ground would "give way" if there is no continuous slab foundation of sufficient thickness and with proper reinforcement.
Just make a sketch and mark the forces (downward, lateral).
The wall is subjected to forces from above due to its own weight. Soil "pushes" from the outside, water "pushes" from the inside.
However, the floor experiences the full weight of the water (36 tons at 1m (3.3 ft) fill height). That is significant...
@Steven
Okay, the strip footing, or in this case the ring beam, was planned anyway. I just have some doubts about whether it’s really necessary or simply oversized. After all, this is a pool and not a residential building.
I will embed the steel directly into the foundation rather than drilling it in later, which will provide more stability. I might also place full reinforcement cages in the foundation instead of just single bars.
According to the manufacturer’s load specifications, the 17.5 cm (7 inches) blocks are sufficient for use under traffic load.
@superzapp
The floor will be concreted on the inside. So basically, the exterior walls will be erected first, then the gravel and a 10 cm (4 inch) slab with reinforcement will be placed inside. The slab wouldn’t actually be necessary, since the pool will be lined with a membrane. A layer of compacted sand would have sufficed, but when installing the membrane, indentations appear on the floor that can’t be easily smoothed out, hence the 10 cm slab. I originally planned for just 5 cm (2 inches), but I’m worried it might crack under pressure.
Once the slab is in place, it can’t detach from anything.
In general, it’s natural soil and the subsoil is heavily compacted clay, with a rock layer starting just below.
Okay, the strip footing, or in this case the ring beam, was planned anyway. I just have some doubts about whether it’s really necessary or simply oversized. After all, this is a pool and not a residential building.
I will embed the steel directly into the foundation rather than drilling it in later, which will provide more stability. I might also place full reinforcement cages in the foundation instead of just single bars.
According to the manufacturer’s load specifications, the 17.5 cm (7 inches) blocks are sufficient for use under traffic load.
@superzapp
The floor will be concreted on the inside. So basically, the exterior walls will be erected first, then the gravel and a 10 cm (4 inch) slab with reinforcement will be placed inside. The slab wouldn’t actually be necessary, since the pool will be lined with a membrane. A layer of compacted sand would have sufficed, but when installing the membrane, indentations appear on the floor that can’t be easily smoothed out, hence the 10 cm slab. I originally planned for just 5 cm (2 inches), but I’m worried it might crack under pressure.
Once the slab is in place, it can’t detach from anything.
In general, it’s natural soil and the subsoil is heavily compacted clay, with a rock layer starting just below.
H
HilfeHilfe26 May 2020 11:53Once again, a really great forum
*Popcorn*
*Popcorn*
K
knalltüte26 May 2020 11:54My prediction is that if the foundation is not continuous (under the wall), a crack will develop at the marked location (regardless of vapor barriers, tiles, waterproof coatings, or whatever else is used).
Additionally, the wall must be properly connected to the foundation with sufficient reinforcement (as has already been mentioned) to prevent the forces acting on the wall from pushing it outwards, which would cause a horizontal crack to form.
However, I would recommend consulting a professional or visiting a specialized forum for pool construction, as already suggested.
Building it the way a non-professional might think could work, but it is usually not advisable—sorry. You were probably hoping to hear something different.
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