Hello, greetings from Russia.
I am building my house here. Temperatures reach up to +45°C (113°F) in summer and down to -20°C (-4°F) in winter. Two years ago, I poured the foundation with 18 mm (0.7 inch) reinforcing steel inside.
Groundwater appears already at 50 cm (20 inches) depth, so I raised the foundation. It is 50 cm (20 inches) deep and 50 cm (20 inches) high.
Now I have noticed a crack that was not there last year. I am not exactly sure of the cause, but first, I had 200 cubic meters of soil delivered and raised the plot. I suspect the groundwater at depth froze.
The crack runs from the top down to about half the height of the foundation, as if it was pushed up from below.
My question is, how dangerous or problematic could this crack become? I am considering pouring a 15 cm (6 inch) high slab completely over it, including on the foundation.
I am building my house here. Temperatures reach up to +45°C (113°F) in summer and down to -20°C (-4°F) in winter. Two years ago, I poured the foundation with 18 mm (0.7 inch) reinforcing steel inside.
Groundwater appears already at 50 cm (20 inches) depth, so I raised the foundation. It is 50 cm (20 inches) deep and 50 cm (20 inches) high.
Now I have noticed a crack that was not there last year. I am not exactly sure of the cause, but first, I had 200 cubic meters of soil delivered and raised the plot. I suspect the groundwater at depth froze.
The crack runs from the top down to about half the height of the foundation, as if it was pushed up from below.
My question is, how dangerous or problematic could this crack become? I am considering pouring a 15 cm (6 inch) high slab completely over it, including on the foundation.
S
Simon-18911 Nov 2021 14:26Peug408 schrieb:
I planned it like this: gravel in, properly compacted, waterproofing, reinforcement steel, and concrete poured over the entire foundation, so that it sits about 15cm (6 inches) higher. However, this only results in a 15cm (6 inches) layer of concrete that has no structural connection with the rest of the strip foundation.
What is the spacing of the stirrups? Or did you install rebar mats bent into cages? You should bond your new longitudinal reinforcement with stirrups downwards into the existing foundation. I would even place it at the same spacing as the already installed stirrups, just shifted by 10cm (4 inches), and bonded at least 50cm (20 inches) in length, as a rule of thumb. What does the structural engineer say about the reinforcement? What is the concrete cover thickness? Could it possibly be too low?
I suspect your crack is caused by compaction. The soil inside was compacted downward and pushed back up underneath the foundation.
Nobody here knows about structural engineering; I already looked for someone but couldn’t find any.
Rebar cage with 10mm (0.4 inch) spacing, 30cm (12 inches) apart, resulting in 18mm (0.7 inch) reinforcements arranged in 3 by 2 rows.
The compaction could actually be feasible; I have considered that as well.
I can increase the thickness of the foundation slab to 30cm (12 inches) or even more.
I was thinking of drilling into the strip footing from above at 20cm (8 inches) intervals, moving the drill so that larger holes form inside the foundation, then inserting anchors and filling them with cement. Once the cement sets, I would pour the slab on top.
The new reinforcement will be arranged in a 20 by 20cm (8 by 8 inches) grid.
Rebar cage with 10mm (0.4 inch) spacing, 30cm (12 inches) apart, resulting in 18mm (0.7 inch) reinforcements arranged in 3 by 2 rows.
The compaction could actually be feasible; I have considered that as well.
I can increase the thickness of the foundation slab to 30cm (12 inches) or even more.
I was thinking of drilling into the strip footing from above at 20cm (8 inches) intervals, moving the drill so that larger holes form inside the foundation, then inserting anchors and filling them with cement. Once the cement sets, I would pour the slab on top.
The new reinforcement will be arranged in a 20 by 20cm (8 by 8 inches) grid.
Hello,
I stopped by a construction site where 17-story apartment buildings are being built and had a chat with the site manager.
He checked it out two days later and said I can ignore my concerns since the load on the foundation is not significant.
I have now compacted the topsoil as much as possible using a vibratory rammer, then filled it up with about 10cm (4 inches) of a gravel-sand mixture up to the edge, which I leveled with a heavy-duty vibrating plate.
I drilled vertical holes every 30cm (12 inches) along the strip footing and installed anchor stirrups, through which I inserted 10mm thick reinforcement bars.
There is also waterproofing applied, with reinforcement spaced 20cm by 20cm (8 inches by 8 inches).
The concrete slab is 20cm (8 inches) thick.
Now I am waiting for the rainy days to pass before ordering 26 cubic meters (34 cubic yards) of concrete.
I stopped by a construction site where 17-story apartment buildings are being built and had a chat with the site manager.
He checked it out two days later and said I can ignore my concerns since the load on the foundation is not significant.
I have now compacted the topsoil as much as possible using a vibratory rammer, then filled it up with about 10cm (4 inches) of a gravel-sand mixture up to the edge, which I leveled with a heavy-duty vibrating plate.
I drilled vertical holes every 30cm (12 inches) along the strip footing and installed anchor stirrups, through which I inserted 10mm thick reinforcement bars.
There is also waterproofing applied, with reinforcement spaced 20cm by 20cm (8 inches by 8 inches).
The concrete slab is 20cm (8 inches) thick.
Now I am waiting for the rainy days to pass before ordering 26 cubic meters (34 cubic yards) of concrete.
Peug408 schrieb:
But first, I had 200 cubic meters of soil delivered and raised the plot. Peug408 schrieb:
Now that I’ve raised it, it shouldn’t freeze anymore. Peug408 schrieb:
No, the soil inside was delivered by me, and it’s still settling. Peug408 schrieb:
I compacted the topsoil as much as possible with a tamping rammer, then filled about 10cm (4 inches) of a gravel-sand mix up to the edge, which I leveled again with a large vibrating plate. Sorry, to me this sounds like serious poor workmanship. The first thing I learned during our house build is the difference between soil and sand/gravel, and the fact that the structure of soil/topsoil retains moisture, while sand allows moisture to pass through.
Therefore, I would not build residential houses directly on topsoil.
Hello,
Why is that? I'm not building directly on the topsoil; the strip foundation supports the ground slab, and beneath the slab, there is gravel with XPS insulation boards.
It is more like a concrete ceiling supported from the center.
In total, there is 130cm (51 inches) of concrete on the facades.
The crack did not occur due to frost; the concrete settled poorly at that spot. I noticed this when I was preparing the connection with the hammer drill.
After about 4 to 5 cm (1.5 to 2 inches), the drill simply went through.
Why is that? I'm not building directly on the topsoil; the strip foundation supports the ground slab, and beneath the slab, there is gravel with XPS insulation boards.
It is more like a concrete ceiling supported from the center.
In total, there is 130cm (51 inches) of concrete on the facades.
The crack did not occur due to frost; the concrete settled poorly at that spot. I noticed this when I was preparing the connection with the hammer drill.
After about 4 to 5 cm (1.5 to 2 inches), the drill simply went through.
And how do you ensure that the self-made aerated concrete has not appeared in several places and that the building can stand on it without any issues?
Still, that impression can easily arise when trying to make sense of your words and pictures.
On the first page, one can see a kind of strip footing, surrounded on all sides by topsoil. Step one should have been to at least remove this within the building area. The slab that follows later, despite XPS and whatever else is below, must not rest on the topsoil; that must (again) be removed.
Peug408 schrieb:
Why would that be, I'm not building directly on the topsoil, the strip footing supports the slab, and below the slab there is gravel with XPS boards.
Still, that impression can easily arise when trying to make sense of your words and pictures.
On the first page, one can see a kind of strip footing, surrounded on all sides by topsoil. Step one should have been to at least remove this within the building area. The slab that follows later, despite XPS and whatever else is below, must not rest on the topsoil; that must (again) be removed.
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