Good evening everyone,
I don’t have enough knowledge about foundations and groundworks to properly assess my situation.
The soil report states the following:
- Clay
- Good load-bearing capacity
- Poor permeability
- High frost susceptibility
Now regarding the different foundation options from the soil report:
1. Frost skirt AND bedding
The frost skirt (with slab) extends down to 1 meter (3.3 feet), and the bedding under the slab should be at least 70 cm (28 inches) of frost protection material.
2. Strip footings AND bedding
At least 1.2 meters (4 feet) deep (with slab). Bedding under the slab only 20 cm (8 inches).
My groundworks contractor proposes a third option, which has also been approved structurally:
3. Bedding only
Exclusive use of frost protection material under the slab to achieve a 1 meter (3.3 feet) deep foundation.
According to the structural engineer, a plate load test is required. This is not needed for options 1 and 2. He wants this test if the bedding is deeper than 0.9 meters (3 feet).
Now I’m a bit unsure which option is actually the most sensible.
All approaches seem possible and technically sound.
Could you help me understand the pros and cons of each?
Of course, I’m talking to the tradespeople, but independent opinions from you are usually more honest 🙂
Thanks!
I don’t have enough knowledge about foundations and groundworks to properly assess my situation.
The soil report states the following:
- Clay
- Good load-bearing capacity
- Poor permeability
- High frost susceptibility
Now regarding the different foundation options from the soil report:
1. Frost skirt AND bedding
The frost skirt (with slab) extends down to 1 meter (3.3 feet), and the bedding under the slab should be at least 70 cm (28 inches) of frost protection material.
2. Strip footings AND bedding
At least 1.2 meters (4 feet) deep (with slab). Bedding under the slab only 20 cm (8 inches).
My groundworks contractor proposes a third option, which has also been approved structurally:
3. Bedding only
Exclusive use of frost protection material under the slab to achieve a 1 meter (3.3 feet) deep foundation.
According to the structural engineer, a plate load test is required. This is not needed for options 1 and 2. He wants this test if the bedding is deeper than 0.9 meters (3 feet).
Now I’m a bit unsure which option is actually the most sensible.
All approaches seem possible and technically sound.
Could you help me understand the pros and cons of each?
Of course, I’m talking to the tradespeople, but independent opinions from you are usually more honest 🙂
Thanks!
T
toxickill4 Dec 2022 21:25Thank you for your feedback. In my case, only 50cm (20 inches) of soil cushioning is required according to the soil report. I reused this thread because the topic matched (see post #7). The soil report actually refers to floodplain clay and valley clay as the subsoil at the foundation depth (depending on which of the two boreholes). In terms of consistency, I would not describe it as slurry-like or soft, rather quite stiff. If the geotechnical engineer gives the go-ahead by phone tomorrow for a frost protection layer made of frost protection gravel, and we end up 1m (3 feet) below the finished ground level (FGL), we would apply the gravel immediately.
Thanks also for your tip regarding the preparation! I’m not sure if the foundation contractor is familiar with it, but it can’t hurt to mention it 🙂
Thanks also for your tip regarding the preparation! I’m not sure if the foundation contractor is familiar with it, but it can’t hurt to mention it 🙂
I also realized afterward that the first post wasn’t actually written by you, but the rest of your response still fit well 😉
In general, anyone who works with floors for a longer time should know this (well, maybe not everywhere in the north, but from Hannover southwards). Unfortunately, I keep seeing that such issues are often ignored because they make the work more demanding and necessarily more structured.
In general, anyone who works with floors for a longer time should know this (well, maybe not everywhere in the north, but from Hannover southwards). Unfortunately, I keep seeing that such issues are often ignored because they make the work more demanding and necessarily more structured.
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