ᐅ Excavation for soil class 4 – only for the foundation slab or for the entire property?
Created on: 3 Jul 2020 01:24
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FragenaskerF
Fragenasker3 Jul 2020 01:24Hello,
according to the soil report, we have soil class 4 on a relatively small plot of 450m2 (4,921ft2), with a single-family house planned to have 120m2 (1,292ft2) of living space.
The soil report states:
1. Topsoil: humic sands (OH), partially relocated, at a depth of 0.7 or 0.5m (depending on two boreholes) below the ground surface, there is a moderately stony, partially relocated, near-surface, heavily compacted topsoil layer.
The topsoil consists of organic components as well as cohesive, weakly medium sandy fine sands.
=> Soil class 1
2. At a depth of 1.4m (4.6ft): silty sands, soil class 4, soil is not or only partly permeable to water.
3. At a depth of 6m (19.7ft): gravelly clay (sand-silt-clay mixture, stiff consistency), soil class 4, not permeable to water.
No groundwater or perched water was detected in any of the boreholes.
Conclusion:
The topsoil down to a depth of 0.7 or 0.5m (2.3 or 1.6ft) below the ground surface, possibly deeper, must be replaced with non-cohesive sand or gravelly sand.
Now the question:
According to the civil engineering company, the entire soil on the plot should be replaced due to the soil conditions.
Our 20-year experienced, degree-qualified landscaping professional for the outdoor area believes that civil engineering companies often want to replace everything unnecessarily. Instead, it is sufficient to replace only the area of the foundation slab plus 2m (6.6ft) around it and the terrace area. The rest can almost always be planted.
Who is more likely to be correct in our specific case?
according to the soil report, we have soil class 4 on a relatively small plot of 450m2 (4,921ft2), with a single-family house planned to have 120m2 (1,292ft2) of living space.
The soil report states:
1. Topsoil: humic sands (OH), partially relocated, at a depth of 0.7 or 0.5m (depending on two boreholes) below the ground surface, there is a moderately stony, partially relocated, near-surface, heavily compacted topsoil layer.
The topsoil consists of organic components as well as cohesive, weakly medium sandy fine sands.
=> Soil class 1
2. At a depth of 1.4m (4.6ft): silty sands, soil class 4, soil is not or only partly permeable to water.
3. At a depth of 6m (19.7ft): gravelly clay (sand-silt-clay mixture, stiff consistency), soil class 4, not permeable to water.
No groundwater or perched water was detected in any of the boreholes.
Conclusion:
The topsoil down to a depth of 0.7 or 0.5m (2.3 or 1.6ft) below the ground surface, possibly deeper, must be replaced with non-cohesive sand or gravelly sand.
Now the question:
According to the civil engineering company, the entire soil on the plot should be replaced due to the soil conditions.
Our 20-year experienced, degree-qualified landscaping professional for the outdoor area believes that civil engineering companies often want to replace everything unnecessarily. Instead, it is sufficient to replace only the area of the foundation slab plus 2m (6.6ft) around it and the terrace area. The rest can almost always be planted.
Who is more likely to be correct in our specific case?
O
Osnabruecker3 Jul 2020 07:00At what elevation will your house be built?
Do you have any areas around your plot where you can store topsoil? The plot is small, so storing it for later filling would probably not be practical.
Once you have removed the 50-70 cm (20-28 inches) of topsoil, I would deliver 20-30 cm (8-12 inches) of material (sand/gravel depending on the requirements) and use that as the foundation for my slab. Then the finished floor level would be roughly at the same height as the previous ground level...
Regarding the "soil replacement":
The topsoil has to be removed anyway. Are you and the excavation contractor clear on what you mean by this? It sounds like, in your case, the second layer (sand) is supposed to be replaced.
Do you have any areas around your plot where you can store topsoil? The plot is small, so storing it for later filling would probably not be practical.
Once you have removed the 50-70 cm (20-28 inches) of topsoil, I would deliver 20-30 cm (8-12 inches) of material (sand/gravel depending on the requirements) and use that as the foundation for my slab. Then the finished floor level would be roughly at the same height as the previous ground level...
Regarding the "soil replacement":
The topsoil has to be removed anyway. Are you and the excavation contractor clear on what you mean by this? It sounds like, in your case, the second layer (sand) is supposed to be replaced.
Vicky Pedia15 Jul 2020 20:15Absolute nonsense and a rip-off! Just have a proper foundation slab laid, and the rest will follow. When landscaping the outdoor area, add some topsoil, and that's it. The soil class doesn’t matter for the garden. And BKL4 means: nothing special, no additional costs!
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