ᐅ Correct Interpretation of a Geotechnical Site Investigation Report
Created on: 28 Feb 2020 13:00
K
KohorteHello again,
As the planning progresses, more questions arise.
We are building on a slope. One wall of the house will be built into the ground. (Cross-sections: https://www.hausbau-forum.de/threads/Einfamilienhaus-146qm-freistehend-mit-Walmdach.33958/)
The soil survey showed a well-bearing soil of class 4 (class 5 if larger stones are present— isn’t that usually the case?).
Topsoil is 20cm (8 inches). No pressing groundwater. With heavy rainfall, water simply flows through the slope.
Frost level F3 (the requirement is F2).
Three foundation options are recommended:
1.1 Shallow foundation 65cm (26 inches) deep with a 50cm (20 inches) overhang. Then a protective drainage layer is needed.
1.2 Shallow foundation deeper than 80cm (31 inches) with a 65cm (26 inches) overhang. Then the protective drainage is not necessary.
2. Strip footing on the valley side at least 0.5m (20 inches) into soil layer 3, which starts at 60cm (24 inches). (Here the frost-protected foundation depth is >1m (39 inches)).
Drainage is required at any earth-contacting wall in all options.
The shallow foundation is probably cheaper. Even when combined with the protective drainage? Or with 80cm (31 inches) depth?
What is better: making the protective layer thicker or improving drainage?
And how much more expensive are strip footings? Should we generally go for strip footings then? Are their advantages that clear-cut? Of course, we don’t want to cut costs in the wrong place. But if all foundation options are acceptable, we would definitely consider the price.
Regarding earthworks: there is a very brief note about the “reverse method,” where the bedding material should be placed immediately in layers using a “pre-head” dumping technique.
Is this unusual?
I actually have great respect for this part of housebuilding and want to be well-prepared for the discussion and, most importantly, to be able to realistically assess whether the estimated costs are reasonable and how much contingency we need to plan for and which option is the “right” one.
Thanks in advance!!
As the planning progresses, more questions arise.
We are building on a slope. One wall of the house will be built into the ground. (Cross-sections: https://www.hausbau-forum.de/threads/Einfamilienhaus-146qm-freistehend-mit-Walmdach.33958/)
The soil survey showed a well-bearing soil of class 4 (class 5 if larger stones are present— isn’t that usually the case?).
Topsoil is 20cm (8 inches). No pressing groundwater. With heavy rainfall, water simply flows through the slope.
Frost level F3 (the requirement is F2).
Three foundation options are recommended:
1.1 Shallow foundation 65cm (26 inches) deep with a 50cm (20 inches) overhang. Then a protective drainage layer is needed.
1.2 Shallow foundation deeper than 80cm (31 inches) with a 65cm (26 inches) overhang. Then the protective drainage is not necessary.
2. Strip footing on the valley side at least 0.5m (20 inches) into soil layer 3, which starts at 60cm (24 inches). (Here the frost-protected foundation depth is >1m (39 inches)).
Drainage is required at any earth-contacting wall in all options.
The shallow foundation is probably cheaper. Even when combined with the protective drainage? Or with 80cm (31 inches) depth?
What is better: making the protective layer thicker or improving drainage?
And how much more expensive are strip footings? Should we generally go for strip footings then? Are their advantages that clear-cut? Of course, we don’t want to cut costs in the wrong place. But if all foundation options are acceptable, we would definitely consider the price.
Regarding earthworks: there is a very brief note about the “reverse method,” where the bedding material should be placed immediately in layers using a “pre-head” dumping technique.
Is this unusual?
I actually have great respect for this part of housebuilding and want to be well-prepared for the discussion and, most importantly, to be able to realistically assess whether the estimated costs are reasonable and how much contingency we need to plan for and which option is the “right” one.
Thanks in advance!!
Similar topics