Hello everyone,
our soil report arrived last week, and the earth appears to be of good quality and can be used for backfilling.
Unfortunately, a water exposure class W2.2-E was identified, and the developer therefore recommends a waterproof concrete basement structure ("white tank") due to the presence of groundwater pressure. The construction site is a vineyard with a gentle slope, and the winemaker who has worked the land for over 30 years told me in a conversation that he finds this surprising and does not understand where the groundwater pressure would come from.
Of course, we are both laypeople, so my question is: I have heard that soil experts nowadays tend to be cautious and assume a worst-case scenario. Would you install a waterproof concrete basement in this exposure class? What information would you need to be able to give advice on this?
Thank you!
our soil report arrived last week, and the earth appears to be of good quality and can be used for backfilling.
Unfortunately, a water exposure class W2.2-E was identified, and the developer therefore recommends a waterproof concrete basement structure ("white tank") due to the presence of groundwater pressure. The construction site is a vineyard with a gentle slope, and the winemaker who has worked the land for over 30 years told me in a conversation that he finds this surprising and does not understand where the groundwater pressure would come from.
Of course, we are both laypeople, so my question is: I have heard that soil experts nowadays tend to be cautious and assume a worst-case scenario. Would you install a waterproof concrete basement in this exposure class? What information would you need to be able to give advice on this?
Thank you!
H
hanghaus20232 Apr 2023 16:55Are you the first ones building there?
I’d say you don’t need to be. :p
I’d say you don’t need to be. :p
It is a new residential development with about 30 building plots, but unfortunately, it has not yet been approved by the developer, which is expected to happen next Thursday. Therefore, no one is building there yet. The site located next to it at the same elevation is probably around 50 to 60 years old.
A
Allthewayup2 Apr 2023 21:18The vintner typically only cultivates the topsoil; the statement is worth about as much as the meteorologists' forecast for summer 2023.
Was groundwater or perched water encountered during the survey or drilling? If so, at what depth?
Were any nearby groundwater monitoring points mentioned?
What is the precise soil profile (soil layers, composition, and thickness)?
Occasionally, precipitation water may temporarily accumulate as perched water.
I wouldn’t say that the geologist was being particularly cautious in my soil report.
Was groundwater or perched water encountered during the survey or drilling? If so, at what depth?
Were any nearby groundwater monitoring points mentioned?
What is the precise soil profile (soil layers, composition, and thickness)?
Occasionally, precipitation water may temporarily accumulate as perched water.
I wouldn’t say that the geologist was being particularly cautious in my soil report.
The report states: Groundwater was not encountered. The sandy gravel is highly permeable. There may be layer water inflows (perched groundwater) starting at ground level (GOK).
And further down:
4.8 Infiltration of Rainwater
Infiltration of rainwater is possible in the sandy-gravelly stones. A hydraulic conductivity value (kf) of up to 1·10^-4 m/sec can be assumed for preliminary sizing. This should be verified by an infiltration test.
As mentioned, this doesn’t mean much to me as a layperson.
And further down:
4.8 Infiltration of Rainwater
Infiltration of rainwater is possible in the sandy-gravelly stones. A hydraulic conductivity value (kf) of up to 1·10^-4 m/sec can be assumed for preliminary sizing. This should be verified by an infiltration test.
As mentioned, this doesn’t mean much to me as a layperson.
A
Allthewayup2 Apr 2023 22:59The kf-value is the soil’s permeability coefficient, which is estimated in the report based on the soil grain size distribution. The exact value can only be determined through infiltration tests.
With a value of 1x10^-4, water infiltrates purely by gravity at a rate of 0.0001 m/s (0.0003 ft/s), meaning 36 cm (14 inches) per hour. This is a low rate, even though the report describes it as “well permeable.” This value is likely the reason for the perched groundwater layers. I have a value of 5x10^-3, which corresponds to a theoretical infiltration rate of 18 m/h (59 ft/h). This indicates well-permeable soil.
Here are a few points to consider:
- No construction company will take responsibility if the construction method does not follow the recommendations in the report.
- Weather events tend to increase in intensity.
- A waterproof basement (WU basement) is an investment in the quality and long-term value stability of the property.
- After a sufficiently large damage event, the insurance company may send an expert. If the expert finds inconsistencies in the construction during their investigations, it could become problematic, as this might be considered a breach of pre-contractual disclosure obligations, potentially leading to exclusion from natural hazard insurance or its invalidity.
- If you sell the house one day and only built a black tank (unsealed basement), you are obliged to disclose that the basement’s water exposure class was not met. (My expert strongly confirmed this to me.)
- After all, you want to be able to sleep peacefully in your new home during storms and heavy rain, right?
At least you don’t have permanently standing groundwater, which means you don’t need groundwater lowering for the basement construction. That saves a lot of money.
With a value of 1x10^-4, water infiltrates purely by gravity at a rate of 0.0001 m/s (0.0003 ft/s), meaning 36 cm (14 inches) per hour. This is a low rate, even though the report describes it as “well permeable.” This value is likely the reason for the perched groundwater layers. I have a value of 5x10^-3, which corresponds to a theoretical infiltration rate of 18 m/h (59 ft/h). This indicates well-permeable soil.
Here are a few points to consider:
- No construction company will take responsibility if the construction method does not follow the recommendations in the report.
- Weather events tend to increase in intensity.
- A waterproof basement (WU basement) is an investment in the quality and long-term value stability of the property.
- After a sufficiently large damage event, the insurance company may send an expert. If the expert finds inconsistencies in the construction during their investigations, it could become problematic, as this might be considered a breach of pre-contractual disclosure obligations, potentially leading to exclusion from natural hazard insurance or its invalidity.
- If you sell the house one day and only built a black tank (unsealed basement), you are obliged to disclose that the basement’s water exposure class was not met. (My expert strongly confirmed this to me.)
- After all, you want to be able to sleep peacefully in your new home during storms and heavy rain, right?
At least you don’t have permanently standing groundwater, which means you don’t need groundwater lowering for the basement construction. That saves a lot of money.
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