ᐅ Excavation/Foundation Construction in High Groundwater Areas – Experiences?

Dear community,

We are facing a challenge as our earthworks were actually supposed to start since this/last week. However, our plot is located in a high groundwater area, and the earthworks are complicating things. I haven’t received clear statements from our earthworks contractor, so I would like to hear about your experiences.

Situation:
- Basement floor slab with overhangs needs to be poured
- Groundwater is currently about 1.85 m (6 feet) below the plot surface
- Excavation for the basement floor slab must reach 3.55 m (12 feet) deep → thus, the earthworks will be 1.70 m (5.5 feet) below the groundwater level
- Planned earthworks measures: 3 boreholes for dewatering; pipeline route to sewer 470 m (1,540 feet), diameter of sewer pipe into which we can discharge: 40 cm (16 inches)
- Additionally: We have installed a soakaway well on the property, reaching a depth of 8 m (26 feet), theoretically allowing further water discharge
- Weather forecast for the next two weeks looks rather positive (2-3 rainy days, otherwise mostly dry); on dry days, the water level drops about 1-2 cm (0.4–0.8 inches) per day

Further info: At the very beginning, sheet piling was considered. However, no clear necessity was explained to me, so I decided against it—mainly due to the risks of damaging neighboring houses.

Currently, our earthworks contractor is installing the pipes and planned to start pumping from Friday.

Now my main question to you: How do you see the situation? How optimistic can I be that it will work out, on a scale from 0 (very pessimistic) to 10 (very optimistic)?

Thank you all.

Best regards

I’m tagging @Allthewayup, who has also built with a high groundwater level...

An open dewatering system was sufficient for me. I had one pump at the cistern excavation and another pump in the basement.
We waited until the groundwater level was very low.

Time pressure can actually be counterproductive.

It should work well with a lowering well. What did the geologist suggest?

@hanghaus2023 Thanks. How much did you ultimately have to lower the water level with the measures you took?
The geologist was basically relaxed. The problem isn’t the possibility itself. At the beginning, we were just not told that the sewer would be the limiting factor, since it was originally assumed we could pump into a small stream.

Now I’m at a loss with this problem and want to assess how realistic it will be to lower the water sufficiently given our conditions.

gregman22 schrieb:

We are facing the challenge that our earthworks were actually supposed to start this week/last week. However, our plot is located in a high groundwater area, and the earthworks are causing us problems.

Oh! – Aren’t you the one from Munich with the expensive architect? To me, this sounds like a serious oversight in design phase 1, if there is any surprise about the situation you describe. @Gerddieter is probably right about not trusting that group of architects...

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https://www.linkedin.com/company/bauen-jetzt/

@11ant Yes. I want to put the topic of "blame" on hold for now and revisit it later. At the moment, I am more in fight mode to better assess the situation.