ᐅ Lowering of Groundwater According to Geotechnical Report – Your Experiences?
Created on: 8 Apr 2022 14:42
A
Allthewayup
Hello everyone,
according to the soil report, groundwater lowering is necessary during the basement construction, and it can only be discharged into the sewer system. During the boreholes, groundwater was encountered at a depth of 2.5m (8 feet). The Danube River flows approximately 500m (1,640 feet) away in a straight line, so we had already anticipated this. Over the past few months, we have contacted numerous companies regarding water management. Despite follow-ups, we have never received a response. Either there is no interest in such small projects, or we were told to get in touch again just before the start of construction in autumn. Based on the soil report and the neighbor’s references, we have fairly reliable estimates of the volume of water to be pumped. We have set aside €30,000 for this scope of work but remain uncertain about reliable estimates from the company to be hired. The neighbor had to handle this independently because they did not commission a soil report, and the water only emerged after they had already begun the foundation slab. So it was a chaotic situation that ended after 5 days.
My question to users here with experience on this topic:
What costs did you incur for your water management, and how was it carried out? (open, closed, vacuum systems)
What difficulties did you encounter during implementation?
What would you do differently if you were in the same situation again?
To avoid discussions about “omitting the basement,” it must be said that we absolutely need the space, and on a 300sqm (3,230 sq ft) lot, it would not be possible to build it close to ground level.
according to the soil report, groundwater lowering is necessary during the basement construction, and it can only be discharged into the sewer system. During the boreholes, groundwater was encountered at a depth of 2.5m (8 feet). The Danube River flows approximately 500m (1,640 feet) away in a straight line, so we had already anticipated this. Over the past few months, we have contacted numerous companies regarding water management. Despite follow-ups, we have never received a response. Either there is no interest in such small projects, or we were told to get in touch again just before the start of construction in autumn. Based on the soil report and the neighbor’s references, we have fairly reliable estimates of the volume of water to be pumped. We have set aside €30,000 for this scope of work but remain uncertain about reliable estimates from the company to be hired. The neighbor had to handle this independently because they did not commission a soil report, and the water only emerged after they had already begun the foundation slab. So it was a chaotic situation that ended after 5 days.
My question to users here with experience on this topic:
What costs did you incur for your water management, and how was it carried out? (open, closed, vacuum systems)
What difficulties did you encounter during implementation?
What would you do differently if you were in the same situation again?
To avoid discussions about “omitting the basement,” it must be said that we absolutely need the space, and on a 300sqm (3,230 sq ft) lot, it would not be possible to build it close to ground level.
A
Allthewayup20 Dec 2022 17:00andimann schrieb:
Hi,
this effort really paid off. One question: What is the total volume of water collected in the end? The initial calculation was 20 l/s (5.3 gallons per second), which equals about 5 swimming pools per day! Is that really that much water?
Best regards,
Andreas We pumped around 7,300 m³ (9,550 cubic yards) of water over 14 days.
This is partly due to a lower groundwater level than assumed in the calculation and also because we positioned the house 10 cm (4 inches) higher than planned. In practice, we only managed to keep the water about 30 cm (12 inches) below the foundation slab instead of the 50 cm (20 inches) assumed. Various soil factors, no rain during the 14 days, and other influences also play a role. There are practical cases where twice as much was pumped compared to the calculations—these things are just hard to predict beforehand. We had registered a withdrawal volume of 29,500 m³ (38,600 cubic yards).
Adam2112 schrieb:
If, for example, only the foundations are underwater, you can simply cast the concrete. The concrete displaces the water. Usually, regular submersible pumps can’t handle the dewatering anyway. Under certain conditions, this might be possible, but economically it only makes sense in rare cases, since special anti-segregation concrete must be used. Pouring normal concrete underwater leads to washout of fine particles and/or cement slurry, which dilutes the concrete. This jeopardizes the structural integrity and the concrete’s properties. The water-cement ratio for such concrete also needs to be especially high. Any competent structural engineer would try to avoid this. Ignoring a small puddle might be possible, but pouring concrete “in the water” is not something I would recommend to anyone.
Wow!
That’s almost 20 swimming pools! Although not Olympic-sized, but the smaller local pools measuring 25 by 10 meters (82 by 33 feet), still impressive! I didn’t expect such volumes to accumulate, but fortunately, we didn’t have to deal with this issue ourselves.
Thanks for the reply and best of luck with the ongoing construction!
Kind regards,
Andreas
Allthewayup schrieb:
We pumped around 7,300 m³ (257,500 cubic feet) of water in 14 days.
That’s almost 20 swimming pools! Although not Olympic-sized, but the smaller local pools measuring 25 by 10 meters (82 by 33 feet), still impressive! I didn’t expect such volumes to accumulate, but fortunately, we didn’t have to deal with this issue ourselves.
Thanks for the reply and best of luck with the ongoing construction!
Kind regards,
Andreas
A
Allthewayup20 Dec 2022 17:55andimann schrieb:
Wow!
That’s almost 20 swimming pools! Not Olympic size, but the "small" local pools measuring 25 x 10 m (82 x 33 feet), but still impressive! I wouldn’t have expected such volumes, but fortunately we didn’t have to deal with this issue.
Thanks for the reply and best of luck with the ongoing construction!
Best regards,
AndreasYes, seeing it flow just over the sand barrier of the settling basin was quite impressive. I hadn’t expected the water to infiltrate the ground so quickly either. But the water pressure was remarkable. It already gives you an idea of what the waterproof basement will have to withstand eventually—and hopefully for the entire life of the house.
In the end, that adds up to 7.3 Olympic-sized swimming pools. 🙂
Thank you very much!
Allthewayup schrieb:
We pumped about 7,300m³ (9,540 cubic yards) of water in 14 daysThat’s seven times the volume of the burst aquarium in Berlin 😳 and theirs only took seconds to drain 🙄.
You did a great job with that; it really shows why it’s important when both kids and adults play with water.
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