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.
G
Grobmutant9 Apr 2022 09:37We had to pump out a significant amount of groundwater around the excavation site for about three weeks using wellpoints.
Costs:
€9,500 gross paid to the general contractor
+ Approximately €2,000 in fees (Lower Saxony)
+ Electricity costs (no exact figures yet)
Fortunately, we were able to let the water infiltrate into a pasture. Discharging it into the sewer would definitely have been more expensive.
I can't imagine that pumping it out with our own pumps would have worked here. Quite a few liters of water accumulated.
Costs:
€9,500 gross paid to the general contractor
+ Approximately €2,000 in fees (Lower Saxony)
+ Electricity costs (no exact figures yet)
Fortunately, we were able to let the water infiltrate into a pasture. Discharging it into the sewer would definitely have been more expensive.
I can't imagine that pumping it out with our own pumps would have worked here. Quite a few liters of water accumulated.
A
Allthewayup17 Apr 2022 22:11Grobmutant schrieb:
We had to pump out quite a bit of groundwater around the excavation pit for about three weeks using wellpoint systems.
Costs:
9,500 euros gross paid to the general contractor
+ About 2,000 euros in fees (Lower Saxony)
+ Electricity costs (I don't have exact figures yet)
Fortunately, we were able to let the water infiltrate into a pasture. Discharging it into the sewer system would probably have been even more expensive.
I can’t imagine that pumping it out with our own pumps would have worked. There were several liters of water coming in. Thanks for the information. We have now decided to try it ourselves first. We have a buffer of 6 to 8 weeks from demolition to actual construction start. At the base of the excavation pit, I will lay about 30 meters (100 feet) of drainage pipes leading to a deeper sump. There, we will install a submersible sewage pump with a capacity of 15,000 liters per hour (about 4,000 gallons per hour). We’ll run it like that for a few days and see what happens. The materials will cost no more than 1,000 euros. If it still doesn’t work, we’ll call in the professionals.
A
Allthewayup18 Apr 2022 08:05Nida35a schrieb:
Where are you pumping the water to at low cost?
Is the distance to the discharge point far, and what hose diameter are you planning to use? It won’t be cheap; we have to obtain a water use permit to legally discharge the water into the sewer, and we’ll also need to rent a sand trap container. The distance to the sewer (about 25m (82 feet)) runs through my parents’ property, so that’s not an issue. I’ve chosen a pump with a 1 1/2 inch C-connection. The hose itself is 2 inches in diameter. What I’m still unsure about is whether the drainage pipes will allow enough water to flow through in such a short time. I have no prior experience with this. I’m attaching pictures of the components that will be used; maybe someone will have suggestions. We place the pump in the large shaft, and it fits well thanks to its outlet being on top. On the left and right sides, yellow drainage pipes are connected through reducers. We install a blank plug on the third opening at the front. The drainage pipe is basically routed in a loop around the excavation pit. Ah, and a second pump will be installed in the settling container to pump the water into the sewer.
We had an open trench around the base slab to avoid pumping up too much sand or clay.
It depends on the soil type.
If there is too much of it, you can wrap the drainage pipes with geotextile fabric, about 1.5 layers.
With the container, you can measure how much water is being pumped out.
It will be fine.
It depends on the soil type.
If there is too much of it, you can wrap the drainage pipes with geotextile fabric, about 1.5 layers.
With the container, you can measure how much water is being pumped out.
It will be fine.
A
Allthewayup18 Apr 2022 10:18At the foundation level, we have quite a gravelly, permeable soil, which probably results in larger amounts of water. The drainage pipe is covered with a “sock” to minimize clogging by sand. There is also a sand trap below the base of the soakaway pit. I am already considering installing a second pit on the opposite side because a pump might not be sufficient.