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.
Allthewayup schrieb:
Do you still remember how high the costs related to the authorities were and how many days in total you had to pump? You probably don’t remember the subsidized cubic meters anymore 🙂 That would still be interesting. We pumped for about 4-5 months until the house was backfilled. Thirty years ago, there were no fees from authorities for that.
Today it would be more expensive, although if you do the sewer cleaning/flushing yourself, my argument would be to save some money.
You still have the water costs even if a company does it, plus the equipment rental, labor, and their profit.
Nida35a schrieb:
We have experienced this several times,
then the water from the drainage flows into the basement light wells 😳.
So we closed the basement light wells, placed the pump inside the vertical drainage pipe, and pumped for 2-8 weeks until the groundwater level dropped again. It doesn’t happen to me. But if it doesn’t work for you, then it can’t be my fault.
A
Allthewayup18 Apr 2022 22:51TmMike_2 schrieb:
I would have the excavation for the basement done and install 2 wellpoints as suction wells into the ground.
The idea with the drainage pipe is good, but I can only imagine it working if the pipe is at least 1.2–1.5 m (4–5 feet) below the basement slab. I found an illustration in a technical book that exactly describes my approach. Unfortunately, I couldn’t find it again quickly. Since the drainage pipe forms a closed loop around the excavation pit, 50 cm (20 inches) is indeed enough to keep the soil free of groundwater. Of course, water can still push up from below to some extent, but due to the good permeability of the soil, it flows relatively quickly to the sides, so no large water column can build up. If I work with only 2 wellpoints, I have to install them deep enough to achieve a sufficient drawdown radius where the water level falls off. I have some concerns about having to lower the water level “too much” around the wells. I want to cause as little disturbance as possible to the ground.
Allthewayup schrieb:
I found an illustration in a technical book that exactly describes my approach. Unfortunately, I couldn’t find it again quickly. Since the drainage pipe forms a closed ring around the excavation, 50cm (20 inches) is actually enough to keep the base free from groundwater. Of course, water might push up slightly from underneath, but due to the good permeability of the soil, it drains relatively quickly to the sides, so no significant water column can form. When I work with only two injection lances, I have to insert them quite deep to achieve a sufficient drawdown radius to which the water level falls. I am a bit concerned about having to lower the level “too much” around the well. I want to cause as little disturbance as possible in the soil. Then use drainage pipe wrapped with coconut fibers. A slight slope shouldn’t hurt either.
The effort with the lances would obviously be 10 times less. If necessary, just use 4 of them.
Or build the basement in August, maybe then there won’t be any water 😀
When was the survey prepared?
How much does the Danube’s water level fluctuate throughout the year?
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Allthewayup18 Apr 2022 23:01Nida35a schrieb:
We pumped for about 4-5 months until the house was backfilled. Thirty years ago, there were no authority fees for that.
Today it would be more expensive, but if you do the sewer cleaning/flushing yourself, my argument would be that you could save some money.
You still have the water costs either way, but if a company does it, there are also equipment rental fees, labor costs, and their profit. The water costs are present in both cases, that’s clear. Back then, that was probably the standard procedure. Today, it should be possible to complete it within 6-8 weeks. Usually, the basement would be watertight by then. I just hope we’re not taking on too much with handling the drainage ourselves. The neighboring houses are all about 6m (20 feet) away and also have basements. A professional company could, of course, advise on the best and safest way to do this, but so far, no one has shown any interest...
Allthewayup schrieb:
The water costs are present in both options, that’s clear. Back then, that was probably still the standard practice. Today, this should be achievable within 6–8 weeks. Usually, the basement will be completed by then. I just hope we don’t overextend ourselves by managing the drainage on our own. The neighboring houses are all only about 6m (20 feet) away and also have basements. A professional company could of course tell us right away how to handle this most efficiently and safely, but unfortunately, no one has shown any interest so far… Something different—does your utility room with supply lines go into the basement?
You could immediately install a deep well there for about 1000€.
During the basement construction, you lower the water table by about one meter (3 feet).
Later, you can use it for garden irrigation.
Then, the 1500 euros including the pump are not even lost, but rather a sensible investment.
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