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
Allthewayup5 May 2022 14:42I just checked regarding water ingress into the drain pipes. The manufacturer states: 80 square centimeters of water entry area per meter. That means for a length of 50m (164 feet), there is 0.4 square meters (4.3 square feet) of entry area. After deductions for water surface tension and resistance due to the filter sleeve, etc., there is still enough “free” water entry area to allow the required 13.3 liters per second (3.5 gallons per second). The slope is actually more critical here. If water pools in the pipe, the entry area becomes “blocked.”
It should work out fine :-)
It should work out fine :-)
Allthewayup schrieb:
It's bound to go wrong 🙂Little boys dam streams, and big boys have fun with lowering water levels, drainage, pumps, and hoses. An interesting phase of construction for you. Watching the company do it isn’t nearly as much fun.
A
Allthewayup5 May 2022 19:52Nida35a schrieb:
Watching the company do the work isn’t very enjoyable.And I wouldn't have learned nearly as much over the past few weeks. Valuable insights have been gained about soil conditions, their relationships, and everything involved. In a way, it’s quite rewarding to grow through such challenges.
And as a bonus, one finally gets to operate heavy machinery again :-D
Allthewayup schrieb:
And I wouldn’t have learned nearly as much over the past few weeks. Valuable insights have been gained about soil composition, its interactions, and everything related. It’s also kind of enjoyable to grow through such challenges.
And on top of that, finally being able to operate heavy machinery again :-D Finally arrived at the housebuilding stage! That’s the right spirit.
One piece of advice I want to give you:
I don’t know your soil conditions or the water situation.
Think carefully about how you want to lay your drainage pipes, so your trench doesn’t keep collapsing.
But I have no experience in this area either. I always only see the option with lance drains.
A
Allthewayup6 May 2022 11:02TmMike_2 schrieb:
I want to give you one more piece of advice.
However, I don’t know your soil conditions or the water situation.
Think carefully about how you want to lay your drain pipes; you don’t want your milled trench to keep collapsing.
I have no experience in this area either. I only ever see the method using lances. The risk of collapse is indeed still worrying me a bit. Since we’re doing this as a team of two, installing the pipe simultaneously with the milling progress should prevent the trench from collapsing. It only gets difficult if the water washes out the soil too much during milling. But since we still have some time until construction starts, in the worst case I would drill 4 to 6 additional shafts and install vertical soakaway shafts. That would cost another 2,000 to 3,000 for machine rental, pumps, and electricity, but it should work then.
Something can always go wrong; a little tension is part of the process 🙂
*Edit:*
The lances are a vacuum method (closed water control) used in rather impermeable soils like sand, silt, and clay. Since we have well-draining soil (a lot of gravel), gravity drainage is possible.
A
Allthewayup9 May 2022 08:33Update from May 9th, 2022:
This morning, the first and so far only offer arrived by email.
The good news upfront: The professionals planned the system almost exactly as I had designed it, without us having discussed it beforehand. So, my technical planning is basically confirmed 🙂
But now the downside: nearly 40,000 for a really straightforward water management system is simply outrageous. I have to say that clearly. Since I have now studied the topic extensively and the positions in the offer are unambiguous to me, I can only shake my head. They are clearly trying to make a big profit. I have to be careful not to comment too emotionally, but one thing really bothers me: “The wells become the property of the client after construction” basically means: “If the neighboring houses sink into a hole or the street floods, that’s not our problem, and oh yeah, you have to handle the deconstruction yourself or pay us handsomely for it.” That is hardly reassuring regarding the quality of their work. Of course, no one can fully see underground, but if I hire professionals who boast years of experience, in my opinion, that’s just weak.
I don’t want to go into detail about individual positions, but if I didn’t trust myself to manage this, I would seriously consider leaving out the basement altogether. Because if I also include the services that, according to the offer, “must be carried out by the client,” I would end up with wastewater fees well over 60,000. That is completely disproportionate and absolutely unacceptable. I also think the industry is starting to lose its footing, and now they are trying to really squeeze those who still build at these high price levels.
Sorry if I sound a bit emotional, but I really needed to get that off my chest.
This morning, the first and so far only offer arrived by email.
The good news upfront: The professionals planned the system almost exactly as I had designed it, without us having discussed it beforehand. So, my technical planning is basically confirmed 🙂
But now the downside: nearly 40,000 for a really straightforward water management system is simply outrageous. I have to say that clearly. Since I have now studied the topic extensively and the positions in the offer are unambiguous to me, I can only shake my head. They are clearly trying to make a big profit. I have to be careful not to comment too emotionally, but one thing really bothers me: “The wells become the property of the client after construction” basically means: “If the neighboring houses sink into a hole or the street floods, that’s not our problem, and oh yeah, you have to handle the deconstruction yourself or pay us handsomely for it.” That is hardly reassuring regarding the quality of their work. Of course, no one can fully see underground, but if I hire professionals who boast years of experience, in my opinion, that’s just weak.
I don’t want to go into detail about individual positions, but if I didn’t trust myself to manage this, I would seriously consider leaving out the basement altogether. Because if I also include the services that, according to the offer, “must be carried out by the client,” I would end up with wastewater fees well over 60,000. That is completely disproportionate and absolutely unacceptable. I also think the industry is starting to lose its footing, and now they are trying to really squeeze those who still build at these high price levels.
Sorry if I sound a bit emotional, but I really needed to get that off my chest.