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
Allthewayup18 Apr 2022 23:12TmMike_2 schrieb:
Then use drain pipe wrapped with coconut fibers. A slight gradient should still be beneficial.
The effort with the lance system would of course be 10 times less. If necessary, just use 4 pieces.
Or you could build the basement in August; maybe there won’t be any water then 😀
When was the survey conducted?
How much does the Danube’s water level fluctuate throughout the year? A gradient is definitely necessary—no question. A construction equipment dealer has a large trenching machine that can go about 70cm (28 inches) deep, which would be ideal. Then, some gravel from the paved driveway, which will have to be torn up anyway, could be used to bed the pipes. I would love to start in August, but unfortunately that wouldn’t suit the general contractor. Actually, water levels are lowest in autumn rather than in midsummer, as one might assume. The survey is from early December 2021 and showed normal water levels, with no significant rainfall in the days before.
I also think stressing over this day and night only drives you crazy. We have now significantly increased the pumping capacity (from 15 to 27 cc/h), and if that still isn't enough, we’ll add another pump with 15 cc/h. After accounting for losses, we should still achieve about 35 cc/h. If even then we can’t keep the pit dry, it’s better to stop. Because if we end up unintentionally “washing out” everything around us, we’ll have far bigger problems.
A
Allthewayup18 Apr 2022 23:16TmMike_2 schrieb:
Something different—will your utility room with supply lines be located in the basement?
You could build a deep well for about 1000€ at the same time.
During the construction of the basement, you lower the water table by about one meter (3 feet).
Later, you can use it for garden irrigation.
Then, the 1500€ including the pump isn’t even sunk cost but a sensible investment. We already have a well on the property (ideally located in the corner), which we want to preserve throughout the construction period. Since it penetrates the impermeable layers and reaches a depth of about 12 meters (39 feet), unfortunately it is not suitable for groundwater lowering. By the way, that was our first (foolish) idea to try.
Allthewayup schrieb:
We already have a well on the property (ideally located in a corner), which we want to keep throughout the construction period. Since it penetrates the impermeable layers and goes down to about 12m (40 feet) deep, unfortunately it is not suitable for lowering the groundwater level. By the way, that was our first (foolish) idea to try. Who says that?
For $20k, I’d dig a 2.5m (8 feet) deep hole for 2 hours at the other end of the well.
If water accumulates, you just run the pump for 2 days and connect it with a hose to the sewer.
I’d be surprised if nothing happens.
A
Allthewayup19 Apr 2022 07:20TmMike_2 schrieb:
Who says that?
For $20,000, I’d dig a 2.5m (8 feet) hole at the other end of the well for about 2 hours.
If water starts to accumulate, you run the pump for two days straight and drain it through a hose into the sewer.
I’d be surprised if nothing happens. The geologist said that if water is extracted too quickly from below impermeable layers, a volume replacement for the removed water can’t occur in a short time, so the layers above can eventually settle. In the worst case, this can cause sinkholes. So if I wanted to make the neighbor’s house completely disappear, I could do that :-)
But I prefer to stick to working above that layer :-)
A
Allthewayup5 May 2022 12:05A brief update on this topic.
After numerous phone calls with the city (environmental office) and the municipal services regarding carrying out the work independently, the following situation has emerged:
I am now submitting an application for temporary groundwater lowering. For this, I have prepared a detailed report that, among other things, includes a justification for the dewatering during construction, calculations of the inflow into the excavation pit, and a hydraulic calculation. Since I have been working on this topic for several months, I also wrote a construction description of the entire dewatering system along with a site plan of the installation.
How did I proceed?
The soil survey provided all the necessary data to calculate the amount of water flowing into the excavation pit. After calculating the volume, I chose the appropriate dewatering method. I decided on a drainage system with two infiltration wells – explaining the reasons in detail would go beyond the scope here. There are diagrams that indicate the optimal method depending on soil permeability and lowering depth, so just look for those. AND of course, it is important that the system can handle the calculated water volume. Next, I sized the system components: pumps, hoses, grit traps, discharge pipes, sewer capacities, etc. The results of the hydraulic calculation can be used to select these components correctly. Then it had to be determined where to place the drains and infiltration wells. This depends, among other things, on the construction site, available space, groundwater flow direction, and the amount by which the groundwater level needs to be lowered. Once these details were clarified, I visited all the construction equipment rental companies in the city to inspect the required machines and verify technical feasibility. For example, I checked the milling depth of the trenching machine to install the drains in the ground, examined the multi-loader and drill attachment to embed the infiltration wells, assessed the maximum possible height clearance for the discharge pipe on the sidewalk crossing, and so on...
Finally, I listed all required materials and assigned prices (most of which are available online). For those interested:
- Material costs: €2,450
- Equipment rental: €1,720
- Wastewater fee for calculated volume (29,500 m³ (35,000 yd³)): €19,175
- Electricity and official fees: €3,025
- Earthworks for 2 shafts: €750
TOTAL: €27,310
It is a huge advantage that we are allowed to place the system on my parents’ property and, thanks to an optimal slope, we do not need additional pumps to discharge the water. This saves electricity and pump rental or purchase costs. By the way, I highly recommend buying the pumps! Renting would have cost roughly the same as buying, and once we are done, we can sell the pumps for about the same price. The same applies to fire hoses, Storz couplings, water meters, etc. The next person will need these too.
I estimate that we will save around €10,000 or more compared to contracting a professional company for the work. If the city approves our application, I think we won’t be far off in quality from a professional company 🙂 According to the municipal services employee, we are the first builders to prepare the application, calculations, and construction description ourselves. That’s something to be proud of :-D
Since there is almost no information from other builders online about groundwater lowering, I will try to keep this thread going and provide updates when there are news or changes in status.
This is not intended as a general recommendation to carry out dewatering independently at all costs. We were forced to do it ourselves because we couldn’t find a specialist contractor willing to take on the job. Probably, for such a small site, it is simply a waste of time for companies, as such systems earn most of their easily made money when they just keep running. Setup and dismantling is likely unnecessary wear and tear.
After numerous phone calls with the city (environmental office) and the municipal services regarding carrying out the work independently, the following situation has emerged:
I am now submitting an application for temporary groundwater lowering. For this, I have prepared a detailed report that, among other things, includes a justification for the dewatering during construction, calculations of the inflow into the excavation pit, and a hydraulic calculation. Since I have been working on this topic for several months, I also wrote a construction description of the entire dewatering system along with a site plan of the installation.
How did I proceed?
The soil survey provided all the necessary data to calculate the amount of water flowing into the excavation pit. After calculating the volume, I chose the appropriate dewatering method. I decided on a drainage system with two infiltration wells – explaining the reasons in detail would go beyond the scope here. There are diagrams that indicate the optimal method depending on soil permeability and lowering depth, so just look for those. AND of course, it is important that the system can handle the calculated water volume. Next, I sized the system components: pumps, hoses, grit traps, discharge pipes, sewer capacities, etc. The results of the hydraulic calculation can be used to select these components correctly. Then it had to be determined where to place the drains and infiltration wells. This depends, among other things, on the construction site, available space, groundwater flow direction, and the amount by which the groundwater level needs to be lowered. Once these details were clarified, I visited all the construction equipment rental companies in the city to inspect the required machines and verify technical feasibility. For example, I checked the milling depth of the trenching machine to install the drains in the ground, examined the multi-loader and drill attachment to embed the infiltration wells, assessed the maximum possible height clearance for the discharge pipe on the sidewalk crossing, and so on...
Finally, I listed all required materials and assigned prices (most of which are available online). For those interested:
- Material costs: €2,450
- Equipment rental: €1,720
- Wastewater fee for calculated volume (29,500 m³ (35,000 yd³)): €19,175
- Electricity and official fees: €3,025
- Earthworks for 2 shafts: €750
TOTAL: €27,310
It is a huge advantage that we are allowed to place the system on my parents’ property and, thanks to an optimal slope, we do not need additional pumps to discharge the water. This saves electricity and pump rental or purchase costs. By the way, I highly recommend buying the pumps! Renting would have cost roughly the same as buying, and once we are done, we can sell the pumps for about the same price. The same applies to fire hoses, Storz couplings, water meters, etc. The next person will need these too.
I estimate that we will save around €10,000 or more compared to contracting a professional company for the work. If the city approves our application, I think we won’t be far off in quality from a professional company 🙂 According to the municipal services employee, we are the first builders to prepare the application, calculations, and construction description ourselves. That’s something to be proud of :-D
Since there is almost no information from other builders online about groundwater lowering, I will try to keep this thread going and provide updates when there are news or changes in status.
This is not intended as a general recommendation to carry out dewatering independently at all costs. We were forced to do it ourselves because we couldn’t find a specialist contractor willing to take on the job. Probably, for such a small site, it is simply a waste of time for companies, as such systems earn most of their easily made money when they just keep running. Setup and dismantling is likely unnecessary wear and tear.
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