Lowering of groundwater according to soil report - Your experiences?

Then use drainage pipe wrapped with coconut fibers. A slight slope should still be no problem.

The effort with the lances would of course be 10 times less. In a pinch, just take 4 pcs.

or you build the basement in August, maybe there won’t be any water then :D

When was the expert report made? How much does the Danube water level fluctuate over the course of the year?

A slope is necessary anyway – no question. A construction machinery dealer has a large slot mill that goes about 70 cm deep, that would be ideal. Then some gravel from the paved driveway, which has to be torn up anyway, to bed the pipes. I would love to start in August but the general contractor won’t like that, unfortunately. Actually, the lowest water level is in autumn and not in midsummer as one might assume. The expert report is from early December 2021 and there was a normal water level and no heavy rainfall in the days before. I also think that racking one’s brain day and night now just drives you crazy. We have now significantly increased the pumping capacity (from 15 to 27 ccm/h) and if that is not enough, contrary to expectations, we will add one with 15 ccm/h. After deducting losses, there should still be 35 ccm/h achievable. If even that doesn't get us a dry pit, we better leave it. Because if we inadvertently “wash out” everything around us unnoticed, we will have much bigger problems.

something different, do you have the technical room with supply lines in the basement?
You could just build a deep well there for about 1000€.
While constructing the basement, you lower the water table by one meter.
Later, you use it for garden irrigation.
Then the 1500 including pump is not even lost, but sensibly invested.

We already have a well on the property (optimally placed in the corner) which we want to preserve during the construction period. Since it penetrates the water-impermeable layers and goes down to about 12m depth, unfortunately it is not suitable for groundwater lowering. By the way, that was our first (stupid) thought to try it that way.

We already have a well on the property (optimally placed in the corner) that we want to preserve during the construction period. Since it penetrates the water-impermeable layers and goes down to about 12m deep, unfortunately it is not suitable for lowering the groundwater level. By the way, that was our first (stupid) idea to try it that way.

Who says that?
For 20k, I would dig a 2.5m hole for about 2 hours at the other end of the well.
If water forms, you turn on the pump for 2 days and run a hose into the sewer.
I would be surprised if nothing happens there.

Who says that?
For 20k I would dig a 2.5m hole for 2 hours at the other end of the well.
If water forms, you turn the pump on for 2 days and let it run into the sewer with a hose.
I would be surprised if nothing happens.

So the geologist said: If water is extracted too quickly below impermeable layers, no volume compensation for the withdrawn water can occur in a short time, so that the layers above can eventually sink. In the worst case, this results in sinkholes. So if I want to make the neighboring house disappear completely, I can do that :-)
But I prefer to stay above this layer with my tinkering :-)

A small update on this topic.

After numerous phone calls with the city (Environmental Department) and the municipal utilities regarding carrying out the work independently, the following situation has arisen:

I am now submitting an application for temporary groundwater lowering. For this purpose, I have written a multi-page report that includes, among other things, a justification for the construction water retention, I had to calculate the inflow into the excavation pit, and I prepared a hydraulic calculation. Since I have been dealing with the topic for months, I also wrote a construction description of the entire system for construction water retention along with a site plan of the system.

How did I proceed?

The soil survey provided all the necessary parameters to calculate the water inflow into the excavation pit. After calculating the amount, the choice of the appropriate water retention method followed. I decided on a drainage system with 2 recharge wells – why and how exactly would go beyond the scope here. There are diagrams that show the optimal method depending on soil permeability and lowering depth, just look for those. AND it is of course important that the calculated water quantity can be absorbed or diverted by the system. Then I proceeded to dimension the system: pumps, hoses, sand trap containers, drain pipes, sewer capacities, etc. The results of the hydraulic calculation can be used for the proper selection of these components. Then it had to be clarified where these drains and recharge wells should be placed. This depends, among other things, on the construction site, the available space, the groundwater flow direction, and the level to which the groundwater table is to be lowered. After these things were clarified, I visited all construction equipment rental companies in the city to look at the machines needed and clarify technical details regarding feasibility. For example, to clarify the milling depth for the trench mill to install the drains in the ground, to inspect the multi-loader and drilling attachment to sink the recharge wells, the sidewalk crossing in terms of the maximum possible height for the discharge pipe, and so on...

Finally, I listed all the required items and assigned a price (most of it you can get online). For those interested:

- Material costs: €2,450
- Rental equipment: €1,720
- Wastewater fee for calculated amount (29,500 m³): €19,175
- Electricity and official fees: €3,025
- Earthworks for 2 shafts: €750

TOTAL: €27,310

It helps enormously that we are allowed to place the system on my parents’ property and that we don’t need additional pumps to drain the water thanks to an optimal slope. This saves electricity and rental or purchase costs for the pumps. Although here I really recommend buying the pumps!!! Renting would have cost the same as buying, and when we are finished, we can sell the pumps for roughly the same price. The same applies to fire hoses, Storz couplings, water meters, etc. The next person will need those again anyway.

I estimate that we save about €10,000 or more compared to having a specialist company carry out the work. If the city approves our application, I think we won’t be far from a specialist company in terms of execution :) At least, according to the employee of the municipal utilities, we are the first builders who have put together the application along with the calculations and construction description themselves. That makes one a bit proud :-D

Since it is almost impossible to find any information on groundwater lowering from other builders on the internet, I will try to keep this topic going here and provide updates on news and the current status.

This is not a "general encouragement" to carry out water retention on your own at any cost. We were forced to do so because we couldn’t find a deep foundation contractor willing to do it. Presumably, at such a small site, it is simply a waste of time for the companies since they make most of their (easiest) money when the systems just run. Setup and teardown is probably unnecessary wear and tear.

Thank you very much for the interesting insight!