Earthworks/basement construction in high groundwater areas – any experiences?

Thank you So it is urgent for you. Soil survey available? If yes, soil permeability value? Size of the excavation pit? Distance to neighboring buildings? Approval for the lowering obtained from the local water authority? 1.7m is already a lot but not impossible with well-permeable soil. I would rely on 2 extraction wells going down to 4.50m depth. The discharge into the sewer (liters per second) must be clarified and you must know what quantities to expect when pumping! Especially for the dimensioning of the system. Someone must monitor the system (24/7). If it fails overnight, pumping for 2 days is wasted and if the basement walls are already standing and there is too little load on the floor slab, it could worst case scenario float up. Are there photos of the status quo? *Edit: 470m??? Is it uphill/downhill there? Even horizontally that means an immense pumping capacity. Are you aware of the costs of this operation?

Yes, unfortunately I am in a hurry. These were many technical questions. I will try to answer them to the best of my knowledge.
- Soil report available; Kf value - I searched for it and came across this table
- Dimension of the base plate (including overlap) approx. 13.10m x 18.10m
- Distance to the outbuilding: There is only an attached double garage on one side. On the other sides there are several meters to the buildings (estimate 4-7m)
- Water law permit and permit for dewatering: Yes, all available - we are already in the process of laying the pipes
- Extraction well: Can you define this differently for me as a layman? Today I am talking about 3 drillings for dewatering, whose pipes are laid to the sewer; additionally, we have installed a deep injection well on the property. What additional measures do you recommend?
- Water quantities during pumping: Good question - no idea
- Monitoring of the system 24/7: So we have an emergency power generator. But how should the pipes be monitored additionally? I cannot hire a security guard for that. At most, I could ask the neighbors to keep an eye on it as a favor
- Photo status quo - see below

Thank you!

Are you doing the lowering independently? Who submitted the application to the authority? They usually want all technical data about the project, including the water quantity.
So the [Schluckbrunnen] is your extraction point? It is deep enough. The pump must then be correspondingly powerful. But what do you mean by the other 3 drillings? What is placed in the borehole? A metal pipe with holes/slits?
Extraction wells are relatively simple: these are concrete shaft rings that are excavated with a special excavator ([Seilbagger], shaft grabber) and thus sink deeper and deeper into the ground. Basically, handover shafts are also created with it, but just not as deep.
The measures result from the framework conditions.
For example, the distance to neighboring buildings of 4-7m is critically low. Settlement damage cannot be ruled out at 1.7m. And it won’t stay at 1.7m. Then the excavation pit is just dry, but you need about 30cm of dry soil below the floor slab. Specialist literature even assumes 50cm, but no one does that in practice. I have to check my calculation regarding the kf-value tomorrow. Seems to be well permeable. In the photos, I see gravelly soil which helps you on one hand (gravity drainage), but on the other hand a lot of water flows in, which increases the effort (energy, system dimensioning, etc.). Your neighbors can only be partially sensitized to this. That means you currently don’t live nearby either to check on things often? I had my system redundantly designed. Two wells, two pumps, different power sources used, and drained from the settling basin purely by gravity into two different sewers via two separate outlets. A failure of one pump or malfunction of one extraction point would not have affected the second.

By the way, it shouldn’t look like this.

The measures are being carried out by a specialist company, an earthworks contractor who has frequently worked with water management. However, the gentleman (managing director) has reacted very emotionally in recent weeks and does not clearly state whether we will be able to achieve the water lowering as planned or not. The applications to the authorities (including water law permits) were organized by the earthworks contractor in coordination with our general contractor. The general contractor, on the other hand, since he has not subcontracted the earthworks contractor, is somewhat holding back here. I am really sorry to respond to you with such layman knowledge. But I think I need to make some adjustments to your summary. The first installed injection well is not intended for extraction, but for additional infiltration. To my knowledge, drilling is done at three different locations and pumps are connected to these drillings. Now the water is widely lowered and pumped through the pipes into the sewer. The injection well is supposed to serve as an additional infiltration point (besides the sewer) to presumably lay a fourth pipe. I also raised the question of whether a second injection well at another location might also make sense. Apart from my other questions, whether we might possibly achieve our goal with this. I can definitely check on things daily (travel time 30-40 minutes), but obviously cannot ensure 24/7 monitoring :)

By the way, this is how it should not look.

That is downright dreadful. It definitely should not look like that and hopefully never will.