Lowering of groundwater according to soil report - Your experiences?

Here is the promised list. Of course, every project is different and this list makes no claim to completeness. It provides an insight into the scope that should not be underestimated. Certain things will also certainly change during the construction due to local conditions,

Quantity	Requirement	Description	Amount
1	Wastewater pump	Grundfos AP50.12	360.00 €
2	Wastewater pump	Güde Pro 2200	300.00 €
1	Wastewater pump	HOMA HBP503 WA	130.00 €
15	Slotted drainage pipe	DN100 solid pipe 2.5m each	150.00 €
2	Riser pipe DN400	1900mm length	130.00 €
2	Riser pipe DN315	1000mm length	60.00 €
2	KG end cap + socket plug	DN400	60.00 €
1	KG end cap	DN315	30.00 €
1	Drainage cover	DN100 per 50m	45.00 €
8	B-/C-hoses with fixed coupling	2" and 3"	130.00 €
tbd	KG bend DN125/DN110	various angles	30.00 €
tbd	KG pipe DN125/DN110	various lengths	50.00 €
1	Flexible rubber sleeve	DN100 to DN125	15.00 €
1	Storz B 3“ male	Fixed coupling external thread	5.00 €
2	Reducer piece	Storz B to A	35.00 €
2	Storz check valve	2“	100.00 €
1	Storz check valve	3“	100.00 €
2	Coupling wrench	Storz B / C	10.00 €
1	PE construction foil	300µ	70.00 €
1	Plastic water meter	DN100 flanged	200.00 €
2	Storz coupling 4“ A	4“ male	20.00 €
2	Threaded flange	DN100 with 4“ internal thread	65.00 €
16	Screw connection	M16x70	25.00 €
2	Traffic sign	Traffic sign 123 / Traffic sign 239 + Traffic sign 1022-10	70.00 €
4	Permanent light	Rotating beacon, red	80.00 €
4	Drainage gravel 765kg big bag	16/32	240.00 €
	Various small materials	Adapters/screws/accessories	200.00 €
	Rental equipment
1	Trench cutter VTX300	incl. trailer	400.00 €
1	Skip container	7m³ incl. delivery/pickup	900.00 €
1	Traffic safety	Barrier fence, adjustable feet, etc.	300.00 €
	Electricity	4500kWh	2,025.00 €
	Sewage fees	29,500m³	19,175.00 €
	Fees City of Ingolstadt	Environmental office	320.00 €
	Fees City of Ingolstadt	Traffic office	200.00 €
	Traffic safety seminar	MVAS / RAS	180.00 €
3	Additional earthworks	Excavation of shafts up to 1.7m	800.00 €
		TOTAL	27,010.00 €

Update from 15.08.2022

In the meantime, the notification from the city regarding the closure of the bike path has arrived, even though the "specialist company" said that this would be impossible to get approved, which is why they recommended that I lay the channel inside the property. :rolleyes:
Now everything that needs to be approved has been approved. I have to admit, that has already been quite a bit of work, but with almost a year's net salary as the cost of the trade, anyone can figure out how many hours could theoretically be "sunk" into it.

What’s next?

The house demolition and thus the trial excavation for the actual groundwater level was postponed by one week to 29.08. Current measurements from the city show a significantly lowered level. This is definitely due to the much too dry weather so far and of course works in our favor regarding the height to be lowered and ultimately the amount of water to be pumped out.

In mid-October, the civil engineering work on public land is to be carried out, which we had to contract to a local civil engineering company. Since the work is absolutely manageable, we also agreed on billing based on hourly rates after being informed of the prices.

I can’t report much more at the moment. Updates will follow once we know the exact groundwater level, set the wells, and then build the system in October. Setting the wells could be problematic because we did not want to commission a well driller (for many different reasons) and we now hope to get deep enough by excavation. One must consider that with these works we are already below the waterline, so I foresee some difficulties (slope failure/slips, quicksand, soil liquefaction, and endangerment of the stability of surrounding infrastructure). If it becomes too risky for us, the entire excavation pit will have to be filled and compacted so that the large well drill can be brought in. Should that become necessary, we are talking about approximately 25k additional costs for earthworks and civil engineering.

Update from 22.10.2022:

The existing building has now been completely demolished, and the excavation pit is partially prepared. Partially because the groundwater is currently about 2.4m below the ground surface and we cannot excavate any deeper yet. We ultimately decided against the 400mm KG pipes and instead had two DN1000 concrete shafts installed at a depth of 5m. This way, we have created a larger surface through which water can be collected in the shafts. Today was the setup of the system. Everything went as planned so far, but unfortunately the hoses were not in very good condition, so I had to do quite a bit of patchwork. As a test, the system ran for 30 minutes today to see if everything was as tight as possible and if enough water could drain by gravity. Here I made a small careless mistake and used a DN110 pipe instead of a DN125 pipe. Unfortunately, I can no longer correct the error because the pipe is laid under the sidewalk. As a result, I have to supply the second channel with 3 hoses instead of one as planned. Not a big deal, it just ties up resources in the form of hoses. There are other ways to solve this, but I just wanted to use what I already had. Currently, two pumps are in operation. Here too, I am considering replacing one of the two with a more powerful pump (from 30 to 42 cubic meters per hour). The groundwater really flows back quickly, you wouldn’t believe it. And as soon as you turn off the pump, the well fills with water very quickly again. So I assume that the pumps will actually run almost 24 hours a day for about 16 days, then the basement will be backfilled. Enough talking, I’ll let a few pictures speak.

To close the topic here:

We completed the basement construction as planned after about 2 weeks and were able to turn off the pumps promptly. The actual amount of water pumped was, to our great joy, significantly below my calculations, but too many factors play a role here to explain it conclusively now. We’re happy about it in any case. The purchased equipment is already 90% resold, and the expenses for it could almost be fully compensated. Not all items have been settled yet, but we can already say that the groundwater lowering will total about 10k when excluding the purchased and then resold equipment. We are super proud to have accomplished this and thereby saved, in principle, a small car. As a reminder, the offer made to us, including some additional services to be performed on site, was around ~40k. Of course, I was under constant pressure for 2 weeks because I was responsible for the pumps running 24/7. Sometimes I went over to the construction site at 1:00 a.m. when a hole in the pressure hose discovered in the afternoon wouldn’t let me sleep. Once a pump failed because the retaining rope had wrapped together with the power cable around the pressure hose, and when the pump started, the rotational impulse was so strong that the pump itself spun and kept switching off repeatedly. Problem identified, solved, and we carried on. The pumps actually ran 24/7 for the first 3 days. From day 4, they went into intermittent operation every few hours, and in the last 4-5 days, the run and stop times were about equal. The frequent switching on and off stresses the pumps immensely, which is why care had to be taken that the cycles did not exceed the switching cycles specified by the manufacturer. Here, good “tools” pay off; otherwise, the risk of failure would be significantly higher. Fortunately, I never had to switch to a backup pump because the pumps reliably performed their service.

All in all, we were also lucky with the soil. With clayey, very sandy, or peat-containing soil, this would not have been possible for us due to the immensely more complex system technology.

Hi,
that was definitely worth the effort. One question: How much water has been collected in total in the end? The initial calculation was 20 l/s, which is 5 swimming pools per day! Is it really that much water?

Best regards,

Andreas

If, for example, only the foundations are underwater, you can simply pour concrete. The concrete displaces the water. Usually, normal submersible pumps can't manage to pump it out anyway.