ᐅ Infiltration of Rainwater into Clay Soil

Hello, we moved into our new build last year and have been working on the outdoor areas this year: terrace, driveway, etc. – including managing stormwater infiltration (discharge into the sewage system is not allowed; infiltration must take place on the property).

We hired a landscaping company to install a soakaway system (plastic, 6000 liters (1600 gallons)) for this purpose. Rainwater from the roof and gutters is directed into it and is supposed to drain into the ground.

After recent heavy rains, we noticed the soil around the soakaway has slightly settled. When digging up the area, it became clear that large cavities had formed in the soil around the soakaway. The landscaper now plans to fill these with soil once the ground has completely dried.

I have never dealt with soil conditions before, but after this incident, I looked into it more closely: our soil is very clayey. According to the soil report, the soil mainly consists of glacial till – which, as I’ve learned, is not suitable for infiltration and is basically not appropriate for a soakaway system.

Has anyone had experience with this? What does it mean for the soakaway? Could everything eventually collapse? Could this pose a risk to the house (the soakaway is about 3 to 4 meters (10 to 13 feet) away from the house)? Can we just leave everything as it is and fill the cavities in the soil, or does the entire soakaway need to be removed?

I would appreciate any input. Maybe someone has an idea how to fix this.

We had to build a surprisingly large soakaway with a volume of 23 cubic meters (810 cubic feet) in soil that doesn’t allow infiltration. The municipality required it, although the experts thought it was unnecessary. The regulations have been met, and so far there was one heavy rainfall event that caused water to run from the property onto the street. So it’s working, in a way.

Don’t worry about the house itself; the soil conditions were taken into account there. Adding some fill material around the soakaway as the landscape gardener suggests is sufficient.

After that, no need to give it any more thought.

hampshire schrieb:


Don’t worry about the house; the soil conditions have already been taken into account. Adding some fill around the soakaway, as the landscape gardener suggests, should be sufficient. Then you can stop worrying about it.

Phew, I don’t think I’ll be able to stop worrying about it that easily 😉 According to the landscape gardener, the soakaway was probably just full… and I’m guessing that caused the ground to become saturated, causing all the mud to collapse in on itself… and I keep wondering what it must look like underneath the soakaway 😱

Reluctance schrieb:

and I keep wondering what it might look like underneath the soakaway 😱

Just install a periscope 😉 . Time helps—after a year you won’t give it a second thought.

New construction, everything settles. This is normal.

Reluctance schrieb:

Hello, we moved into our newly built house last year and this year we have been working on the outdoor areas: terrace, driveway, etc. Among other things, we also dealt with the infiltration of rainwater (discharge into the sewer system is not permitted; infiltration must take place on our own property).

We hired a landscaping company for this, and they installed a soakaway (plastic, 6000 liters (1585 gallons)) for infiltration. Roof and gutter water is directed into it and is supposed to seep into the ground.
After recent rainy days, we noticed that the soil around the soakaway is slightly sinking. Excavating the area showed that large voids have formed in the soil around the soakaway. The landscaper now says he wants to fill these voids with soil once the ground has completely dried.

Until now, I’ve never dealt with topics like soil conditions, but after this incident I researched a bit more: our soil is very clay-rich. According to the soil report, the soil primarily consists of glacial till - and from what I have read, this is not permeable at all, so basically completely unsuitable for a soakaway.

Has anyone had experience with this? What does this mean for the soakaway? Will everything eventually just collapse or sink? Could it become dangerous for the house (the soakaway is about 3 to 4 meters (10 to 13 feet) away from the house)? Can we just leave everything as it is and fill the voids in the soil, or does the entire soakaway need to be removed?

I would be glad if someone could share some advice on this. Maybe someone has an idea how to fix this.

Hello Reluctance,
Could you please share how things developed for you? We have the same problem here and I have no idea what to do now.
Best regards