ᐅ PVC pipe for ventilation in the foundation slab (also known as the ground slab or concrete slab)

Hello everyone,

We recently bought a house built in 1978. It is located on a slope and does not have a basement. Currently, we have excavated around the side to apply new waterproofing and add external insulation.

During this work, we noticed two soil pipes (KG pipes) on the slope side that extend from the concrete slab and each is fitted with a ventilation hood. When looking inside, a cavity can be seen behind them. It is also noticeable that there is a draft coming from these openings.

Our energy consultant could not provide a clear explanation for this either.

Regarding the structure:

Masonry: Poroton, approximately 30 cm (12 inches)
Additional air gap: about 6 cm (2.5 inches)
The cavity seems to be located behind the masonry
Inside, a traditional screed layer
The house rests on a strip or pier foundation
According to the map, we are not in a designated radon area

Now our question is:
Should these pipes or the cavity stay open, or would it be better to close them?

Has anyone seen something similar or knows what function such soil pipes might serve in this context? It could possibly be a form of rear ventilation, drainage ventilation, or perhaps something related to moisture control—though we are not certain.

We are hesitant to close anything that might have an important function.

Thank you in advance for your insights!