In densely built-up areas, the foundations of buildings must be inspected toe decide on any measures to support and secure them.
Some 5,000 shafts are being dug manually to the bottom edge of the foundations along the new U2 and U5 routes. Samples are stored in so-called compartment boxes.
The condition of the masonry is also documented using photos and sketches.
Construction technicians analyse the information collected and, if necessary, the foundations are improved, which not only improves safety but also the long-term condition of the building.