Southern arm of the industrial canal Freiburg

A new shell for an aged arch

During a structural inspection in 2011, KREBS+KIEFER discovered that the freshwater canal was displaying loose brickwork, as well as damage caused by water pressure from the outside and penetrating roots. In the course of the new construction of a central metropolitan railway line, the city of Freiburg commissioned KREBS+KIEFER to undertake the renovation work. In addition to this there was also the outline planning, tender design, site supervision and health and safety coordination to be carried out. The section of the canal to be renovated was a 122-metre-long arch constructed of pure, natural stone.

The stone was first cleaned with high-pressure water jets. Divided into work sections of approximately 20 metres in length, the arch was given a 12-centimetre thick sprayed shotcrete shell using a dry shotcreting procedure Where necessary, a dimpled sheet is used all the way around to provide protection against water pressure. 2,700 shear studs connect the natural stone arch with the shotcrete shell.

The renovation work was to be carried out within a period of just six weeks, during which time the canal was closed. Other challenges were the very cramped conditions and the lack of fresh air (ventilation).