Schwarzach near Nuremberg
Canal trough bridge
Schwarzach bei Nürnberg, Germany / 06.2021 - 03.2022
The Hamburg Underground is one of the city’s most iconic infrastructure projects. The first section of what is now the U3 line was built between 1906 and 1912 as a circular route around the Alster. As part of the partial refurbishment of the section between the main station and Baumwall, the tunnel trough at Mönkedamm was completely renewed from 2021 onwards. PORR special civil engineering manufactured 105 micro piles for this purpose to transfer the loads from the new reinforced concrete trough base into the load-bearing subsoil.
Facts & Figures
Company
PORR Spezialtiefbau GmbH
Type
Rehabilitation
Runtime
06.2021 - 03.2022
Construction pits and shoring solutions for the rehabilitation of a sewer bridge
Four construction pits, each around nine metres deep, had to be excavated to carry out the planned rehabilitation work on the bridge’s wing walls. The aim was to create the necessary working areas for the subsequent post-tensioning of the wing walls using steel strand straps. The excavation of the construction pits took place in confined spaces in the immediate vicinity of the bridge structure and required a shoring solution tailored to the local conditions.
Construction pit shoring with sheet pile walls and Soil nailing
Various specialist civil engineering methods were used to secure the construction pits. The longitudinal walls were secured with braced sheet pile walls, whilst the up-slope end walls were constructed as shotcrete structures with ground nailing. To temporarily secure the bridge wing walls during construction, bracing systems comprising steel girders were installed on three levels. These transferred the necessary support forces from the sheet pile walls to the existing structural elements. PORR special civil engineering has many years’ experience in the field of soil nailing. The company was involved in the development of the method and holds a general building authority approval (Z-20.01-104) for the system used.
Strand anchors in confined spaces
In addition to the excavation works, four trial strand anchors, up to 50 m in length, were installed and tested at the bridge abutments. The works were carried out under restricted headroom conditions and in confined spaces in the vicinity of the existing bridge structure. Planning and execution therefore had to be adapted to the local conditions.
Vibroflushing method for challenging ground conditions
The sheet pile walls were installed in the canal embankment slopes parallel to the wing walls of the bridge abutments. Due to the terrain, it was not possible to drive the double sheet piles – up to 13 m long – using a pile driver. The piles were therefore driven free-standing. In some sections, the so-called vibroflushing method was also used. The auxiliary water flushing enabled soil obstructions as well as hard-to-penetrate soil layers to be overcome.
Planning and execution from a single source
Colleagues from PORR special civil engineering support the project by carrying out the structural analysis of the excavation shoring as well as the soil-nailed shotcrete face walls. In addition, the detailed design and technical specifications for the excavation shoring and Soil nailing were drawn up. Thanks to the close integration of design and execution, the excavation solution could be tailored to the requirements of the bridge structure and the local conditions.
The basis for the rehabilitation of the canal trough bridge
The construction of the construction pits, the sheet pile walls as well as the soil nailing structures, and the wire-strand test anchors created the conditions necessary for the rehabilitation of the Schwarzach canal trough bridge. The specialised civil engineering works thus formed the basis for the rehabilitation of a structure on the Main–Danube Canal.