Replacement is being designed for future demand

The A29 motorway, in particular the section known as the Oldenburg Eastern Bypass, plays a central role in the transport network of north-west Lower Saxony, both as a regional long-distance transport link and for urban traffic in and around Oldenburg.

About four kilometres east of Oldenburg's city centre, there was a bridge built in 1978 over the Hunte river. Calculations showed that the long-term load-bearing capacity of the bridge was no longer guaranteed. In addition, traffic censuses predicted a significant increase in daily traffic volume by 2030. Therefore, the Niedersächsischen Landesbehörde für Straßenbau und Verkehr planned a replacement structure, for which the Autobahn GmbH des Bundes has been responsible since 1 January 2021. With a span of 441 metres, a width of 31 metres and a height of almost 30 metres, it has the same dimensions as the existing bridge.

High pile-driving resistance and a narrow pile arrangement were a challenge

In contrast to its predecessor, the new bridge rests on 14 V-shaped pillars instead of 36 individual pillars. Frankipiles NG® transfer the loads into the load-bearing sand layers of the subsoil, which follow at a depth of around 15 metres on a subsoil of fillings, peat and clay. Due to an old soil improvement, an increased driving resistance was detected at axes 20 and 80, which made it necessary to carry out loosening boreholes. FRANKI pile drivers were and are being used to install a total of 260 Frankipiles NG® with a diameter of 610 millimetres and a length of up to 15 metres. Static pile load tests carried out in December 2020 confirmed the required load-bearing capacity and made it possible to optimise the number and length of the piles.

Lars Brömstrup, the PORR branch manager, describes the challenges: ‘Due to the high pile-driving resistance and the close arrangement of the piles, the execution required all of our special civil engineering expertise. In addition, the single-lane access to the construction site along the Hunte river required close communication with all project participants.’

Protecting the Hunte, as well as the flora and fauna in the floodplains, is a high priority at the construction site. Therefore, hazardous substances are stored in trays, oil binders are kept on hand and not a single drop of fuel may reach the subsoil when refuelling the equipment. All employees at the construction site are instructed in these environmental protection measures.