In September 2020, a Finnish construction company faced an incident while launching a bridge in Umeå, Sweden. Mammoet, a company of experts, was called in to assist with the bridge’s salvage and ensure safe construction. Mammoet’s intervention helped the construction company avoid tearing down the bridge entirely and instead save most of its original structure.
The bridge was a part of a new highway that bypasses the city of Umeå and crosses over the Umeå River in northern Sweden. It was 464 meters long, had four spans, weighed 3,050 tonnes, and was built over a regular bend (800-meter radius) and a 2.25% downward slope. The bridge was constructed using an incremental launching process, where the front section is pulled forward over supporting piers, and each new piece is connected to the previously launched section until it reaches the opposite side of the river.
During the bridge’s second launching stage, it moved uncontrollably for over 130 meters, causing it to rest in an unstable condition. The impact caused serious damage to sections of the steel deck resting on the first two concrete piers, resulting in the bridge twisting out of alignment and the backend falling from the abutment. Mammoet engineers quickly responded to the incident and proposed a salvage solution, which they implemented on-site after further analysis.
The solution involved installing several temporary shoring towers with hydraulic capacity to lift the complete bridge and release the load from the concrete piers. The non-damaged portions of the deck were separated from the damaged ones, and the most damaged section was cut and pulled back to the launching pad for repairs to be carried out at ground level. Temporary shoring towers were erected around the two concrete piers to release the bridge and allow for the necessary cuttings and repair operations to happen. A cantilever gantry was also used to lift the back section off the ground and raise it up to the launching level at the abutment, close to the launching pad.
In addition to lifting the bridge, it needed to be realigned and straightened back to its due geometry. Hydraulic jacks were installed on top of each tower to move the bridge up and down, right and left, and back and forth. The system was computer-controlled, providing constant, real-time monitoring of all the bridge’s loadings, allowing it to be moved in any direction. Mammoet had to adapt their standard launching equipment to create a new solution that combined two different jacking systems to lift the bridge to a height of more than 2 meters.
The complex engineering rescue project is still ongoing, with Mammoet’s assistance. The bridge is being salvaged and constructed with the company’s help. This innovative project has allowed the company to create a new jacking system for bridge launches.
