Sarens Raises New Bowstring Bridge In France
Sarens installs and jacks down a 950-tonne bowstring bridge in Aix-Noulette, France
September 2019

Picture Courtesy Le Department, Pas de Calais

April 2019:  This past October, Sarens was on site in Aix-Noulette, France, to install and jack down a 950-tonne bowstring bridge for client Eiffage. But although Sarens has left its mark on many bridges around the world, this particular project came with its own unique challenges.

During the engineering phase it became clear that this would be no ordinary bridge installation. First, the surrounding terrain, as well as the bridge itself, were sloped in two directions-along both the bridge length and width. Second, there was another bridge in the immediate vicinity, and it would remain operational at all times. This meant that no equipment could exceed the width of the bowstring bridge in the direction of the neighbouring bridge.

Finally, the bridge had to be installed along its longitudinal axis, which required carefully-selected equipment including 40-axles SPMT, a CS600 jacking system, and an HSL 450 strand jack. As project manager Tom Jonckers explains, "Each piece of equipment was carefully selected for this project, especially the CS600 jacking system, which met the specific requirements of being compact yet fast enough. Compact equipment was required because the neighboring bridge limited our working space, whereas jacking speed was necessary to meet the deadline for the road opening."

The operation required several carefully-coordinated steps:

  • SPMTs picked up the bridge on the upper platform, driving until the first set of SPMTs were blocked by the abutment. One side of the bridge was then lowered onto the abutment and the SPMTs were removed.
  • The SPMTs were disassembled and transferred to the lower platform. There, they were installed below a pre-assembled transport structure featuring the CS600 system that would be used for jacking down in later phases of the project.
  • SPMTs then lifted the bridge again and, during a total road closure, drove it over the highway until the second set of SPMTs were blocked by the abutment. Once there, the second side of the bridge was placed on the abutment, on Teflon plates.
  • The SPMTs were then removed and the bridge glided the remaining distance, thanks to the traction force generated by a combination of the SPMT and a strand jack. This phase finalised the bridge position along its longitudinal and transverse axis.
  • Next, the bridge was synchronously jacked down by a metre on both sides, until it rested on its final supports. Sarens crew and the client's crew communicated closely during this important phase, as Sarens jacked down one side of the bridge and the client jacked down the other.
  • Finally, Sarens continued jacking down the bridge over a height of 1.5 metres until the second side was installed on its final supports.

The 6-member crew successfully executed this operation within two nights. Sarens commends everyone involved in coordinating this precise operation!