THE FOUNDATION OF THE CROZET BRIDGE. A CASE STUDY

The Crozet bridge is located on the Grenoble-Col du Fau motorway, in the Grenoble- Sisteron intinerary, fifteen kilometres south of Grenoble, Frace. It crosses a 350 m wide valley and the RN75 national road. The adaptation of the bridge to the lanscape has involved an arch design with three bays (direction of Grenoble-Sisteron) and one bay (direction of Sisteron-Grenoble). The supports of the structure were difficult to build because of a huge horizontal force and a low dis- placement tolerance. The low stiffness and strength characteristics foreseen led to a geotechnical in- vestigation by cyclic pressuremeter tests with a friction angle and cohesion interpretation. The foun- dation calculations were carried out by the CESAR-LCPC program to determine the support rigidity. A complete computation of the bridge was done with the calculated support rigidity which showed that displacements of the arches were lower than the tolerance limit. The bridge is located in the area of low seismic activity and the design takes into account the maximum foreseeable magnitude. The soil liquefaction risk was analysed as well. Monitoring carried out for completion of the bridge in 1999 and along the surveying shows dis- placements lower than tolerance values. Since 1999, the bridges has withstood huge service weights without any difficulty.