Foundation design for a large arch bridge on alluvial soils

Abstract

The Crozet bridge is located on the Grenoble–Col du Fau motorway, on the Grenoble–Sisteron route, 15 km south of Grenoble, France. It crosses a 350 m wide valley and the RN75 national road. The adaptation of the bridge into the landscape has involved an arch design with three bays (in the Grenoble–Sisteron direction) and one bay (in the Sisteron–Grenoble direction). The supports of the structure were difficult to build because of the huge horizontal force and the low displacement tolerance. The low stiffness and strength characteristics foreseen led to a geotechnical investigation by cyclic pressuremeter tests with a friction angle and cohesion interpretation. The foundation calculations were carried out by a finite element calculation using the CESAR-LCPC program to determine the support rigidity. The complete computation of the bridge was done with the calculated support rigidity, which showed that displacements of the arches were lower than the tolerance. The bridge is located in a low seismic area of France, and the design takes into account the maximum foreseeable magnitude, and analysis of the soil liquefaction risk. Monitoring carried out for completion of the bridge in 1999 and along the surveying shows displacements lower than tolerance values. Since 1999, the bridge has withstood huge service weights without any difficulty.