Foundation-Soil-Inclusion Interaction Modelling for Rion-Antirion Bridge Seismic Analysis

The Rion-Antirion Bridge in Greece will span a total length of 352 1 m, which includes a five span cable-stayed bridge 2252m in length and two approach viaducts. Upon completion in 2004, the bridge will be the longest cable-stayed bridge in the world. The main factors affecting the foundation design involve high seismicity, poor in-situ soil conditions, deep sea water (65m) and high ship impact force. These factors called for an innovative foundation design for each of the 90m diameter piers by the foundation designer, Geodynamique et Structure (GDS) from France. The proposed design consists of vertical open-ended steel cylinders (called “inclusions”), 25 to 30m long and 2m in diameter, which will reinforce the in-situ soils. The inclusions are to be spaced at 7 to 8m beneath each pier footing supporting a 230m tall pier and pylon structure. These inclusions are not connected structurally to the footing. Beneath each footing is to be placed a layer of gravel in which the inclusion heads are to be embedded. The interface between the pier base and gravel is to serve as a sliding shear fuse under extreme earthquake loading, involving a base isolation concept. This design was checked independently by the Checker - Buckland & Taylor Ltd. (B&T), using nonlinear finite element analyses of the foundation and soil subjected to equivalent seismic or ship impact loading consisting of a horizontal monotonic or cyclic force acting at a representative height (lever arm) above the seabed. The failure mechanisms observed in centrifuge model tests and in field sliding tests of the footing were closely examined and compared with the failure behavior predicted by the finite element soil-structure interaction modeling. The hysteretic damping characteristics of the foundation under horizontal cyclic loading obtained from the above analyses were used in the dynamic global bridge seismic analysis. The Checker’s independent analyses confirmed the viability of the proposed design