PERFORMANCE BASED DESIGN OF EARTH RETAINING STRUCTURES AND BUILDING CODES

The design of a geotechnical structure under seismic loading is frequently carried out by means of the pseudostatic approach, checking the system against any possible geotechnical and structural ultimate limit states. In the paper this simplified design approach is examined for the case of a flexible retaining wall to highlight the influence on practical design of a seismic action that is a function of the permanent displacements and of the use of partial factors on geotechnical parameters. The analysis will show how the design procedure implied by both Eurocode 8 and Italian Code leads to an over-conservative geotechnical design. A practical design procedure is proposed instead in which the structure is first designed for static limit states according to Eurocode 7 and then its performance under seismic loadings is checked by verifying that the displacements cumulated before and after the critical acceleration is reached fulfills requirements for serviceability. Keeping in mind the importance of strength hierarchy and ductility concepts when designing for seismic conditions, the present paper shows that methods of current practice may well be used efficiently for seismic design if performance based design principles are taken into account.