Performance-Based approach in seismic design of embedded retaining walls

The increasing use of the underground spaces and the last seismic events in the urban areas have driven many researchers of different countries to deepen the knowledge on the dynamic behaviour of the structure embedded in the subsoil. This thesis attempts to give some contributes on the application of the performance based approach for the seismic design of the embedded retaining walls. After an overview on the earth pressure theories proposed by different authors, the static and seismic design methods commonly adopted in the current practice and based on pseudostatic approaches are recalled. Several limitations on these procedures can be recognized: the difficulties on the definition of the seismic coefficient; the calculation of the expected earthquake-induced displacements around the construction. Moreover, in the framework of the Performance-Based Design, these methods do not able to describe the response of the retaining systems to a given earthquake. The seismic displacements of the flexible walls are evaluated by means of Newmark sliding block procedures, that were developed for rigid structures, and the yield sequence of the different structural components can not be predicted. Then, the application of the hierarchical resistance criteria in the dimensioning of the various parts can not be applied. In this thesis, different level of analysis are highlighted in relation to the importance of the structure and to the design phase. An innovative procedure that can be included in the framework of the "pushover analyses" is also proposed for the seismic design of the embedded retaining walls. Finally, the results obtained by the application of the different methods for the ideal case study of cantilever diaphragms embedded in dry loose and dense sand are presented. The material properties used in the analyses are referred to the Fraction E (BS 100/170) of the Leighton Buzzard sand, for which a series of triaxial and torsional tests on reconstituted samples was conducted.