Keywords: retaining walls, distress, dynamic response, amplification, wall-soil-structure interaction.

Retaining systems, such as cantilever walls, are very frequently used worldwide for serving various purposes in structures and infrastructures (deep excavations, embankments, bridges, ports, etc). The seismic response of various types of walls that support a single soil layer has been examined by a number of researchers in the past [1,2,3]. Nevertheless, the dynamic interaction of the retaining walls with the structures that they usually retain has not been investigated. It is evident, however, that during a seismic event the dynamic response of each component of this complex system (wall, soil, structure) may affect substantially the response of the rest, and vice versa.

The phenomenon of dynamic wall-soil-structure interaction (DWSSI) is a rather complicated issue that includes: (a) the dynamic interaction between a wall and a retained single soil layer (DWSI), and (b) the "standard" dynamic soil-structure interaction (DSSI) of a structure with its underlying soil. The aforementioned dynamic interaction issues are not considered with the proper realism in the modern seismic codes [4,5,6]. In the present study, using numerical two-dimensional simulations, the influence of the wall flexibility on the free-field ground shaking behind the wall is investigated. Emphasis is given on the impact of the wall's presence on the amplification of the base acceleration of the retained soil layer, an amplification generally ignored by the seismic design codes.

Consequently, a structure founded on the retained soil is included in the numerical models, as a single-degree-of-system (SDOF). A parametric study has been performed in order to examine how the location and/or the fundamental eigenperiod of the SDOF system affects the earth pressures induced on the retaining wall. In addition, the parametric study investigates to what extent the presence of the wall may affect the inertia forces imposed on the structure. Despite the fact that many "open issues" exist, the numerical results of the current study provide a clear indication of the direct dynamic interaction between a retaining wall and its retained structures. This justifies the necessity for a more elaborate consideration of this interrelated phenomenon on the seismic design, not only of the retaining walls but of the nearby structures as well.

1

Veletsos A.S., Younan A.H., "Dynamic response of cantilever retaining walls", ASCE Journal of Geotechnical and Geoenvironmental Engineering, 123(2), 161-172, 1997. doi:10.1061/(ASCE)1090-0241(1997)123:2(161)

2

Iai S., "Seismic analysis and performance of retaining structures", in Dakoulas P., Yegian M., Holtz R.D., (eds), Proc. Geotechnical Earthquake Engineering and Soil Dynamics III, Geotechnical Special Publ. No. 75, Vol. 2, ASCE, Reston, Va., pp. 1020-1044, 1998.

3

Psarropoulos P.N., Klonaris G., Gazetas G., "Seismic earth pressures on rigid and flexible retaining walls", Soil Dynamics and Earthquake Engineering, 25(7-10), 795-809, 2005. doi:10.1016/j.soildyn.2004.11.020

4

EC8, "Eurocode 8: Design of structures for earthquake resistance", European standard CEN-ENV-1998-1, European Committee for Standardization, Brussels, 2004.

5

EAK, "Greek seismic code", Ministry of Public Works, Athens, Greece, 2000.

6

Mylonakis G., Gazetas G., "Seismic soil-structure interaction: beneficial or detrimental?", Journal of Earthquake Engineering, 4(3), 277-301, 2000. doi:10.1142/S1363246900000175

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