The sliding stability of rigid waterfront structures, as caisson quay walls, is here analyzed using the traditional pseudo-static approach and the displacement method, according to the recent Italian Building Code (D.M. 14/01/08). The available proce-dures to calculate the forces acting on such structures under seismic conditions are discussed firstly. The presence of excess pore water pressure within the backfill is accounted for in the analysis using the pore pressure ratio ru (assumed to be constant). Re-ferring to the case of a partially submerged backfill the design procedure is analyzed, assuming that the sliding mode of failure governs. The influence of some factors is highlighted, such as the design approach suggested by the Italian code, the method to calculate the seismic soil thrust and the excess pore water pressures within the backfill. Then, current methods available in the literature, based on the Newmark sliding block procedure, are briefly discussed and the dimension of the structure obtained by the displacement-based method is compared with that obtained by the traditional pseudo-static method for different values of the allowable displacement. Finally, the influence of the water level, the soil shear resistance angle (φ) and the soil-wall friction angles (δ, δ_b,) is analysed. The results of this study indicate that (1) Design Approach 1 of the Italian Building Code is always more conservative than Design Approach 2; (2) calculating the soil thrust by a force-based approach implies a more eco-nomical design when the excess pore water pressure is neglected, whereas it becomes more conservative than a pressure-based approach for increasing values of r_u; (3) for a given peak acceleration the method recommended by Eurocode 8 to calculate the seismic soil active thrust leads to an over-conservative design; (4) the assumption of a fully submerged backfill is always on the safe side; (5) for a given seismic input and a given soil-wall friction angle at the base of the caisson, 6b, the displacement-based method can be more economical than the pseudo-static method, provided that the allowable displacement exceed a limiting value of a few centimetres; (6) this limiting value of allowable displacement is found to be substantially independent of and δ, whereas it significantly decreases with increasing δ_b.
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