Seismic Design of Bulkhead and Foundation in Stratified Soft Clay and Liquefiable Soils

This paper presents the design analysis and approaches used for the new bulkhead and foundation system developed for the Port Cristobal Berth 10 Expansion project in Panama. The project generally consisted of extending the existing Berth 10 by about 220 meters. The subsurface soils within the footprint of the new wharf extension generally consist of inter-layered, loose, liquefiable, sandy soil and soft silt and clay determined to be susceptible to significant shear strength reduction under large seismic event. The wharf will be constructed in a 2.0-horizontal to 1.0-vertical dredge slope that is potentially unstable and will impose significant pressure onto the foundation system under large earthquake event. Both the ground improvement and structural foundation option were considered to mitigate the seismic slope instability. A cost analysis revealed that the structural foundation option - consisting of large diameter drilled shafts (1,370-mm diameter) and steel batter piles (762-mm diameter) - is more cost effective and was selected for this project. Both the force-based method (using computer program SAP2000) and the deformation-based method (using numerical modeling computer program PLAXIS and FLAC) were used in the design.