An Innovative Method of Enhancing Deep Water Wharf Stability

This paper outlines the gravity and seismic stability analyses conducted during the design of a deep water wharf for an industrial facility. The multi-purpose wharf was initially designed to be supported by a system of large diameter, plumb steel pipe piles in upwards of 100 feet (30.5 m) of water. The dead load exceeded 800 psf (38.3 kPa) in many areas due to the utility requirements for deep deck sections filled with ballast. The stability of the wharf was determined by utilizing analytical techniques derived from ACI 318-05 and MOTEMS 2005. The large gravity loads, combined with the overall slenderness and layout of the piles, resulted in seismic instability issues. The need to limit seismic displacements while increasing the wharf lateral stiffness under service loading required an innovative design strategy. Consequently, lead rubber bearing (LRB) seismic isolation dolphins were added in strategic locations. The dolphins consisted of four battered steel pipe piles supporting a precast concrete platform. LRBs were mounted to the top of each platform and connected to the wharf deck by means of a steel retainer frame. This proved to be an elegant and economical solution, whereby the lateral stiffness of the wharf was increased, the number of plumb piles was minimized, and the overall cost of construction was reduced.