Impacts of Sediment Mounds under Pile Supported Wharf Structures

The accretion of steep sediment mounds under pile supported wharf structures is not a new phenomena in waterfront engineering. However, comprehending their behavior and their impact on the waterfront structures is a significant challenge. The development of mounds presents unique and formidable aspects associated with classical geotechnical engineering, soil-structure interaction behavior, and structural engineering. Experience shows that the mounds have the potential to affect port operations, maintenance dredging, stability problems and can adversely impact the structures. Two case histories will be provided showing the extent and growth of mounds from original berth construction to present, the geotechnical engineering properties of the mounds presented, and an overview of the stability of the mounds. Each case will include a description of formal geotechnical studies undertaken to gather information and the overall impacts of the mounds on the structures. In one instance, the movement of berths was corroborated with measured tidal fluctuations and the unstable sediment mounds. In the second instance, the potential for deep-seated slope failure and the resulting lateral loads on the piles supporting the berths is discussed. The two sites where valuable information has been gathered and analyzed are Berths 12 through 21 at the North Port in Port Klang, Malaysia and Berths 1 through 9 at the North Carolina State Ports in Wilmington, North Carolina.