Seismic Improvements and Upgrade of Uniform and Tango Wharves Located on U.S. Naval Base Guam

The U.S. Territory of Guam is located in a seismically active region and has experienced several major earthquakes in the past. The 1993 earthquake, with a moment magnitude of 7.7, caused significant damage throughout the island. During that event, the existing Uniform wharf wall experienced significant seismically induced settlement and lateral spreading. The adjacent Tango wharf also experienced some damage. The damage at Uniform wharf was so great that the wharf became non-operational after the earthquake. Both Uniform and Tango wharves are being upgraded to meet a two-level design earthquake and seismic performance criteria. New king pile-sheet pile systems with tie-rods connected to vertical pile-supported anchor blocks were designed to upgrade the wharves. Backland liquefaction within the immediate zone behind sheet piles is mitigated using a stone-column ground improvement technique. Acceptance of stone column performance was based on frequent verification borings in the field as well as additional laboratory testing. Driven piles were investigated with a dynamic pile analyzer to optimize anchor pile length and develop pile acceptance criteria. The paper focuses on the seismic design philosophy, geotechnical field investigation, site characterization, seismic analyses, and ground improvement design. In addition, the paper also discusses construction challenges and how they were overcome.