Seismic Improvements and Upgrade of a Wharf Using an Innovative Ground Improvement Scheme

During the magnitude (M_w) 7.7, 1993 Guam earthquake, which caused significant damages to coastal structures throughout the area, X-Ray Wharf in the island showed signs of liquefaction and lateral spreading and seismically induced settlement up to 30 cm. The existing wharf is approximately 450 m long and consists of a combination of steel sheet pile bulkheads with a single level of tie-backs and steel sheet pile bulkheads with relieving platforms. Even though the damage to the wharf was not significant during the 1993 earthquake, it was found that the existing wharf would not meet the current two-level seismic performance criteria per the latest unified facilities criteria, (UFC) 4-152-01 (DoD, 2005, 2012). Among the various concepts evaluated to upgrade the existing wharf, constructing a new wharf in front of the existing wharf was found to be the most effective solution and taken forward for final design. A new sheet pile bulkhead wall approximately 10.7 m away from the existing sheet pile bulkhead will be constructed and the space between the new and old sheet pile bulkheads will be filled with improved granular backfill. Cement deep soil mixing (CDSM) was selected as the most cost-effective ground improvement technique to improve the granular fill and weak foundation materials. Construction of the new wharf is presently under way. The paper discusses the seismic design philosophy, geotechnical field investigation, site characterization, seismic analyses, and ground improvement design in an informative manner useful to practicing engineers.