1018 14TH ST 2023-02-09 - Laserfiche WebLink

SHANNON&WILSON,INC. during the 200-year ground motion. We also recommend installing a groundwater monitoring well to periodically measure the groundwater level behind the bulkhead. 4.1.2 Seismically Induced Settlement Loose, granular soils that are susceptible to liquefaction are also susceptible to earthquake-induced densification. The resulting permanent ground surface settlements may not occur uniformly over an area, and the differential settlement can be damaging to existing or future structures supported on the loose soil. Settlement can also occur in loose soil above the groundwater table. Seismically induced settlement estimates were made for the subsurface conditions encountered in the borings performed at the site. Settlement estimates were made using the procedures by Tokimatsu and Seed (1987), Ishihara and Yoshimine (1992), and Pradel (1998) for the 200-year design ground motion. The results indicate that up to 2 inches of settlement may occur at Segments A, B, and C. At Segment D, where the extent of predicted liquefaction is greater based on boring B-1 B, up to 8 inches of settlement could occur. 4.1.3 Lateral Spreading Lateral spreading occurs when a sloped site or a site near a free face(such as the bulkhead) moves toward the free face as underlying soils liquefy. This phenomenon has been experienced at numerous waterfront facilities during a seismic event. The potential of lateral spreading at the site for the 200-year design ground motion is low, considering that the liquefaction areas are localized. We prepared a letter to the Port, dated April 16, 2013, identifying the risks and related damage associated with lateral spreading for the IBC design ground motion. 4.2 Bulkhead Design We understand that the existing bulkhead will be replaced because of the age and deterioration of the existing timber and steel structure. At the request of the Port, the seismic design of the bulkhead will be based on the 200-year design ground motion. Based on the 90 percent plans prepared by MNE (2014),we understand that the proposed replacement consists of a steel sheet pile wall with one row of deadman anchors. The deadman anchorage system will consist of a buried, continuous concrete block, located 30 to 45 feet behind the wall, with regularly spaced steel cables connecting the wall face to the buried concrete block. The proposed bulkhead would be located 3 to 10 feet from the outboard side of the existing bulkhead. 21-1-21761-003-R I fdocx/W ricip 21-1-21761-003 10