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

SHANNON 6WILSON,INC. As discussed in Section 1.3,the geometry of the existing bulkhead at Segment D is different than the other segments. A riprap slope is present in front of the existing 8-foot-high timber wall. A wharf extends out over the riprap slope that is timber pile supported. We understand that the proposed bulkhead will be located at the edge of the existing wharf,therefore, compacted fill will be placed behind the new bulkhead to fill in the area between the old and the new bulkhead. The Segment D bulkhead is not included in the 90 percent plans, and will be designed at a later date. The following sections present geotechnical recommendations for the design of the bulkhead. 4.2.1 Lateral Earth Pressures Recommended lateral earth pressures for the design of the proposed bulkhead are shown in Figure 5 for Segments A, B, and C, and Figure 6 for Segment D. Earth pressures are provided for static and seismic conditions (200-year design ground motion). Because the soil configuration is different at Segment D, we provided a separate design recommendation considering that compacted backfill that will be used behind the new bulkhead. We assume that compacted structural fill would be present from about elevation +2 to +17 feet, based on the proposed location of the new bulkhead in front of the existing bulkhead (see Figure 6). We developed our lateral earth pressure diagrams based on the following assumptions and considerations: ■ The analyses assumed outboard water level is elevation 0 foot. Design inboard water level is elevation+2 feet. This assumes that a drainage layer is placed behind the wall and that the water can drain through weep holes such that water does not build up above elevation + 2 feet behind the wall. ■ The new bulkhead will have one anchor level, which results in approximately triangular pressure distributions behind the wall. ■ The new bulkhead will be constructed behind the existing bulkhead for Segments A, B, and C. ■ The 200-year design seismic ground motion would result in minimal localized liquefaction (see Section 4.1.1). Therefore, liquefied soil pressures are not included in the earth pressure diagrams. Note that this may not be applicable for Segment D (Figure 6), as discussed below. ■ The slope on the outboard side of the wall varies based on bathymetric survey information provided by the Port. Figures 5 and 6 include recommendations that consider slope variations ranging from 2H:1 V to 4H:1 V. The variable slope is assumed to extend no deeper than elevation -12 feet. 21-1-2 1761-003-R I fdocx/wp/c1p 21-1-21761-00 3 11