The Port of Seattle’s Pier 36 belongs to the United States Coast Guard (USCG). The deepening project called for demolition of the old pier, a deck-on-pile structure. Underneath the existing pier the ground sloped down to the bottom of the harbour; the top part of the slope was faced with riprap (sand, gravel and crushed rock) with a concrete cover. Concrete and timber bulkheads had been installed to stabilise the old pier, while the lower part of the slope consisted of mud. In order to accommodate the new Coast Guard’s vessels, it was decided to develop a new, deeper quay by 2003.
The cross-section (Figure 1) shows the existing mud layer reaching up to a level of approximately -3m (equivalent to -10 feet). Removing the stone revetment beneath the old pier would have implied high costs. It was therefore decided to dredge the mud down to the depth of 12m necessary for the docking of the Coast Guard’s vessels. An underwater cantilever sheet pile wall was chosen to hold back the rocky top part of the slope.
A new deck on piles was constructed behind the sheet pile wall. The deck is made of precast concrete panels resting on precast concrete piles. The inclination of the rock slope was slightly changed to incorporate the timber bulkhead. Since Seattle is situated in an active seismic zone, earthquake loads were considered for the design of the new facility at Pier 36.
The first step in the construction of the new quay was the driving of the underwater steel sheet pile wall at the end of the rocky slope. The contractor, M.A. Segale Inc., fabricated his own template