The PCT trestle and platform are supported by 123 precast concrete units and 2,903 cubic yards of concrete. Several of the precast concrete units weigh more than 250,000 pounds. The 180-foot piles weigh about 150 tons each and were driven as single units to save time and maintain construction schedules. Each pile has a placement margin of less than six inches to fit precast pile caps. Great Northern Engineering designed the project, which included more than 4,400 pages of design calculations, 285 sheets of plan drawings and details and 390 pages of technical specifications. A team from Pacific Pile & Marine drove approximately 200 piles. The project included constructing the PCT trestle and loading platform, building the mooring dolphins, and installation of utilities as well as the petroleum and cement handling infrastructure. Nearly 125 of the piles were later removed. “They built a temporary trestle while they were building the permanent trestle,’’ Jager said. “They needed something that they could work from. Once they were done, they were able to pull back many of the piles.” One of the twists in the pile-driving was the inclusion of “bubble curtains” to protect sea mammals by reducing underwater pile-driving noise. Bubble curtains are created by positioning a concentric sleeve and perforated ring around piles that are being driven. The pile driving also needed to cease at several points when beluga whales entered the vicinity in the Upper Cook Inlet. The whales are an endangered species, and federal regulations prohibit pile driving when endangered marine mammals are sighted in a protected area that extends about 1.5 miles around the PCT site. A team of mammal ob - servers monitored the protected area and notified construction officials to cease construction activities when whales entered the vicinity. Withstanding Earthquakes The modernization plan also required the upgrades to withstand the impact of earthquakes. Alaska has more earthquakes than any other region in the United States, and a 9.2 quake near Anchorage in 1964 resulted in 131 deaths. The 2018 earthquake was certainly a wakeup call for the port. It oc - curred about 10 miles north of Anchorage, registering 7.1. The Na- tional Tsunami Warning Center issued warnings for nearby coastal areas, including Cook Inlet. As a result of the 38-second quake, 20 percent of the pilings of the newest dock at the Port of Alaska – built in 1974 – failed. “Had it continued for another seven seconds,’’ a report in Alaskalandmine.com reported, “widespread liquefaction could have occurred, possibly leading to a total failure and collapse of one or more of the port docks.”
Construction officials took strong measures to guard against future interruption to port services due to earthquakes. One interesting aspect of the project was the installation of three roof hatches on the trestle. Manufactured by BILCO, a manufacturer of specialty access products, the hatches are 10 x 20 feet. Due to the size, the leaves needed to be shipped separately and assembled on site. The hatches allow access to fuel piping expansion joints. “The hatches were specified to shelter containment pans, which are installed to protect environmental contamination should the piping expansion joints fail in a seismic event,’’ said Brett Gunderson of Haskell Corporation, a mechanical and structural subcontractor. “The hatches also allow access to the expansion joints should they need to be replaced.” Gunderson added: ”The stainless-steel construction was important, but we also chose BILCO because the hatches were very large, and we knew that BILCO would design and fabricate them to operate easily and safely.” Unacceptable Failure Alaska’s reliance on the port cannot be overstated. It has been de- scribed as the “economic heart of Alaska,” with more than 3.5 million tons of products coming through the port each year. The port supports $14 billion worth of economic activity in the state, and 90 percent of Alaskans depend on goods handled by the POA. While the port is not exceptionally large, its importance is unques - tionable. “We are a small port, but that’s a function of Alaska being a relatively small state,’’ Jager said. “The size of the facility is never going to be one of the nation’s largest ports. But we do have critical roles, in the state, nation and even internationally. We are incredibly important to the commerce and economic health of many people. This modernization project is something we need to get done. The port is essential to our economy.”
THOMAS RENNER writes on building, construction, architecture and other trade industry topics for publications throughout the United States.
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csengineermag.com
October 2022
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