Port of Alaska Modernization

The Port of Alaska is the largest and most important commercial port in the state. Already outdated and deteriorating, the facility suffered significant structural damage during a 7.1 magnitude earthquake in 2018. The port needed new, more resilient, marine infrastructure. The ambitious Port of Alaska Modernization Program (PAMP) set out to give it a generational upgrade with a new loading platform and approach trestle that would withstand the area’s challenging marine conditions.

The large scale of marine construction combined with extreme weather and tidal conditions made for a challenging project. Seasonal weather was also an issue—in Alaska you can’t exactly build all year—so the team had to plan around a short construction window.

GeoEngineers conducted temporary works design during bid preparation and then final design for this $200 million, multi-phase, marine construction project as a partner to the general contractor and project lead Pacific Pile & Marine. Services included structural design for a temporary work trestle, geotechnical design and pile driving support, bubble curtain design, and design for a variety of custom structures and devices required to move and place the extremely large piles and precast elements used in this project.

Approach

Structural Design for Temporary Access Trestle: GeoEngineers’ construction design team designed the large temporary access trestle built during the project’s first phase. A total of 48 24-inch and 36-inch diameter piles were required to support the 320 x 45-foot structure. The work trestle needed to support both a 400-ton and a 225-ton crawler crane during pier construction. Engineers used additional piles and X bracing to account for the very strong lateral loads created by a combination of exposed pile depth, dynamic currents, and high wind speeds in the area. The temporary trestle also needed extra support at the transition to land, so the team designed a complex MSE wall for added stability.

Geotechnical Design and Pile-Driving Support: GeoEngineers provided comprehensive geotechnical services for both phases of the project, including soil analysis, deep foundation recommendations, and pile-driving support. Extreme weather conditions combined with the scale and speed of construction made the project very challenging. The contractor needed to load the phase 1 piles as soon as three or four days after installation, so the team couldn’t simply design for long-term loading capacity. To save money and more accurately estimate the axial capacity of the piles, the team used data from a recent load testing program that had been performed near the project site. The team performed PDA testing of the piles four days after installation and found the bearing capacities to be right in line with their capacity estimates.

Dolphin Pile Template Design: Phase 2 of the project required the installation of nine 12-foot-diameter monopile dolphins that would be used to moor large vessels. GeoEngineers designed a stiff template to support these massive 220-foot-long piles as they were placed for installation with as little as 10 feet of embedment at the toe. The template remained in place during vibration and impact driving for added support and included a number of features intended to streamline installation, such as variable length legs, two levels of hydraulic actuated pile guides, a worker platform for safe access, and built-in bubble diffuser rings. The 12-foot-diameter, 200-foot-long monopiles are thought to be the largest full-length piles ever driven in a marine construction project on the West Coast of the United States.

Additional Custom Devices and Precast/Cast-in-Place Concrete Support: The project included a lot of heavy piles and precast elements that required specialized equipment and careful planning—the monopile dolphins alone were 315 tons each. The GeoEngineers team designed a variety of custom devices to allow the contractor to safely move and place these very large and heavy loads, including a barge-mounted tipping table and a robust below-the-hook lifting bar that were needed to safely hoist the piles into place. The team also designed precast support brackets, infill soffits, and additional falsework required for construction.

Bubble Curtain Design and Protected Species Monitoring: The GeoEngineers team was also responsible for monitoring underwater noise produced by the pile installations and designing bubble curtain devices to mitigate the sound for both project phases. Noise from pile driving can travel for many kilometers and affects sensitive marine species like the Beluga Whale.

Results

The team dealt with massive loads and challenging site conditions to rapidly modernize the Port of Alaska in the wake of the 2018 earthquake—completing final construction just a few years later in 2022. The new loading platform and trestle are designed to survive a 1000-year seismic event, and will provide reliable marine shipping services for the people of Alaska for many decades to come.