Ketchikan Water Street Trestle No. 2

New Cliff-Side Bridge Ensures Community’s Connections for Years to Come

Building a road along a cliff face next to a waterway is a complex task no matter the location. Add in residential structures, historical considerations and a cold, rainy environment where paving can take place for just four months of the year and overcoming the challenges becomes even more impressive.

HDR oversaw the construction of a new $25 million roadway along historic Water Street in Ketchikan, Alaska. Built in 1979, the original trestle bridge was deteriorating to the point that the road could no longer support heavy loads, including garbage trucks, heating oil suppliers, or emergency vehicles.

We served as construction manager for the three-year project, tasked with inspections, materials testing, and overseeing construction. The trestle reconstruction was a technically challenging project, perched on a steep cliff in a historical district and in a dense, actively used and space-constrained residential area. The ground beneath the existing 1,130-foot bridge sloped down dramatically. One side touched the ground while the other was up to 50 feet off the ground.

Recognizing the difficulty and innovations involved, the project was given a National Recognition Award this year from the American Council of Engineering Companies.

Affixing a new bridge in a tight spot on steep terrain made the project unique and required the use of an innovative piece of construction equipment called the “panel launcher.” Each panel needed to be set perpendicular to the roadway, but tight confines limited movement on the street. The panel launcher would pick up each new 6-foot-wide, 25-foot-long precast concrete deck slab from the delivery truck and bring them up the road length-wise. From there, because power lines and homes rest adjacent to the roadway, limiting the side-to-side movements, each panel was turned sideways and set in place.

The unique construction concerns didn’t end there. The 24 homes that line the historic street each had unique, individual foundations. Some were on pilings while others were built into rock walls. In some cases, the bridge’s foundation was literally holding up the yard or part of the homes. Construction included work to keep houses and driveways from leaning on the bridge, sometimes pouring new fill under existing homes.

Given the long period of time the area has been inhabited, the project also turned up pockets of historical artifacts during construction.

HDR’s team included an on-site archaeologist, who catalogued items of historical note that were discovered during construction.

The 40-year-old bridge was replaced with three separate structures designed to last the next 75 years: a bridge section, a retaining wall and a steel supported trestle. The project also included updates to meet ADA guidelines, new sidewalks and replacement of all utilities.

The road’s completion was celebrated in a June 2019 ceremony with local and state officials.

The post Ketchikan Water Street Trestle No. 2 appeared first on Civil + Structural Engineer magazine.



source https://csengineermag.com/ketchikan-water-street-trestle-no-2/

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