R&M Through the Years: Seward Highway Reconstruction MP 54.8-59.3 – Canyon Creek Bridge

August 20, 2019

In celebration of R&M’s 50th anniversary, we are taking a look back at the projects over the last five decades that made R&M into the firm it is today. This month we take a look at a major bridge reconstruction along the Seward Highway designed by R&M in the 1990s.

The Seward Highway is the only route connecting Anchorage to the Kenai Peninsula. During the 1990s, the Alaska Department of Transportation & Public Facilities (DOT&PF) made efforts to improve several sections of the highway, making it safer and easier to traverse.

Large rock cuts.

The Canyon Creek area was the last section of this highway to be updated. This 4.5-mile section of roadway traverses along the mountainside above Six-Mile Creek and crosses Canyon Creek near the Hope Turnoff. R&M was the prime consultant and responsible for design of road improvements, a new 885’ bridge crossing over the creek, scenic overviews, rest areas and trailhead amenities.

The replacement bridge is approximately 30 meters above the valley floor with both horizontal and vertical curvature. Several notable design features were the large rock cuts (580,000 m3), drainage structures for steep mountainside creeks and streams, and erosion protection of the till slopes. Due to difficult foundation soils and the canyon configuration that exists at Canyon Creek, numerous studies were required to develop alternative bridge crossing locations and design alternative bridge types. This included a hydrology and hydraulics study that conducted a HEC-2 analysis of Canyon Creek.

As this is the only route between Anchorage and the Kenai Peninsula, R&M also had to carefully consider traffic control for rock blasting and develop plans to accommodate the trucking, tourist and general public traffic.

Traffic control was essential during construction to maintain access.

In addition, R&M supported DOT&PF during the construction phase on both the bridge structure and highway cut-slope treatments. During this phase, the firm completed design of an adjacent bike trail, which was incorporated into the construction efforts.

This complex and technically comprehensive project encompassed a full range of major civil design and design subspecialties, and highlighted R&M’s expertise in accommodating public agency schedules and developing teamwork amongst all the designers involved. The work included design surveys, geotechnical investigations and reports, highway design (geometric and traffic analysis, safety studies, drainage studies, utility studies and relocations, sign studies, traffic control, earthwork and paving), bridge design (structural design and hydraulic reports), environmental evaluations, permitting, right-of-way acquisition, and public hearings and meetings.

This project won an American Society of Civil Engineers Outstanding Civil Engineering Achievement Award in 1998.

Next month, we will take a look at a new roadway that extended a main transportation corridor through an undeveloped area of Anchorage that R&M designed in the 2000s.