While the park remains in the depths of winter, design work on the Pretty Rocks Bridge has continued indoors. At the beginning of February, the final contract option was awarded for bridge construction!
The series of illustrations below shows the plans for how the bridge will eventually be constructed on the east side of the landslide and then launched across to the west side.
Weekly updates will return to this blog when on-site construction resumes later this spring.
Illustration courtesy of Jacobs Engineering
A project engineer describes the bridge launching process and some of the engineering challenges unique to this project:
The final bridge structure and construction method are really interesting from an engineering perspective. ... Complex site geology includes a folded strata of fractured and intact rock, clay, and ash interlaced with areas of discontinuous, ice-rich permafrost throughout. ... In addition, the project’s location is 45 miles from the nearest public highway and on a steep slope high above the Plains of Murie and the four-month construction season severely limits access for construction operations.
The unique erection process chosen in light of the site constraints involve the assembly of the permanent bridge truss cantilevering out from a temporary launch beam installed adjacent to the east abutment. After assembly of the permanent bridge truss, a temporary truss (launch nose) is erected within the permanent truss and incrementally moved westward to bear on a receiving tower placed on the west abutment, at which point it is rigidly attached to the permanent truss. The combined truss assembly (the permanent truss and the launch nose) is then incrementally moved westward until the permanent truss bears on the receiving tower and is then lowered into place on the west abutment.