Engineering firm tells Little ‘the project corridor is safe’ in letter on Idaho 55 project

highway 55 roadwork
Posted at 3:07 PM, Jul 01, 2022
and last updated 2022-07-01 17:07:19-04

This article was originally published by Margaret Carmel in BoiseDev.

A third-party engineer who consulted on the Idaho Highway 55 project wrote a letter to Governor Brad Little declaring the corridor safe for the traveling public on Thursday.

This comes after reporting from BoiseDev reviewed over 7,000 documents related to the project over the course of six months, which revealed recurring stability concerns at one of the sections of the project where a major landslide narrowly missed a pilot car. The story resulted in Little demanding a report from ITD assessing the ongoing risk to the public at the site, a review of BoiseDev’s reporting and a summary of all media requests to the agency about the project.

ITD’s response to Little included a letter from geotechnical engineering from two McMillen Jacobs staff members who gave an update on the status of the nine rock cuts making up the project and assured the governor the hillside is being closely monitored. The letter was written by Principal Geologic Engineer Bill Gates and Senior Associate Engineering Geologist James Struthers, both members of the project team.

As reported by BoiseDev, McMillen Jacobs was brought on to rework the project’s design and help with rockfall mitigation and slope stabilization following the first landslide hit the project in March of 2021. McMillen Jacobs also consulted on the major landslide on Highway 95 near Riggins in July 2020.

“It is our professional opinion that the project corridor is safe to the traveling public with respect to general, large-scale slope instability and does not require closure…,” the letter said. “The rockslopes were designed in accordance with the present standards of care for rock slope design and mitigation within the constraints of the project. Even with rockfall mitigation, State Highway 55 is an active rockfall corridor and the public should expect typical maintenance issues.”

The letter said that as of the firm’s last visit to the site on June 28th, eight of the nine rock cuts are “substantially complete. Only work on Cut 8, where the large landslide in November 2021 occurred, is ongoing. This is also the area of the hill BoiseDev’s reporting revealed stability concerns over the course of construction.

“To assess the subsurface engineering geology, we installed five (5) geotechnical borings. As part of this construction work, we have installed slope inclinometers above the active construction to monitor potential slope movement,” the letter said. “To date, no movement of the slope has been observed. We anticipate that all work will be completed in the fall of this year.”