Royal Street: what are soil nails and why are they needed?

City Hall posted traffic barriers along Royal Street in 2011 after a section of the road failed. The road was temporarily shored up at the time. The municipal government later this year plans to strengthen a stretch of retaining wall in an effort to prevent another road failure. Park Record file photo

Park City officials plan to strengthen a stretch of retaining wall on Royal Street later this year that was temporarily shored up in 2011 after failing that year.

Matt Cassel, the Park City engineer, said the project will entail approximately 400 feet of the wall. It is located approximately 1,000 feet downhill from the intersections with Golden Eagle Drive. The retaining wall is on the downhill side of the street.

The city engineer said crews will install what are known as soil nails, which are made of steel encased in concrete. They will each be up to 40 feet in length, he said. The soil nails will be driven through the retaining wall and into the earth behind the wall. One soil nail will be put approximately every seven feet, Cassel said.

He said the work is expected to add at least 20 years to that stretch of the retaining wall's lifespan. It was installed in the early 1980s, as Deer Valley was developed.

"It will be the final repair," Cassel said.

The stretch of Royal Street failed in mid-2011. Officials at the time indicated water was washing away soil underneath the road, causing the road surface to crack. The road surface started to slip downhill.

Cassel said repairs were undertaken in 2011 that were expected to last five years. Further study led officials to pursue the upcoming work, he said.

The city engineer said the work is anticipated to start shortly after Independence Day and last up to three months. Royal Street will be open at night and on weekends during the work. Cassel said City Hall plans to ensure one lane is open during work hours. Flaggers will direct traffic when just one lane is open. The project does not include roadwork.

City Hall recently published an advertisement seeking bids for the work. The bid deadline is May 29. Cassel said he anticipates the work will cost in the low seven figures. A contract of that value will require approval by the Park City Council.

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Royal Street: what are soil nails and why are they needed?