Work to repair a slide on Giant Springs Road begins Sept. 25.

The project is scheduled to run through Nov. 6 and will close the south parking lot with trucks and heavy equipment on the road and work on the north side of the guardrail.

In August, City Commissioners awarded a $212,720 contract to Montana Materials and Construction, formerly MRTE, for the project to repair and mitigate the sloughing slope along the road near the River’s Edge Trail, caused by oversaturation of the toe of the slope, according to city staff.

City awards contract for Giant Springs Road slide repair

“The existing road embankment is sloughing, generating a potential future hazard to the public if left uncorrected,” according city staff. “There is a significant risk that the current slide area, if left unaddressed in the years to come, will expand enough to damage Giant Springs Road and the River’s Edge Trail.”

The city has been working on this project for years.

City Commission approves contract change for Giant Springs Road slide repair

A fill-slope failure of the western slope of the Giant Springs Road embankment was first reported by Montana Fish, Wildlife and Parks in January 2021 to the city.

City staff and Terracon confirmed the slide during a site visit, observing a shallow failure on the down slope side of the section, which is the west side, towards the river.

The existing road embankment is sloughing, which can cause a potential hazard to the public, according to the March 2024 staff report.

City amending contract for Giant Springs Road slide repair

In May 2022, the city retained Terracon to conduct subsurface evaluation of the slide area to develop conceptual strategies to select a final repair design option.

Terracon has completed the design phase engineering, including plans and specifications.

This project will repair existing slope sloughing and mitigate future slope failures in the area by shifting drainage of the area to direct surface water down to the drainage basin, limiting ground saturation and preventing undercutting of the embankment and oversaturation of the toe slope, according to city staff.

Giant Springs Road will remain open with no more than one lane closed for short periods of time during construction.

The city received three bids for the project from Montana Materials and Construction; Central Heating and Plumbing; and Shumaker Trucking and Excavating ranging from $212,720 to $257,792.50 with Montana Materials and Construction submitting the low bid.

County approves contract for Giant Springs Road repairs [2024]

The city has budgeted street assessment funds for the project. Earlier this year, staff said they intended to use state gas tax funds toward the project.

In March 2024, commissioners approved a professional services agreement with Terracon for $111,600 to conduct a topographic survey, complete the project design, develop the plans, assemble bid packages, assist with bidding, and complete as-built drawings of the slide repair improvements associated with this project.

During the design phase of the project, the consultant’s understanding of the federal requirements increased, requiring additional work beyond the original project scope agreed upon in the original document, according to city staff, and in February 2025, commissioners amended the contract for another $18,645, bringing the total to $130,245.

City planning road slide repair [2024]

The project will require multiple permits from the Army Corps of Engineers, requiring more work from Terracon, according to city staff, so the amendment will address that additional work for the federal permits, complete design and move into the construction phase of the project.

Three Great Falls area recreation projects receive grants [2022]

The subsurface investigation and monitoring of the landslide included three geotechnical borings used to determine subsurface conditions and failure mechanisms of the slope. Along with the borings, inclinometers were placed across the site to monitor and determine depths and rates of movement over the course of a year, according to staff.

In conjunction with the monitoring, laboratory testing was conducted to determine soil parameters to facilitate slope modeling and analysis of the failed section to design conceptual repair strategies.

The Giant Springs Road site comprises of an existing roadway fill section.

Section of Rivers Edge Trail closed to fix drainage issues [2019]

An upper walking trail parallels and abuts the east/southeast shoulder of the road and the River’s Edge Trail is located downslope and to the west/northwest of the failed area, according to city staff.

Near the north end of the project area is a pedestrian tunnel that goes under Giant Springs Road.

A culvert collects water from east of the road fill and exits the slope near the south end of the pedestrian tunnel on the west side of the embankment, which consists of a shallow fill-slope failure along the northwestern slope of the Giant Springs Road overlooking the River’s Edge Trail to the west, according to the March 2024 staff report.

Giant Springs Road closure for riverbank stabilization project [2024]

The failure is a typical circular failure plane in which the destabilized plane rotates downslope from its original position with a pronounced drop at the top of the failure and a bulge of material moving near the base of the failure.

The adjacent drainage appears to be the primary cause of the slide as the drainage between the natural hillslope and the embankment fill has resulted in saturation and undercutting of the embankment fill along the drainage.

The project will implement the design phase of the improvements recommended in the geotechnical report from March 2023.

Given the surficial nature of the fill-slope failure, two embankment slope repair alternatives are proposed. The first alternative includes grading the slope to a flatter slope condition. The other alternative is installing a rip-rap shear buttress keyed into the bedrock at the embankment toe.

Drainage repair alternatives will need to transport surface water down the drainage to the drainage basin without allowing saturation and undercutting of the embankment fill, according to the staff report.