What Good Looks Like: Fremont Canyon Design and Construct Rockfall Protection
Replacing 60-year-old rockfall barriers at Fremont Canyon required working within location constraints that defined every solution, from the custom lower barrier to the zip-line system that removed 700 cubic yards of debris.
In our 'What Good Looks Like Series' we're examining what good looks like across the different types of work we do, from emergency response slope stabilisation and mining ground support to geohazard mitigation and asset integrity maintenance. These aren't showcases of perfect projects with ideal conditions. They look at real work where solutions had to adapt as conditions changed, where collaboration shaped outcomes, and where technical expertise met practical constraints.
Project Overview
The Fremont Canyon Power Plant sits at the base of steep ravines in Wyoming’s North Platte River canyon, with the river on one side and cliffs rising on the other. Rockfall protection systems installed in 1963 had served the facility for six decades, but the infrastructure required replacement. The lower barrier had reached its retention capacity, and the overall protection system no longer met current performance requirements.
The facility’s location created absolute constraints. Access to the power plant is via a tunnel under the hills. The rockfall protection systems sit behind the plant, completely inaccessible from any area in front of the facility. Helicopter access was almost impossible due to power lines, proximity constraints, and operating restrictions. The only route to the barrier locations was through the ravines.
What does effective rockfall mitigation look like when location, not just terrain difficulty, dictates every solution? At Fremont Canyon, the answer required protection systems that could be installed via a single constrained access route, with all construction activity, equipment movement, and material removal planned around that fundamental condition.
Protection Systems for Retention and Energy Dissipation
Rather than relying on a single high-capacity barrier at the base of the ravines, the south and west ravines required five separate rockfall barrier systems, distributing protection across multiple positions. Four Geobrugg VX Attenuators were installed at different elevations across the two ravines, with a single SVX Attenuator at the lower barrier position.
The upper VX attenuators incorporated basal openings to allow smaller debris to pass through, reducing bounce height and dissipating energy before material reached the lower barrier. This configuration also allowed the upper barriers to be effectively self-cleaning, limiting debris build up and reducing long term maintenance requirements in terrain that is extremely difficult to access. By minimising retained material at higher elevations, the system reduces ongoing intervention and improves lifecycle performance of the ravine protection system.
SVX Attenuator – Modified VX System
The lower barrier installed at the base of the ravines was an SVX Attenuator, derived from the standard Geobrugg VX rockfall barrier system and specifically modified to suit the constraints of this location. Positioned directly behind the power plant, where it provides the final line of protection for the facility, this barrier occupied the most constrained and critical position on site.
The VX system is a proven off the shelf product with well-defined performance characteristics. However, in its standard configuration, the VX system could not be practically installed or sequenced within the access, geometry and construction constraints at Fremont Canyon. Rather than introducing an entirely bespoke system, the VX barrier was deliberately adapted and re-engineered to create the SVX configuration suited to this application.
Modifications were made to geometry, support and anchorage detailing, installation methodology and load transfer assumptions, allowing the barrier to be installed via the ravine corridor using rope access techniques and limited plant support. This configuration retained the performance of the VX system while allowing it to function as the final protective barrier in a highly constrained environment.
Construction Sequencing and Access Constraints
Standard practice for slope stabilisation dictates top-down construction, stabilising upper slopes before working below to protect crews from rockfall hazard. At Fremont Canyon, this meant installing upper ravine barriers before addressing the deteriorated lower infrastructure.
With the south ravine too steep for the Spider excavator and helicopter access almost impossible, the west ravine was the only viable route. The Spider excavator had to navigate this route after upper barriers were installed, requiring careful planning to move equipment past the new installations. The Spider was able to transport built up rockfall material downslope under controlled conditions during its movement down through the work area, progressively clearing accumulated debris and reducing the volume of loose material available to generate future rockfall events within the ravine.
Material Removal with Limited Access
Approximately 700 cubic yards of accumulated debris, comprising decades of rockfall and deteriorated barrier material, had to be moved from the lower barrier location behind the power plant as it both obstructed the installation of the new barrier and was a potential rockfall risk to the facility.
The location created an impossible logistics problem. With no vehicle access behind the plant, no safe manual handling route up the ravines and upper barriers occupying the only access corridor, conventional methods were not viable.
The Geovert-Designed Zip-Line System
To overcome this challenge, Geovert designed and implemented a custom zip line system to enable the removal of this accumulated rockfall material.
The system was engineered to transport debris from the lower barrier location to a collection point at the front of the facility, safely clearing power lines and avoiding the operating power plant structure. Using the Spider excavator to position material and rope access crews to manage loading, debris was placed into dumpy bags and moved along the zip line in a controlled and repeatable process.
The zip line allowed debris removal to proceed in parallel with barrier installation works and eliminated the need for higher risk manual handling or impractical access solutions. The zip line was not a temporary workaround, but a deliberately engineered solution to a fixed site constraint and formed a key part of the overall design and construct methodology.
What Good Looks Like
Effective rockfall mitigation at sites like Fremont Canyon requires working within constraints that cannot be negotiated. The facility’s location, accessible only via tunnel, with rockfall protection systems behind the plant reachable solely through steep ravines, defined every aspect of the engineering and construction approach.
Good design-construct is not the application of standard details but adapting proven systems and methodologies to actual site conditions. At Fremont Canyon, this meant taking established rockfall attenuator systems and re-engineering them to fit the access, geometry and construction sequence. The custom SVX Attenuator at the lower position exemplified this approach.
Just as important was the development of site-specific construction solutions. The Geovert designed zip line system removed decades of accumulated debris from an inaccessible location, making the overall system viable. Without it, the new lower barrier and long-term performance of the protection system could not have been achieved.
Integrated delivery - engineering, construction planning, and execution under one team - enabled these solutions. When design and construction sit within the same organisation, impractical details get eliminated early and solutions emerge that can actually be built within fixed site constraints.