D3 I-15 Rockfall Mitigation, Helena to Great Falls, Montana
The steep canyon slopes along a 27-mile stretch of Interstate 15 between Helena to Great Falls caused a significant safety risk to highway users and increased maintenance efforts for the Montana Department of Transportation (MDT). To improve the overall safety of the corridor, our team was retained by MDT, with federal funding assistance from the Federal Highway Administration (FHWA), to perform investigation, design, and construction services of rockfall mitigation measures for 15 of the most hazardous rock slope sites.

As the Prime consultant, we were responsible for overall project management, public involvement, geotechnical engineering and geologic analyses, and preparation of the plans, specifications, and engineer’s estimate. Our engineers and geologists used 3D photogrammetry and Structure from Motion analysis to identify relevant failure modes of each slope. Stability models and rockfall simulations were used to select, size, and locate mitigation measures for each slope. We assisted MDT during bidding and provided construction engineering inspection for this complex, multi-year project. 
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The I-15 corridor from Helena to Great Falls follows the Missouri River and includes numerous natural rock slopes and rock cuts slopes. CCI-LT identified and designed mitigation measures for 15 of the highest hazard slopes to mitigate risks from rockfall.
Project Highlights
Field investigation and construction support were completed by CCI-LT’s in-house rope access team. Our SPRAT-trained engineers and geologists installed instrumentation to monitor movement of significant rock columns above the highway. Movement data allowed the design team to properly model and design mitigation measures. Project delivery for the 15 sites was broken into three contract phases.
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​We completed numerous rock slope stability evaluations and rockfall simulations as part of the design process. Rockfall and rock slope mitigation measures included trim blasting, scaling, draped-mesh, high-energy retention and attenuator systems, rock bolting, shear-pin buttress installation, triple-rail installation, concrete barriers, and expanding fallout areas. During construction, we supervised traffic control and temporary rockfall protection measures to protect the highway and adjacent railroad ROW. Our team of rope access professionals also provided full-time construction inspection services for the more difficult access elements like trim blasting, rock bolting, and attenuator system installations.
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Crews utilized helicopters to install mesh netting along the I-15 corridor between Helena and Great Falls Montana.
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Crews utilized temporary protection measures to intercept rockfalls while permanent measures were being constructed.
Owner:  Montana Department of Transportation 
More Information: Great Falls Tribute, I-15 rockfall project on schedule