RockSol Consulting Group, Inc.
  • US 85 Widening Design

    US 85 Widening Design

  • US 85 Widening Design

    US 85 Widening Design

US 85 Widening Design, Louviers to Milepoint 191.75


Colorado Department of Transportation


Transportation, Structural & Geotechnical Engineering


Douglas County, Colorado

Project Description:

RockSol conducted structural retaining wall preliminary design, geotechnical engineering, and developed proposed cut slope surfaces to assist CDOT civil engineers on the widening and reconstruction of US 85 between Louviers and milepost 191.75. The project includes a bridge replacement, reconstructing and widening 1.3 miles of US 85 from two lanes to four lanes with concrete pavement, raised medians, curb and gutter, new drainage systems, detention ponds, and realignment of the Highlands Gulch Channel. Additionally, there are two bluffs within the project area initially identified as retaining walls up to 95 feet tall or cut slopes. One of the complexities of this project was a combination of significant grade change (hill-side cut) adjacent to the proposed widened roadway and a limitation of funding to allow construction of a tall, near-vertical retaining wall system.

RockSol’s structural scope of work consisted of preliminary retaining wall design for the cut slope walls. This included developing and evaluating seven feasible alternatives for the cut slope retaining walls. The initial six alternatives were developed to minimize cost and fit within the proposed right-of-way; CDOT requested a seventh alternative to further minimize cost by replacing all the walls with cut slopes on tiers, and revising the proposed right-of-way. The seven alternatives were evaluated in the structure selection report, including estimated quantities and cost, and general layout plans for the recommended structure alternative. CDOT used the Structure Selection Report in their decision to concur with the recommended alternative – the alternative that achieved least cost by replacing all walls with cut slopes on tiers.

In addition to structural engineering, RockSol was responsible for conducting the geotechnical engineering investigation and slope stability analysis for the cut slopes and cut slope retaining walls. RockSol drilled a total of eleven boreholes for this geotechnical investigation, and prepared the Geotechnical Report. Based on the information gathered in the geotechnical investigation, RockSol developed recommendations and conducted stability analyses for cut slope retaining walls, cut slopes in bedrock, and cut slopes through the overburden. For the cut slopes through the overburden material, RockSol recommended either 2.2 to 1 slopes, or reinforced soil slopes at 1 to 1, depending on the available right-of-way. RockSol designed and prepared plans and specifications for the reinforced soil slopes incorporated into the final PS&E package. 

CDOT also asked RockSol to assist with development of proposed cut slope surfaces and tiers along US 85 and around an access road. RockSol first developed a digital terrain model to represent the interface of the bedrock with the overburden material. Then, we used InRoads to develop the modeling for the cut slopes and tiers, and developed the proposed digital terrain models.