Three Benefits of CMGC Delivery: A Case Study on Historic Yankee Jims Bridge

How CMGC Delivery Works

CMGC delivery, which involves hiring a CMGC during a project’s design phase, is an increasingly popular choice among public agencies. The CMCG collaborates with the design team to provide construction insights, cost estimates, and schedule input. Once the design is complete, the CMGC transitions to the role of general contractor, executing the construction work. The early involvement of the CMGC helps identify potential issues, opportunities and solutions, reducing risks and helping the project stay on budget and schedule. The greatest strength of CMGC is the team’s ability to make risk-based engineering decisions. By determining which party—the engineer, contractor, or owner—is responsible for risks and the potential associated costs, the team can minimize and mitigate them. In some cases, the risks (and costs) are retained and built into the estimates. This approach fosters transparency and mutual agreement, leaving no room for surprises.

All CMGC projects include an Independent Cost Estimator (ICE) who has a separate contract with the owner. The ICE develops a contractor-based estimate (also known as a bottoms-up estimate) with specific tasks broken down by projected labor, equipment, and materials. This estimate is used at the 30%, 65%, and 95% stages to validate, backcheck, and provide cost control on the CMGC estimate. Both the CMGC and ICE are required to “open up their books,” show information, agree to cost-estimating assumptions, and then compare results. If there are significant differences in these estimates, this may result in the owner choosing not to go forward with the CMGC, called “taking the off-ramp.” If this occurs, the owner would put the contract out to bid in the traditional sense, where they choose the lowest bid, and the CMGC is prohibited from bidding on the project. Ideally, the owner would never have to take the “off-ramp,” but this happens sometimes when cost differences cannot be reconciled.

Yankee Jims Bridge – A Case Study in CMGC

The Yankee Jims Bridge project is a case study in how CMGC delivery offers three unique benefits—reduction in environmental footprint, implementation of innovative solutions and practical knowledge, and increase in cost control and estimating accuracy. Preserving history and bringing contemporary engineering solutions, this project will build a new bridge parallel to the existing suspension bridge, which will be saved as a historic resource.

Through a previous feasibility study that Consor had been competitively selected for, Consor provided the preliminary design and assessment of 10 different structure alternatives. These alternatives were conceptualized with layout, geometric configuration, and foundations and materials assumptions, with challenges identifiednd evaluated by the County, Caltrans, and key stakeholders. The feasibility study resulted in the selection of two structure alternatives, steel arch and steel girder structures, to be carried forward in the design and environmental phase.

The County solicited again for design services to further evaluate the two alternatives to choose one for final design and environmental clearance, and Consor was selected. These two alternatives were developed to a 35% design level, after which the County solicited a proposal for the selection of a CMGC Contractor for this project. Placer County (owner), Consor (engineering design), and Flatiron Construction (CMGC) completed preliminary designs and quantities, as well as evaluated the constructability and potential environmental impacts of the two pre-determined alternatives. Collectively, the team landed on a steel arch suspension bridge design that would fit aesthetically, mitigate environmental impacts, and minimize cost. This Type Selection Process secured Caltrans concurrence.

Reducing Environmental Footprint

Early CMGC involvement during design allows for more accurate planning and decision-making regarding environmental impacts. In traditional bid-build delivery, engineering designers cannot accurately predict how contractors will need to clear a site, so they typically plan to clear a larger area. This can create a challenge when the designer submits permits to environmental resource agencies because they will have a larger mitigation ratio. Clearing more vegetation also increases the cost, both for removal and replanting. With CMGC delivery, the contractor can narrow in on exactly how much needs to be cleared, which both minimizes cost and helps in the permitting process.

For the Yankee Jims Bridge project, several miles of primitive dirt roads with stacked rock walls, vertical cliffs, and sharp curves made accessing the site challenging. The roads winding down the canyon needed to be improved in key areas so that the heavy construction equipment could make it to the site. Having the CMGC involved from the start meant that the design team could make informed decisions about necessary equipment and access. For example, the CMGC provided a model of the swing radius of the tower cranes, which narrowed down the environmental footprint, resulting in substantial restoration and replanting savings.

With the CMGC’s involvement, the team was able to meet with permitting agencies and avoid impacting the riverbank, eliminating the need for a permit to relocate the protected Sierra Nevada Foothill Yellow-Legged Frogs. The CMGC’s practical knowledge also allowed for precise planning and scheduling around the high rafting season, minimizing recreation disruptions.

Leveraging Practical Knowledge

The CMGC approach fosters innovation by leveraging the contractor’s practical knowledge and on-site testing capabilities. In traditional design-build, the engineer would take a detailed survey of the roadway to the site and complete a detailed analysis via computer model of the roadway sections to verify access for construction vehicles. But because of the CMGC collaboration, the contractor implemented a simple, practical solution to assess where roadway improvements were needed.

In just one afternoon, with one trip to a home improvement store and creative problem solving, the contractor created a rig out of wood beams to simulate the size of the construction equipment. Every time the trailer would go off the road, the team marked that location for improvement. This practical testing demonstration reduced the necessary road improvements from miles to just 18 specific locations—which also lessened the environmental impact of a larger construction footprint.

Implementing Innovative Solutions

The new alignment, downstream of the existing bridge, required substantial hillside cuts. The CMGC team collaborated to determine the best use of materials generated from excavations, minimizing the need to haul material out of the canyon. The solution was using excavated material to create a parking area and formal rafting pull-out and recreation area, creating additional value for the community.

The contractor’s input also refined the structural design. Normally when you have cranes on a construction site, you must make sure there is room and support for the loads. The Yankee Jims Bridge team designed the abutments for the new bridge to be able to hold the temporary crane loads, which reduced the environmental footprint by eliminating the need for a temporary foundation.

Because of the collaboration between the designer and the CMGC, the specific construction sequence can be evaluated, and all the temporary and staged load conditions can be considered, which otherwise might have impacted the erection of the bridge. Having these constructability insights and inputs early on set the course for covering all of this in the initial design, saving time, minimizing impacts to surrounding environmental areas, and reducing potential risk during construction.

Maintaining the Existing Bridge

The decision to build the new bridge parallel to the existing bridge and keep it as a historic resource preserved this piece of infrastructure history. The Yankee Jims Bridge is a “bridge in a box” by the John A. Roebling Sons Company, which is best known for designing and building the Brooklyn Bridge. To maintain the bridge’s historic eligibility, they made only the modifications necessary to use the existing bridge during construction. The CMGC approach enabled the team to expose and assess the bridge’s cable anchorages, refining the design and reducing excavation risks.

The team also created a pulley system that allowed the construction equipment to be pulled across the existing bridge without reaching the bridge’s load limit. That way they only needed to make road improvements on the Colfax side of the river while still being able to construct the bridge from both sides.

Increasing Cost Control and Estimating Accuracy

For the Yankee Jims Bridge project, the CMGC approach provided detailed schedules and clear communication with permitting agencies, facilitating efficient vegetation removal and other environmental actions. The early involvement of the contractor allowed for comprehensive constructability reviews, reducing the risk of rework and keeping the project on schedule and within budget.

In addition to minimizing the roadway improvements needed, the contractor used practical knowledge to manage high-risk tasks like rock removal. Initially, the contractor anticipated a lengthy and costly process involving drilling and blasting. However, a demonstration project revealed that the rock was rippable, which confirmed they needed a shorter construction window.

The Yankee Jims Bridge project showcases the benefits of the CMGC approach. The collaborative efforts of Placer County, Consor, and Flatiron Construction have reduced the environmental footprint, fostered innovation, and minimized costs. Once construction is complete, the Colfax and Foresthill communities will be safer, with better access for emergency response, and enjoy the added benefit of better recreation access and preserved history.