Improving Construction: Terracon’s Use of Progressive Design-Build Changes Business

September 15, 2020

progressive design-build

Construction projects are typically delivered in one of three ways: Design Bid-Build, Design-Build, and Construction Manager at Risk. Terracon is a part of a team that is pioneering a fourth, novel option, called Progressive Design-Build, a hybrid of the previous method.

A review of these three traditional approaches will better the understanding of Progressive Design-Build.  First, the Design Bid-Build (DBB) approach is by far the most typical delivery method from a historical perspective. It’s such a traditional mainstay that the remaining approaches are termed “alternative delivery” methods. In a DBB project, an owner procures the professional services to develop construction designs. The designs are released to contractors to solicit bids, a contractor is selected (usually lowest bid), and construction begins.

The Design-Build (DB) method includes selecting a designer and contractor simultaneously, integrating construction thinking into the design process, and using the selected contractor/designer team to consider cost or time saving options. This has become a common method in many public construction projects, and it is gaining popularity.

The third approach, Construction Manager at Risk (CMAR), starts with an initial design in the more traditional DBB approach and then engaging a contractor to help with constructability considerations during design, ultimately progressing into construction.

The Progressive Design-Build (PDB) delivery method brings both contractor and stakeholder involvement into the delivery process at the get-go to shape the overall project design and construction with full input of all stakeholders. This alternative delivery method combines benefits from each of the other three delivery methods and helps eliminate problems and reduce risk by bringing the designers, contractors and stakeholders together early in the design process. The team then supports the project throughout construction.

PDB is a relatively new way of doing business in the transportation sector and Terracon is excited to be a part of one of the first projects of its kind in the country.

How PDB works

The idea behind the concept is simple: facilitate collaboration between all project stakeholders, including owners, neighbors, designers and contractors early so everyone can contribute in identifying and mitigating challenges that could hinder the project. The process identifies high-risk and potentially costly geotechnical and structural challenges during early project planning and design so they can be managed with creativity.

Pre-construction contracts are awarded not based on cost, but on qualifications, experience, approach and company relationships.

Using PDB in Utah

Terracon’s first PDB project was a recent Utah Department of Transportation project for  a 10-mile long segment of US-89 from Farmington to I-84. Construction on the three-year, 380-million US-89 project is scheduled to start this year. .

This transportation corridor is being completely reconstructed. The work includes multiple bridges, miles of new earth retaining walls, and new pavements, all within residential areas nestled in the foothills of the Wasatch Mountain range and encompassing five separate communities.

Because the team had real-time access to pertinent information, challenges were discovered and resolved early. This  method  significantly altered the project’s design and reduced risk for the state.

The initial project concept included grade separated structures that extended US-89 over cross streets at multiple locations. The PDB process allowed the community’s vision of the project to be integrated into the design concept. Other major geotechnical considerations and project risks were discovered and evaluated before construction started.

Special challenges included:

  • Designing bridges crossing active segments of the Wasatch Fault
  • Development of seismic parameters with near-source affects
  • Understanding variability of subgrade conditions along the project
  • Developing cost-reducing pavement alternatives
  • Construction of a major roadway corridor near established residential communities
  • Accommodation of a concentrated utility corridor
  • Designing earth retaining walls and bridges crossing over and adjacent to significant utilities

Collaboration Leads to a New Design

The project team was able to rethink the project and develop an entirely new concept because of the active collaboration between stakeholders, designers, and contractors. Terracon professionals used data collected from over 200 soil borings and geophysical surveys to form a basis for the new design. Collaboration with the area’s surrounding home and business owners was a great success. It brought value and helped shape the project with an innovative technical design that was pleasing to the community.

In the end, potential constraints and risks required the exploration of innovative solutions, such as ground anchor (post-tensioned) wall systems supporting spread footings, and creative solutions for design of bridge structures spanning an active fault line.

This delivery method allowed input from the community and implementation of their ideas. The transparency of the PDB process meant problems were identified before groundbreaking, before thousands of manpower hours were wasted and potentially millions of dollars lost.

Rick Chesnut is a geotechnical transportation leader in Terracon’s Salt Lake City office. His areas of emphasis include pavement section design (AASHTO 1993 and DARWin-ME Mechanistic Empirical design procedures), deep and shallow foundations, earth and rock-fill structures, slope and landslide stability, geologic hazards assessment, and earthquake engineering.

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