Going Underground to Upgrade Aging Infrastructure

A historic seaport, Olde Towne in Portsmouth, Virginia is bursting with history. You can experience the history before your eyes as you walk past towering 200-year-old-trees, cobblestone driveways and streets, and historic buildings dating back to the 19th century.

 

History is also lurking beneath your feet. As with many historic places, the City of Portsmouth faced the daunting challenge of evaluating and updating its aging infrastructure, particularly in the city’s oldest areas.

 

This infrastructure plan was critical to the city’s larger revitalization efforts to bring new economic development opportunities downtown.

 

Given the historic nature and age of Portsmouth’s water and sewer infrastructure in its downtown area, the city took a holistic approach to this maintenance and improvement project by dividing key areas into “Impact Zones,” each providing unique challenges and opportunities.

Impact Zone 1

 

underground pipe exposed during repairs to infrastructure and sidewalksImpact Zone 1 focused primarily on the downtown business district, a heavily developed land use area with mostly commercial properties and City of Portsmouth government buildings.  The infrastructure upgrade scope for this Impact Zone involved 10,200 LF of 8-inch to 16-inch diameter gravity sewer, 9,530 LF of 8-inch to 16-inch diameter water main, and 920 LF of 12-inch diameter sanitary force main within a 70-acre area.

 

Our team used conventional survey methods to map the project area for design and incorporated existing conditions located from right-of-way to right-of-way.  This approach provided enough mapping information to design not only the infrastructure redevelopment, but also to restore the historic brick sidewalks, curb, and all other distinct features of this Impact Zone. This approach simultaneously improved both the underground utility infrastructure and ground-level features, especially those that assist with stormwater management.

Impact Zone 2

 

Impact Zone 2 encompassed a 10 square block area in Olde Towne Portsmouth and, being historic residential neighborhoods, presented a completely different set of challenges than the first zone.  Historic 200-year-old trees, cobblestone driveway aprons, and historic concrete curb lined the existing streetscape.  Conventional surveying methods would have involved hand measuring each of these features and would significantly delay the design process.

 

Recognizing the limitations of these methods, including time and cost, our team turned to several cutting-edge tools. We deployed survey scanning technologies allowing the team to capture all the historic features (from face of house to face of house) in a fraction of the time and provide real-time photo documentation for reference throughout design and construction.  The 3D scan was particularly insightful because it could be used to create a virtual model of the street and underground infrastructure, allowing the team to better address challenges posed by historic trees and identify superior placement for new or rehabilitated water and wastewater lines.

From the detailed scans and surveys, the design team and city officials were able to evaluate the impacts of a full restoration and determined that curb-to-curb restoration was necessary to minimize the impact of the trees. This decision provided the city with savings of 25% – 40% of the total Impact Zone 2 project cost. Additionally, the advanced scanning information allowed designers to route the new infrastructure to specifically avoid the drip line (root base) of the trees, thus preserving the integrity and beauty of the existing historic streetscape during construction and for years to come.

 

Thanks to a combination of experience and new tools, we helped the City of Portsmouth successfully navigate much-needed infrastructure updates and position the community for greater economic growth.

 

This blog post is part of a series exploring projects and services that have helped clients realize their goals while preserving time and resources. Click here for additional blog posts in this series, which covers a variety of engineering challenges.