Overview
Timmons Group provided complete design services for St. Andrew Street over Lieutenant Run for the City of Petersburg, including bridge design and structural engineering, hydraulic analysis and development of scour mitigation, geotechnical engineering, survey, environmental permitting, roadway and transportation design, utility coordination and relocation design, bid phase and construction phase services, public involvement, and overall construction management.
The replacement structure is a prestressed concrete voided slab superstructure with jointless abutments, resulting in a low-cost and low maintenance structure.
The new structure was designed to span over the abutments of the existing bridge with existing field stone gravity abutments and wingwalls remaining in place, serving three purposes – 1) to provide protection against scour for the new abutment foundations, 2) to reduce the extent of in-stream work required, allowing for a more streamlined environmental permitting process, and 3) to limit the need for costly utility relocations of existing water and sanity lines that span through the existing wingwalls. The team designed additional scour countermeasures, and riprap was placed in areas of the stream channel and embankments where there were no scour mitigation measures in place.
One challenging aspect of the project was the presence of overhead electrical lines at the existing bridge location. To be conscious of cost and schedule, Timmons Group worked with Dominion to determine an approach involving shielding the lines, allowing for reduced clearance requirements. Our structural and geotechnical engineers then worked closely together to develop a deep foundation option constructible in a low overhead clearance environment. Ultimately, we designed Augered Cast-in-Place (ACIP) piles. Because these type piles are not typical in bridge construction and are not covered by current VDOT Road and Bridge Specifications, we also coordinated with VDOT Central Office geotechnical staff and Richmond District S&B staff for approval and recommended project specification requirements.
This project was locally-administered, funded with VDOT State of Good Repair (SGR) funds – a relatively new funding source for localities with strict requirements on which aspects of repair and rehabilitation are eligible for reimbursement. As such, Timmons Group assisted the City in navigating the process and coordinating with the District bridge office to ensure proper SGR procedures were followed.
