GZA served as geotechnical engineer for the design-build team to reconstruct Veteran’s Memorial Bridge, which crosses the Fore River between Portland and South Portland, Maine for the Maine Department of Transportation (Maine DOT). The new bridge will replace a deteriorated, 200-foot long circa-1950 steel bridge with a trapezoidal-box, segmental precast concrete structure. The new bridge alignment will be offset from the existing alignment and skewed to improve traffic flow. In order to accommodate the new alignment, a 1,600-foot long replacement bridge is being constructed across the river, an existing bridge will be widened, a new 600-foot long MSE structure is being constructed near the Portland abutment, and a triangular embankment widening is being constructed for the South Portland abutment and approach roadway.
A key geotechnical challenge was to develop a cost effective concept to widen the 25-foot high South Portland approach embankment in an area underlain with 60 to 90 feet of marine clay. In addition to typical considerations such as settlement, stability, cost and time, the available construction footprint area was limited due to the Maine DOT RFP requirements for allowable impacts in the tidal river.
Settlement mitigation measures were developed by GZA to control settlement and prevent downdrag loads on the new pile-supported abutment and retaining wall. During the RFP phase, GZA developed a preliminary geotechnical design for the approach embankment and foundations. The preliminary design included a preload fill up to 25 feet above the existing mudline that used a temporary, anchored, sheet pile cofferdam to limit the footprint, and prefabricated vertical drains to accelerate the consolidation of the underlying clay. The preliminary design allowed the Design-Builder to meet the project schedule requirements and marine impact limits, and also allowed the piles to be designed without downdrag loads. It is understood that the GZA embankment design was on the order of 1 to 2 million dollars less expensive than the embankment and approach designs prepared by competing design-build teams.
During final design, GZA was the engineer of record for the South Portland Approach. Final design included engineering evaluations to show that post-construction settlement, slope stability and sheet pile design considerations were technically feasible and met the project requirements. Deliverables for the South Portland Approach included Geotechnical Design Reports for the Preload and the Preload Instrumentation Program and contract drawings showing the temporary wall layout, the instrumentation program, the proposed construction sequence, and special provisions pertaining to geotechnical aspects of the work.
GZA’s geotechnical instrumentation plan included settlement monitoring plates, inclinometers, piezometers and optical survey points. GZA provided technical oversight during installation of the instrumentation, and set up the data recording plans for all the instruments. Instrumentation data was collected by a combination of GZA (piezometer baseline readings and inclinometers only) and Contractor.
This project was the winner of the 2012 Engineering Excellence Special Recognition Award from ACEC of Maine for the project's Innovative Embankment Preload Program.