The Maine Turnpike Authority completed the 5-year, $135 million widening and modernization of the southern end of the Maine Turnpike/Interstate 95. The project entailed adding a third travel lane and wider shoulders along 30 miles of interstate highway; reconstructing one interchange; reconstructing 18 bridges (Turnpike underpasses) to accommodate the additional width of the highway and to increase clearance; reconfiguring sideslopes along the widened highway for enhanced safety; and upgrading the drainage systems within the work zone.
GZA completed geotechnical programs for 10 miles of mainline widening and modernization and provided supplemental information for the design of a third segment. Embankment fills as high as about 40 feet and a number of stream crossing structures were included in these segments. GZA’s Saco/Scarborough segment included a ½-mile section where the existing road grade was raised up to 10 feet. Much of GZA’s alignment was underlain by soft, compressible, sensitive glaciomarine clay that is found throughout Southern Maine. Differential settlement of the new and original portions of the roadway, and embankment stability were the chief geotechnical issues. GZA completed extensive and phased subsurface exploration and soil testing programs; performed detailed geotechnical analyses; considered alternative soil improvement options; evaluated impact to existing culvert structures; evaluated reuse of excavated materials; and provided recommendations for the design and construction of the widened roadway and structures.
GZA provided construction consultation and quality control services for the geofoam lightweight fill approach embankments to the Beech Ridge Road underpass. GZA reviewed submittals and observed construction of approximately 1,800 cubic yards of expanded polystyrene geofoam fill. The fill was designed and installed with a wedge-shaped configuration, to limit differential settlement along the approach embankments, and between the approach embankments and the pile-supported bridge. The use of geofoam allowed the Turnpike to complete the bridge replacement on a fast-track schedule, eliminating the time required for ground improvement using wick drains/ surcharging.
GZA was responsible for the geotechnical investigation, and construction-phase monitoring and instrumentation for the bridge foundation and approach embankments for the reconstruction of the Biddeford interchange. The interchange site had challenging subsurface conditions, with up to 60 feet of compressible silty clay and up to 8 feet of artesian groundwater pressure. Embankment design for the bridge approach embankments included rigorous geotechnical analyses, and design and construction monitoring of a wick drain/surcharge and staged construction program to mitigate settlement and stability concerns. GZA installed and monitored settlement platforms and multi-level piezometers to assess the progress of consolidation necessary for safely constructing subsequent phases of the embankments. Recommendations were also provided for foundation design and construction of an integral-abutment bridge, as well as drainage structures. Pre-construction Wave Equation analyses were used to evaluate pile drivability.