| River Road Bridge Over Delaware Canal |
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Location: SR 0032, Section 04B, Upper Black Eddy, Bridgeton Township, Bucks County, PA Client: Pennsylvania Department of Transportation; Subconsultant to Site-Blauvelt Engineers Description: VFL performed a geotechnical investigation to evaluate the adequacy of the existing masonry abutments to carry a new superstructure. Ground penetrating radar was utilized in combination with test borings to determine the thickness and geometry of the masonry abutments. The test borings also served to investigate the nature of backfill against the abutments as well as to determine the bearing levels and the underlying soil and rock conditions. In addition to field explorations, laboratory classifications, consolidations and triaxial testing were performed on representative specimens to accurately characterize the subsurface soils and determine their physical and mechanical properties for foundation analysis and design. The results were utilized to perform stability analyses on the existing abutments under current as well as proposed loading from the new superstructure. AASHTO load group combinations were used in the analysis.
The findings of the analysis indicated that the existing abutments would not be stable under the new superstructure. Therefore, the following alternatives were considered: tiebacks, bracing, jet grouting, posting a reduced (HS15) bridge weight rating, and increasing the width of the abutments by tying reinforced concrete portions to the existing masonry ones. The last alternative was adopted to maintain the original appearance of the masonry abutments. In conclusion, although this is a relatively small project, it represented major design challenges and required innovative engineering to address them. For example, this is the first PennDOT project in which ground penetrating radar was implemented to determine the geometry of old masonry abutments. |
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