This project involved the replacement of the bridge carrying SR 2009 over an Unnamed Tributary (UNT) to the South Branch of Conewago Creek. The existing structure was a two-span cast-in-place reinforced concrete T-beam bridge with an overall length of 66’, supported on concrete abutments and a pier. The bridge had a clear roadway width of approximately 23’-3”, comprised of 11’ travel lanes and 1’± shoulders, and was classified as functionally obsolete. SR 2009 is a rural major collector. The alignment of SR 2009 has a 3,437’ radius curve and a flat profile grade over the bridge. The posted speed limit is 40 mph.
The new bridge is a two-span continuous composite prestressed concrete spread box beam superstructure supported on reinforced concrete abutments and a solid shaft pier. The overall length is 65’, comprised of two 32’-6” spans. The bridge is a tangent structure with a 90° skew. To accommodate the curvature of the road, the width of the deck was increased slightly and the position of the traffic lanes was allowed to vary relative to the edge of the deck. This resulted in a curb-to-curb width of 30’-2½” to carry the two 11’ travel lanes and wider, 4’ shoulders. The new structure provides a waterway opening that is slightly greater than the existing bridge and will not increase flood water levels. A detour of SR 2009 was used for construction of the new bridge.
Subsurface exploration during design identified the presence of karst geology underlying the structure, with extensive voids within the limestone bedrock. A history of sinkholes beneath the roadway and within the streambed adjacent to the structure, coupled with the effect of a quarry adjacent to the site, complicated foundation design. As a result, the construction contract included special provisions for evaluation of subsurface conditions during foundation excavation and mitigation of voids encountered during construction. During construction extensive and deep solution cavities were encountered beneath part of the far abutment. TPD was tasked by PennDOT District 8-0 to develop and design a foundation treatment to support the as-designed abutment spread footing foundation. TPD designed and detailed a free standing pile cap to support the downstream wing wall and specified areas underneath other parts of the foundation to be over-excavated and backfilled with concrete.
TPD provided the following engineering and environmental services for the design of this bridge replacement:
- Hydrologic and hydraulic studies
- Structure TS&L studies and Final Structure Design and Plans
- PADEP GP-11 permit application
- Roadway design and preparation of Roadway Construction Plans, specifications and cost estimate
- Construction cost estimate
- Pre-bid construction schedule
- Right-of-Way Plan and Property Plot Plan preparation
- Maintenance and protection of traffic design
- Construction services such as shop drawing reviews and the design of a free standing pile cap when unexpected voids were discovered beneath the far abutment foundation.
