About this Project

The SR 33 Bridges project involves replacing two adjacent highway structures spanning Bushkill Creek in Northampton County, an area known for sinkhole activity and complex karst geology. The original bridges, installed in the 1970s, slowly sank—one by two feet, the other by one—due to subsurface voids created by limestone erosion. A $10 million replacement effort 20 years ago also failed, with micropiles extending up to 500 feet unable to reach stable bedrock. The current $25 million project, now expected to be completed in fall 2026, is PennDOT’s third attempt to stabilize the corridor. The new design features a large open-grid concrete mat foundation, nicknamed the “waffle mat,” which spreads the structural load across the surface and allows future sinkholes to be plugged through built-in access holes.

AEG is part of the design team tackling these geotechnical challenges. Our responsibilities include preparing the Subsurface Exploration Planning Submission (SEPS), administering the subsurface drilling investigation, and overseeing drilling inspectors and operations. AEG performed detailed geotechnical analyses to support the selection of the mat foundation and provided recommendations for the bridge substructures, catenary supports, and adjacent retaining walls. The drilling program encountered hazardous materials and required specialized handling protocols during both investigation and construction phases. AEG also prepared the roadway geotechnical engineering and structure foundation reports and continues to provide construction consultation services.

The project’s success is critical not only for transportation continuity but also for public safety, as sinkholes have previously forced the demolition of nearby homes and infrastructure. AEG’s technical expertise is helping PennDOT deliver a resilient solution in one of Pennsylvania’s most geologically volatile regions.

Construction photo provided by Michael Baker.

​