Rehabilitation of US 1 Bridge over Big Gunpowder Falls

JMT designed a cost-effective solution to rehabilitate a state highway bridge experiencing early deterioration.

Location

Baltimore County, MD

Client

Maryland Department of Transportation SHA

Belair Road (US 1) is a major thoroughfare carrying four lanes of traffic near Gunpowder Falls State Park. The US 1 bridge over Gunpowder Falls consisted of five large, corrugated metal culverts that allowed passage of the Falls beneath the roadway. In addition to these five passages, a sixth tunnel located on the north bank of the river served as a pedestrian/equestrian path as part of the state park trail.

All six structural cells experienced advanced deterioration including leaking bolt hole locations, with the galvanizing layer completely gone, and severe rusting and section loss noted.

MDOT SHA Office of Structures asked JMT to evaluate various options for repair and/or rehabilitation. JMT determined the primary issue was that the galvanizing had not been oxidized under proper conditions prior to being put into service in a wet environment. The most cost-effective rehabilitation method was an independent structure capable of supporting all loads itself, not reliant on the structural plate pipe for strength.

Each of the five cells was retrofitted with a nine-inch thick, cast-in-place reinforced concrete liner poured inside and against the existing structural plate pipes. The contractor completed construction in two stages, dewatering those cells currently being rehabilitated while maintaining some cells to remain open for water flow. Water stops were installed in the proposed concrete liner at each construction and expansion joint to ensure a watertight connection. Dowels were drilled and grouted into the existing footing to ensure a secure connection to the foundation.

The pedestrian/equestrian tunnel was retrofitted by installing a 14’ diameter tunnel liner plate pipe within the existing 15’ diameter structural plate pipe. Construction consisted of removing the existing concrete pathway and lighting completely. The existing structural plate pipe was cleaned and coated with a waterproofing membrane. The tunnel liner plate was coated with high-density polyethylene on both sides and fit within the existing structural plate pipe. Grout was pumped between the old and the new pipe to fill the void and to ensure a watertight connection and completely independent structure.

The trail head entrance received a new walkway comprised of pervious concrete stabilization blocks, and new LED lighting. The walkway was an improvement from the previous gravel trail, and it allowed stormwater to infiltrate into the ground and not create runoff. This streamlined the permitting process and eliminated any new impervious areas.

The project was located within the Gunpowder Falls State Park, an area under the supervision of Maryland DNR. Extensive coordination was required with DNR for parking locations and alternate means for users to access the trails on either side of the pedestrian structure during the nearly two-year construction period. Another significant factor was construction access to the inside of the existing pipe culverts. With no accessible means to access the river without significant disturbance and the removal of trees within the park, the decision was made to stage construction from the shoulders of US 1, and perform all work from above, by lowering materials into the culverts with cranes and concrete pumps.

The project eliminated reliance on a deteriorating metal structure that supported a four-lane major state highway. The new independent concrete structures will ensure a maintenance-free rehabilitation for many decades.