Replacing the Beards Creek bridge

In early March 1994, fresh water (more than 20 mgd) began pouring into the Retsof Salt Mine about 1,100 feet beneath the Beards Creek bridge in western New York. Despite efforts to stop it, the inflow continued until early 1996 when the 6,500-acre mine became completely flooded. The effects of the inflow were twofold; a loss of ground in and above the limestone aquifer about 600 feet above the mine, and the closure of the mine cavity at and spreading radially from the location of the inflow. These effects manifested themselves in the development of two sinkholes immediately upstream of the bridge. Concurrently with the inflow and development of the sinkholes, the bridge began to settle rapidly and was declared unsafe and taken out of service. By March 1996 the bridge had settled more than 15 feet and moved approximately 5 feet upstream toward the sinkholes. To meet the public need, the bridge was replaced, at its previous location. The authors' firms designed and oversaw the construction of the replacement bridge on an overlapping, fast-track schedule. The approach roadways were restored to a level of serviceability (flood survivability) equivalent to that existing prior to the recent ground subsidence. This required the placement of more than 30,000 tons of new earthfill. The authors' firms also performed close monitoring of displacement and piezometric responses to the fill and structural loadings. This allowed completion and opening of the bridge in less than 10 months while accommodating the anticipated 8 in of construction-phase settlement. This paper presents summaries of the fast-track design and construction process and of the movements of the bridge and embankments during and following construction.