The Lilly Bridge project involved replacement of a cantilever truss bridge with a new 1,220-LF five-span, fabricated steel girder bridge. Carrying WV RT 20 traffic over the Bluestone Lake, the new bridge was erected adjacent to the existing structure. Brayman offered a significant Value Engineering (VE) proposal including substructure and superstructure modifications.
The revised substructure design comprises a single column option, which included semi-integral abutments. Fixed piers distribute the load across the bridge and allow for smaller diameter stems and caps, while the revised superstructure design successfully eliminates one line of girders.
Brayman’s approved VE design provided savings in excess of three million dollars to the project. As a result of the heavily silted lake bottom, the bridge required extremely tall and slender substructure units. In lieu of the original design, Brayman chose single column, architecturally finished piers founded on 10.5-foot diameter caissons. The total vertical length of the piers vary from 142-LF to 160-LF which includes the lengths of the rock socket, the caisson, and the pier shaft. The diameter of the piers from the rock socket to the cap is 10-feet. The pier caps are 7-foot in width and have a 10-foot diameter blister at the transition from the columns.
Although the original design required post-tensioned pier caps, the single column option has no post-tensioning in the caps. Foregoing traditional cantilever-style abutments, the south abutment of the new bridge is founded on a spread footing. The north abutment design includes installation of 30-each, 135-LF micropiles with design load capacity of 117 kip. Micropiles 9.625-inch in diameter and with bond zones from 10-foot to 17-foot drilled through an existing fill of cobbles and boulders. A causeway was installed to allow construction access across the lake to the main river channel were barges were used to facilitate construction. Additional work items included removal of over 250,000-CY of rock in order to re-align the existing roadway onto the new bridge, as well as removal of the old bridge through controlled demolition method.