The Arizona Department of Transportation (ADOT) is currently in the process of designing the new Guthrie Bridge that takes US 191 over the Gila River in Greenlee County, Arizona. The new bridge is located 200- to 400-ft east of the existing Guthrie Bridge and is intended to replace the existing one.

The new bridge structure has been designed as an 8-span bridge with a total length of 1,083-ft. the highest column in the center of the valley has a height of approximately 115-ft.

The original design approach consisted of a 9-span bridge with all spans being 120-ft long. However, potential conflicts with Union Pacific Railroad tracks at the bottom of the valley forced ADOT to remove one column in the center of the bridge, thereby widening the center span to 240-ft. In addition to the increased vertical load, a significant bending moment is induced into the adjacent columns. This eccentric loading condition is transferred to the foundations. The foundations for the new Guthrie Bridge consist of drilled shafts socketed in Gila Conglomerate, a calcite cemented rock.

ADOT retained NCS to provide independent technical review of the geotechnical investigation program performed as well as to prepare an axial and lateral load test program in support of the design currently being performed.

NCS provided the following services as part of the scope of work:

• Site reconnaissance.
• Provide guidance for axial and lateral load analysis.
• Collection and review of available geotech information.
• Reduction of dilatometer data.
• Development of an updated subsurface profile and parameters specific for the load test program.
• Setup of the axial and lateral load test program including discussions and coordination with the Bridge Group for structural analysis and preparation of construction drawings.

This project is currently in the design phase.