*Limited seats available for this event.
SPEAKERS: Greg Bodenheimer, NCDOT and Scott Hidden, NCDOT
TOPIC: "The Bump in the Road; What is NCDOT doing about settling bridge approach slabs?"
Settling bridge approach slabs are a real problem in North Carolina. NCDOT Divisions spend millions of dollars annually lifting approach slabs and filling voids and stabilizing embankments under slabs. In most cases, there are multiple reasons for the movement including end bent and approach fill and slab design, subsurface consolidation, embankment construction methods, hydraulic conditions and heavy truck traffic. Since about 2014, the Geotechnical Engineering Unit (GEU) has been working on the approach slab settlement problem from two different directions; maintenance/repair and design/construction. For maintenance and repair, the GEU has been researching various grouting methods, revising and writing new specifications for different grouting materials and construction methods and piloting NCDOT's first use of compaction grouting on Cary Parkway. For design and construction, the GEU has piloted two projects with end bents on spread footings with abutments walls and completely revised the bridge approach fills for the 2018 Standard Drawings. One of the pilot projects in Anson County, NC consists of geosynthetic reinforced soil (GRS) abutments and the other for the Greensboro Eastern Loop consists of mechanically stabilized earth (MSE) abutment walls. We worked through numerous issues during the design of these projects; those issues as well as the methods used and the results will be summarized in this presentation. In addition, AASHTO has a current agenda item for the 2018 LRFD Bridge Design Specifications regarding foundation settlement and NCHRP recently completed Project 12-103 entitled Bridge Superstructure Tolerance to Total and Differential Foundation Movements. The 4 new types of standard bridge approach fills will also be presented with Structures Management policy for which type to use where. And lastly, we will explain the lessons learned over the past several years and future considerations for working on this issue.