Federal Highway Administration State Planning and Research Funding
Wisconsin Department of Transportation
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer, BEC
Justin Dahlbergdahlberg@iastate.edu email >
About the research
Within the recent past, the Wisconsin DOT changed the bridge approach slab design from a system using only one expansion joint to a system using three expansion joints (SDD 13B2). This change was due primarily to the need to accommodate differential expansion and contraction between the approach pavement and the bridge. Since implementing the new design detail, the Wisconsin DOT has become aware of the detail’s difficulty of constructability. As such, a more easily constructed, new standard design with one expansion joint and a sleeper slab was created (Bridge Standard 12) and has been used more recently. A review and analysis of Wisconsin approach slab performance was completed and other states’ practices were reviewed. As a result of this work, several conclusions and recommendations were made. Several are listed below.
The expansion and contraction requirement does not warrant the use of multiple expansion and contraction joints as seen in SDD 13B2. SDD 13B2 is more highly susceptible to inadequacies within the approach supporting materials. It is critical that the materials are prepared well and methods of preservation are built into the system for long-term performance.
For Bridge Standard 12, it is recommended that the slab design is revisited to ensure it is properly sized and reinforced to act as a bridge between the sleeper slab and abutment paving notch in the event that settlement of the backfill and subbase occurs. The continued use of a sleeper slab at the joint between the mainline pavement and approach slab is recommended. The continued use of polyethylene sheeting between the approach slab and supporting materials/sleeper slab interface is recommended
Attention should paid to the abutment backfill and approach support materials to mitigate potential differential settlement through improved compaction, reduced erosion, and/or use of alternative materials. Consideration should be given to flooding the structural backfill assuming the use of the current materials is maintained to eliminate post-construction collapse of the backfill material. Consideration should be given to alternative backfill materials such as geocomposite drains and/or recycled tire chips.