Geotechnical considerations of the headwall/approach slab detail in semi-integral abutment bridges
Integral bridges are single or multiple span bridges that are built in the form of an integral or a semi-integral configuration. Integral bridges have their superstructures cast monolithically with the abutments. This type construction eliminates costly joints and sealers as well as reduces maintenance costs associated with their use. This generally results in a more economical and low maintenance structure and better overall rideability. A slight modification of the integral abutment bridge is the semi-integral design, which eliminates joints, but still uses conventional bearings. However, unlike conventional bridges, the jointless slab protects these moveable bearings. Semi-integral bridges have end diaphragms (headwalls) integral with the superstructure, but non-integral with the foundations. Semi-integral bridges require a horizontal joint separating the superstructure and the abutment In this research, the behavior of semi-integral bridges was investigated through field monitoring and laboratory testing. For a period of 18 months, the field investigation included the monitoring and testing of all six semi-integral bridges constructed in Louisiana. One of theses six bridge, bridge 39-04-31 was selected for extensive monitoring and testing. In view of the review of existing records and field inspections and monitoring, the overall performance of these bridges was found to be satisfactory. It was concluded that the present design of semi-integral bridges used in Louisiana is structurally sound A small-scale semi-integral abutment bridge model was constructed in the materials lab of Tulane University. Several tests were then performed using this model to study the impact of several variables on the overall performance of the bridge. Displacement of the headwall and the lateral earth pressure are some of the parameters monitored during theses tests. Several sensors were attached to the model to collect the necessary data used in the analysis Results of the tests performed indicated that placing a geofoam between the abutment headwall and the embankment would significantly reduce the earth pressure on the abutment headwall. The use of uncompacted sand would also help in minimizing the magnitude of pressure