The approach system of an integral bridge, comprising of the backfill, the approach fill, the approach slab, the sleeper slab and the foundation soil, are important elements for the long-term performance and serviceability behaviour of integral bridges. Imposed deformations from the bridge deck are transferred to the abutment and the approach slab, which leads to a strong soil-structure interaction in the approach zone. The figure below shows various elements of an approach system.
To ensure efficient performance of the approach system, the following guidelines should be followed (As per IRC SP:115-2018 ) :
a. Minimum recommended length of approach slab is 6 m. The approach slab should be positively attached to the back wall by reinforcing bars
b. The sleeper slab is placed at the roadway end of the approach slab. This slab intends to provide a relatively solid foundation for the far end of the approach slab and to provide a location for limited expansion and contraction . Sufficient allowance for expansion of the super-structure must be accommodated in the sleeper
c. A sleeper slab is placed at the roadway end of the approach slab. The intent of this slab is to provide a relatively solid foundation for the far end of the approach slab and to provide a location for limited expansion and contraction. Sufficient allowance for expansion of the super-structure must be accommodated in the sleeper slab. Otherwise, compression can be introduced. into the slab by closing the expansion gap and subsequently activating the passive pressure behind the sleeper slab, or from contact with the adjacent roadway pavement. The latter can often be a major issue for the spalling and heaving of the adjacent pavement.