usually, a bridge supported from both ends by abutments. cross-section of abutment shown in figure 1. abutment used to retain embankment and resist and transfer vertical and horizontal loads from the superstructure to foundation. the shallow or deep foundations may be used to support abutment. selection of foundation type will depend on soil bearing capacity and loads imposed from the superstructure. stability of abutment shall be checked. overturning and sliding stability shall be checked. Figure no:2 showing different component of the abutment.
Selection of abutment type dependants on different factors such as economic, location and aesthetic. for abutment crossing a river or stream a minimum channel and section shall be considered. for highway, the horizontal clearance and sight-distances is the main concern.
aesthetic and economics are important factors and shall be considered in selecting abutment types.
- Full retaining abutment: this type of abutment built from the bottom of the embankment. therefore, it is considered very expensive. however, the cost of the superstructure may be reduced by reducing span length. overall cost should be considered while evaluating different options. using this type of abutment will pose a problem during backfilling and compacting of embankment between the wing wall of the abutment. limited space between abutment wing wall and backwall will not allow for proper compaction. also using heavy equipment for compacting may affect the vertical alignment of abutment and cause settlement of the foundation. figure no:3 depicts full retaining abutment. this type of abutment will limit horizontal clearance and reduce sigh-distance which may cause collision accidents. therefore abutment should be barricaded with concrete barriers
- semi retaining abutment: this type of abutments are constructed between the bottom and top of the embankment as shown in figure 4. this type provides a bigger horizontal clearance from the road edge. this, in turn, will increase sight distance and reduce collision hazard.
- sill abutment: sill abutments are built on top of road embankment. the cost of constructing of sill abutment is considered relatively low. the superstructure span length will increase. therefore overall cost shall be considered to determine the feasibility. sill abutment will provide large horizontal clearance and sight distance. using of sill abutment will eliminate the issues regarding the compacting and placing of road embankment.