Selection and Types Abutments
The Structure upon which the ends of a Bridge rests is referred to as an Abutment
The most common type of Abutment Structure is a Retaining Wall, Although other types of Abutments are also possible and are used
A retaining wall is used to hold back an earth embankment or water and to maintain a sudden change in elevation.
Abutment serves following functions Distributes the loads from Bridge Ends to the ground Withstands any loads that are directly imposed on it Provides vehicular and pedestrian access to the bridge
In case of Retaining wall type Abutment bearing capacity and sliding resistance of the foundation materials and overturning stability must be checked
Types of Abutments
Standard specification classifies abutments into four types:
full-depth abutments; and
Partial Depth abutments are located approximately at mid-depth of the front slope of the approach embankment. The higher backwall and wingwalls may retain fill material, or the embankment slope may continue hehind the backwall. In the latter case, a structural approach slab or end span desing must bridge the space over the fill slope and curtain walls are provided to close off the open area
Full depth abutment are located at the approximate front toe of the approach embankment,restricing the opening under the structure.
Other Types of Abutments
Selection of Abutments
The procedure of selecting the most appropriate type of abutments can be based on the following consideration:
1. Construction and maintenance cost
2. Cut or fill earthwork situation
3. Traffic maintenance during construction
4. Construction period
5. Safety of construction workers
6. Availability and cost of backfill material
7. Superstructure depth
8. Size of abutment
9. Horizontal and vertical alignment changes
10. Area of excavation
11. Aesthetics and similarity to adjacent structures
12. Previous experience with the type of abutment
13. Ease of access for inspection and maintenance.
14. Anticipated life, loading condition, and acceptability of deformations.
Forces on Abutments
Earth pressures exerted on an abutment can be classified according to the direction and the magnitude of the abutment movement.
1.At-rest Earth Pressure
When the wall is fixed rigidly and does not move, the pressure exerted by the soil on the wall is called at-rest earth pressure.
2) Active Earth Pressure
When a wall moves away from the backfill, the earth pressure decreases (active pressure)
3) Passive Earth Pressure
When it moves toward the backfill, the earth pressure increases (passive pressure).