Selection and Types Abutments




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:

Stub abutments,

partial-depth abutments,

full-depth abutments; and

Integral abutments.

Partial-Depth Abutment

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

Full depth abutment are located at the approximate front toe of the approach embankment,restricing the opening under the structure.

Integral Abutment

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).

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