Construction methods · Piers, pylons and abutments

Seat-type and cantilever abutments

A concrete wall with a bearing shelf, retaining the approach fill and carrying the end of the deck on bearings, with an expansion joint between deck and backwall. The conventional abutment; simple to build, and the place where most bridge maintenance happens (joints, bearings, approach slabs).

How bridges get built · Piers, pylons and abutments · Seat-type and cantilever abutments

Also called: seat abutment, wall abutment, cantilever abutment

Seat-type and cantilever abutments — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Build the footing or pile cap; cast the stem wall in lifts with wing walls.
Cast the bearing shelf and backwall; set bearings and the approach slab seat.
Backfill with free-draining granular material in compacted layers with drainage behind the wall.

Where it fits

Bridges over about 60-100 m where thermal movement needs a joint; tall fills; skewed and curved decks.

Where it does not

Short bridges where an integral abutment removes the joint for nothing.

Plant, pace and money

PlantFormwork, crane, compaction plant.

ProductivityFour to eight weeks per abutment.

CostUSD 500-800 per m3 of concrete; the wall is often 300-800 m3.

Risks and controls

What goes wrong

Backfill settlement behind the wall (the bump at the end of the bridge), drainage failure, joint leakage corroding the bearings.

Quality assurance

Compaction tests every layer, drainage inspection, bearing level survey.

Examples

Most Korean and Japanese highway bridges; the game's MSE abutment variant puts the seat on a reinforced-soil wall.