MSE (reinforced soil) abutments

How bridges get built · Piers, pylons and abutments · MSE (reinforced soil) abutments

Also called: mechanically stabilised earth abutment, reinforced earth, GRS abutment

How it is done

Check foundation bearing, global stability and settlement; treat or replace soft ground, then cast an unreinforced levelling pad to line and level.
Set the first row of facing panels with clamps and temporary bracing, battered back slightly to allow for outward movement during compaction.
Place select granular fill in 200–300 mm lifts, compacting with heavy rollers away from the face and only light plate compactors within about 1 m of it; lay each layer of strips or geogrid flat and perpendicular to the face and connect it to the panels.
Repeat row by row, checking face alignment and batter on every row and covering panel joints with filter fabric.
For a true MSE abutment, cast the seat footing on the reinforced fill within the bearing limit and setback; for a mixed abutment, install the piles first and carry them through the fill in sleeves so the seat rests on the piles.
Cast the coping, the barrier with its moment slab, the underdrain and surface drainage, and the approach slab.
Monitor face movement and settlement, particularly where the wall sits on compressible ground or preloading was used.

Key numbers

Heightcommonly 4–15 m; reinforcement length at least 0.7H and not less than 2.4 m (AASHTO)
Select fillat most 15 % passing 0.075 mm, PI not over 6, compacted to 95 % of AASHTO T 99 maximum dry density in 200–300 mm lifts
Electrochemical limits for steel reinforcement (FHWA): pH 5–10, resistivity at least 3,000 Ω·cm, chlorides at most 100 ppm, sulfates at most 200 ppm
True MSE abutmentbearing pressure on the reinforced fill usually limited to about 200 kPa
Differential settlement along the faceabout 1/100 tolerable for precast panels with 20 mm joints

Where it fits

Fills of 4-15 m on competent ground, highway interchanges, sites where formwork and cranes are scarce, seismic regions (ductile).

Where it does not

Soft foundation soils without treatment, aggressive or saline fill (corrosion of steel strips), scour-exposed river banks.

Choosing it

Choose MSE over a cast-in-place cantilever wall abutment when the retained height is more than about 4–5 m, the ground is compressible but adequate, and cost and speed matter.
Prefer a mixed abutment (seat on piles through the reinforced fill) over a true MSE abutment when foundation settlement is significant, the deck is continuous or sensitive, or seat bearing pressure would exceed about 200 kPa.
Prefer geosynthetic reinforced soil (GRS-IBS) for single short spans on low-volume roads, where the deck can sit directly on the reinforced fill.
Prefer geosynthetic or protected reinforcement over bare steel strips in saline, wet or stray-current environments, or use a concrete wall.

Plant, pace and money

PlantSmall crane or excavator for panels, compaction plant, no formwork.

Productivity1-2 m of wall height per day.

CostUSD 250-450 per m2 of face, roughly half of a concrete wall.

Risks and controls

What goes wrong

Fill of the wrong grading, corrosion of reinforcement in wet or saline fill, panel bulging from poor compaction, seat settlement on a true MSE abutment.

Quality assurance

Fill grading and electrochemical tests, compaction tests per layer, panel alignment survey.

Origins

Henri Vidal patented Reinforced Earth in France in 1963; the first US Reinforced Earth wall was built on California State Route 39 in 1972, and MSE abutments became common in highway practice from the 1980s.

Examples

Highway interchanges worldwide since the 1970s; Gulf highways use them almost exclusively.

Case studies

State Route 39, San Gabriel MountainsUSA · 1972The first Reinforced Earth wall in the United States, which opened the way for MSE walls and abutments on US highways.

Bowman Road Bridge, Defiance County, OhioUSA · 2005The first geosynthetic reinforced soil integrated bridge system (GRS-IBS): the short-span superstructure bears directly on the reinforced fill without piles.