Reinforced Backfill

When building a reinforced earth wall the reinforced backfill is an important component to the design.

Reinforced backfill is the material that will be placed and compacted between the geogrid layers. The National Concrete Masonry Association in there design specifications recommends a sandy backfill or better.

USC soil types: GP, GW, SW, SP, SM

The gradation is listed below

Sieve Size                            % Passing

4 inch                                    100-75

No. 4                                     100-20

No. 40                                   0-60

No. 200                                 0-35

Plasiticity Index < 20

A strength reduction (higher damage factor) on soil reinforcements is required when reinforced backfill larger than 3/4'” in size is used.

Many times import backfill material is required for the reinforced soil zone. This may represent a significant cost to the project. That is why mse walls are usually better suited as fill walls versus cut walls. A cut wall would require removal and replacement of clayey site soil.

Proposed backfill materials of a silty nature, >35% fines (#200 sieve), would be considered marginal backfill. Clayey soils are not a desirable reinforced backfill material for multiple reasons. They are difficult to work with, they have a tendency to swell and soil reinforcement poorly connects to clay.