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Seth Morgan
Construction Superintendent
Asked a question last year

Which best material for backfill of retaining wall?

Which best material for backfill of retaining wall?

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The best material for the backfilling of a retaining wall is gravel, and it should be well graded. The main reason for using gravel is because it does not retain water (small void ratio); hence lateral loads experienced will be minimal.

You should also have weep holes for draining excess water that may be retained.

Gravel is also good since, when compacted, gives good load-bearing properties hence can be built on if need be.

Flenn Hale
Construction Manager

It relies upon whether you need it to be structural, for example, are you working over the wall, or whether it should drain.

For a draining area, sandy soil might be your smartest choice, or sandy gravel, since water goes through this material effectively, and it will, in general, reduced effectively as well. You can include a seepage pipe at the base of the holding divider to keep the water from moving through the solid, causing recoloring and flowering, as well.

For a retaining wall where a structure will be based on the fill, you need a more grounded soil mix, either sandy dirt, or silty sand that compacts to meet the auxiliary necessities. This should be dictated by a geotechnical engineer if the load is basic since settling can make shear and dynamic powers be made against the holding divider, and relying upon conditions, the holding divider could even be overwhelmed by these powers. In any case, it would be to your greatest advantage to fill and reduced the inlay in lifts with the goal that it doesn’t settle subsequent to filling.

Henry Newman
Water resource engineer

For draining area, sandy soil or sandy gravel is best for retaining wall backfilling material, because It cause easily water draining.

If your retaining wall is built on filling material then you have to use strong soil blend like silty Sand and sandy clay That should be meet the requirements of structure requirements and geotechnical properties.

yes but due to gravel fill result in an increase in active earth pressure so we need to design retaining wall for higher resisting force so is it economical?

Hunter May
Commercial energy assessor

When it comes to backfill, the best material is a combination of gravel and native soil. By combination, I don’t mean mixture. But, the retaining wall must be backfilled to a thickness of at least 15 cm by gravel of nominal size not exceeding 10 mm. Then behind that, a layer of native soil as much as the need be. Also, if the land above the backfill is to be used for plant or grass growth, then the native soil layer of not more than 10 cm thickness must be placed vertically above the gravel.

Now, gravel won’t retain water. So, actually, it won’t increase active earth pressure as compared to clay or silt, which could hold water. Also, even if there is a larger design pressure with gravel, still overdesigning is the wiser choice because if not done, the wall or footing may corrode due to water and would have to be rebuilt, creating extra cost.

Thus when it comes to backfill, it refers to the dirt behind the wall. In order to provide proper drainage, atleast 12 inches of granular backfill (gravel or a similar aggregate) should be installed directly behind the wall. Compacted native soil can be used to backfill the rest of the space behind the wall.