compacting Gravel

[Jeff Jones]

I'm going to be building a retaining wall and placing 3/4" washed gravel behing it. I need to know how much does this type of gravel compact,i.e. does a 12' lift compact down to 9"??? Need to know so that i can order the right amount needed

thanks for Your help
Jeff
Ridgewood Remodeling Inc.
Ridgewood NJ

[norfleet]

you can compact gravel with a large vibratory compactor, but you do not want to do it near the rear of a retaining wall (it can cause the wall to fail). It is very rare in our area (northern calif) for subdrain back fill behind a wall to be compacted (so not to damage wall). If it really concerns you, talk with the engineer and see if pea gravel is an acceptable substitute. Pea gravel is rounded and self compacts - that is one of the reasons that is it used as under ground tank bedding/back fill.

[Mike Krall]

norfleet,

I thought, whether right or wrong, that even crushed rock of one size would compact completely through the placement process. You are saying only rounded particles have this capability? Help me out on this, please.

Mike Krall

[norfleet]

yes, you do need to compact gravel (all it is, is large sand). The more angular the individual gravel pieces, the "looser" (less dense) they will be when they are just dumped into place. This is one of the reasons why the gravel subgrade beneath roads is compacted. Most people do not realize it, but gravel can also liquify during large earthquakes (just like sand).