A cubic yard of earth measured in its natural position swells to more than a cubic yard after it is excavated. This occurs because of an increase in voids.
Swell is expressed as a percentage of natural volume, for example, if 10 yd3 in the ground becomes 13 yd3 after excavation, the swell factor is 30%.
The following table lists swell factors for various engineering materials.
| Material | Swell (%) |
|---|---|
| Clay | |
| Dry | 40 |
| Wet | 40 |
| Clay and gravel | |
| Dry | 40 |
| Wet | 40 |
| Coal, anthracite | 35 |
| Coal, bituminous | 35 |
| Earth, loam | |
| Dry | 25 |
| Wet | 25 |
| Gravel | |
| Dry | 12 |
| Wet | 12 |
| Gypsum | 74 |
| Hardpan | 50 |
| Limestone | 67 |
| Rock, well blasted | 65 |
| Sand | |
| Dry | 12 |
| Wet | 12 |
| Sandstone | 54 |
| Shale and soft rock | 65 |
| Slate | 65 |
| Traprock | 65 |
JohnKump says
June 11, 2015 at 7:26 amwe are doing a project in Nyc. Hammering rock it is kind of peeling off what is the swell on this some of it turns to powder and we are in negotiations to be paid I know it’s hard to say with out seeing I can email you photo and video thank you.
Leon Hall says
September 10, 2015 at 12:16 pmWhat is an appropiate swell factor for in place rock that is excavated and crushed down to 1.5 inch minus crushed stone? I was estimating it to be 15%
Larry says
June 9, 2017 at 10:32 amIf swell for gravel is 12%, then would shrink for compaction be around 10% given it’s not going to be 100% compaction? I was thinking more like 15-20% off hand. If I place a 12″ layer of gravel and compact it with compaction equipment, I would expect it to settle at least 2″, which would be around 17%
Joseph odia says
May 3, 2018 at 12:14 pmHello roseke I have a question on swelling clay.pls at what swelling percentage do well classify a clay as a swelling and non swelling clay?
L. Coffie says
September 23, 2018 at 2:59 pmDear Mr. Roseke:
I want to fill my now empty in-ground pool with sand. Can wet sand be compacted? Or dry sand for that matter? Thank you.
Bernie Roseke, P.Eng., PMP says
September 27, 2018 at 9:19 amSand is generally not used for engineering purposes. Neither wet nor dry sand will compact. If you want to build something on top of the pool, use gravel, which can be compacted and then take some loading. Get a “crushed” gravel, place it in 6 inch lifts, and run over it with a small compactor about 6 times (in each spot)
pepe says
October 24, 2019 at 7:38 pmIf a swell is 25% that means that the swell factor is 1.25?