| DESCRIPTION OF BACKFILL MATERIAL | UNIFIED SOIL CLASSIFICATION | ACTIVE PRESSURE | AT-REST PRESSURE |
| Well-graded, clean gravels; gravel-sand mixes | GW | 30 | 60 |
| Poorly graded clean gravels; gravel-sand mix | GP | 30 | 60 |
| Silty gravels, poorly graded gravel-sand mix | GM | 40 | 60 |
| Clayey gravels, poorly graded gravel-and-clay mix | GC | 45 | 60 |
| Well-graded, clean sands; gravelly sand mixes | SW | 30 | 60 |
| Poorly graded clean sands; sand-gravel mixes | SP | 30 | 60 |
| Silty sands, poorly graded sand-silt mixes | SM | 45 | 60 |
| Sand-silt clay mix with plastic fines | SM-SC | 45 | 100 |
| Clayey sands, poorly graded sand-clay mixes | SC | 60 | 100 |
| Inorganic silts and clayey silts | ML | 45 | 100 |
| Mixture of inorganic silt and clay | ML-CL | 60 | 100 |
| Inorganic clays of low to medium plasticity | CL | 60 | 100 |
| Organic silts and silt clays, low plasticity | OL | | |
| Inorganic clayey silts, elastic silts | MH | | |
| Inorganic clays of high plasticity | CH | | |
| Organic clays and silty clays | OH | | |
