Crushed Stone Gradations: Which Material Do You Need?
Not all gravel is created equal. Picking the wrong gradation can lead to poor drainage or an unstable, rutted subgrade:
| Gravel Type | Size | Density (lb/yd³) | Tons / Cu Yd | Best Use Case |
|---|---|---|---|---|
| #57 Clean Crushed Stone | 1/2" to 1" angular | 2,700 lbs | 1.35 tons | Under concrete flatwork, French drains, and septic fields (free draining). |
| Crusher Run / DGA (Dense Grade) | 3/4" down to stone dust | 2,850 lbs | 1.42 tons | Driveways and paver patios (locks together like asphalt). |
| Pea Gravel | 3/8" rounded river rock | 2,600 lbs | 1.30 tons | Garden walkways, dog runs, and decorative seating areas (comfortable underfoot). |
| #4 Clean Drain Rock | 1.5" to 2.5" ballast | 2,650 lbs | 1.32 tons | Muddy construction entrances, erosion control, and deep ditch stabilization. |
Why You Must Account for Compaction (15% Allowance)
When a dump truck drops crushed rock at your job site, the material contains substantial voids between angular stone edges. Once you run a 3,000-pound vibratory plate compactor over the area, stone particles shift and interlock tightly together, reducing total thickness by 12% to 18%.
The Golden Rule of Excavation Depth:
To achieve a finished, load-bearing 4-inch compacted sub-base, you must spread approximately 4.6 to 4.8 inches of loose gravel before compacting. If you only order the exact raw mathematical volume without a compaction factor, your finished base will come up half an inch short!
Subgrade Excavation & Geotextile Fabric Best Practices
1. Strip Organic Topsoil
Never place crushed stone over grass, roots, or dark garden soil. Organic matter rots over time, leaving underground voids that cause catastrophic settling and cracked slabs.
2. Lay Geotextile Fabric
On clay or silty soils, always roll out heavy-duty non-woven geotextile landscape fabric before dumping rock. The fabric prevents heavy gravel from sinking into the soft subgrade mud.
3. Compact in 2" Lifts
Vibratory plate compactors can only compact up to 2 to 3 inches of stone effectively. If your design calls for a 6-inch base, lay down 3 inches, compact thoroughly, then lay the remaining 3 inches and compact again.