Aggregate Compaction Factors
When gravel, road base, and soil are dumped from a haul truck, they exist in a "loose state" filled with 20% to 35% air voids. Under mechanical vibration and rolling, those voids collapse. If you do not account for compaction shrinkage, your driveway, patio subbase, or foundation pad will end up dangerously thin.
The Delivered Volume Equation
Never order based solely on in-ground hole dimensions. To determine delivered truck yardage:
Loose Truck Volume (yd³) = In-Place Compacted Volume (yd³) × (1 + Compaction Factor)
Example: A 6-inch compacted base requiring 15 yd³ at 20% compaction = 15 × 1.20 = 18 cubic yards delivered.
Material Compaction Rates & Multipliers
Engineered factors based on ASTM D698 (Standard Proctor) and field vibratory plate compaction trials:
| Material Type | Compaction Rate | Order Multiplier | Loose Density | Compacted Density | Best Application |
|---|---|---|---|---|---|
| Crusher Run / Dense-Graded Aggregate (DGA) | 15% – 20% | 1.15 – 1.20 | 2,600 lbs/yd³ | 3,000–3,150 lbs/yd³ | Driveway subbase & paver foundations |
| Road Base (Class 2 / Crushed Concrete) | 18% – 22% | 1.18 – 1.22 | 2,500 lbs/yd³ | 2,950–3,100 lbs/yd³ | Heavy vehicle parking & slab underlayment |
| Decomposed Granite (DG with binder) | 15% – 20% | 1.15 – 1.20 | 2,700 lbs/yd³ | 3,100–3,240 lbs/yd³ | Pathways, patios & rustic borders |
| Coarse Bedding Sand (Concrete Sand) | 10% – 15% | 1.10 – 1.15 | 2,600 lbs/yd³ | 2,860–2,990 lbs/yd³ | 1-inch paver screed layer |
| Washed Clean Stone (#57 / Pea Gravel) | 5% – 8% | 1.05 – 1.08 | 2,700 lbs/yd³ | 2,835–2,915 lbs/yd³ | French drains, weeping tile & top dressing |
| Fill Dirt & Clay Excavation Subsoil | 20% – 25% | 1.20 – 1.25 | 2,100 lbs/yd³ | 2,520–2,625 lbs/yd³ | Deep hole filling & landscape rough grading |
| Screened Loam / Garden Topsoil | 10% – 15% | 1.10 – 1.15 | 2,000 lbs/yd³ | 2,200–2,300 lbs/yd³ | Lawn seeding, sod base & garden beds |
The Mechanics: Dense-Graded vs Open-Graded Aggregate
Dense-Graded Base (High Compaction: 15–20%)
Materials like Crusher Run, 21A, and DGA consist of stone particles sized from 3/4-inch crushed granite all the way down to microscopic stone dust. As a vibratory plate passes over, the dust and smaller grit vibrate downward into the voids between larger angular rocks, creating an almost impenetrable, concrete-like interlocked mass.
Open-Graded Stone (Low Compaction: 5–8%)
Washed clean #57 stone and pea gravel have been washed to remove all stone dust. Because every rock is approximately the same size, there are no smaller particles to fill the open air gaps. Clean stone achieves rapid friction interlock with minimal height loss, making it optimal for subsurface drainage and pipe bedding.
Job-Site Rule: The 2" to 4" Lift Limit
A common homeowner error is dumping all 6 inches of road base into a patio trench at once and running a plate compactor over the top. Standard walk-behind vibrators (3,000 to 5,000 lbs centrifugal force) only compact the top 3 inches. The bottom 3 inches remain loose and uncompacted, inevitably leading to sunken pavers or cracked concrete slabs within 12 to 18 months.