Inputs
Results
Field dry unit weight
—
kN/m³
Degree of compaction RC
—
percent
Void ratio e
—
dimensionless
Porosity n
—
percent
Saturation Sr
—
percent
Wet unit weight for target RC
—
kN/m³
Compacted volume
—
m³
Loose volume
—
m³
Estimated roller passes
—
passes
Approx. tonnage
—
t
Example Data
| Wet unit weight | Moisture % | MDD | RC % | Gs |
|---|---|---|---|---|
| 20.5 kN/m³ | 8.5 | 18.6 kN/m³ | 95 | 2.65 |
| 19.3 kN/m³ | 10.0 | 17.8 kN/m³ | 92 | 2.70 |
| 21.8 kN/m³ | 7.0 | 19.2 kN/m³ | 97 | 2.62 |
Formulas Used
- Field dry unit weight γd,field = γwet / (1 + w), where w is decimal.
- Relative compaction RC (%) = (γd,field / MDD) × 100.
- Void ratio e = (Gs · γw / γd,field) − 1.
- Porosity n (%) = e / (1 + e) × 100.
- Degree of saturation Sr (%) = (w · Gs / e) × 100.
- Wet unit weight for target RC γwet,req = (RCtarget/100) × MDD × (1 + wtarget).
- Volumes Vcomp = Area × Thickness; Vloose = Vcomp / (1 − Shrinkage).
- Pass estimate Passes ≈ ceil(max(0, RCtarget − RCcurrent) / Gainper pass).
How to Use
- Select your unit system and reference test.
- Enter field wet unit weight, moisture w, and lab MDD.
- Optionally enter Gs to compute e, n, and Sr.
- Add area, thickness, and shrinkage to size volumes.
- Set target RC and placement moisture to get γwet,req.
- Adjust gain per pass to estimate roller passes.
- Click Calculate, then export CSV or PDF for records.
Typical Compaction Specifications
| Application | Target RC (% of MDD) | OMC Tolerance (%) | Max Lift Thickness (m) | Notes |
|---|---|---|---|---|
| Subgrade (granular) | 95–100 | ±2 | 0.20–0.30 | Vibratory smooth drum often preferred. |
| Subgrade (fine‑grained) | 95–98 | +1/−3 | 0.15–0.25 | Sheepsfoot or pneumatic; moisture sensitive. |
| Base course (aggregate) | 98–100 | ±2 | 0.15–0.20 | Roadway specs typically stringent. |
| Structural backfill | 95–100 | ±2 | 0.20–0.30 | Critical near foundations and walls. |
| Trench backfill | 90–95 | ±3 | 0.15–0.25 | Place in lifts to minimize settlement. |
| Embankment fill | 90–95 | ±3 | 0.30–0.45 | Granular allows thicker lifts; proof‑roll. |
Moisture Adjustment Guide
| Moisture vs OMC | Expected Density Trend | Recommended Action |
|---|---|---|
| −4% of OMC | Low; dry side, dusty | Add water, mix thoroughly, retest. |
| −2% of OMC | Below peak; stiff response | Light watering and additional passes. |
| At OMC | Near peak density | Maintain moisture; standard pass plan. |
| +2% of OMC | Wet side; decreasing density | Aerate or reduce water; more passes. |
| +4% of OMC | Too wet; pumping risk | Scarify, dry, recondition, then compact. |
Roller Pass Planning Guide
| Soil Type (USCS) | Typical Roller | Pass Range (~200 mm lift) |
Notes |
|---|---|---|---|
| GW/GP gravels | Vibratory smooth drum | 3–6 | High energy; fast densification. |
| SW/SP sands | Vibratory smooth drum | 4–8 | Watch for pumping near water table. |
| SM/SC silty/clayey sands | Pneumatic / vibratory | 6–12 | Moisture control is critical. |
| ML/CL silts & lean clays | Sheepsfoot / pneumatic | 8–16 | Prefer slightly dry of OMC. |
| CH fat clays | Sheepsfoot | 12–20 | Thin lifts; extended kneading. |
FAQs
Maximum Dry Density (MDD) is the peak dry unit weight from a compaction test. Field dry unit weight is compared to MDD to evaluate compaction success.
Typically within −2% to +2% of OMC depending on specification and soil type. Enter your intended moisture to see the required wet unit weight.
It’s a planning aid. Actual passes depend on roller type, lift thickness, support conditions, and moisture. Calibrate the gain-per-pass value to local experience.
Yes. Use the gauge’s wet unit weight and moisture. The formulas are general and apply to sand cone tests as well.
Leave it blank. Void ratio, porosity, and saturation are optional outputs that require Gs. Many soils have Gs around 2.60–2.75.
Choose the unit beside each field. The calculator handles unit conversions and reports volumes consistently.
Use the CSV or PDF buttons. The export captures your inputs, calculated outputs, and a timestamp for traceability.