Calculator
Enter jetty section details and allowances. Submit to view totals above this form.
Example data table
Sample inputs and typical output format. Replace with your project values.
| Length (m) | Height (m) | Crest (m) | Slopes (Sea/Land) | Toe (count × W × t) | Bulk density (t/m3) | Waste + Cont. (%) | Adjusted volume (m3) | Total rock (t) |
|---|---|---|---|---|---|---|---|---|
| 120 | 4 | 6 | 2.0 / 1.5 | 1 × 2 × 1 | 1.70 | 5 + 5 | ~4,752 | ~8,078 |
Formula used
This tool models a jetty as a trapezoid prism (plus optional toe berm).
| Item | Expression |
|---|---|
| Bottom width (m) | B = T + (S_sea + S_land) × H |
| Area (m2) | A = (T + B) ÷ 2 × H |
| Main volume (m3) | V_main = A × L |
| Toe volume (m3) | V_toe = N_toe × W_toe × t_toe × L |
| Adjusted volume (m3) | V_adj = (V_main + V_toe) × (1+bulking) × (1+waste) × (1+contingency) |
| Rock mass (t) | M = V_adj × ρ_bulk |
How to use this calculator
- Enter your jetty length, crest width, height, and side slopes.
- If you have toe berms, set toe count and their width and thickness.
- Select a density mode: bulk density, or solid density with porosity.
- Add bulking, waste, and contingency to reflect construction reality.
- Optionally split totals into armor, underlayer, and core percentages.
- Click Calculate. Download CSV or PDF for reporting.
Technical note
1) Purpose and scope
This calculator estimates rock quantities for a straight jetty reach using a trapezoidal cross‑section and optional toe berms. It converts geometric volume into placed tonnage, then into logistics metrics such as truckloads for procurement and planning.
2) Geometry inputs that drive volume
Volume depends most on length, height, crest width, and the two side slopes. Bottom width is calculated as crest plus (seaward slope + landward slope) times height. For example, a 6 m crest, 4 m height, and 2H:1V plus 1.5H:1V slopes gives a 20 m bottom width.
3) Density and allowances for ordering
For logistics, converting mass to loads is a quick reasonableness check. A 20 t truck moving 8,000 t implies roughly 400 deliveries. If you barge rock, use barge capacity in tonnes and apply the same division. Always align delivery rates with placement productivity, access constraints, and safety exclusion zones during tides.
Placed bulk density typically ranges from 1.6 to 1.9 t/m3, depending on gradation and placement. If you only know solid density, the tool can derive bulk density using porosity; 2.65 t/m3 with 35% porosity yields about 1.72 t/m3. Add waste (often 3–8%) and contingency (commonly 5–10%) to reduce shortages.
4) Layer splits for armor, underlayer, and core
Designs often separate armor, underlayer, and core materials for stability and filtration. The calculator applies your percentage split to total tonnage, then estimates each layer’s volume using its density. This helps align quarry sizing, stockpile areas, and transport schedules across material classes.
5) Reporting and quality checks
Use the CSV export for spreadsheets and the PDF summary for site files and approvals. Cross‑check results against drawings, chainage breaks, and any variable seabed profiles. If the section is tapered or curved, run multiple segments and sum totals for a more defensible estimate.
FAQs
1) What density should I use?
Use a placed bulk density from project specifications or quarry test data. If unavailable, start around 1.7 t/m3 and refine after trial placement and measured as-built voids.
2) Why does the tool normalize layer percentages?
Field inputs often total slightly above or below 100%. Normalizing keeps the split consistent without changing the total tonnage, so your layer breakdown remains comparable and usable.
3) When should I include a toe berm?
Add toe berms when designs specify scour protection or stability at the slope toe. Enter the berm width, thickness, and whether it exists on one or both sides along the reach.
4) How do waste and contingency differ?
Waste covers handling losses, trimming, and spillage. Contingency covers uncertainty: survey variance, minor design changes, and construction tolerances. Using both gives a more realistic order quantity.
5) Can I model a jetty with changing geometry?
Yes. Break the jetty into segments with different heights, slopes, or crest widths, run the calculator for each segment, then add the totals. This is also useful for phased construction.
6) Do truckloads include return trips or haul delays?
No. Truckloads are a simple tonnage divided by truck capacity, rounded up. For scheduling, add cycle times, availability, weather constraints, and loading rate limits.
7) Why is my tonnage higher than geometric estimates?
Your result includes toe volume and the combined allowance factor. Check bulking, waste, and contingency inputs, and confirm that density units are t/m3 rather than kg/m3.