Find the fill for the gap around the tube.
⚙️Calculation Parameters
📊Calculated Output
How Tube and Excavation Gap Calculator Works?
To size the backfill gap, the Tube and Excavation Gap Calculator subtracts the tube cylinder from the hole cylinder and returns the ring of space between them. The process takes 4 steps.
Enter the hole
Type the dug hole diameter and depth.
Enter the tube
Type the tube outer diameter.
Subtract
The tool subtracts the tube volume from the hole volume.
Read the backfill
The calculator shows the annular gap in cubic feet (ft³), cubic yards (yd³) and tons of fill.
Tube and Excavation Gap Calculator Formula
The Tube and Excavation Gap Calculator finds an annulus.
Gap volume
V = π × ((D_h ÷ 24)² − (D_t ÷ 24)²) × (H ÷ 12)D_h hole and D_t tube diameter.
Gap width
g = (D_h − D_t) ÷ 2Space on each side.
Compacted fill
V_loose ≈ V × 1.15 to 1.25Loose fill shrinks when tamped.
Worked example: 12 in tube in an 18 in hole, 48 in deep
- V_hole = 7.069 ft³ and V_tube = 3.142 ft³
- V_gap = 3.927 ft³
- Loose fill to tamp ≈ 4.71 ft³ at 1.2 × compaction
Tube and Excavation Gap Calculator Conversion Table
The excavation gap conversion table lists the annular backfill for 6 tube and hole pairs at 48 in (122 cm) deep, per hole and for 10 holes.
| Tube | Hole | Gap each side | Gap ft³ per hole | ft³ for 10 holes | yd³ for 10 holes |
|---|---|---|---|---|---|
| 8 in | 12 in | 2 in | 1.745 | 17.45 | 0.646 |
| 10 in | 16 in | 3 in | 3.403 | 34.03 | 1.261 |
| 12 in | 18 in | 3 in | 3.927 | 39.27 | 1.454 |
| 12 in | 24 in | 6 in | 9.425 | 94.25 | 3.491 |
| 16 in | 24 in | 4 in | 6.981 | 69.81 | 2.586 |
| 18 in | 30 in | 6 in | 12.566 | 125.66 | 4.654 |
Tamp backfill in 6 in (15 cm) lifts to hold the tube plumb.
What is Tube and Excavation Gap Calculator?
A Tube and Excavation Gap Calculator is a backfill calculator that finds the volume of the ring between a Sonotube and the wall of its dug hole.
Holes are dug wider than the tube so the tube can be set and plumbed. The gap gets backfilled with soil or gravel, and some builders fill the bottom of the gap with concrete. An 18 in hole around a 12 in tube leaves a 3 in gap holding 3.93 ft³, more than the 3.14 ft³ inside the tube.
The calculator answers 2 questions: how much backfill to tamp, and how much extra concrete the job uses, if the gap is filled with concrete.
What are the uses of Tube and Excavation Gap Calculator?
There are 4 main uses of the Tube and Excavation Gap Calculator.
Backfill planning
Crews stage soil or gravel to fill around tubes.
Gravel orders
Builders order drainage stone for the gap.
Concrete collars
Contractors price filling the gap with concrete.
Spoil reuse
Site leads see how much dug soil goes back in.
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Sonotube Volume Calculator
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Sonotube Cubic Yards Calculator
See your concrete in cubic yards.