Enter tunnel details
Example data
| Profile | Sample inputs | Perimeter | Lining surface | Lining volume |
|---|---|---|---|---|
| Circular | {"shape":"circular","unit":"m","diameter":9,"tunnel_length":120,"lining_thk":0.3} | 28.274 m | 3,392.920 m² | 1,017.876 m³ |
| Rectangular | {"shape":"rectangular","unit":"m","width":7.5,"height":6.2,"tunnel_length":80,"lining_thk":0.25} | 27.400 m | 2,192.000 m² | 548.000 m³ |
| Horseshoe | {"shape":"horseshoe","unit":"m","width":8,"wall_height":2.2,"tunnel_length":150,"lining_thk":0.35} | 24.966 m | 3,744.956 m² | 1,310.734 m³ |
Examples are illustrative and use simplified lining volume.
Formula used
- Circular: P = π × D
- Rectangular: P = 2 × (W + H)
- Elliptical: Ramanujan approximation
P ≈ π × [3(a+b) − √((3a+b)(a+3b))], where a=major/2, b=minor/2 - Horseshoe (semi-arch): semicircle + two walls + flat invert
P = πr + 2Hwall + 2r, where r=W/2 - Segmental arch + walls:
θ = 2asin(c/2R), arc = Rθ, P = arc + 2Hwall + c
Surface uses Perimeter × Tunnel length. Volume uses Surface × Lining thickness and is a simplified estimate.
How to use this calculator
- Select the tunnel profile that matches your design section.
- Choose your unit system and keep inputs consistent.
- Enter the required dimensions for the chosen profile.
- Optionally add tunnel length for lining surface estimates.
- Optionally add lining thickness for lining volume estimates.
- Press Calculate, then export results for project records.
For complex sections, model the nearest profile and document assumptions in your design notes.
Perimeter-driven lining quantities
Perimeter is the controlling length for shotcrete, membrane, and segment joints. For a 9 m circular bore, the perimeter is about 28.274 m, so every 100 m of drive implies roughly 2,827 m² of lining contact area before allowances. If segments are 1.5 m long, that 100 m contains about 67 rings for gasket and bolt layout checks.
Profile selection and geometric inputs
Choose the cross-section that matches your excavation support: circular, rectangular, elliptical, horseshoe, or segmental. Small input changes scale quickly; increasing diameter from 8.5 m to 9.0 m raises perimeter by about 1.571 m, affecting reinforcement, waterproofing rolls, and inspection scope. For rectangular headings, adding 0.2 m to both width and height increases perimeter by 0.8 m.
Elliptical approximation and accuracy notes
Elliptical perimeters have no simple closed form, so the calculator uses a Ramanujan approximation used for engineering estimation. For near-circular ellipses, the approximation is usually very close; accuracy decreases as the major-to-minor ratio grows, so document the axis values and assumption. When comparing options, keep one parameter fixed, such as clearance, then evaluate the perimeter shift.
Unit discipline and field measurement practice
The calculator does not convert units, so keep one system across inputs and reports. Record where dimensions came from: as-built surveys, TBM ring drawings, or excavation profiles. In field checks, confirm whether dimensions are internal clear opening or excavation line, and note any lining offsets to keep perimeter and quantities aligned. Capture revision dates, chainage limits, and survey tolerances so perimeter calculations remain traceable during audits later.
Exportable results for QA documentation
Use the CSV to archive inputs and outputs in cost and quality folders, and the PDF for site sign-off packs. Pair the perimeter with length to estimate lining surface, then apply lining thickness to create a simplified volume check. A 28.274 m perimeter, 250 m length, and 0.30 m thickness gives about 2,120 m³. Add contingency for overbreak, trimming, and joints based on project specs and observed advance conditions.
FAQs
1) Which tunnel shapes are supported?
You can calculate circular, rectangular, elliptical, horseshoe, and segmental arch sections. Pick the profile that best matches your design or as-built survey and enter the required dimensions for that option.
2) Does the calculator convert between units?
No. The units selector is for labeling results only. Enter all dimensions in the same unit system and keep your tunnel length and lining thickness in that same system.
3) How is lining surface area estimated?
When you provide tunnel length, the tool multiplies perimeter by length to estimate lining surface contact area. This is useful for membrane, shotcrete coverage, and inspection planning.
4) How is lining volume estimated?
If you also enter lining thickness, the tool multiplies surface area by thickness to give a simplified lining volume. Use it as a check and add allowances for joints, overbreak, and waste.
5) Is the ellipse perimeter exact?
No. The ellipse calculation uses a proven approximation that is accurate for many engineering cases. For highly elongated ellipses, verify with your design software and document the assumption.
6) Why do I see an error for segmental inputs?
A segmental arch requires the chord width to be no greater than twice the radius. If the chord is larger, the arc is not geometrically possible, so correct the inputs to proceed.