The whole bore.
One pass. No block.
Clearance, alignment and headroom along every metre of the tunnel — not at the few chainages someone had time to reach. Walked between trains, with the track in place.
- Traffic
- No blockwe work between trains
- Per day
- 8–10 kmof line, one operator
- Captured
- One passportal to portal, no joins
- Geotagged to
- ±2 cmcontrol carried in by total station
Length is what breaks a tunnel survey.
A static scanner sees one position at a time, and a bore blocks every sight line beyond the next few tens of metres. Across a kilometre that becomes dozens of setups — each one more time on the track, and another join where error accumulates.
On a live railway, time on the track is the expensive part.
One pass. No joins.
The scanner positions itself from what it sees as it moves, so the whole tunnel arrives as a single continuous record rather than a set of separate scans brought together afterwards.
- No block needed — we work between trains
- No setups, no targets, nothing placed on the track
- One operator, 8–10 line km in a day
- One dataset, not a chain of registrations
- Geotagged — control carried in from outside, to ±2 cm
Tunnel No. 06. 299 metres. Gradient verification.
March 2025. One operator, the backpack unit, and a live section of track.
Walked, not closed.
A 299 metre bore, surveyed end to end by one person on foot while the line stayed open. No possession, no equipment on the track, nothing to clear before the next service.
That is the difference between a survey that waits for the railway and one that fits around it.
A tunnel has no GPS. The coordinates still have to be real.
A scan that only knows where it is relative to itself is useful for shape and no use for position. We run a total station traverse from known control outside the portal and transfer points into the bore, then tie the scan to them.
The result is geotagged to ±2 cm — so a chainage in the report is a chainage on the ground, and an infringement can be found again by somebody holding a tape.
Two answers, from one walk.
The tight point is rarely where anyone expects it. A survey that samples chainages measures the places someone could reach. A complete scan finds the one that governs — and that is the only one that matters.
Before you ask
How long a tunnel can you do in one pass?
Length is not the limit — walking time is. We cover eight to ten line kilometres in a day on reasonable going, and a tunnel is recorded as one continuous dataset however long it runs.
How do you get position inside a tunnel with no GPS?
A total station traverse from known control outside the portal, transferring points into the bore. The scan is tied to those points, so everything is geotagged to ±2 cm rather than floating in its own local frame.
Do you need a block?
No. We work between trains. Capture is one person walking, so there is nothing to set up on the track and nothing to clear off it — the scan stops and starts around traffic instead of waiting for it.
What do we receive?
- Clearance report — the bore checked against the Schedule of Dimensions along its whole length, with every infringement located by chainage and measured.
- Least headroom — the governing figure for electrification, and the headroom profile along the tunnel.
- As-built alignment — the track centre-line through the bore, against your design.
- Cross-sections — at the chainages you specify, and at any others you ask for later.
- The registered point cloud of the complete bore, portal to portal.
Delivered in the formats your survey team already works in.
Will a tunnel take OHE?
That is a headroom question, and headroom is what the scan measures — including the one tight point a sampled survey is most likely to miss.
Where do you work?
All India.
Tell us about the tunnel
Length, section and what you need verified. We will come back with scope and cost — or say plainly if this is not the right tool for it.