Tunnel Surveyors

[Ian Wilson]

OK. This is for real.

We have a project with a tunnel that slopes down through the property. There is a spring in the tunnel. The water has backed up to about a foot deep at the door to the tunnel and, of course, fills up the tunnel some distance back.

We need to locate the tunnel horizontally and vertically relative to the surface over the tunnel.

Has anyone got any idea of how to get survey data on this tunnel?

The attached image is the top end and the door heading into the tunnel and down the hill.

[William Magee]

I'm familiar with using a crawler version of the following for inspecting and mapping drainage systems. Basically the camera provides info on spot slopes and measurement of the tether gives the distance down line.

https://www.deeptrekker.com/product/dtg2-smart/

[Rob_LS]

Interesting problem! First, ensure enclosed space safety measures are in place: LEL meters and an air blower come to mind. I wouldn't suggest weight belt and fins, but your scuba tank, and mouthpiece ($$$ write off) may come in handy if the situation goes bad while you are inside. Is the tunnel a constant size and grade, or is that what you need to determine? Either way, survey the tunnel alignment and topography - obviously GNSS will not work inside, but use GNSS to set a control point and backsight point at each end (or do it all conventional and traverse back over the top). If you need to traverse through, set control points in the ceiling, and set up under them with a negative HI to the axis of rotation of your scope. Lay the alignment out on the ground over the top. You may need to treat the data sets as three different surveys when you import them so you can create three individual surfaces - OG over the top, tunnel ceiling, and tunnel floor. Then do some CAD magic. This procedure works great in my brain. How well this will work in the real world could be a different story all together. Sounds like a great topic at the CSU Fresno Conference! Lay out the problem, and ask the attendees (professionals, working technicians, and students alike) brainstorm solutions. Ask for suggestions only from one group at a time!

[E_Page]

Daryl Moistner went through training for underwater surveying for offshore oil rigs several years back. You might try contacting him to see what types of instrumentation they would have used and what special procedures they had for underwater confined spaces.

[dedkad]

Can you pump the water out faster than the spring can fill it?