Control For Tunneling

Just my first thought but I would prefer three on each end. Two to determine your azimuth and the third as a check. It's very unlikely that with three that you would have movement that you could not detect during the build process if one subsides or shifts horizontally.

Are they drilling from both sides or just one way?

The current plan is for only one direction. Most likely they will be using a TBM with a guidance system (machine control at work).

Heck. If they are drilling one way then it comes out where it comes out doesn't it? 🙂

I still like three for any work though. It is my way of avoiding forgetting to zero set or other fat finger mistakes that can happen and muck up a survey.

I was involved in some tunneling in the Atlanta area. We had 3 static gps positions at each end. Transferred down the shaft to dowelled 1" rebar. We would traverse in to the tbm and out (up to 5 miles one way before we broke through)to maintain the horizontal position. We would also run three wire levels in and out turning through "spads" we would hammer drill in to the rock to verify vertical. These were water reclamation tunnels. They ranged from 2 meters to around 10. I believe we broke through within a few tenths or so. The tbm had a leica robot guiding it.

Yeah, that was the way I was thinking. Maybe they don't want any at the end.....you know, no news is good news. 🙂

No one has mentioned control at the end but I would think that it would be a formality, for closeout.

I would think for the asbuilt that they may require a tie in at the end, plus it does continue to someplace else so control there sounds like a necessary part of the scope. Setting three, while you are already on site is little in the way of costs increase in my opinion.

I would think you would want some control at the exit - especially vertical - so that some calculations could be made for head pressures, etc. If the pipe tunnel is supposed to be level, you need to prove it. If the pipe is going to have slope, you would need to know how much. Horizontal location may not matter very much (as long as it's close), but vert could be critical for pumping.

Actually, It depends on what the tunnel is being used for.

Any thoughts on monument materials? I'm leaning toward recommending the Geodetic Survey's simple concrete monument design for a poured concrete monument and their design for a survey disk set in a rock outcrop. Being in the mountains, you would think that there are a few outcrops available.

The GPS control needs to have a clear horizon with sight lines to the shaft collar.

We've used 8 inch diameter drilled and sonnet tube monuments to 8 to 10 feet depth with a belled bottom. Bedrock is better.

How will you take control down the shaft?

The client is just looking to provide good control for the contractor to start with. Anything within the tunnel will be the contractor's responsibility.

I would specify that the contractor needs to use a gyro theodolite for alignment.

I have seen old Swiss reports on their methods in ultra-high precision control surveys for tunnels and dams in that they installed permanent bronze "hollow plugs" to allow special fittings on the base of their instruments to be inserted into the holes in the plugs. These bronze "Swiss-standard" fittings ensured that instrument set-ups to be better than ±0.1 mm in X-Y-Z. Reference "Swiss-standard" markers allowed the instruments' targets to be set in similar precisions.

Arranged in multiple sets for redundancy, that should provide the insurance you desire. I'll bet Brunson Instrument Company (near St. Louis, MO.) has some fittings designed for just such a purpose. Consider stainless steel fittings for Optical Tooling applications, too.

Kern theodolites use a forced centering adapter.

http://www.alibaba.com/product-free/243424599/Kern_forced_centering_adapter_196_5811/showimage.html

Try this link:

http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-11425.pdf

Control Surveys for Underground Construction of the Superconducting Super Collider

“CONCLUSIONS
…..The installation of very accurate, stable surface reference networks combined with precise transfer operations and extensive underground control consisting of dual zig-zag traverses with reciprocal gyro-theodolite measurements has enabled the design accuracy requirements to be met….”

Those two methods sound good to me.

Should be adequate for the control.

Actually what we found on the Super Collider, was that the gyro-theodolite measurements were much more reliable for bearing/azimuth than the dual zig-zag traverses.

> Actually what we found on the Super Collider, was that the gyro-theodolite measurements were much more reliable for bearing/azimuth than the dual zig-zag traverses.

Did you build the forced centering monuments at the SCSC? I set on many of those with Traylor Bros. We had a two mag shafts and about 9 miles of tunnel if I remember correctly. I sometimes still think about those monuments an d wonder what they cost to set.

Control For Tunneling - Roadhand

I designed the monuments for the construction of the SSC. The simple pedestal monuments were between $12K and $20K each. The ones with inverted pendulums were between $18K and $35K each. The cost variability depended on the depth of the foundation.

Simple elevation monuments, NGS 3-D type, were typically between $500 and $1K.