Any suggestions on how to set an alignment for a TBM 25 metres down a shaft? I need two points at the bottom for the alignment but can not see down into the hole. The dimensions of the hole are 3 metres wide by 6 metres long (usable space at the bottom).  the bore is 300 metres long so any error in the setout of the points at the bottom will make a great big ops at the end.

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the better way for me is rent a laser proyector to transport a coordinates vertically to the bottom of the shsft, and a giroscopic theodolite to transport your azimuth from the surface.

Thank you for the responses all really good stuff. I think I am going to try the resection to confirm my work. I did use a string line strung between two surface nails on line and an optical plummet to align myself  along the string at the bottom ( checked with my Total station & 90 eye piece set to zenith). Cool 360 pic of the pit  if you are instructed,

A product from The Netherlands, It can made a verticaal laser-line. 


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