I wrote an article for October 2003’s T&TI about a program I’d written to help tunnellers deal with the problem of out-of-plane circle joints in segmental linings. The article described the program, and offered it free to anyone who wanted a copy.
There were two reasons for giving the program away; Firstly, it seemed a shame to have invested a lot of time and effort to solve a problem, then only have one or two people use it on a single project. Secondly, the idea of having largely a graphical output, rather than just a table of numbers, came from feedback from the Inspectors, rather than suggestions from other engineers, and it seemed possible that feedback from a wider group might result in further improvements.
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Since the article was published a number of people have obtained the program, and to date I know of 27 people with copies. There has not been much feedback so far in terms of specific ideas for improvements, however at least two recipients replied with grave warnings that the program depended on having a flat plane to measure from (it does actually point that out in the program’s instructions).
On the Arrowhead’s TBM, the bulkhead surface used as a reference is flat, but awkward to get to. There is a step in the tailskin that would be convenient to make measurements from, but it’s not flat. So the program would be more useful if it could correct for an uneven reference surface.
I have now added this feature to the program. It makes it possible to do a survey on any convenient reference surface, enter the survey results into the program, and then take measurements to the segments from that surface, with the program doing the necessary corrections to the measurements. The program assumes a linear variation in the reference surface for any measurement falling between the points it knows about.
A good way to do such a survey would be during TBM assembly; with the body of the TBM standing on its nose, do a level survey round the edge of the bulkhead – a suitable set of measurement corrections is the fill heights from the bulkhead to an arbitrary elevation above it.
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By GlobalDataIn use in the tunnel, if the program finds a set of correction data entered, one of the printed reports will show both the raw measurements to the segments, and also the calculated measurements from the segments to the theoretical flat reference surface.
Anyone wanting the new program can email me as before. Since the October article I’ve changed both countries of residence and email addresses. My new email address is Alex@Lowson3973.freeserve.co.uk
Alex Lowson
Mott MacDonald
