Modern high precision high speed measurement of segments and moulds

Abstract

The precision that is required for the manufacture of the moulds that are used in the casting of segments for tunnel linings is frequently not stated. The tender documents for a typical segmentally lined tunnelling project frequently only give the dimensional tolerances for the finished segments. In some cases however only the tolerances for a sample build of 2 test rings is given. Increasingly tight tolerances that are now included in specifications for segment dimensional accuracy, demand a fast, accurate and reliable method for determining these values. Delays in the overall progress of these projects are increasingly considered to be detrimental; consequently geometrical control of the moulds now frequently takes place at an early stage in the project, directly at the mould supplier’s fabrication plant, this calls for easy to transport measurement equipment. In addition to checking linear dimensions, the angular properties of the moulds also need confirmation in order to fine tune the moulds, (if and when necessary) before any segment fabrication.Should any modification be necessary, the mechanics need to know exactly where to modify, how much and in what direction and have verification shortly after. The use of a Laser interferometer system now enables the accurate digitization of surfaces by direct polar coordinate measurement. Measurement to a single spherical retro-reflective prism enables the skilled operator to comprehensively measure the full profile of the object to be measured with over 20 segments per shift being achievable. State of the art software enables near real time processing of the measurements with comparison to original CAD drawings. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Elsevier”.