New gyro-based guidance system
New gyro-based guidance system Nov 2009
Dr E. W. Janes, Principal, Alignment Surveys Ltd
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Total station checking  (Photo by - L Sytosc)

UK contractor Morgan Est, took the bold move to move away from the industry standard of a laser guidance system for tunnel alignment control on its multi-million pound contract to upgrade Belfast's sewer system for Northern Ireland Water and embraced instead advanced gyro technology. After various problems on site, Morgan Est discussed the suitability of the gyro system known as, TEDSSTM (Tunnel Engineers Directional Software System), with Alignment Surveys Ltd, owner of the system. This resulted in a successful test period after which, and because of the potential reduction in down-time that the system offered, the gyro system immediately replaced the laser system.
Given that most tunnel-drives for utility projects are getting longer, with more complex curved alignments, the laser systems, as demonstrated in Belfast and other contracts, have limitations, specifically the severely restricted laser windows. The TEDSSTM system can be used effectively for a tunnel project affected by the tight alignments and restricted laser windows. It can also be used for more conventional alignments and thus offers a complete tunnel guidance system in any environment.
More rings/shift and increased safety
The use of gyros for azimuth (heading) information on small diameter pipejacking and segmentally lined tunnelling has benefited TBM operations by reducing down time caused by system guidance failures and TBM survey checks. Additionally the reduction of manual survey checks and survey control advance within the cramped tunnel environment enhance the safety standards of TBM operations. Therefore For Morgan Est the TEDSSTM on the Belfast project accrued considerable savings and increased levels of safety for the workforce involved.
The gyros used for TEDSSTM are laser gyros which are compact and more reliable than mechanical gyros, providing greater accuracy with less power consumption. These are for use as a stand-alone unit within a pipe-jacking environment or as part of an integrated system, incorporating a robotic total station, for use within conventional TBM tunnelling.
The Belfast Stormwater Management Works Contract was the topic of the November 2009 meeting of the British Tunnelling Society. A packed auditorium at the Instituion of Civil Engieers in Westminster listened as W Gowdy, Project Sponsor, Northern Ireland Water, Dr Alan Skates, Project Manager, Atkins and Paul Ronicle, Project Manager for the Morgan Est/Farrans JV described the progress and challenges of excavating 9.6km of tunnels varying in diameter from 1.5m to 4m and at depths of between 10m and 30m through complex and highly variable geology. The project also included the sinking of 19 access shafts located throughout the city. The new sewer project is designed to alleviate the risk of flooding in central Belfast and improve the water quality of the River Lagan and its tributaries by significantly reducing the pollutant loadings from a number of combined sewer overflows. All excavation is now complete and the project is due to come online in 2010.
Alignment Surveys Ltd

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