TECHNICAL | MECHANISED TUNNELLING/HS2


Right:


TBM ‘Florence’ exceeded expectations, achieving a record-breaking advance of 42m in a day; 226m in a week; and a best month of 842m


3 million m3


of chalk from the tunnel excavations.


After water was extracted from the slurry, the resulting chalk cake is retained on site, removing the need for hundreds of lorry movements on local roads. The chalk is to be used to landscape the area once the construction site is decommissioned. The 16km tunnel length also led to a grout batching


plant being incorporated onto the TBMs, which was essential to support TBM production. “We need just-in-time preparation of grout so


having the plant on the TBMs meant the grout was not travelling the length of the tunnel,” says Jacques.


Another innovation was the invert slab concrete


bridge that worked about 200m behind the TBM. This concreted the invert – again with very limited human intervention being required – which provided increased width to allow two lanes, rather than the usual one, for support vehicles. The result was greater flexibility and efficiency, and it allowed construction of the 38 cross passages and five adits while TBM excavation progressed. Efficiency was also gained through continuous boring,


made possible by Align and Herrenknecht developing a ‘Centre of Thrust ‘principle, rather than having


Right:


Concreting the invert behind the TBM enabled two-way traffic so the 38 cross passages and five adits could be built while boring was underway


12 | July 2024


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