WORKSHOP REPORT | BTSYM


● The Glacial Till layer: is a highly variable and non- homogeneous layer, with possible grain sizes ranging all the way from clay to boulders; usually of good strength and stiffness due to its well-graded and over-consolidated nature; the possible presence of boulders presents great challenges to TBM operations; this stratum is also a lot less well-studied in general.


Secondly, look at the surroundings, which can have a major influence over the choice of tunnelling method. For example: ● The existence of metro and city usually will impose very tight ground movement control (volume loss) limits to tunnelling.


● The presence of a nature reserve is likely to impose restrictions on groundwater draw-down and contamination.


● The tunnels have very low ground cover next to the portals; this leads to relatively higher distortion of the tunnel lining and may require ground treatment.


Thirdly, a tunnel engineer should bear in mind the reasons behind popular choices of tunnelling methods and how they differ from each other. For example: ● TBMs are used for their efficiency for long tunnels and capabilities to deal with ground hazards in themselves; in soft ground conditions tunnel shield and segments are likely to be used; in dry and stable grounds roadheaders may be suitable.


Above and below: Stress-Strain graphs representing three principal construction materials - concrete, steel, and soil - for the key, vital, differences between the apparently similar-looking models to be discussed in the workshop


August 2025 | 31


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