WORKSHOP REPORT | BTSYM


● The groundwater offers no resistance (in terms of shear capacity);


● The ground deforms when providing resistance: When prevented from deformation, the ground cannot provide resistance; and, When limited to less deformation, the ground provides less resistance; Ground ‘relaxation’ is a term referring to a form of ground deformation, where the ground is unloaded, expands and moves, ‘activating’ a new internal structural arrangement.


● The later (in space or time) the structure is installed, or the less stiff the structure is: The more the ground moves; and, The less loading the structure attracts.


The graph that follows – ‘Ground pressure on support - v - Convergence’ – relates only to experience and effects where tunnelling is (principally) horizontal (i.e., shafts are different). Also, loading conditions are static (seismic or other


dynamic loadings were not considered in the graph, or workshop), and such tunnels are not excavated at exceptional depths (hundreds of metres). It does not, therefore, cover potential conditions for


tunnels that are very deep (e.g., approaching depths of 1000m or even greater), where overburden is so high that upon a void being created by excavation the


rock’s inherent strength cannot contain it intact. In such instances, and sometimes even after excavation support has been put in place, as the rock mass self-adjusts its natural structure to seek stress-energy alleviation, the consequence can be explosive. These ‘rockbursts’ are a specialist area of tunnelling, and thus is part of the ‘Knowledge Tree’; but the topic, though, was not addressed in the workshop.


SUMMARY In the workshop titled ‘Connecting the Dots: A Tunnel Engineering Knowledge Framework’, the author, a tunnel engineer, mainly conveyed the following messages to tunnel engineers at their early career stage: ● Establish a ‘Knowledge Tree’ and continue to develop it throughout a career;


● Approach engineering processes from the practical challenges first and then trace back to the theories;


● Don’t be afraid to confuse yourself - this is progress, ultimately, rather than a setback. It is questioning, in a ‘growth stage’; and,


● Understand the principles of ‘ground-structure interaction’.


ACKNOWLEDGEMENTS Si Shen would like to thank BTSYM Chair, Arabel Vilas, for her encouragement in this initiative and the whole Committee for facilitating the workshop.


Below:


One of the diagrams used at the workshop: Support load -v- Convergence


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