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Chapter 8.5 Tunnels and underground excavations
(caverns)
Dr. Robert Hack
ITC, University Twente
For credits and references is referred to ‘2018 PAO-Chapter 8.5 - Tunnels and underground excavations (caverns) – by Robert Hack’.
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Tunnels and underground excavations (caverns)
Excavation & supportWhy is support needed Excavation
Support
Tunnel Boring Machine (TBM)
Groundmass properties and parameters important for underground excavations
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Excavation & support
Excavation & support are linked items
excavation depends on support and vice versa
and
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Excavation & support
Support only required (if required at all) to keep ground material in the excavation wall at its place; the ground caries itself !
(see Chapter 4, Ground Mechanics)
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Mechanical vs blasting – Non-cyclic vs cyclic
Weaker vs stronger rock mass
Ease of excavation & more support vs difficult excavation & less support
Everybody can excavate everything; even with bare hands and nails but
may take forever and not be very economical
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Cutting & grinding
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Blasting
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Specials – chemical expansion
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Very special
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Support
Grouting - cement milk in pores and discontinuities
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Shield tunneling – tunnel boring machine
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Shotcrete
Shotcrete most popular means of support
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Bolts, dowels & anchors
Keep the ground together and increase shear strength
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Combined support
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Yielding steel arches
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Timber
Timber is bad – compresses too much – allows ground to move – reduction shear strength and integrity
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Tunnel Boring Machine (TBM) – soft ground)
‘Soft’ ground types of TBM may also be used in ‘mixed’ (hard & soft) ground or ‘hard’ ground with water bearing and discontinuities filled with loose material15
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Jacked tunnel
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Tunneling risks
Everything on the scheme is a risk and many more….
Even a manager who forgets his cell phone may be a major hazard for the project (nobody can contact him if something has gone wrong)
Tunneling risks
Best approach is to study a tunnel project nearby in similar ground,
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Tunnel progress and production
Wonderful articles are written on tunnel progress, production, and risks, but what the value is ?
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