2 62 Excavation principles
by improved cutter technology or by combining the explosive and
cutting/mucking processes in the machine’s cutting head. The TBM
advance rates will not increase so much because the whole tunnelling
system (the thrust reaction grippers, the electro-hydraulic power sys-
tem, installation of support elements, maintenance, etc.) has to keep
up with the increased penetration rate, which involves many practical
difficulties.
(e) New methods of excavation are not likely to be introduced in prac-
tice. There has been considerable research over the years into alternative
methods of fragmenting and removing the rock and, whilst many of
these methods (e.g. flame cutting, electrical and magnetic disintegration,
nuclear techniques) have advantages, they also have significant practical
disadvantages.
15.3 Additional points
The increasing demands on surface space, greater environmental aware-
ness, and the technical and safety-related advantages of using under-
ground excavations have led to considerable use of underground space
for civil engineering purposes as evidenced by the list below.
Civil and military defence, nuclear shelters, aircraft hangers, emer-
gency centres
Conventional and nuclear power stations
District heating
Drinking water transportation and storage
Dry docks
Hot water storage
Hydroelectric projects
Living quarters
Radioactive waste storage and disposal
Rail transport and stations
Refuse management and incineration
Research facilities, particle accelerators, wind tunnels
Road tunnels
Shopping malls
Sports, concert, theatre, religious and museum halls
Storage of food, drink, documents, aggregates, minerals
Storing petroleum products
Storm water drainage and storage
Waste water management and treatment plants
There will be increasing underground excavation in the years ahead
to supply society with further civil and mineral resources. The maximal
excavation size depends on the type of rock mass. In a strong, unfvactured
granite, large spans are possible, e.g. 100+ m spans, because the stress
concentrations do not depend on excavation size. In weaker, fractured
rocks, the spans are limited because of the need to support the rock, the
support requirements increasing with excavation size. Most caverns to
date have been excavated at depths shallower than loo0 m. The cavern