Geology Reference
In-Depth Information
Shallow foundation
on rock
Piles end bearing
on rock
Building on skin
friction piles
2.3.2 Tunnels
Engineering geologists are often closely involved in the investigation
of tunnel routes, preparation of reference ground conditions for con-
tracts, tunnel design and during construction. Tunnelling has been car-
ried out since ancient times, originally probably making use of techniques
developed in mining, which date back many thousands of years.
Aqueduct tunnels for water supply were constructed in ancient Rome,
Greece and the Middle East. Modern tunnelling really started with the
development of extensive canal systems in the UK and mainland Europe
in the C16 and C17 where the alternatives to tunnelling were either deep
cuttings or long detours around hills. Originally, tunnels were hand-dug,
using gunpowder where necessary. Many modern tunnels are con-
structed in a similar fashion; improvements include computer-controlled
drilling for blast holes, rapid and sophisticated support methods and
much better ventilation and safety systems.Generally,drillandblast
tunnels involve a cycle of drilling, blasting, mucking-out and support,
generally advancing a few metres per pull. Hand-excavation is also
sometimes used, employing essentially mining techniques, perhaps
using powerful road headers moved across the face to dislodge soil and
rock but not taking out the full tunnel pro
le at one time. It is often the
engineering geologist who, during this type of tunnelling, will examine
the exposed ground and make decisions on the degree of temporary
support that is required, together with any special requirements for
further investigation or ground treatment before the tunnel is advanced.
One advantage of drill and blast is that methods can be modi
ed quickly
to suit changing and dif
cult ground conditions. Another advantage is
that mobilisation is fast
tunnelling can be begun quickly and carried out
in remote areas of the world. The disadvantage is that it is often much
slower than by using a tunnel boring machine (TBM).
TBMs were gradually introduced for excavation, in particular for the
underground railway tunnels in London. In an early attempt at tunnel-
ling beneath the Channel, a 2.13m diameter boring machine tunnelled
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