171) The “25 Euro Silver-Niobium
Coin Series": Part (xi): 2003 onwards minted by the Austrian Mint by using Niobium
and Niobium metal insertion technology for the first time anywhere in the World
of Numismatics: The Eleventh coin in the Series: “Tunnel Construction”:
Tunnel
Construction:
A tunnel is an underground
or underwater passage dug through the surrounding soil/earth/rock and enclosed
except for an entrance and exit at each end.
Tunnel construction
is basically of three types:
- Cut-and-cover
tunnels constructed in a shallow trench and then covered over.
- Bored
tunnels, constructed in situ, without
removing the ground above. They are usually of circular or horseshoe
cross-section.
- Immersed
tube tunnels, sunk into a body of water and sit on, or are buried just under
its bed.
One of the most
mountainous countries in Europe, Austria has been a pioneer in the development
of tunnels.
Built between 1848 and
1854, the vertex tunnel of the Semmering Alpine Railway was the World’s
first Alpine tunnel. The “New
Austrian Tunnelling Method”, which uses the geographical stress of
surrounding rock to strengthen a tunnel, was developed from 1957 – 1965 by
Ladislaus von Rabcewicz, Leopold Muller and Franz Pacher, which has gone a long
way in revolutionising tunnel construction around the World.
Milestones
in Tunnel-construction:
- Tunnels
were hand-dug by several ancient civilisations in the Indian and Mediterranean
regions. In addition to digging tools and copper rock saws, fire was sometimes
used to heat a rock obstruction before dousing it with water to crack it apart.
The cut-and cover method – digging a deep trench, constructing a roof at a
predetermined height within the trench and covering the trench above the roof
(a tunnelling technique still employed today) was used in ancient Babylon some 4000
years ago.
- In
1681, the first advancement over hand digging came with the use of
gunpowder to blast a 515 ft. (160 metres) long canal tunnel in France.
This photo taken at Mahaballipuram , near Chennai during our recent trip in August 2014, reminded me of this process. Notice the small holes on this rock, through which controlled amounts of gunpowder can be inserted to have a controlled explosion/blast to split the rock into a pre-determined size.
- Around
1850, Nitro-glycerine (stabilised in the form of dynamite) replaced the
less powerful “black powder” (gunpowder) in tunnel blasting. Steam and
compressed air were used to power drills to create holes for the explosive
charges. This mechanisation eventually replaced the manual process by using heavy
sledge hammers and pounding steel chisels which could cut deep holes into solid
rock.
- Between
1820 and 1865, tunnelling shields were developed which enabled
construction of two tunnels under the Thames River in London. A rectangular or
circular enclosure (the shield) was divided horizontally and vertically into
several compartments. A worker in each compartment could remove one plank at a
time from the face of the shield, dig ahead a few inches and replace the plank.
When space had been dug away from the entire front surface, the shield was
pushed forward and the digging process was repeated. A team of workers at the
rear of the shield lined the tunnel with bricks or cast iron rings.
- In
1873, a compressed air technique was used to keep water from seeping
into a railroad tunnel under construction below the Hudson river. This
technique, though fraught with risks, is still in use today. Workers have to
spend time in decompression chambers at the end of their shifts, hence in the
case of an emergency evacuation, there could be casualties. The pressure within
the tunnel must be carefully balanced with the surrounding earth and water
pressure otherwise any imbalance can cause the tunnel to collapse or burst
which will end up in flooding.
- Soft
soil is prone to collapse and it can clog digging equipment. To stabilise the
soil, it is frozen by circulating coolant through pipes embedded at intervals
throughout the area. This technique has been in use since the early 1900s.
Another stabilisation and water-proofing technique used since the 1970s
is to inject grout (liquid bonding agent) into soil or fractured rock
surrounding the tunnel route.
- Shotcrete
is a liquid concrete that is sprayed on surfaces since 1907, it has been
used as both a preliminary and a final lining for tunnels since the 1920s.
- In
1931, the first drilling jumbos were devised to dig tunnels.
These jumbos consisted of 24-30 pneumatic drills mounted on a frame welded to
the bed of a truck. Modern Jumbos allow a single operator to control several
drills mounted on hydraulically controlled arms.
- In
1954, a Tunnel Boring Machine (TBM) was introduced which is a
cylindrical device with digging or cutting heads mounted on a rotating front
face that grinds away rock and soil as the machine moves forward slowly. Modern
TBMs are customised for each project by matching the types and arrangement of
the cutting heads to the site’s geology. The diameter of the TBM is also
required to be equal to the diameter of the designed tunnel (including its
lining).
New
Austrian Tunnelling Method (NATM) – Salient Principles:
NATM integrates the
principles of the behaviour of rock masses under load, as well as, monitoring
the performance of underground construction during tunnel building. Of the 22
Principles that define NATM, the undernoted ones are most significant:
- Mobilisation/exploitation
of the strength of rock mass: The inherent strength of
the soil or rock around the tunnel domain should be preserved and deliberately
mobilised to the maximum extent possible. The primary support is directed to
enable the rock to support itself.
- Shotcrete protection: The
mobilisation can be achieved by controlled deformation of the ground. Excessive
deformation that will result in loss of strength or high surface settlement
must be avoided. This is achieved by applying a thin layer of shotcrete
immediately after surface advance. Initial and primary support systems
consisting of systematic rock bolting or anchoring and thin semi-flexible
sprayed concrete lining are used to achieve the particular purposes given in
permanent support works are usually carried out at a later stage.
- Closing of invert: The
closure of the invert and creating a load bearing ring should be adjusted with
an appropriate timing that can vary, depending on the soil or rock conditions.
It is particularly crucial in soft ground tunnels where no section of the
tunnel should be left open even temporarily.
- Measurement & Monitoring: Laboratory
tests and monitoring of the deformation of supports and ground should be
carried out without delay. Every deformation of the excavation needs to be
measured. NATM requires installation of sophisticated measurement
instrumentation. It is embedded in the lining, ground and bore-holes.
- Flexible support:
The primary lining is thin and reflects recent strata conditions. Active,
rather than passive support is used and the tunnel is strengthened not by a
thicker concrete lining but by a flexible combination of rock bolts, wire-mesh
and steel ribs.
- Flexible Contractual
arrangements & ongoing cooperation during building of the tunnel: Those
involved in the execution, design and supervision of NATM construction should
understand and implement the NATM and react cooperatively in resolving any
problems. Changes in support and construction method, as tunnel construction
work progresses, are possible and the contractual arrangements should embody
clauses to enable such changes.
- Rock mass classification
will determine support measures: There are several main
rock classes for tunnels and corresponding support systems for each one, which
serve as guidelines for tunnel reinforcement. The measured rock properties lead
to the appropriate tools for tunnel strengthening. Nevertheless, the length of
the unsupported span should be left as short as possible.
The
NATM concept focuses on using geological stress of the surrounding rock mass to
provide stabilisation and support to the tunnel itself. Originally developed
for use in the Alps, where tunnels are commonly excavated at depth and in high
stress situations, the Principles of NATM have become fundamental to modern-day
tunnelling.
Philosophy
and controversial names:
Interestingly, there is a
paradox which has led to difference of opinions – whether the NATM is a
philosophical approach or it is an actual technique/method in tunnel excavation
and construction.
For example, NATM has also
been referred to by such diverse names as the Sprayed Concrete Method (SCL - This method consists of a
thin sprayed concrete lining, closure of the ring at the earliest possible
moment by an invert to a complete ring – called an “auxiliary arch”, the deformation
of which is measured as a function of time until equilibrium is obtained. The 3
key points are – application of thin-sprayed concrete lining known as
“shotcrete”, closure of the ring as soon as possible and the systematic
deformation measurement), the Sequential
Excavation Method (SEM – which also refers to the NATM, is a concept
that is based on the understanding of the behaviour of the ground as it reacts
to the creation of an underground opening), the Cross Diaphragm Method (CDM), the Centre Dividing Wall or Cross Diaphragm Method (CDW or CRD-NATM)
and the Upper half Vertical Subdivision
(UHVS).
Interestingly, for this
widely used Tunnelling method, the scientific community is not able to arrive
at a single unified name.
In 1980, the
definition of NATM was redefined by the Austrian National Committee in
Underground Construction of the International Tunneling Association as “a concept whereby the ground surrounding an
underground opening becomes a load bearing structural component through
activation of a ring like body of supporting ground”.
NATM
is a Design Philosophy or a Method?
The above nomenclatures have
led to some confusion in the exact definition and principles of NATM leading to
three group of thought – one group which supports the NATM, anther which
opposes it and a third neutral group.
NATM
as a Design Philosophy:
Leopold Muller, one of the
pioneers of this method, suggested that NATM was a tunnelling concept defined
by a set of principles. It was not to be
viewed as a method for construction, as this actually implied a means by which
to advance or drive a tunnel. This led to a school of thought that believes
that NATM is more of a Philosophy rather than a set of excavation and support
techniques.
NATM is termed a Design
Philosophy because of the under mentioned features:
- The
strength of the ground around a tunnel is deliberately mobilized to the maximum
extent possible.
- Mobilisation
of the ground strength is achieved by allowing controlled deformation of the
ground.
- Initial
primary support is installed having load-deformation characteristics
appropriate to the ground conditions and installation is timed in relation to
ground deformations.
- Instrumentation
is installed to monitor deformations in the initial support system, as well as
to form the basis of varying the initial support design and the sequence of
excavation.
Nevertheless,
whichever way one looks at it – method or philosophy, , NATM has several
beneficial features in comparison to the more conventional tunnelling methods
and is widely being accepted in the construction of tunnels today. NATM has
helped revolutionise the modern tunnelling concepts. Many of the most famous
tunnels all over the world have used this excavation technique.
NATM and Soft-ground
Tunnel Construction:
NATM
is being widely used in soft-ground tunnel excavation and construction around
the World.
In
soft ground tunnels, shotcrete in combination with lattice girders and some
form of ground support are installed as excavation takes place, followed by the
installation of a final lining at a later date.
Tunnel
Construction: Soft Rock and Underwater:
Tunneling through soft
rock and tunnelling underground require different approaches – Blasting in
soft, firm rock such as shale or limestone is difficult to control.
Therefore, Tunnel-Boring Machines (TBMs) or Moles
are used in creating a tunnel. TBMs are
enormous pieces of equipment with a circular plate on one end. The circular
plate is covered with disk cutters which are chisel shaped cutting teeth, steel
disks or a combination of both. As the circular plate rotates slowly, the disk
cutters slice into the rock, which falls through spaces in the cutting head
onto a conveyor system. The conveyor system carries the debris to the rear of
the machine. Hydraulic cylinders attached to the spine of the TBM propel it
forward, a few feet at a time.
TBMs also provide support
while boring the tunnel. As the machine excavates, two drills just behind the
cutters bore into the rock. Then the Tunneling team pumps materials into the
holes & attaches bolts to hold everything in place until the permanent
lining is installed. The TBM assists by using a massive erector arm which
raises segments of the tunnel lining into place.
An image of a Tunnel boring Machine (TBM)
An image of a model of a Tunnel Boring Machine which has been taken to the reverse of this Silver-Niobium coin.
On the other hand, for
underwater tunnel construction, the cut-and-cover
method is used. Construction is carried out by dredging a trench in the
riverbed or ocean floor. Long pre-fabricated tube sections made of steel or
concrete and sealed to keep out water are floated to the site and sunk into the
prepared trench. Then workers dive into the water and connect the sections and
remove the seals. Any excess water is pumped out and the entire tunnel is
covered with backfill.
The 25 Euro
Silver-Niobium coin titled “Tunnel Construction”:
On the Obverse of this coin is shown a
present day Tunnel Boring Machine (TBM) in the Niobium Core, its rotating motion
symbolised by three arrows. The outer silver ring shows the mountains through
which the machine is drilling. On the upper left periphery is mentioned the
denomination of the coin “25 EURO” and the year if issue “2013”. On the lower
periphery is depicted the name of the issuing country “REPUBLIK OSTERREICH”
(meaning “Republic of Austria”).
The
colour of the Niobium Core is a brilliant ice blue.
On the Reverse of this coin is shown
one of the many road tunnels that are found on Austria’s Alpine landscape. A
tunnel worker is shown using a pneumatic drill to loosen rock in the silver
ring. The word “TUNNELBAU” (meaning
“Tunnel construction”) is inscribed on the lower periphery of the coin in the
outer silver ring.
The specifications of the coin
are:
Face value: 25 Euros; Metallic composition: Outer
ring: Silver (Ag) 900 – 9 gms, Niobium 998 – 6.50 gms; Diameter: 34 mm; Weight:
16.50 gms; Edge: smooth.
The mintage of this coin was limited to a maximum of 65000 pieces.
This coin has won the best Bimetallic Coin in the prestigious Krause Publications Competition held in 2014:
This coin has won the best Bimetallic Coin in the prestigious Krause Publications Competition held in 2014:
Every year, since 1984, Krause Publications holds a
competition for “Coin of the Year” Awards in which there are 10 sub-categories
(Best Gold Coin, Best Bimetallic Coin, Most Artistic Coin, Most Historically
Significant Coin, Best Contemporary Event Coin, Best Silver Coin, Most Innovative
Coin, Most Inspirational Coin, Best Crown, Best Circulating Coin) apart from
the overall “Coin Of The Year” (COTY).
The coins nominated for the Competition should have
elegant and diverse styles, themes and technology used by mints from across the
Globe.
The recently concluded Competition saw 94 elegant
coins being nominated from 45 different countries which were all issued in
2013. Out of the ten categories, Austrian Mint coins won best coin in three
categories - Most Artistic Coin Category (Austrian Mint – 2013 “Wildlife
in Our Sights” Red Deer 100 Euro Gold Coin – KM No. 3225), Best Bimetallic
Coin Category (Austria – 2013 Tunnelling or Tunnel Construction – KM 321) Silver & Niobium 25
Euro Coin, and Best Gold Coin (Austria – 2013 “Klimt and His Women –
The Expectation” 50 Euro Gold Coin – KM 3218).
The following coins have been issued in this Series:
2003 – 700 years old Hall City in Tyrol or Tirol
2004 – 150 years Semmering Alpine Railway
2005 – 50 years of Television
2006 – The European Satellite Navigation
2007 – Austrian Aviators
2008 – Fascinating Light
2009 – Year of Astronomy
2010 – Renewable Energy Sources
2011 – Robotics
2012 – Bionics
2013 – Drilling tunnels
2014 – Evolution
2015 - Cosmology
Links:
For posts on COTY (Coin of the Year) winners since 2015 in a competition held by Krause Publications of Germany, please visit the following links:
Links:
Links to posts on Federal Republic of Germany issues and other posts on this blog:
For posts on COTY (Coin of the Year) winners since 2015 in a competition held by Krause Publications of Germany, please visit the following links:
Sumita Chaudhry has commented:
ReplyDelete"Wow ! I will never be able to JUST pass through a tunnel now!! That was a lot to process! "
Even I was fascinated going through the reference material for this post.
DeleteRamchandra Lalingkar has commented:
ReplyDelete" Very interesting information about 'Tunnel' construction which otherwise would not have been read. Thanks for such an informative sharing ! "
Thank you for your appreciation.
Delete