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Introducing
a new chapter in the continuing story of rock reinforcement technology
THE
SELF DRILLING ANCHORS OF AUSTRIA
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| Pride
of MAI: The complete range of self drilling anchors and accessories
which now represent an important addition to the Atlas Copco rock
reinforcement service. |
From
the towering peaks of the Austrian Alps to the mountains of Turkey, Japan,
and Taiwan, self-drilling anchors are used by reinforcement specialists
whenever they encounter poor ground and fractured geology in mines and
tunnels.
SDAs, as they are known, are unique reinforcement tools, which, unlike
all other types of rock bolts, are equipped with a drill bit of their
own which allows them to be installed in one operation in rock, highly
fractured weak formations and even soil.
The MAI technology is widely recognized as outstanding and now the company's
complete range of self-drilling anchors and accessories is being made
available on a global scale through the worldwide Atlas Copco organization.
From Alpine
beginnings
The SDA concept was born, literally, on the side of a mountain in Feistritz
an der Drau, a small community in the Austrian Alps close to the Italian-Slovenian
border. It was here, in 1965, that the family firm of Ankerteknik GmbH
was founded and started producing expansion shell anchors for tunnelling
and mining.
With the arrival of NATM (New Austrian Tunnelling Method), these products
were soon replaced by SN-Anchors (Soil&Nail) and in 1984 the first
MAI grouting pump was produced - the MAI Pump - which subsequently became
the world's most widely used grouting pump for tunnelling applications.
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| Above,
the MAI factory nestling in the Austrian mountains. |
The next milestone was reached in 1992 with the development and production
of self drilling anchors - a revolutionary product which completely changed
the structure and future direction of the company. Exports soared - from
less than 20% in 1991 to approximately 90% in 2001.
Such rapid growth gave birth to a new factory which went into operation
in 1996, and in 1997 the company won ISO 9001 certification. Some four
years later, in 2001, Atlas Copco acquired the business from MAI International
and a new companywas launched on July 4, 2002.
New chapter
begins
With the support of Atlas Copco's international organization, a new chapter
has begun in the MAI history book as these specialized rock reinforcement
products are made available worldwide and new foundations are laid for
further development.
The SDA range, or Self-Drilling Anchoring system, complements the Atlas
Copco range of Swellex rock bolts and offer significant advantages to
customers using Boomer, Boltec and ROC drill rigs.
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| A
helping hand: Herbert Papousek, General Manager of Atlas Copco MAI,
with a rope-threaded rod for an SDA. |
Herbert Papousek, General Manager of the new Atlas Copco MAI, explains:
"Firstly, by consolidating these complementary technologies and by
focusing on innovation, our customers can rely on one supplier to meet
all their rock reinforcement needs in difficult ground conditions.
"Secondly, it means that we will be able to offer more effective
solutions than ever before through joint development of these specialized
rock bolts together with the Atlas Copco drill rigs that our customers
use."
Unique concept
There are five different systems in the Atlas Copco MAI anchor range being
manufactured at the Austrian plant. These run from 42-130 mm and include
many different varieties to match each unique application together with
a wide selection of accessories. The products are shipped out to customers
worldwide via the Atlas Copco sales organisation as well through Atlas
Copco MAI's many local distributors.
The SDA system is a unique concept based on a threaded steel bar which
can be drilled in and set without the use of a casing. The bar has a hollow
core which is used for simultaneous flushing or grouting and its left-hand
rope thread allows it to be connected to all conventional drilling systems.
The system can be installed in a variety of different soils and ground
conditions ranging from sand and gravel to inconsistent fill, boulders,
rubble and weathered rock, as well as through footings and base slabs.
Underground
applications include:
- radial
anchoring for stabilisation of tunnel circumference during NATM-style
excavation
- as
forepoles, spiles or as an umbrella for advance protection of the
excavation
- as
roof piles for reaction load of steel support arches
- slope stabilisation of a tunnel portal (See M&C 3/2001,Technically
Speaking)
The system
has five main components: bar, NG-coupler, hexagonal nut, bearing plate
and drill bit.
The bar is manufactured from API standard heavy walling steel
tubing, cold rolled to form a standard ISO rope thread profile. The
rolling process refines the grain structure of the steel, increasing
the yield strength, producing a durable drill rod suitable for a range
of applications. The standard rope thread produces an excellent bond
between the bar and grout, as well as enabling connection to all Atlas
Copco Boomer and surface drill rigs.
It is produced in 12 m lengths and then cut to size depending on requirements.
Standard delivery lengths are 1 m, 2 m, 3 m, 4 m and 6 m. Recommended
maximum shot lengths are: R25N, 3.0 m, R32N & S 4.0 m and R38N 4.0
m. For R51 and T76 system, special shot lengths up to 12 m can be used
and are available on request. In combination with the NG-extension coupler
system, most design lengths can be produced.
The NG-coupler features a patented design that enables direct
end-to-end bearing between each rod, reducing energy loss and ensuring
maximum percussive energy at the drill bit. It has a thread arrangement
in which the top half of the thread is rotated against that of the lower
half, providing a centre stop for each bar. All couplers exceed the
ultimate strength of the bar by 20%. To enable the correct seating of
each bar within the coupler, all bars have a precision cut at right
angles to enable end-to-end bearing. A quarter turn back of the coupler
on the lower bar will ensure optimum seating of the upper bar within
the coupler.
The hexagonal nut, which is machined with right-angled edges
on both ends from high precision steel, is tempered to meet any stringent
specifications and the daily operations of underground works. All nuts
exceed the ultimate strength of the bar by 20%.
The bearing plate is a formed steel plate with a centre hole,
allowing articulation of seven degrees in all directions. All functional
parts are constantly tested in line with the company's rigorous quality
assurance policy.
The sacrificial drill bit is the most crucial part of the anchor
system and is responsible for the productivity of the installation.
Atlas Copco MAI maintains a large range of drill bits to suit the changing
demands of geology encountered on different projects. In order to improve
on performance and cost efficiency, data is collected from projects
around the world, and incorporated into the design with the aim to improve
penetration speed, bit life and to reduce their manufacturing costs.
The result is a system that is particularly suitable for very difficult
and unstable ground conditions. Re-drilling time due to collapsing boreholes
is avoided, and speed of installation is high, with no primary drilling
required. The drilling, placing and grouting of the anchor is performed
in one single operation, reducing the drill labour required for cased
boreholes.
Since conventional rotary-percussion drilling equipment is used, the
method of installation is very similar for all ground conditions, and
the bolts can be installed in all directions, including upwards. And
there is an option to use simultaneous drilling and grouting techniques
during installation, to consolidate any surrounding loose ground.
The anchor bar's full-length left-hand rope thread gives the flexibility
to adjust the bar length to the actual requirement. This is especially
useful if anchoring has to be performed in a confined space.
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| Welcome
aboard! Staff at the MAI facility in Austria celebrate with a group
photo after it was announced that the company would continue its
successful development in rock reinforcement technology as part
of the Atlas Copco Group. |
Easy to learn
process
Installing SDAs is an easy-to-learn process and requires the experience
of a drill operator with an understanding of the anchor characteristics
and the ground in which the bolts are to be installed.
The products have been used on a wide variety of projects around the
world, among them, a conveyor belt tunnel at the Monte Giglio quarry
in Italy, a road tunnel at Pakuashan in Taiwan and in the Channel rail
link tunnel at North Downs in England.
Protective
umbrella
The Monte Giglio quarry project is a typical example. This 9.3
km-long, 4.5 m-diameter conveyor belt tunnel was initially driven using
a TBM in flysch, but some way into the job weak ground conditions were
detected which brought excavation to a halt.
Contractor Strabag Del Favero determined that the tunnel would have
to be reinforced before excavation could continue, and opted for MAI
Self Drilling Anchors to spile a protective umbrella into the crown.
Using an Atlas Copco Boomer H145 drill rig equipped with COP 1440 rock
drills, a total of 24 SDAs, type R51 ES fitted with 100 mm button bits,
were installed in lengths of 9-m. They were set at an angle of 5-degrees
with a spacing of 30 cm and an overlap of 3 m.
This formula allowed 6 m sections of the tunnel to be excavated with
a pneumatic breaker, step by step, at a rate of one metre at a time.
Simultaneous grouting of the SDAs was carried out by an operator working
from a separate platform on the rig and followed up by the installation
of steel arches, 8x10 m wire mesh and shotcrete before the next umbrella
was placed. No radial bolting was necessary.
Access was certainly difficult in the narrow conditions but progress
was fast and efficient. It took just 18 hours to complete each umbrella
and the contractors were soon back in good ground and able to continue
the drive by TBM.
In Taiwan, however, the SDAs played an integral part in the reinforcement
operations of the 5 km-long Pakuashan tunnel, part of the Hanbau-Tsaotwen
Expressway. Here, pre-support consisted of 3 m-long forepoling using
SDAs around the arch and sidewalls of the tunnel with spacings of 0.5
m.
Lattice arches were then set at 1 m centres along with 4 m and 6 m grouted
SDAs, two layers of wire mesh and 300 mm thick shotcrete. One in every
50 SDAs installed was subjected to a 17 tonne pullout test. Maximum
advance on top headings was 3.3 m per 24 hours.
It was a similar story at the Channel Tunnel Rail Link project
in England. The 3.2 km-long North Downs tunnel section being driven
by Eurolink - a joint venture between Beton und Monierbau of Austria,
Miller of the UK and Dumez/GTM of France - was constructed through difficult
chalk formations.
Keeping
progress on track
At the London portal, a systematic ground support concept was employed
to allow NATM tunnelling to proceed. First, 17 m long horizontal Self-Drilling
Soil Nails were installed with a spacing of 2 m. Then, after the installation
of additional roof support consisting of 24 roof pipes, 115 mm in diameter
and 15 m deep, using the Atlas Copco Boodex system, a false portal was
built at the entrance. The spacing of the steel arches was continued
at 1.5 m intervals as the tunnel was able to advance with the continual
support of the Self-Drilling Spiles.
All these projects had one thing in common - poor ground conditions
which threatened to jeopardize efficient and safe progress for the contractors.
That's where Atlas Copco MAI's self-drilling anchors, in combination
with Atlas Copco drilling equipment, can save the day.
For
more information on Atlas Copco's rock reinforcement technology, please
visit:
www.rockreinforcement.com
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