Faster? Safer? Cheaper? Get it done with Swellex - Atlas Copco

In tunnelling, as well as in mining, the
market demands are quite simple to
identify. Increased safety, increased
ergonomic design and, above all,
increased operational economy. Rocket
Boomer rigs are an excellent example
of Atlas Copco’s answer to all these
requirements. In particular, better
economy is reached by constantly
reducing drilling time. The response
from the market is normally very positive,
with a great majority of customers
prepared to invest in advanced
drilling technology, in order to get the
lowest cost per metre of advance. An
Atlas Copco drillrig may be a bit more
expensive to purchase, but its higher
productivity will pay back the initial
investment.
The same attitude is valid for all
phases of the excavation cycle, including
rock reinforcement. In fact, it is
almost a technical nonsense to invest
in advanced drilling rigs and use an
obsolete mucking system, or a low-
performance blasting system, or
simply a malfunctioning ventilation
system. The excavation cycle will be
penalised most, but the weakest phase
in the sequence, and the benefits
from the most advanced rigs, will be
frustrated.
Swellex is not the cheapest rock
bolt available on the market. Cement
grout and simple steel rebars are quite
inexpensive materials. However, rock
reinforcement is about stability, safety
and productivity in the tunnel, and is
not about cutting the purchase price
of the materials.
Swellex is the perfect partner for
contractors and mines prepared to
invest in advanced rock reinforcement.
Invest to reduce the installation time,
and therefore the total cost.
Swellex is faster to install than traditional
rock bolts. Even more important,
Swellex grants a higher degree of
repeatability in its installation. Less
TALKING TECHNICALLY
Faster? Safer? Cheaper?
Get it done with Swellex
It’s a Swell Bolt in
Every Way
Over the past two decades, the
Swellex rock bolting system has
become world famous as the
simplest, fastest and most reliable
ground reinforcement technology
available.
The Swellex bolt is a folded steel
tube, which is inserted into a predrilled
hole in the rock. Water is
pumped into the tube at high
pressure, blowing out the fold and
expanding the tube into the exact
shape of the hole, adapting to
every irregularity.
Bolt installation takes less than
30 seconds, and provides full and
immediate support along the entire
hole length, in ground conditions
ranging from the hardest rock, to
clay, and even sand.
The system speeds up rock reinforcement
considerably and, over
the years, has built up an enviable
reputation for saving time and
money, as well as providing a safer
underground environment for
miners and tunnellers alike.
Summary of Swellex® benefits
● Swellex provides immediate rock reinforcement in most rock types and
conditions
● Swellex installation procedure ensures that every bolt installed will provide
optimum reinforcement
● Swellex rock bolts are quickly installed and very little training is needed to
use the equipment
● Swellex rock bolts provide full column interlock with the surrounding rock
without the need for mechanical devices or grouting agents
● Swellex requires no environmentally harmful chemical grouts to anchor the
bolt in the rock
● The quick and easy installation, and the assurance that every bolt provides
immediate full load-bearing capacity, makes Swellex a highly competitive
rock reinforcement system
Interactions between rock and Swellex.
trouble with grout or chemicals allows
the miners to get more bolts per hour,
measured on long term statistics.
The impact of Swellex on an excavation
cycle depends on many parameters
such as tunnel size, mechanised
or manual installation, length of the
bolts, and type of rock. For this reason
Atlas Copco has developed a specific
software called Time Based Cost
Comparison (TBCC). Atlas Copco Rock
Reinforcement Team is available to run
TBCC for customers. Our own empirical
data, collected in a mining operation
in Canada, for instance, has
shown that we can almost double the
weekly production of rock bolts
installed.
In several cases, Swellex has also
modified the global approach of rock
reinforcement used in a specific
tunnel. Providing immediate rock support
with a guaranteed function,
Swellex has replaced steel arches, has
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TALKING TECHNICALLY
expanded the role of rock bolts in a
broader variety of formations, and has
modified working sequences.
In addition to data collected by
Atlas Copco, the experience of contractors
and mining companies all over
the world confirms the potential of
Swellex as a cost-effective solution for
rock reinforcement.
In Hong Kong, Swellex has been
the tool to speed up production in
hard granite. NEAT, the Swiss super
project, has standardised on Swellex as
primary support in a large variety of
rock conditions. In this edition you can
read about the Mitholz section of the
Lotschberg tunnel.
Similarly, at Dresden and Plabutsch
Swellex is coping with variable and
difficult rock conditions.
Coated Swellex ® Fights
Corrosion
Conventional types of rock bolts made
from carbon steel are susceptible to
corrosion. In most conditions, the corrosion
process will eventually turn the
carbon steel into iron oxide. When the
ph-value in the corrosive environment
is between 4 and 7, the rate of corrosion
in carbon steel is 0.1 mm per
year. This means the entire exposed
area will be changed to iron oxide or
rust to a depth of 1 mm in 10 years.
When estimating the corrosion of
rock bolts, the overall impact on the
reinforcement of the entire area is the
primary problem, rather than the
effect on individual bolts. The Swellex
bolt is pressed very hard against the
sides of the hole, preventing water
from running freely between the bolt
and the rock, while the welded seals
inhibit internal corrosion.
Nevertheless, to meet the requirements
for protecting rock bolts from
corrosion, Atlas Copco has developed
a special Coated Swellex with a corrosion-protective
coating. When expanded,
the bolt becomes fully
protected as the coating forms a barrier
between the rock and the bolt,
preventing water and moisture from
interacting with the steel.
Although Coated Swellex has been
widely applied in recent years, it will
be some time before samples of sufficient
age can be retrieved for corrosion
analysis. However, the inherent
advantages of the Swellex concept,
combined with the corrosion protective
coating, are regarded as double
assurance for long-term rock reinforcement
in corrosive environments. As an
added bonus, Coated Swellex forms
part of the permanent support system.
Total System Approach
The cost and time involved in rock
reinforcement compels project engineers
to evaluate a total system
approach. The cost of the rock bolt
itself, or such properties as tensile
strength, is seldom of primary interest.
Rockbolting
sequence for
installation of
Swellex.
The decisive factors are the resulting
safety, the total cost, and the time
required to fulfil the mission.
To summarise, when the Swellex
bolt is installed in heavily fissured rock,
the radial stresses enhance the contact
forces between blocks of rock surrounding
the bolt, leading to an
increase in rock mass strength. In soils,
Swellex bolts provide consolidation
immediately around the bolt, leading
to an increase in the strength of the
material, and improved anchoring
capacity of the rock bolt. In hard rock,
0.5 m of anchored Swellex rock bolt
gives a pull-out resistance equal to the
breaking load of the bolt.
There are Swellex rockbolts for
almost any environment and purpose.
In highly corrosive conditions with
demands for long life, Stainless Swellex
may be the choice. In situations where
very long bolts are required,
Connectable Swellex offers fast installation
of up to 12 m-long bolts. In the
very near future, Atlas Copco SDR self
drilling rockbolts will become available
following comprehensive testing in
Turkey, Spain, Italy and Madeira.
Atlas Copco delivers integrated solutions
for underground excavation:
Swellex is part of a series of equipment
for rock reinforcement in which Boomers,
Boltecs, Swellex pumps and installation
chucks are coordinated in a complete
programme to boost productivity.
by Federico Scolari
14 FACE DRILLING