Article written for Tunnels & Tunnelling International. It is not currently available from their archives, so I\'ve put an early draft here as a tearsheet.

1. 33APRIL 2005 Tunnels & Tunnelling International
DRILL AND BLAST
D
rill and blast has come a long way since the
early adopters of black powder circa 1242.
Dynamite with it’s paper packaging for ease
of handling was one of the first significant
milestones when introduced in 1868 by
AlfredNobel.Theriseofthepneumaticjacklegrockdrillsin
the mid 20th Century, operated by one man with an airleg
to push feed the drill steel, was similarly revolutionary
in its time. The next major step was mechanised drilling,
which saw jacklegs being superseded by single or multi-
boom drill rigs. In the last 25 years, technology has further
evolved from pneumatic to electro-hydraulic. We are now
living in the computer age and it is pertinent to ask what
recent developments have been brought to drill and blast
and what may be coming in the future?
For all of the improvements over the years, the basic
work cycle for the drill and blast technique remains the
same. The face is marked up and drilled; this will include
a cut, the section of the round that will form a second face
for the blast; the easers or stopers, the charge holes that
will work to break the rock into the cut; plus any contour
holes that will usually be charged to a lower specific
chargeweight for profiling and to minimise damage to
the surrounding wall rock. The holes will then be charged
and the round initiated. After fume clearance, crews will
wash down, check for misfires and carry out scaling. At
this time, primary ground support may be required. The
round can be mucked out and any further scaling and
ground support carried out. The cycle begins again.
Talking to T&TI, Gunnar Nord, senior construction
advisor for Atlas Copco, described a contemporary drill
and blast work cycle for a 22m2
headrace tunnel using
5m long rounds with 48mm diameter chargeholes and
102mm diameter relief holes. The drilling takes 134
minutes, followed by 29 minutes charging. Once the
round is blasted, 30 minutes is allowed for ventilation and
fume clearance. An allowance of 96 minutes was given for
mucking by wheel loader and trucks, with 45 minutes also
allocated to scaling. Primary wet shotcreting at 12m3
/hr
takes 71 minutes and the bolting part of the cycle takes
50 minutes on an assumed bolt density of 4.5 bolts/metre
of tunnel. This gives a total cycle time for the 5m long
advance of just over 7.5 hours if all activities are able to
be carried out consecutively. Less easily quantified are the
impacts on the work cycle of requirements for mesh or
arches, pregrouting or grouting, spiling and any surveying
to be carried out at the face.
Contemporary advances
T&TI asked Nord to describe what he considered the most
important developments for improvements in tunnel
excavation rates over the last decade. He was quick to
praise Atlas Copco’s latest drill, the recently launched COP
3038 (T&TI, July 2004, p14). It has a 50% higher percussion
rate than the COP 1838 ME (Atlas Copco’s standard for
tunnel rigs 10 years ago). Nord said the new drill could
shorten the total drilling time for a round by up to 25%.
This would equate to a saving of nearly 34 minutes for
our example above, although at the time of the 3038’s
launch last year, Atlas Copco was keen to stress that the
improvements in speed may be better realised by being
able to specify a rig with one less boom, allowing capital
cost savings and less maintenance.
Drilling accuracy was another crucial area where Nord
felt significant advances had been made, saying the
improvements were due to computer guidance of booms
and feeds. Attempting to specify the benefit, Nord said:
“What that means, with respect to time, is difficult to
specify in general terms, but it certainly means a lot for
the scaling, noticeable reduction of shotcrete quantities
and a single figure percentage on the mucking time.”
Charging is next in the work cycle and Nord
immediately identified the most important development
being the introduction of site sensitised emulsion (SSE),
see box, citing the safety benefits it brings. Whilst safety
is paramount, planners and blast design engineers will
be gratified to see that it has led to significant decreases
in the length of time it takes to charge a face. Nord
went on to explain that the quality of the charging had
improved with SSE due to the correct quantities now
being measured into the holes and likened the associated
benefits to those described above for improved hole
Faster cycle times –
the future of D&BDrill and blast
remains one of
the predominant
means of excavation
in hard rock
tunnelling. Patrick
Hudd, assistant
editor, interviewed
representatives
from drill rig
manufacturers Atlas
Copco and Sandvik-
Tamrock, together
with explosives
supplier Exchem
to discuss recent
developments
in drill and blast
tunnelling and
their impact on
productivity.
Above: Operator’s view
from an Atlas Copco drill rig,
showing the high level of
computerisation
Right: Fig 1 - Atlas Copco’s
Measure While Drilling (MWD)
module, part of its Tunnel
Manager software, which
allows analysis of blast and
probe hole data
PHUDD

2. Tunnels & Tunnelling International APRIL 200534
DRILL AND BLAST
accuracy.
Mucking speeds
Mucking for many drill and blast tunnels is carried
out using a wheel loader and trucks. This area is the
second longest cycle section and of note has been
the introduction of spoil conveyors for drill and blast
tunnelling. The utilisation of conveyors for this purpose
will be familiar to many TBM tunnellers, yet it is not
common on drill and blast projects. Nord said: “It is not
unlikely that in the best case a 25% reduction time could
be achieved when compared to regular loading.” This
would give a time saving in our example of 24 minutes,
although it can be assumed that the cost and relative
inflexibility of the conveyor installation would suggest a
long tunnel or multiple headings trammed to a common
haulageway given the sporadic muck generated in drill
and blast as opposed to a TBM.
Less specific to drill and blast, although part of the
overall cycle, are shotcreting and rockbolting. Nord
described the size of the pump and the supply of concrete
as the limiting factors for shotcreting. He went on to add
that the improved accelerators brought onto the market
has made it possible to increase spraying capacity by up
to 50%. This can reduce the spraying part of the cycle by
up to 25%.
There is a presumption bolthole drilling will have
benefited from similar progress to blast hole drilling. Bolt
installation times vary from bolt to bolt depending on
what is specified, although boom mounted carousels for
mechanised bolt installation will have undoubtedly sped
up the procedure. Pekka Nieminen, sales and marketing
manager for Sandvik-Tamrock, echoed this view as he
drew attention to mechanised bolt installation also
being a safer and more reliable operation than manual
installation.
Given that drill and blast has a heritage in both civil
tunnelling and mining projects,T&TI asked the companies
what overlap they had between the two product areas
and if there were any readapted mining innovations
that we could expect to see being adopted for civils
tunnels? Nieminen replied that the quality requirement
was typically higher in civils tunnels, with overbreak
reductions equated to significant cost savings in concrete
lined tunnels. He said performance was important for
either operation, but that mining usage favoured long
term reliability due to higher utilisation, whereas civils
applications generally had more time between rounds for
maintenance.
Hans Fernberg, senior mining advisor for Atlas Copco,
agreed, but added that with the rise in mine contracting,
especially during start-up or expansion phases, there
are “ample opportunities to extract the best from both
schools”.
Optimum round lenghts
Discussingoptimumroundlengths,Fernbergsaidtheface
area governed the length, with stiffer drill rods giving the
best results due to less hole deviation, citing 45mm and
48mm diameter holes as the most common. Nieminen
said the hole sizes had increased as customers wanted
higher penetration rates, with associated faster drilling
speed, which were only achievable with a bigger rockdrill
and drill rod combination. He added that longer rounds
normally led to increases in progress subject to geological
constraints on unsupported lengths and contractual
limits relating to vibration or noise.
Both manufacturers offer varying levels of
computerisation and control of their drill rigs such
as precise, repeatable hole positioning, datalogging,
navigation to tunnel lasers and boom collision control.
Tamrock offer the TDATA or TCAD and TLOG systems
to allow site engineers to develop different drilling
patterns and follow how they work. Fernberg said the
computerisation era offered unique opportunities,
comparing the step in productivity to the change from
pneumatic to hydraulic rigs twenty years ago. Atlas Copco
offers MeasureWhile Drilling (MWD) as a component of its
Tunnel Manager software for its rigs working in tunnelling
or drifting applications. Aside from the control parts of
the software that creates tunnel profiles, alignments
and drill patterns, the MWD module allows analysis of
blast and probe hole data (Figure 1). The data can be
displayed as a 3D view of the drill holes, or variations in
the hardness of the rock in section or plan views. The
parameters recorded and interpreted are feed pressure,
Site Sensitised Emulsion (SSE)
Malcolm Ingry, general manager special projects for Exchem Explosives part
of the EPC Group, talked toT&TI about the use of repumpable emulsions in
underground tunnelling. Recent advances in site sensitised emulsion can
be an attractive proposition for tunnelling contractors as the raw materials
are not explosive until mixed at the loading nozzle.Transportation and
storage are greatly facilitated, plus the explosive is fully coupled to the hole
due to the nature of it being pumped in, this leads to greater efficiency and
improved fume characteristics.
The EPC Group has developed a unit, termed Morse, for the production of
bulk emulsion in underground operations that can be fitted on a trailer or
truck.With a gross weight laden of 3t, it consists of a removable bin to store
the non-explosive matrix, a volumetric metering pump, tanks and pumps for
the gassing agents and lubricating water, two hoses for loading and a PLC
computer to control all safety, production and quality parameters.The matrix
is sensitised at the nozzle of the loading hose by a static mixer, limiting the
mass of explosive in each hose to less than 50g.
One representative round used in the field trials of the unit at Mitholz in
Switzerland was for a 62m2
tunnel. A 4.4m round was drilled using 45mm
diameter holes to a 1.1m by 1.1m pattern. A total of 93 chargeholes and 25
profile holes were used together with an initial two, later revised to four, void
holes in the parallel cut of 105mm diameter. Average time to load the face
using both hoses was 30 minutes, with the best time being 19 minutes. In
tests in Sigirine, also in Switzerland, the use of SSE allowed an optimised blast
pattern with a 30% reduction in explosive energy.This is because the SSE
completely fills the holes and transmits the explosive energy better to the
surrounding rockmass.The SSE also has improved fume characteristics.
The EPC Group currently has 19 units operational and Ingry toldT&TI it was
“the future”of drill and blast.
A twin boom Atlas Copco Rocket
Boomer L2C drill rig using
the new COP 3038 drills for a
development round at LKAB’s
Malmberget operations in
Northern Sweden. This was part
of Atlas Copco’s end-user field
testing regime for the new drill.
PHUDD

3. 35APRIL 2005 Tunnels & Tunnelling International
DRILL AND BLAST
dampener pressure, penetration rate, impact pressure,
rotation pressure, rotation speed, water pressure and
water flow. Fernberg conceded that in homogenous
ground, MWD did not bring any benefit to engineers and
operators, but in different circumstances it was perfect
for delineating variations in the geology or identifying
expected transition zones.
An interesting initiative being developed by 20 major
machine manufacturers, mining and construction
companies and relevant third parties is IREDES, the
International Rock Excavation Data Exchange Standard
(T&TI July 2001, p42). It defines a common interface
language for underground equipment and control
systems. Atlas Copco committed to have all of its new
generation drill rigs compatible with IREDES by the
end of last year. Once fully established, this means the
tunnel could be planned on CAD software, which is
then transposed into the drill pattern software. This
is transmitted to the drill rig to set it up for automatic
drilling.The rig will generate IREDES compatible logs such
MWD, described above. The charging equipment will be
able to use the logs to adjust the charge for each hole
according to the rock conditions. After the blast, a tunnel
scan can be carried out to enable complete feedback on
the performance of the blast, allowing for refinements for
subsequent rounds.
Nieminen described a less glamourous, but equally
important aspect of today’s drill rigs, versatility of the
equipment to handle multiple tasks in the cycle. Tamrock
addresses this at the design stage, with most tunnelling
jumbos able to be configured with alternative booms
such as service baskets and rod handling systems. This
allows the contractor to offset a huge capital cost for
two discrete items of plant. In addition, modularity and
standardisation of main componentry is considered
vital said Nieminen. He described the advantages as
two-fold; the possibility to design and build in different
configurations effectively for the equipment supplier,
plus easier adaption to operation and service of different
machines for the contractor with increased availability
and interchangeability of spares. TT
Tamrock Axera T12 Data-415, a
four boom jumbo for tunnels
and caverns between 20 -188m2
in section. It features TDATA, an
automatic control system for
drilling functions and boom
positioning as well as TLOG,
a system for data logging and
reporting.