BLAST DESIGN

1. TUNNELING AND DRIFTING

2. Review…
• Cycle of operations
• Methods of TUNNNELING
FULL FACE HEADING
PILOT HEADING
HEADING AND BENCHING
• Types of cuts and blast hole design:
CYLINDRICAL CUTS
BURN CUTS
CRATER CUTS
ANGLED CUTS (V , FAN & PYRAMID )
• DRIFTS
• MARKING OUT DRILLING PATTERNS

3. T T
CYCLEOF OPERATIONS
DRILLIING CHARGING
BLASTING
MUCKING
SCALING
SUPPORTING
INSPECTION
VENTILATING

6. TWO WAYS TO CARRY OUT THE PROCESS;
• 1.WITH THE USE OF MOVABLE PLATFORM
• 2. OR MAKING THE USE OF BLASTED MUCK
FROM THE PREVIOUS BLAST AS A PLATFORM FOR
DRILLING AND CHARGING .
• However, the use of multi boom jumbos
eliminates the use of platforms and can help in
excavating upto 110m2
• But with faster advancement and high
mechanization incurs greater cost as compared to
other tunneling methods.

7. Pilot Heading
• Here a pilot hole is driven prior to the main
excavation
• It can be either at the top , bottom or centre
of the tunnel face.
• Helps in getting advance information about
the nature of the strata

8. Comparison…
Full face heading
• For large tunnels upto
110m2
• High mechanization and
faster advancement
• Multi boom jumbos are
used mostly
• Requires high capital
Heading and
Benching
• Upto 100m2
• Comparatively low rate of
advancement
• Jumbos and jacklegs are
used
• Lower capital investment
than full face
Pilot heading
• Useful for cross sectional
area upto 50m2
• Low to med rate
• Crawler drills and
jacklegs can be used
• Low to med capital
investment

9. CYLINDRICAL CUTS

10. • This type of cut consists of one or two uncharged or relief blastholes towards
which the charged holes break at intervals.
• At the moment, this type of cut is most frequently used in tunnelling and
drifting, regardless of their dimensions. It is considered to be the evolution
or perfection of Burn Cut.
• The larger diameter blastholes (65-175mm) are drilled with reamer bits
which are adapted to the same drill speed which is used to drill the rest of
the holes.
• All the blastholes in the cut are placed with little spacing, in line and parallel,
which explains the frequent use of jumbos which come with automatic
parallelism
• The of cylindrical cut most used is the four section, as it is the easiest one to
mark , cut and execute.

11. CUT SPREADER HOLES : Nearest to cut holes
CONTOUR HOLES : consists of Roof holes and Wall
holes; They establish final shape of
the tunnel; Placed with little spacing
LIFTER HOLES : Floor holes
STOPING HOLES : Between cut spreader holes,
contour holes and lifter holes.

12. BREAKING DIRECTION OF THE
STOPING HOLES
FIXATION FACTOR, f S/B RELATIONSHIPS
UPWARDS AND HORIZONTLY
DOWNWARDDS
1.45
1.20
1.25
1.25
If a mine drift is to be excavated in the rock (c=0.4) by means of blasts with parallel
blastholes and four section cut, knowing that the geometric dimensions and drilling
data are:
Tunnel Width AT = 4.5m
Abutment Height = 4.0m
Height of Arch = 0.5m
Relief Hole Diameter D1 = 102mm
Drilling Diameter D1 = 45mm
Lookout angle of the contour blasthole γ = 3⁰
Angular Deviation α = 10mm/m
Collaring Error e’ = 20mm
The explosive to be used has RWS with respect to ANFO of 1.09(109%) and the
available cartridges have a diameter of 25, 32, and 38mm which give linear charge
concentrations for a density of 1.2g/cm3, of 0.59,0.97 and 1.36 kg/cm respectively.

13. ADVANCE PER ROUND

14. • The advance of the rounds is limited by the diameter of the relief hole and the
deviation of the charged holes.
• As long as the latter is maintained under 2%, the average advances X can reach 95% of
the blasthole depth L.
X=0.95L............................................ eqn 1
• In the four sections cuts, the depth of the blastholes can be estimated by the following
equations:
L=0.15 + 34.1D2 – 39.4D2
2 ...............eqn 2
where: D2 = Diameter of empty hole(m)
• When cuts of more than one Relief holes are used instead of only one large diameter
drillhole, the former equation is valid making
D2=D’2 X (NB)0.5................................ eqn 3
where D’2 is the diameter of the empty blastholes and NB is the number of Relief
Holes
ADVANCE:-
Considering Four Sections of Cuts;
the Depth of the Blastholes can be estimated from eqn 2 as, L= 3.2m
And, from eqn 1 Average Advance is calculated as, X=3m
ADVANCE PER ROUND

15. CUT AND CUT SPREADER

16. • The general geometric pattern of a four section cut with parallel
blastholes is shown in the figure:
CUT AND CUT SPREADER

17. • The distance between the central blasthole and those of the first section should
not be more than 1.7D2 to obtain fragmentation and satisfactory movement of the
rock.
• The condition of the fragmentation vary greatly depending upon
– type of explosive
– Rock properties
– The distance between the charged blasthole and the relief hole
CUT AND CUT SPREADER
• For burdens larger than 2D2, the break
angle is too small and a plastic deformation of the
rock between the two blastholes is produced.
• Even if the burden is under D2, but the
charge concentration is high, a sinterization of the
fragmented rock and cut failure will occur.
• For this reason, it is recommended that the
burdens be calculated from,
B1=1.5D2.........................eqn4