1. BASICS OF DRILLING-3
I. Satyanarayana,
M.Tech,MBA,MCA
Dy. Manager, Project Planning, SCCL
isnindian@gmail.com,
visit at
www.slideshare.net/isnindian
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2. Inclined hole drilling
If the strata conditions permit, inclined blastholes allow better distribution of the
explosives
Advantages:
More fragmentation and displacement
Eliminate front row toe burden and digging problem
Probability of cut offs reduced
More useful in higher benches
Less over break
New face formed is smooth and sound
Less ground vibration
Reduce secondary blast requirement
Cost effective
Disadvantages: Angled versus vertical blastholes
Difficult to drill (requires sophisticated drilling equipment) and increased drilling cost.
Requires close supervision
Risk of bore hole collapse
Difficult in charging and loading of explosives.
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3. DRILLING PARAMETERS
• Blasthole diameter (D): Generally, the cost of drilling and blasting decreases as hole diameter increases. The
relationbetween blasthole diameter and face height is approximately:
D = 0.001 to 0.02 H
• Burden (B) : This is the distance in metres from a blasthole to the nearest free face and has the following approximate
relation:
B = 25D to 40D
Or B = 25D to 30D for hard rock
B = 30D to 35D for medium rock
B = 35D to 40D for soft rock
• Spacing (S) : This is the distance in meters between adjacent blastholes and is measured perpendicular to the burden.
Usually the relation between drilled burden and spacing is:
S = 1 to 1.8B
• Charge length (L): This is the explosive column in a blasthole and should be at least 20D in order to utilize fully the
explosion-generated strain in the rock.
• Stemming (T): This is the inert material filled between the explosive charge and the collar of the blasthole to confine
the explosion gases. The stemming material could be water, drill cutting, sand, mud or crushed rock. The best is the
dry angular crushed rock (<30mm) as it tends to form a compaction arch, which locks into the blasthole wall, increasing
its resistance to ejection. A stemming length shorter than 20D usually causes flyrock, cut-offs and overbreak problems.
It is also suggested that the stemming length should not be less than the effective burden B.
• Powder factor or specific charge or blasting ratio: This is the ratio between the mass of explosives required to break a
given uantity of rock and is normally expressed in kg/m3 or kg/t3.
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4. EVALUATION OF DRILL PERFORMANCE
Drill hole deviation
Drills equipped with hydraulic shock wave
reflex dampening system
To maintain ideal feed rate, maintain
verticality,achieving higher drilling rates
and drill steel economy
Computerised drilling control to control feed
force, torque,and penetration rates
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5. • Drill machine navigation systems
1. GPS guidance system
2. The coordinates of each drill hole is sent
via a radio network to the drill from the
planning office
3. The data of actual drill position is sent to
the planning cell for necessary
computation
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6. Benefits of monitoring drill
performance
• Higher rate of penetration
• Reduced over drilling
• location of weak and strong strata
• Optimum blasting
• Adequate fragmentation
• Higher bit life
• Lower maintenance cost &
• Higher accuracy of data and reports
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7. Drill monitoring
Drill monitoring system offers the ability to
collect information
• Drill production statistics
• Ore and waste interactions
• Exact collar location
• Hole position and depth
• Maintenance information
• Consumable tracking
• Blastibility index(BI)
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8. DRILLABILITY
• Rock drillability is defined as the penetration
of a drill bit into the rock expressed in metres
per minute.
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