E. Drilling

Drilling and blasting a material is an inexact science

with many unknowns. Without a thorough study of the

physical parameters of the material to be drilled and

blasted, only broad estimates can be made. As often as

not in a preliminary feasibility study, there is little

or no physical data on which to base the drill calculations.

The calculation procedures in this study guide give enough

data for the engineer to make a reasonable estimate of

the required rock parameters. It will also enable you to

arrive at probable drilling scenario and the necessary

equipment for the jobo

1. Selecting a blast hole diameter -- There are no

prescribed calculation methods to determine a blast

hole diameter. In general, the hole size is determined

by experience, blasting procedures at nearby mines,

and a "rule-of-thumb" that the hole diameter in inches

should be in the range of theluLLe_depth in feet!!/

divided by a factor of 4 to /7. As an example, an"

estimated hole diameter for drilling an overburden

depth of 60, feet would be from 8 tO/k2 inches. Bit

sizes and the drill pipe diameters are shown in

Table 4-12.

2. Drilling pattern

See Figure 4-3 for various typical drilling patterns

and dimensional relationships.

77

Faca IE-SI~

O O O O O O

O O O O O

:/O O O O O

Square Pattern

S, = B, SI=1.4B 2 S2 = 2B 2

Face

B2o o o o o

o o o o o

o o o o o o Face

~52-t-5,--lJ

Offset Pattern

S2= BI 52 = 2B2 SI =1.4B 2

Face

O

O

Pattern

O

O

O

O

O

Face

O

O

~oEquilateral

Figure 4-3 -- Various basic blasthole drill patterns.

78

ao Burden

B = (Kb) (D)12

B = burden distance, in feet

Kb = rock hardness factor

25 hard rock

30 average hardness

........ ' •.J l· 35 soft rock

D = hole diameter in inches

NOTE: Two correction factors can be applied to the

rock hardness factor. The first is to adjust for

different rock densities. The adjustment factor is

considered to be equal to the cube root of the ratio------_._---._-..-

of the average in-place density (160 pcf) to that of

the specific material being blasted or:

0.33X = /160\

\cr-/

d = in-place density of rock to be blasted (see

Table 4-9)

79

JIl'

1,

TABLE 4-90 WEIGHTS OF VARIOUS ROCK MATERIALS

Solid Broken---------------- ----------------Pounds/ Cu.Ft./ Pounds/ Cu.Ft./

Material Density Cu. Ft. Ton Cu. Ft. Ton------------------- ------- ------- ------- ------- -------Caliche 2.0-2.4 140 14.3 78 25.6

Clay - natural bed 2.0-2.4 126 15.9 104 19.2- dry 1.6-2.0 115 17.4 93 21.5- wet 2.1-2.4 130 15.4 104 19.2

Clay & gravel - dry 1. 5-1. 9 104 19.2 89 22.5- wet 1.6-2.0 115 17.4 96 20.8

Coal-bituminous 1.2-1.5 85 23.5 61 32.9-lignite 1.3-1.6 90 22.2 65 30.8

Decomposed rock 1.9-2.8 142 14.1 107 18.7

Dolomite 2.8-2.9 180 11.1 129 15.6

Earth - dry packed 1.7-2.2 119 16.8 94 21.2- loam 1.3-1.7 96 20.8 78 25.6

Gypsum 2.3-3.3 175 11.4 125 16.0

Limestone 2.4-2.9 165 12.1 118 17.0

Sand - dry, loose 1.4-1.8 100 20.0 89 22.5- damp 1.7-2.1 119 16.8 106 18.9- wet 1.9-2.6 130 15.4 115 17.4

Sand & gravel - dry 1.7-2.2 120 16.7 107 18.7- wet 2.0-2.5 139 14.4 126 15.9

Sandstone 2.0-2.8 150 13.3 107 18.7

Shale 2.4-2.8 160 12.5 114 17.5

Siderite 3.0-3.9 215 9.3 154 13.0

Slate 2.5-2.8 165 12.1 118 17.0

Top soil 1.1-1.6 85 23.5 59 33.9

Trap rock 2.6-3.0 175 11.4 121 16.5

80

The second rnodifying factor is for the physical

properties of the explosive used. This factor is

equal to the cube root of the product of the density

and the detonating velocity squared of the explosive3

used (see Table 10-)) to that of the standard or:

2 0.33Y = j(Density) (Velocity) \

\ 187,000,000 j

The net correction factor = (X) (Y)

b. Spacing distance

s = (Ks) (B)

s = spacing, in feet.

Ks = spacing factor, 1 to 2, see Figure 4-3

B = burden, in feet

c. Maxirnurn hole depth

<2\'lIJ ¡) ::, )

H (Kh) (B),

= r :el

\

H = Hole depth, in feet -t.,c_ -r-. t ,'l •.

Kh = 1.5 to 4.0 (2.6 Íor average rock)

.! '..,t'V--.

B = Burden, in feet,/ ,

J :: _ r - J \.1 "S

d. Subgrade drilling (if the bottorn of the blast hole

ended at the top of the coal searn there would be no

subgrade drilling)

SB= (Kj)(B)

-..J::.. SB = Subgrade drilling depth,

Kj = 0.2 to 0.4 ,j

in f t . \,oíee [D ,Joro /

! !? '2í =- O' 7 rrv . .> (J

B = Burden, in feet

!""

,.,...v., \ e., (~-H -:: 1-1 - /

81

3. Drill penetration rate

P = (61 - 2810g P.C)/W\/RPM\10 \0/\300/

P = Penetration rate, feet per operating hour

rzc = Uniaxial compressive strength, in thousands

of P8I, see Table 4-10

WO = Weight per inch of bit diameter, in thousands

of pounds, see Table 4-11

RPM = Revolutions per minute of drill pipe

4. Maximum drill rotation horsepower

2.S 1.SHp = (K) (N) (D ) (W

Hp = Rotary horsepower

K = Formation constant (adapted from AIME, 8ME

Mining Engineering Handbook, 1973.)

Formation Type K-------------- -------------

-SVery soft ... 14 x 10

-S80ft ........ 12 x 10

-SMedium-soft . 10 x 10

-SMedium ...... 8 x 10

-SHard ........ 6 x 10

-SVery hard ... 4 x 10

N = Rotary speed, RPM

D = Drill bit diameter, in inches

W = Bit loading in thousands of pounds, see

Table 4-1182

TABLE 4-100 ROCK CLASSIFICATION AND TYPE OF BIT

RockClassification

Soft

Medium

Medium-hard

Hard

Very hard

Compressive RockStrengtho PSI

6,000 maximum

6,000 - 12,000

12,000 - 25,000

25,000 - 50,000

50,000 +

TypicalFormations

Shale .lvClay ú'r,·.,·.I/;..

Hardpan /idrd S-'{J$D;!(c: Ji e f.tJ')

Limestone ,:;..;¡ 2:,

Sandstone cf,Q'L;sc::­

Marble ;,;.: r.• ,,:> (

Hard limestonesoft graniteGneiss

DioriteHard granite

QuartziteTaconite

Bit Type

Milled-tooth,kerf, drag,scraper

Milled-tooth,kerf, diskCt(C.:)/~l'l¡r:.t

Tungsten car­bide button,roller orkerf

Tungsten car­bide button

Tungsten car­bide button

,-TABLE 4-11.

BIT WEIGHT AS A FUNCTION OF ROCK STRENGTH AND BIT SIZE

Rock StrengthviiO

Weight perin. of Dia.

lbs.

vJRecommended Bit Loading for Bit

Size Indicated - Lb.4 - 6 in. 6 - 9 in. 9 - 12 in.

Very soft formationsi 1,000- 4,000- 6,000- 9,000-overburden, softshales, limestone andevaporites 4,000 24,000 36,000 48,000

Medium formationsi 3,000- 12,000- 18,000- 27,000-limestones, dolomite,and sandstones 5,000 30,000 45,000 60,000

Hard and very hard 4,000- 16,000- 24,000- 36,000-formationsi basalt,granite, quartzite,taconite 8,000 40,000* 60,000* 100,000

* Maximum weight for largest bit size indicated.

Source: AIME, SME Mining Engineers Handbook, 1973.

83

1 1

i'!

l'likJ

5. Air flushing requirements

a. Air velocity required to flush hole of cuttings

0.6V = (54600) (P) (Z )

P + 62.4

v = Maximum air velocity, in feet per minute

P = Rock density, in pounds per cubic foot, see

Table 4-1 or Table 4-9

Z = Chip diameter produced, in feet

b. Air quantity required to flush hole of cuttings

2 2Q = V(D - d }

183.3

Q = Required air quantity, in cubic feet per minute

v = Maximum air velocity, in feet per minute

D = Hole diameter, in inches

d = Drill pipe, outside diameter in inches

c. Check the results with Table 4-12. The calculated

values should be in the same range.

84

TABLE 4-12

AIR VOlUMES REQUIRED FDR DRILLIN6

15,000 Ft. and 7,000 Ft. per minute anoualar velocityl

------------ ------------ -------------- --------------. . .Hale Dia.- Pipe O.D.- 5000 FPN 7000 FPMinthes IDl loches Id) free aír (VI free air IV)

------------1------------1--------------.--------------

Hale dia.- Pipe dia.- 5000 FfM 7000 FPMioches (D) ioches Id) free air (VI free air IV)

18521431878630

2331193614881222798

2888263519111317

2749232617791526

1964166212111090

13231022627450

166513831063873570

206318821365941

4 1125 1126 5/877 3/4

77 3/48 5/89

77 3/48 5/89

8 5/89

1010 3/4

9 7/8

12 1/4

11892742596

557458305162

542374221

687535392

102571B535

3872b7158

398327218116

4913B2280

732513382

637530426

2 7/83 1124

2 3/82 7183 1/24

2 3182 7/83112

2 71831124

3 1124 1/25

6 114

4 1/4

5 118

4 112

5 5/B

------------ ------~----- -------------- --------------

él 3/4

7 3/8

7 718

311244 11255112

3 1/24 1125 112

3 1124 1125 1126 114b 5/87

908805690560408

1150932658

13571138867625493355

127111279bb784571

16101305921

190015031214875690497

13 3/4

15

17112

1010 3/4

1010 3/41213

131416

24292004

3409298522091527

374330071370

34002806

4772417930932138

524042101918

,ii)-.,i'1:

85

6. Summary of drill selection data

- Hole diameter

- Drill pipe diameter

inches

inches

- Pull down force

- Bailing airvelocity/. l' ó-r .... (. (A !-."'-

- Air volume (r-o, ~\c.I)

- Rotational horsepower

- Type bit

- Type stabilizer

----o pounds

feet/minute

cubic feet/minute

horsepower

7. Drill cycle time per drill hole

Drilling Ave. hole depth-ft.Penetration rate-fpm

Adding pipe

Pulling pipe, breaking, and hoisting

- Moving' between holes

Leveling drill

mino

0.2 to 0.8 mino

0.2 to 1.0 mino

1.0 to 5.0 mino

0.4 to 0.7 mino

Total cycle time

8. Drill size calculations

a. Work parameters

- Scheduled hours per day (8)

- Mechanical and electrical

mino

availability (A), generally 50 to 80%

- Utilization (U), between 80 to 95%

- Job efficiency (J), 90% +

- Net operating hours per shift (OH)

OH = (S) (A) (U) (J)

86

b. Calculations

Shot pattern, burden x spacing in feet

~ Cubic yards of material shot per foot

of hale depth (CY/FT.)

- Average hole depth, in feet

- Total cubic yards of materialbroken per hole

Total CY = (CY/Ft.) (Hale depth)

- Cubic yards requiring blasting per year (Y) BCY/Yr.

\(Y - -;-'l/:!'- e... t J í

- Number of holes to be drilled per day

Holes per day = Y-,.(----V-=-)..,....(S---D---M=D~)

Y = the required yardage to be blasted per year

v = the bank cubic yards of material to blasted

per year

SD = scheduled operating days per year

MD = major moving days in which no drilling will

take place

- Number of holes drilled per shift by one drill

Holes/Shift/Drill = Drilling hours per shiftDrill cycle time

Drill shifts required per day

Drill shifts/Day = Holes required per dayHoles/Shift/Drill

- Number of drills required

Drill(s) required = Drill shifts/DayA

A = mechanical and electrical availability

87

c. Drill selection

- A drill can be selected from the manufacture's

specifications for a particular drill modelo

The drill selected should fit the working

parameters and the general working conditions.

This includes the type of travel surface, the

the frequency and length of major moves, the

variation of the material being drilled, and the

skill of the drillers. Once the drill has been

selected, the calculations should be run again

to see if the number of drills required remains

the same.

88