1. Drilling Rock and Earth
Chapter 12
Drilling Rock and Earth
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2. DRILLING ROCK & EARTH

3. DRILLING ROCK
When work on the Hoosac Tunnel first began in the 1850’s hand drills were still the primary method used to create holes for loading explosives in hard rock. Charles Burleigh of Fitchburg, Massachusetts developed the first truly successful pneumatic drill and in 1866 it was first used in the Hoosac.

4. BURLEIGH DRILL Working in the Hoosac Tunnel.
Courtesy of the North Adams Public Library

5. DRILLING ROCK

6. CONSTRUCTION DRILLING
Blast holes for removal of rock, in a construction excavation or for quarrying.

7. CONSTRUCTION DRILLING
Rock anchor/bolts in excavations and tunnels

8. CONSTRUCTION DRILLING
Tunnels

9. CONSTRUCTION DRILLING
Foundation
grouting

10. DRILLING PRODUCTION ESTIMATE
To begin a drilling production estimate it is first necessary to make an assumption about the type of equipment that will be used. Tables 12.7 & provide information to guide that first decision.

11. DRILLING PRODUCTION ESTIMATE
The final equipment decision should only be made after test drilling the formation. Test drilling should help to quantify:
Penetration rate
Drilling method
Bit size / Bit type

12. Penetration rate is a function of: The rock The drilling method
The size & type of bit

13. THE ROCK Hardness Texture Tenacity Formation
The rock properties which effect penetration rate are:
Hardness
Texture
Tenacity
Formation

14. HARDNESS
A scientific definition of hardness is a measure of a material's resistance to localized plastic deformation.
It is measured by the MOH scale (Friedrich Mohs).

15. HARDNESS
The Moh hardness classifications are based on the resistance of a smooth surface to abrasionthe ability of one mineral to scratch another.

16. HARDNESS
Moh’s scale for rock hardness

17. HARDNESS
Hardness affects drilling speed.

18. TEXTURE Texture is the grain structure of the rock.
A loose grained structure
(porous, cavities) drills fast.
Grains large enough to be seen
individually (granite) will drill
medium.
Fine-grained rocks drill slow.

19. TENACITY
Describes how the rock
breaks when struck.

20. TENACITY Shatters - into small pieces from a light blow
Brittle - breaks easily with a light blow
Shaving - when shaved off in pieces they break easily
Strong - resists breaking when hit hard
Malleable - flattens instead of breaking

21. TENACITY Shatters - fast Brittle - fast to medium Shaving - medium
Characteristic Drills
Shatters - fast
Brittle fast to medium
Shaving - medium
Strong slow to medium
Malleable - slow

22. Formation describes how the rock mass is structured.
Solid mass - drills fast
Horizontal strata (layers) -
drills fast to medium
Dipping planes - drill slow
to medium

23. DRILLING METHOD ROTARY
Rotary drilling uses high push-down pressure on the bit and rotation to grind the rock. Compressed air, water, or drilling mud carry the cutting out of the hole.

24. DRILLING METHOD ROTARY
Feed pressure and rotation rate control drilling speed.
Soft rock - use lower feed pressure and faster rotation.
Hard rock - use high feed pressure and slower rotation.

25. ROTARY DRILL
These drills are suitable for drilling soft to medium rock, such as hard dolomite and limestone, but are not suitable for drilling the harder igneous rocks.

26. DRILLING METHOD ROTARY-PERCUSSION
The piston provides striking energy to the rock through
the drill steel. There is rotation so the bit strikes fresh rock with each blow.

27. ROTARY PERCUSSION
Drill steel

28. DRILLING METHOD
ROTARY-PERCUSSION
Compressed air or water is used to flush the drill cuttings from the hole.
Drilling penetration (speed) decreases with depth.

29. CUTTINGS
Flush the cuttings from the hole.

30. DRILLING METHOD DOWN HOLE (DH)
The DH drill provides striking energy directly to the bit. There is rotation so
the bit strikes fresh rock with each blow.

31. DRILLING METHOD
Down Hole Drill maintains constant penetration rate at all depths.
Hammer mechanism

32. DRILLING METHOD DOWN HOLE
Compressed air conducted through the drill steel is used to flush the drill cuttings from the hole.
Performance will not decrease as depth increases.

33. BIT SIZE

34. BIT TYPE
Insert bit
Button bit

35. CARBIDE INSERT BITS
Susceptibility to breakage increases with hardness. However, abrasion resistance also increases.
If excess insert breakage occurs, a softer grade should be tried.

36. BUTTON BITS
Button bits can yield faster penetration rates in a wide range of drilling applications.
Fewer bit changes are required.
Most button bits are run to destruction and never reconditioned.

37. PRODUCTION ESTIMATE

38. STEP 1 DEPTH OF HOLE
When drilling for blasting it is often necessary to subdrill the hole below the planned final grade elevation.
SUBDRILLING
FIG 12.3, page 339

39. STEP 1 DEPTH OF HOLE
DRILL DEPTH (ft) =
Height of face
+ subdrilling

40. STEP 2 PENETRATION RATE
The penetration rate will be an average rate (ft/min) from the field drilling tests based of specific equipment, bit type and bit size.

41. STEP 3 DRILLING TIME
DRILLING TIME (min) =

42. STEP 4 CHANGE STEEL
Steel

43. STEP 4 CHANGE STEEL
Shank (Striking Bar)
Steel
Coupling
Bit

44. Steel STEP 4 CHANGE STEEL
The length of steel for rotary drills varies considerably, in the range of 20 to 60 ft. These rigs have mechanized steel handling.

45. Steel STEP 4 CHANGE STEEL
The time to change steel is approximately constant for all diameters, but varies with length.

46. STEP 5 BLOW HOLE
After completing the drilling it is necessary to clean out all cutting from the hole. The time to clean out will be dependent on the depth of hole.

47. STEP 6 MOVE TO NEXT HOLE
Travel time depends on distance, terrain, and the type of drill mount. A discussion of travel speed is given on page 353.

48. STEP 6 MOVE
May have to lower the mast

49. STEP 6 MOVE TO NEXT HOLE
If drilling for blasting operations distance will be set by the blasting pattern. An 8 X 10 pattern means 8 ft between rows and a 10 ft spacing between holes. Therefore, the travel distance moving along the row is only 10 ft.

50. STEP 6 MOVE TO NEXT HOLE
The travel time may not be controlled by the drill.

51. STEP 7 ALIGN STEEL
Once over the hole location it is necessary to position the mast or steel for the proper angle of attack. This is usually vertically but not always.

52. STEP 7 ALIGN STEEL Time to align is discussed on page 353.
Outrigger for leveling

53. STEP 8 CHANGE BIT
Bits, shanks, couplings and steel are all high wear items that must be replaced frequently.

54. STEP 8 CHANGE BIT
The time allowance for replacement is a factor of both the actual time to remove and replace, and the frequency of such changes. Table provides frequency information.

55. STEP 8 CHANGE BIT CHANGE BIT TIME (min) =
If you do not have any company and rock specific data, average life of bit data is provided in Table

56. STEP 9 TOTAL TIME Total time (min) = Drill (min) +
Change steel (min) +
Blow hole (min) +
Move (min) +
Align Steel (min) +
Change bit (min)

57. STEP 10 OPERATING RATE
OPERATING RATE =

58. STEP 11 EFFICIENCY
Experienced drillers working under good conditions should have a 50 min-hr efficiency on a production job. Under sporadic drilling conditions efficiency may go down to 40 min-hr.

59. STEP 11 EFFICIENCY
Terrain is a critical factor impacting efficiency.

60. STEP 12 PRODUCTION
HOURLY
PRODUCTION (ft/hr) =
Efficiency (min/hr) *
Operating rate (ft/min)

61. Drilling Through Soil

62. Why Do We Drill Through Soil?
To obtain samples
Locate good locations for mining
Install piles
Wells
Ventilation shafts

63. Common Methods Hollow Stem Auger Solid Stem Auger
Rotary mud/ wash drilling
Percussion Drilling
Coring

64. Underreaming

66. DRILLING EARTH
When drilling earth with continuous fight auger drills the cuttings are carried up on the auger, so the hole is cleared when the auger is removed.

67. DRILLING EARTH
Some auger drills are not continuous fight, the auger must be raised every few feet and the cuttings discharged.