39. Assume that the P&H 250XPC drill is used to drill a 9-7/8" diameter hole. Assume that

the minimum bailing velocity desired is 5000 ft/min. Select the nozzles and the drill stem. What is the final configuration?

40. For problem 39, assume that the minimum desired bailing velocity is 7000 ft/min. Select the drill stem and the nozzles.

41. Use the nomograph in Figure 10.39 to determine the air velocity for a 10-5/8" diameter bit, a 8-5/8" pipe size and 1400 cfm. Is this a good combination? Why or why not?

42. Use the cost calculation formula to evaluate the situation where by increasing the rotary speed one can increase the penetration rate by 30% but the bit life will decrease by 50%. Is this a good tradeoff?

43. At a large iron mine, 18 drill shifts are scheduled daily on a two shift basis to produce 140,000 tons of ore and waste per day.

a. If the bench height is 35 ft, the rock has a specific gravity of 3.0, the pattern is 22 ft x 22 ft, the hole diameter is 9", and the subdrilling is 6 ft, how many feet of hole are drilled per drill shift.

b. It is proposed to switch from ANFO to an emulsion explosive. How might this impact the drilling?

44. The production at a mine is 28,000 tons of ore per day and 22,000 tons of waste.

The mine works 7 days per week. Atlas Copco Pit Viper drills are used to drill 9" diameter holes to a depth of 39 ft. The bench height is 33 ft. The burden is 20 ft and the spacing is 22 ft. The specific gravity of the rock is 2.56 and the stemming length is 14 ft. If the drill can drill 450 ft of hole per shift, how many drill shifts per day (assuming that drilling is also done 7 days/week) are required to meet production requirements? Which Pit Viper model might be chosen?

45. At an open pit mine it is planned to use blast holes 12-1/4" in diameter. To do this, the mine is considering to buy one of the drills in the Sandvik rotary drill product fine. Go to their website and select an appropriate model. The rock has an unconfined compressive strength of 18,000 psi. Choose an appropriate Sandvik tricone insert bit for this application. Assume that the rock is of medium density

a. Recommend a pulldown weight and a rotation rate for the bit. What penetration rate would be expected?

b. Select the nozzles for the bit

c. Select the drill pipe

d. What is the expected bailing velocity?

e. Assume that you would like to increase the penetration rate by 20%. Would it be better to increase the weight on the bit or the rotation rate? Explain.

46. Repeat problem 45 using a Caterpillar/Bucyrus-Erie drill and Adas Copco Secoroc tricone bits

47. Repeat problem 45 using a P&H drill and Varel International tricone bits.

48. At a limestone mine, the rotary drills used to drill the 6" diameter holes rotate at 110 rpm. The pulldown capacity of the drilling machine is 35,000 lbs. The recommended loading of the bit is 4000 lbs/in. The hole length is 45 ft. There is no subdrilling due to the presence of a parting plane. The upper 20 ft of the formation is quite soft due to weathering (unconfined compressive strength = 10,000 psi). The lower part of the formation has a strength of 15,000 psi. The drill can drill 25 ft in a single pass but carries 4 pieces of drill steel and has automated rod handling. The time to add or subtract a piece of steel from the string is 1 minute. The rod hoisting speed is 100 ft/minute. The time between holes is 10 minutes (moving, setup, etc).

a. How long does it take to drill one hole?

b. Assume that the drill is scheduled 1-8 hr. shift/day, 5 days/week and 50 weeks/year.

The availability during the scheduled time is 90%, the utilization is 80% and the operating efficiency is 85%. How many hours is the drill string actually rotating (making hole)/year?

c. Assuming a rock density of 2.49 g/cm3, how many tons will the drill block out/year? In other words, "What is the drill production/year expressed in tons?"

49. A rotary blasthole drill has been selected for a proposed mining operation. The following information applies: o rock compressive strength = 8000 psi o drill rotation rate = 90 rpm o bit type = insert type (medium rock) o bit cost: 12-1/4" bit = $8000 15" bit = $16000 o bit life = 4000 ft for both bits o drill operating cost = $600/operating hour a rock specific gravity = 2.65 a bench height = 40'

a. Calculate the following for both hole diameters:

- recommended maximum bit weight (lbs/in)

- recommended maximum bit weight (lbs)

- expected penetration rate (ft/hr) at maximum bit weight

- hole length

- blast pattern (assume S = 1.15 B)

- bit cost/hole ($)

- drill operating cost/hole ($)

- total drilling cost/hole ($)

- drilling cost/ton ($/ton)

b. Based on your answer to part (a), which hole size would you choose?

50. The rotary drills on a mining property use 9" diameter medium formation tungsten carbide bits. The bench height is 35 ft. In ore, the blasthole pattern is 21 ft x 21 ft. In waste, the pattern is 24 ft x 24 ft. The explosive is ANFO. The ore in place density is 4300 lbs/yd3. In waste, the density is 3800 lbs/yd3. Assume that the Ash-based formulas have been used for designing the blasting patterns. Ore production at the mine is 18000 tons per day. The stripping ratio is 2.8:1. The mine works

6 days per week and 2 shifts per day. Drill productivity is 520 ft/shift in both ore and waste.

a. How many drill shifts are required per week to meet the ore tonnage?

b. How many drill shifts per week are required to meet the waste tonnage?

c. How many drills should the property have? Explain.

51. A mine is using 9-7/8" diameter medium formation tungsten carbide rotary bits. Production is 75,000 tons/day of waste and 40,000 tons/day of ore. The blast pattern is such that they achieve 30 tons/ft of drilling. The hole production per drill per shift is 900 ft.

The rock density is 2.65 g/cm3. Hole spacing is 1.15 B. The bench height is 30 ft. ANFO is used.

a. If the rock has a compressive strength of 25,000 psi, the drill rotation rate is 85 rpm and the pulldown applied is that recommended for the bit, what would be the estimated penetration rate?

b. What percentage of the 8-hr shift is actually spent with the bit penetrating the rock?

c. How many feet of drill hole are required per day?

d. How many drill shifts are required per day to maintain production?

e. If the drill pipe has a diameter of 8-5/8" and the air velocity needed to remove the cuttings is 6000 ft/min, what size compressor would be required?

52. Using the Smith-Gruner bit selection chart, what would be the:

a. Weight per inch of bit diameter

b. Rotation rate

c. Pulldown recommended for a 12-1/4" diameter bit in rock having a compressive strength of 35,000psi?

53. Using the formula for penetration rate suggested by Bauer (1971), together with the values obtained in Problem 52, compare the estimated penetration rates.

54. Data for rotary drills from the 2011 edition of the Cost Reference Guide has been included in Chapter 2. Summarize the data presented for drills with 125,000 lbs of pulldown.

Briefly describe the meaning of the different cost categories (how calculated, what's included).

55. Using the data in Chapter 2, summarize the hourly

- Ownership

- overhaul

- field repair and fuel expenses for a rotary drill capable of drilling a 12-1/4 inch diameter hole. What are the total operating costs/hour and the total hourly costs?

56. The drill in problem 55 is used to drill blast holes 12-1/4" in diameter and 50 ft in length in one pass. The move time from hole to hole is 5 minutes, leveling requires 45 seconds, and collaring requires 30 seconds. The average penetration rate is 70 ft/hour.

Hoist speed is 80ft/min. If the drill is operated 6 hours per shift, how many holes could be drilled in a shift?

57. If the driller in problem 56 makes $24.00/hour (including fringes), the life of the bit is 6000 feet, and the life of the drill pipe is 50,000 feet, what would be the operating cost per foot of hole? If the hole spacing is 30 ft and the burden is 25 ft, the bench height is 40 ft and the specific gravity of the rock is 2.8, what would be the drilling cost (operating) per ton?

58. Tests indicate that the required bailing velocity for the material drilled in problem 56 is 5500ft/min. The drill is equipped with an air compressor having a capacity of 2200

CFM. What sizes of drill pipe could be used with this bit? What size would you recommend? If the compressors provide air at 65 psi and the fine losses are 10 psi, what are the appropriate nozzle sizes to be used with the bit?

SHOVELS

21. Define the following terms:

- Bank weight

- Loose weight

- Swell

- Percent swell

- Swell factor

- Fillability

- Fill factor

22. Can you think of a practical way to get a handle on the fillability factor?

23. Often unit operations are considered as separate entities or even "kingdoms." But there is a very clear connection between the fragmentation achieved and the efficiency of the loading operation. How would one optimize the process, that is, when is it of interest to spend extra resources on the fragmentation?

24. Material has been classified as easy digging, medium digging, medium-hard digging and hard digging. How is this distinction being made? How would you do it?

25. A curve relating the optimum cutting height to the dipper capacity has been prepared based on earlier models of loading machines. Does this curve also represent the new models presented in this chapter?

26. Check the old rule-of-thumb that for good cutting the dipper should fill in a cutting height of 2 to 3 dipper lengths, i.e. compare the dipper stick pivot position to the approximate dipper length.

27. Carefully review and understand the calculations and input data leading to the estimation of production per shift.

28. An old rule-of-thumb is that during an 8-hr shift a shovel should load 1000 short tons/cubic yard of dipper capacity. Hence for the P&H 4100XPC shovel equipped with an 82 yd3 dipper, one would expect it to load 82,000 tons over an 8-hr shift. Peruse the mining literature and/or check with mining operations to determine the applicability

today.

29. Wheel loaders are often used both as primary and secondary excavators in mining operations today. One problem is that they do not have the same digging height capability as rope shovels and thus have problems in scaling bench faces. How is this to be overcome?

30. If one applies the rule that a shovel should fill a truck to capacity in 3 to 5 swings, what size trucks should be assigned to the P&H line of shovels?

31. How is shovel capacity influenced by the number of trucks assigned to the shovel, the loading time and the haul time?

TRUCKS