Introduction to Mining Engineering MCQs Questions & Answers | Mining Engineering

Definition of Terms:
Bucket Capacity: The maximum volume of material a shovel's bucket can hold.
Loading Cycle Time: The time taken to complete one loading cycle (digging, swinging, dumping).
Bucket Fill Ratio: The ratio of the actual volume of material loaded in a bucket to its maximum capacity. It's always less than 1 because the bucket is rarely completely full.
Rock Looseness Factor: The ratio of the volume of broken rock *in situ* (in its natural position) to the volume of the same rock after excavation and loading. A factor greater than 1 indicates that the excavated volume is larger than the in-situ volume due to fracturing and loosening during blasting.
Shovel Working Time Utilization Factor: The fraction of the total time the shovel is actually working (loading) versus being idle (maintenance, moving, etc.).

Explanation:
First, calculate the effective bucket volume considering the fill ratio:
Effective Bucket Volume = Bucket Capacity × Bucket Fill Ratio = 5 m³ × 0.8 = 4 m³
Next, determine the volume of *in situ* ore loaded per cycle considering the rock looseness factor:
In-situ Volume per Cycle = Effective Bucket Volume / Rock Looseness Factor = 4 m³ / 1.5 ≈ 2.67 m³
Now, account for the shovel's working time utilization factor to find the actual volume loaded per cycle:
Actual Volume per Cycle = In-situ Volume per Cycle × Shovel Working Time Utilization Factor = 2.67 m³ × 0.6 ≈ 1.6 m³
Finally, calculate the hourly output by considering the loading cycle time:
Hourly Output = (Actual Volume per Cycle / Loading Cycle Time) × 3600 seconds/hour = (1.6 m³ / 60 seconds) × 3600 seconds/hour = 96 m³/hr

Therefore, the correct answer is Option C: 96
The other options are incorrect because they don't accurately account for all the factors affecting the shovel's productivity (fill ratio, looseness factor, and utilization factor).

Definition: Incombustible Dust
Incombustible dust refers to dust that will not burn or support combustion. It's used in underground mines, particularly coal mines, to suppress coal dust explosions.

Definition: Free Silica
Free silica is crystalline silica (SiO2) that exists in a form that is not chemically bound to other elements. It's a common component of many rocks and minerals, including coal. Breathing in free silica dust can cause serious lung diseases like silicosis.

Correct Answer: Option A (5%)
Regulations for underground coal mines strictly limit the percentage of free silica in incombustible dust used for dust suppression. This is because, while the dust itself is incombustible, the presence of free silica poses a significant health risk to miners. A limit of 5% free silica is a common standard to minimize the risk of silicosis while still providing effective dust suppression. Higher percentages significantly increase the risk of respiratory illnesses.

Why other options are incorrect:
Options B, C, and D (10%, 15%, and 20%) represent significantly higher percentages of free silica. These higher percentages would greatly increase the risk of silicosis and other respiratory illnesses for miners, making them unacceptable according to safety regulations. The lower the free silica content, the safer the dust is for use in underground coal mines.

Goaf Definition:
A goaf is a void or cavity created underground after the extraction of minerals, such as coal, in a Bord and Pillar or Longwall mining method.

Correct Answer: A: Coal has been extracted but now not a working place
Once the coal is extracted in a Bord and Pillar or Longwall system, the area becomes a goaf. It's no longer actively used for mining operations because the coal has already been removed. The goaf is essentially a large, empty space left behind. Safety measures are often implemented to manage the goaf, as it can present risks like roof collapse or gas accumulation.

Why other options are incorrect:
B: Coal has been extracted but still a working place - This is incorrect. A goaf, by definition, is the area where the coal has already been extracted, and thus it is no longer a working place.
C: Coal is about to be extracted - This describes an area ready for mining, not a goaf. A goaf is the space *after* extraction.
D: People has lawful access - While access to a goaf might be permitted under specific circumstances (e.g., for inspections or maintenance), it is not the defining characteristic of a goaf. The primary characteristic is the void created by the removal of extracted material.