Opencast Mining MCQs Questions & Answers | Mining Engineering

The correct answer is option A, Burden.

Primary blasting is a technique used in mining and construction to break rock or concrete using explosives. The degree of fragmentation refers to the size and distribution of the pieces of rock or concrete after blasting.

The burden is the distance between the explosive charge and the free face of the rock or concrete. By increasing the burden, the explosive energy is spread over a larger area, which can lead to a decrease in fragmentation. On the other hand, decreasing the burden concentrates the energy in a smaller area, resulting in increased fragmentation.

Therefore, the correct way to increase the degree of fragmentation in primary blasting is to increase the special charge (the amount of explosive per unit length of the borehole) and decrease the burden.

Option B, Spacing, refers to the distance between the boreholes and has an impact on the overall effectiveness of the blast, but not directly on the fragmentation.

Option C, Height, refers to the depth of the borehole and has a minimal impact on fragmentation.

Option D, Density, is not directly related to fragmentation, but it may affect the strength of the rock or concrete being blasted.

The injury rate per 1000 person employed can be calculated using the following formula:

Injury rate = (Total number of injuries / Total number of persons employed) x 1000

Using the values given in the question, we can calculate the injury rate as follows:

Injury rate = (16 / 800) x 1000 = 20

Therefore, the correct answer is option C, 20.

The injury rate per 1000 person employed is a common metric used in occupational health and safety to measure the frequency of workplace injuries. The DGMS (Directorate General of Mines Safety) is a regulatory agency in India that sets safety standards and guidelines for the mining industry. As per DGMS norms, an injury rate of 20 or less is considered acceptable for opencast mines.

The open-cast mining method that eliminates drilling and blasting is the surface miner.

Surface miners are machines that use a cutting drum to extract rock or minerals from the surface of the earth. They can selectively extract material without the need for drilling and blasting, which can reduce the environmental impact and improve safety.

Option A, dozer, is a type of earthmoving equipment used for pushing soil, rocks, or other materials. Dozers are not typically used for extraction of minerals or rock.

Option B, shovel, is a type of excavation equipment that uses a bucket to dig and load material. Shovels may require drilling and blasting to extract rock or minerals from the earth.

Option C, dragline, is a large excavation machine that uses a bucket attached to a cable to dig and remove material. Draglines are often used in strip mining operations and may require drilling and blasting to extract rock or minerals from the earth.

Therefore, the correct answer is option D, surface miner.