Question

Statement (I): In close-range works of excavation, power shovel is suitable.

Statement (II): Power shovel has greater rigidity and gives greater output than draglines.
1. Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)
2. Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)
3. Statement (I) is true but Statement (II) is false
4. Statement (I) is false but Statement (II) is true

Answer 1

Correct Answer - Option 2 : Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)

Concept:

Power Shovel:

Power shovels are used predominantly for hard digging above track level and loading units.

They are capable of excavating all classes of earth, except the solid rock without prior loosening.

The size of a shovel is indicated by the size of bucket of dipper, expressed in cubic meters and varies from 0.375 m³ to 5 m³.

Output of Power Shovel

• The output of power shovel is expressed in cubic meter per hour based on bank-measure volume.
• If no allowance is made for any lost time, then

\(Output\;of\;shovel = Bank\;measure\;capacity\;of\;dipper \times \frac{{3600}}{{Cycle\;time\;in\;seconds}}\left( {{m^3}/hr} \right)\;\)

In general cases,

\(Output\;of\;shovel = \frac{{Loose\;volume\;of\;dipper}}{{1 + swell\;friction}} \times \frac{{actual\;time\;in\;sec./hr}}{{cycle\;time\;in\;sec.}} \times efficiency\) 

Expressed in cubic meter/hr.

Dragline:

The basic character of this machine is dragging the bucket against the material to be dug, it is called as dragline.

A dragline has distinct advantages compared with a power shovel because of its long light boom.

Advantages of dragline over power shovel:

1. A dragline usually does not have to go into a pit or hole for excavating the earth. It may operate on natural firm ground. Therefore it is more useful when the earth is removed from a ditch, canal or pit containing water.

2. When the excavated earth is to be deposited on nearby banks or dams, it is better to use dragline with a long boom enough to dispose of the earth in one operation, eliminating the need of hauling units thereby reducing the cost of handling the earth.

3. A dragline is excellent for excavating trenches without shoring.

Disadvantages of dragline over power shovel-

1. As compared to a power shovel, the output of the dragline in terms of excavation of earth is about 75 to 80% for the same size of bucket capacity.