Lesson 2/Learning Event 2
Final Dimensions. The final quarry floor is the ultimate bottom of the quarry. It is determined by the
geology, rock requirements, and area restrictions. This ultimate bottom may be achieved in several lifts
or working floors in the case of a multiple bench quarry. For example, you determine that the rock must
be excavated to a depth of 60 feet (18 meters) over a given area to obtain the required volume of rock.
You also determine that the optimum bench height is 20 feet (6 meters). Therefore, the quarry floor will
be exposed at the third lift. Geologic factors which may limit the depth of a quarry include the depth of
the water table and the thickness of usable material. It may be possible to work below the water table in
some cases, but plans must be made to control the amount of water in the quarry throughout the
operation.
Area restrictions as a limiting factor are particularly applicable to subsurface quarries. In planning the
layout of a quarry, particularly a subsurface quarry, the minimum length of a uniformly sloping access
road will be equal to the depth of a quarry divided by the grade limitation of the loaded hauling
equipment. Ten percent is a good figure for trucks. For example, if trucks are used to haul from a
quarry 60 feet (18 meters) deep, the approximate minimum length of the haul road required to leave the
pit will be:
60 feet
= 600 feet (approximately 180 meters)
0.10 grade
After the levels of the quarry floor have been determined, the surface dimensions of the quarry are
determined based on the total rock volume required. The relationship is simply:
total rock volume required
Total Bench (Surface) Area Required
=
average bench height
For example, a bench 30 feet (10 yards) high is used and the total volume of rock to be quarried is
1,500,000 cubic yards. The bench surface required is:
1,500,000 cubic yards
= 150,000 square yards
10 yards
If the quarry is to be worked as a hillside quarry, you could obtain the necessary area by adding the
volume of each working level, as follows:
Top Level...................................................................
10,000 square yards
30-foot Level..............................................................
40000 square yards
60-foot Level.............................................................. 100,000 square yards
For a subsurface quarry, you could use a surface area of 150,000 square yards with one working level or
75,000 yards with two working levels and so on. When you determine the surface dimensions of a
quarry, you should also consider:
the optimum length and width for minimum overburden removal
traffic patterns and access road requirements
boundary limitations
proximity of inhabited dwellings or structures subject to blast damage
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