Lesson l/Learning Event 2
generally durable. Because of the variable nature of the types of grains and cement, each
deposit must be evaluated individually.
Limestone. Limestone is widely used for road surfacing, in concrete, and for lime.
Gneiss. Most varieties of gneiss have good strength and durability and make good road
Quartzite. Quartzite is both hard and durable. Due to these qualities, it is an excellent rock for
construction, although it is often difficult to quarry.
Marble. The texture and color of marble make it very desirable for dimension stone, and it can
be used for base course or aggregate material.
QUALITY OF MATERIAL
Estimation of Quality. The quantity of material available at a site must be carefully estimated to include
margin of safety. Unforeseen difficulties may arise which can reduce the estimated output. For
example, excessive seepage may develop or material quality may decrease. All other factors being
equal, it is better to select a site containing more material than is required, rather than one which just
meets immediate requirements.
The quantity of quarry rock available is estimated by multiplying the average depth of the quarry face by
the working area:
Qt (volume) = depth x working area
Then subtract waste rock and overburden to get a final estimate of volume. The following formula may
Qp = Qt [1 - (W/100)]
Qp = volume of product available
Qt = total quantity of available material in deposit
W = percent of spoil or by-product expected after processing
Weight-Volume Relationships. Earth materials occupy a greater volume (loose volume) when they are
loosened and removed from the ground. Bank rock or volume refers to earth materials naturally in
place. The bulk volume of excavated material decreases when compacted. Where possible, the weight
and volume relationships of materials should be measured during site investigation in order to accurately
determine your requirements and potential yield. Where hasty estimates must be made, the values given
in Table 3 may be used.
For example, you are managing a basalt quarry and need to estimate its yield. The average depth of the
face is 30 feet. The quarry has a usable working area of 90,000 square yards. You know that about 10
percent of the rock is weathered and will be wasted. Determine how many cubic yards of loosened blast
rock you can obtain.