Page 102 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

2.52 THE WORK

Body capacity should be indicated by a printed plate. It is usually in yards, but may be in cubic
feet. It ordinarily does not include sideboards, or other removable extensions which increase its
volume. The extra load between added boards may be found by the proportion between the heights
of the body wall and of the board. For example, if a straight-sided body with 4-foot sides holds 8
yards, a 1-foot sideboard added on each side will increase capacity by one-fourth, or 2 yards.
If there is no plate, size can be determined by measurement of the inside length, width, and
height, usually in feet and fractions of feet. These are multiplied together, to obtain cubic feet that
are divided by 27 to get cubic yards.
Heaps. The heap on top of a load can be measured only approximately because of its shape. It
is usually calculated on the basis of an assumed even slope of the material. The slopes from oppo-
site sides are continued until they meet. In general, the volume of a heap is determined by the
slope of the material and the area of the body. A steep slope and a wide body give it maximum
yardage.
According to S.A.E. (Society of Automotive Engineers) standards, a heap is figured on a basis
of slopes of 3 to 1 (3 horizontal feet to each foot of rise) inward from the top of the body walls.
This covers most conditions, but some materials will stack up much higher, particularly if the trip
is short and smooth, as in a dragline bucket, which a few will slide or flow to flatter slopes as the
container is moved or shaken.
Truck Bodies. Bodies such as are mounted on highway trucks have a rectangular floor and verti-
cal body walls, with provision for increasing the height of sidewalls by adding wood or metal exten-
sions. The rear wall (tailgate) is hinged to dump the load when the body is raised at the front. Most
of such bodies are 7 feet wide inside. Some standard heights and capacities are shown in Fig. 2.45.
Bodies of off-the-road trucks are difficult to measure, as they may slope outward from bottom to
top and the sloped fixed tailboard ends at a much lower level than the body sides. Ratings general-
ly assume a load struck off by a plank resting on the two sides and moved from front to rear. In the
absence of indications to the contrary, manufacturers’ ratings for struck load may be accepted.
1
The more important rating for off-the-road trucks is capacity in tons. This is usually 1 ⁄ 2 times
the rating in yards. The trucks are designed to carry a certain payload, and the body is designed

Length, Height, Capacity,
inside, in sides in cubic
feet inches yards
9 15-1/2 3
20-7/8 4
25-3/4 5
9-1/2 14-3/8 3
19-1/2 4
24-1/2 5
10 18-3/4 4
23 5
10-1/2 20-1/8 4-1/2
22-1/4 5
11 20-7/8 5
25 6
12 23 6
31 8
38-3/4 10
14 33-3/8 10
FIGURE 2.45 Capacity of standard truck bodies.