Chapter 18 Draglines and Clamshells (pdf) - HDRE, Inc

Chapter 18
Draglines and Clamshells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

DRAGLINES AND
CLAMSHELLS
Drag buckets and
clamshells are
attachments hung
from a lattice-
boom crane.

DRAGLINES AND
CLAMSHELLS
A dragline excavator is especially
useful when there is need for extended
reach in excavating or when material
must be excavated from underwater.
Clamshell excavators provide the
means to excavate vertically to
considerable depths.

DRAGLINES
The Monighan Co. patented a walking
mechanism for draglines in 1913. These
machines were used extensively in
building levees on the Mississippi River.

DRAGLINES

DRAGLINES
A dragline works, as the name
implies, by dragging a dragline-
type bucket toward the machine.

DRAGLINE
BUCKET
A dragline bucket consists of three
parts: the basket, the arch, and the
cutting edge. Buckets are generally
available in three types: (1) light duty,
(2) medium duty, and (3) heavy duty.

DRAGLINES
The greatest advantage of a
dragline over other machines is
its long reach for digging and
dumping.
A dragline does not have the
positive digging force of a
hydraulic shovel or hoe.

DRAGLINES
Draglines are used to excavate
material and load it into hauling
units
or to deposit it in levees and spoil
piles near the pits from which it
is excavated.

DRAGLINES
Dragline components consist of a drag
bucket and a fairlead assembly. Wire
ropes are used for the boom suspension,
drag, bucket hoist, and dump lines.

DRAGLINE
PRODUCTION
The output of a dragline should be
expressed in bank measure cubic yards
(bcy) per hour. This quantity is best
obtained from field measurements.
Table 18.2 gives approximate dragline
digging and loading cycles for various
angles of swing.

OPTIMUM DEPTH
OF CUT
A dragline will produce its greatest
output if the job is planned to permit
excavation at the optimum depth of cut.
Based on using short-boom draglines,
Table 18.3 gives the optimum depth of
cut for various sizes of buckets and
classes of materials.

EFFECT OF DEPTH OF
CUT AND SWING ANGLE
Table 18.3 presents ideal dragline
production capability based on
digging at optimum depths with a
swing angle of 90°.
The table also assumes maximum
efficiency, for example, a 60-min
hour.

EFFECT OF DEPTH OF
CUT AND SWING ANGLE
For any other depth or swing angle, the
ideal output of the machine must be
adjusted by an appropriate depth-swing
factor.
The effect of the depth of cut and
swing angle on dragline production
is given in Table 18.4.

EXAMPLE
A 2½-cy short-boom dragline is to be
used to excavate wet, sticky clay. The
depth of cut will be 14.8 ft, and the
swing angle will be 60°. Determine the
probable production of the dragline.
There are 65,000 bcy of material to be
excavated. How long will the project
require?

Step 1. Ideal
Production
Determine the ideal production
from Table 18.3:
Based on a 2½-cy bucket size and
wet, sticky clay material:
Ideal production = 175 bcy.

Step 2. Optimum
Depth of Cut
Determine the percent of
optimum depth of cut,
Eq. 18.1.
Optimum depth of cut
Table 18.3: 12.3 ft.

Step 2. Optimum
Depth of Cut
Optimum depth of cut
Table 18.3: 12.3 ft.
Percentage of optimum depth of
cut Eq. 18.1
14.8
12.3
ft
ft
× 100
= 120%

Step 3. Cut/Swing Angle
Correction Factor
Step 3. Determine the depth of
cut/swing angle correction factor
from Table 18.4:
• Percentage of opt. depth = 120%
• Swing angle = 60°
Depth of cut/swing angle correction
factor = 1.09

Step 4. Efficiency Factor
Determine an overall
efficiency factor based on the
expected job conditions.
Draglines seldom work at better
than a 45-min hr:
Efficiency factor =
45
60
min
min
=
0.75

Step 5. Production
Determine production rate.
Multiply the ideal production by
the depth/swing correction
factor and the efficiency factor:
175 × 1.09 × 0.75 = 143 bcy/hr

Step 6. Production
Determine soil
conversion, if needed
(Table 4.3). Not necessary
in this example.

18.2:
Step 7. Time
Determine total hours, Eq.
65,000
143
bcy
bcy/hr
=
Total hr = 455 hr

CLAMSHELLS
The clamshell
is a vertically
operated
bucket capable
of working at,
above, and
below ground
level.

CLAMSHELLS
Clamshells are used
primarily to remove
materials from
vertical excavations
such as cofferdams,
pier foundations,
and sheet-lined
trenches.

CLAMSHELLS
There are hydraulic clamshell
buckets that are mounted on the
stick of
hydraulic hoes.

CLAMSHELL BUCKETS
The two jaws
of a clamshell
bucket clamp
together when
the bucket is
lifted by the
closing line.

CLAMSHELL BUCKETS
Clamshell
used to
cleanout 8 ft
diameter
steel piles.

CLAMSHELLS
PRODUCTION RATES
Because of the variable factors that
affect the operations of a clamshell, it is
difficult to give average production
rates. The critical variable factors
include the difficulty of loading the
bucket, the size load obtainable, the
height of lift, the angle of swing, and
the method of disposing of the load.

SAFETY
Keep personnel away from the swing
area of dragline and clamshell cranes.
These machines must be operated so as
not to expose persons in the area to a
hazard. The crane operator must not
swing the boom and bucket, whether
loaded or empty, over the top of trucks
and drivers.

SAFETY
Another common accident, with cranes
equipped as draglines or with clamshell
buckets, is where a machine falls into
the excavation it is digging. These
accidents often happen when ground
conditions deteriorate after a rain.
Management must always be cognizant
of changing ground conditions.