An excavator has been
defined as a power-driven
mounted on crawler tracks.
The major types of excavators
used in construction include
excavators and the members
of the crane-shovel family.
scrapers are also capable of
excavating soil and rock.
Type of Excavators
Hydraulic power is the key to the versatility of many
Hydraulic front shovels are used predominantly for hard
digging above track level and for loading haul units.
Hydraulic hoe-type excavators are used primarily to
excavate below the natural surface of the ground on which
the machine rests.
The loader is a versatile piece of equipment designed to
excavate at or above wheel/track level. Unlike a shovel or
hoe, a loader must maneuver and travel to position the.
bucket to load or dump.
Additionally, there are a variety of excavators available for
Advantage of Hydraulic controls
hydraulic control of machine
– Faster cycle times.
– Positive control of attachments.
– Precise control of attachments.
– High overall efficiency.
– Smoothness and ease of operation.
Bucket payload can be measured by
volume or weight
Volume is typically stated as struck
measure of loose volume meaning that
the material excess is scraped off flush
with the top of the bucket.
Heaped at a specific angle of repose
An excavator’s bucket payload (actual amount of
material in the bucket on each digging cycle) is
dependent on bucket size, shape, and certain
soil characteristics, i.e., the fill factor for that
soil. Fill factors for several types of material are
Average Bucket Payload = (Heaped Bucket
Capacity) x (Bucket Fill Factor)
Excavator operating Ranges
A Maximum loading height of
bucket with teeth
B Maximum reach at ground level
C Maximum digging depth
D Maximum vertical wall
E Maximum depth of cut for level
bottom (straight clean up)
F Maximum bucket hinge pin
G Maximum height, to bucket
teeth at highest arc
Operating Ranges for different Booms
Excavator load capacity for different
boom and buckets
*Liftingcapacity @ 20 ft.
t Lifting capacity @ 25 ft.
Maximum excavation depth required
Maximum working radius required for digging
Maximum dumping height required
applicable, i.e., handling pipe and trench
Excavator Production Estimate
Bucket heap capacity Q in LCY
Fill factor F
Cycle time t in sec
Efficiency in min/hr E
Production in BCY=
A crawler hoe having a 3~-cy bucket is being
considered for use on a project to excavate very
hard clay from a borrow pit. The clay will be
loaded into trucks having a loading height of 9 ft
9 in. Soil-boring information indicates that below
8 ft. the material changes to an unacceptable
silt material. What is the estimated production
of the hoe in cubic yards bank measure, if the
efficiency factor is equal to a 50-min hour?
Size of bucket, 3 1/2 cy
Bucket fill factor (Table), hard clay 80 to 90%; use average 85%
Typical cycle element times. Optimum depth of cut is 30
to 60% of maximum digging depth
8/23 = 0.34
8/27 = 0.3 within limits
Swing with load
Efficiency factor = 50 min/hr
Production= (3600x3.5x0.85/22) + (50/60) + (1/
= 300 BCY/hr
Check maximum height for loading= 21 to 22 ft
available is ok for dump truck height
Digging should be planned so that dipper teeth cut as near as
possible to the line of the digging cable.
Length and depth of cut should be judged to produce a full
dipper at every pass. Full loads on every pass produce more pay
dirt than a faster cycle with partly filled dipper. Full loads should
be the first objective, followed by speed increases for fast cycles.
A hoe will dig fairly hard materials. Where possible, blasting will
often be less expensive than bulling through hardpan and rack
strata with the hoe dipper.
Using the dipper teeth as a pick axe by extending handle to
maximum reach, then dropping Front end to break ledge rock is
very bad practice, the result being serious Front end damage.
Once the trench is open, ledge rack can be broken by pulling
dipper up under the layers. Top layers are pulled first with one or
two layers lifted at a time
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