EXCAVATORS
Mansoor Azam Qureshi
NUST
Islamabad
EXCAVATOR
An excavator has been
defined as a power-driven
digging machine, usually
mounted on crawler tracks.
 The
major
types
of
excavators
used
in
construction
include
hydraulically
powered
excavators and the members
of the crane-shovel family.
 However,
dozers
and
scrapers are also capable of
excavating soil and rock.

TYPE OF EXCAVATORS





Hydraulic power is the key to the versatility of many
excavators.
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 specialty applications.
MAIN COMPONENTS OF EXCAVATOR
MAIN COMPONENTS OF EXCAVATOR
ADVANTAGE OF HYDRAULIC CONTROLS
 The
hydraulic control of machine
components provides
 Faster cycle times.
 Positive control of attachments.
 Precise control of attachments.
 High overall efficiency.
 Smoothness and ease of operation.
BUCKET CAPACITY
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

BUCKET PAYLOAD
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 listed below.
 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
height
G Maximum height, to bucket
teeth at highest arc
OPERATING RANGES FOR DIFFERENT
BOOMS AND STICKS
EXCAVATOR LOAD CAPACITY FOR
DIFFERENT BOOM AND BUCKETS
*Liftingcapacity @ 20 ft.
t Lifting capacity @ 25 ft.
SELECTING EXCAVATOR
Maximum excavation depth required
 Maximum working radius required for digging
and dumping
 Maximum dumping height required
 Hoisting capability required (where applicable,
i.e., handling pipe and trench boxes

EXCAVATOR PRODUCTION ESTIMATE

Depend upon






Bucket heap capacity Q in LCY
Fill factor F
Cycle time t in sec
Efficiency in min/hr E
Swell factor
Production in BCY=
x
x
CYCLE TIME FOR TYPICAL EXCAVATOR
EXAMPLE

A crawler hoe having a 3.5-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. Soilboring 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





Load bucket
Swing with load
Dump Load
Return swing
Cycle Time
7 sec
6 sec
4 sec
5 sec
22 sec
Efficiency factor = 50 min/hr
 Swell factor
= 35%
 Production= (3600x3.5x0.85/22) + (50/60) + (1/[1+0.35])
= 300 BCY/hr
 Check maximum height for loading= 21 to 22 ft
available is ok for dump truck height

TYPE OF BUCKETS ATTATCHMENTS
HELPFUL HINTS




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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