12-04-2023

Hydraulic Excavators

Construction Equipment
• Boom and Stick Excavators – Classified based on
the digging motion of the swinging bucket.

Management
• An upward motion machine is known as ‘Front
Shovel’.
• The boom of the shovel swings in an upward arc to
load. The material face is above the running gear.
• A downward motion machine is known as ‘hoe’.
CMT 522 • The downward swing dictates usage for excavating
Session 5 & 6 – Concepts and Illustrations below the running gear.
• It develops excavation force by pulling the bucket
Excavators: Shovel, Hoe & Scrapers towards the machine and curling the bucket
inwards.

Aritra Halder
| Aritra Halder | Assistant Professor
Assistant Professor | School of Construction

Excavator Operating Ranges Shovel and Hoe Stick

cylinder
Boom Boom
Stick Boom Boom Stick Cylinder
• A: Dumping Height Stick
cylinder Cylinder
Cab

• B: Digging Reach Bucket Cab

Cylinder
• C: Maximum Digging Depth A Bucket Bucket
Cylinder
Bucket

B Hydraulic Shovel
Hydraulic Hoe

• Used for hard digging above track level & loading haul • Used for excavating below the resting surface.
units.
C • They can handle max. 10,000 lb loads @ 20 ft radius with
• The material excavated should have high standing capacity. all outriggers down.
• They are front heavy with the front assembly carrying 1/3rd • They are not production excavators, used mostly for
of the superstructure load. mobility and general purpose work.
• Typically crawler mounted with speed @ 3mph • The ability to excavate is maximum @ bottom of the swing
arc.
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

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Shovels Factors of selecting a shovel

• The size of shovel is indicated by the size of the bucket (expressed in cubic
yards) Size of the job (higher cost of job can justify the deployment of a large costly
shovel)
• The bucket capacity needs to be adjusted based on the fill factors.
• Fill factors account for the void spaces between individual material particles of Mobilization Cost
Cost per cubic yard
respective material types within the bucket.
• Fill factors are multiplied with rated heaped capacity of the bucket to account Combined cost of drilling, blasting and excavating. (larger shovels reduces the
for the correction. requirement of blasting and drilling)
Hardness of excavated material

Job conditions Nature of material to be removed

under which the
shovel works
Size of the available hauling units. The bucket size should be 1/5th of the hauling
unit’s carrying capacity

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Production rate of shovels Height and Swing Adjustment

• Optimum Height:
• Loam, sand, gravel = 30% of max.

Maximum Height of cut

Calculate heaped Apply Bucket fill
Estimate a peak cycle
time based on
height
Set the unit of Calculate the
bucket load volume
from manufacturer’s
factor based on type
of machine and class
material type, job Apply an efficiency
measurement as per production rate by • Sticky Clay, Blasted Rock = 50% of
condition, angle of factor.
data sheet. of material. swing, depth of cut,
requirement. formula. max. height

Optimum Height of cut

travel distance etc.
• Common earth = 40% of max height

• Percentage of optimum depth

Actual Height of cut

𝟑𝟔𝟎𝟎 𝑺𝒆𝒄/𝒉𝒓 × 𝑸 × 𝑭 × (𝑨𝑺:𝑫) 𝟏 = × 100
• Production = 𝒕
×𝑬× 𝑽𝒐𝒍𝒖𝒎𝒆 𝒄𝒐𝒓𝒓𝒆𝒄𝒊𝒐𝒏
• E = Efficiency or (Actual mins worked per hour)/60 mins

• Volume correction is applied to convert loose volume into bank volume.

• F = Fill factor, (AS:D) = swing height correction factor, E = efficiency, Vol. correction= 1/(1+swell factor)
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

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Height and Swing Adjustment Height and Swing Correction Factor

• Angle of swing is the horizontal
angle expressed in degrees
between the position of the
bucket when it is excavating and
the position where it discharges
the load.

• Ideal production of shovel is

based on the assumption that it
is operating at 90o swing and
optimum height of cut.
Angle of swing

• The cycle time is the sum of

digging, swinging to dumping • For 75 degree swing and percentage of depth = 60%, the AS:D
position, dumping, returning correction factor = 0.96
back to the digging position.
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Illustrative Example of Shovel Production Hoe

• 5 cubic yard heaped capacity of bucket Production = • Hoes are used to excavate below
• Working on a 12 feet high rock heap (poorly blasted)
the natural surface of the ground
• Maximum rated digging height = 34 feet 𝟑𝟔𝟎𝟎 𝑺𝒆𝒄/𝒉𝒓 ×𝟓×𝟎.𝟖𝟓 ×𝟏.𝟎𝟖 𝟔𝟎 𝒎𝒊𝒏 𝒉𝒓

• Swinging angle = 60 degree

𝟐𝟏 𝑺𝒆𝒄
× 𝟔𝟎 𝒎𝒊𝒏 𝒉𝒓 on which the machine rests.
• Cycle time = 21 sec (ideal condition) • Hoes are also known as back shovel
= 787 cubic yard (loose)
• Full efficiency (60 min working in an hour) or backhoe.
• Calculate the loose cubic yard production in conservative estimate.
• A hoe can be selected based on the
following-
– Maximum excavation depth
Optimum height =
50% X 34 feet = 17 required.
feet
Size of bucket = 5
Bucket fill factor = Unit of measurement Calculated using – Maximum working radius required
85% (conservative 21 second cycle time. Percentage of is loose cubic yard; formula = 787 loose
cubic Yard
estimate) optimum height = efficiency factor = 1 cubic yard/hr. for digging and dumping.
12/17 = 0.71
AS:D = 1.08
– Maximum dumping height required.
– Hoisting capability required.

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

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Multipurpose Attachments Rated Lifting Capacity

Hydraulic Ram • Rated Hoist Load < 75% of the
Round Base bucket
tipping load
• Rated Hoist Load < 87% of
excavator’s hydraulic capacity
• Rated Hoist Load < Machine’s
Structural Capabilities
Clamshell bucket

Grappler

Front Lifting Capacity Contours

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Output of Excavators (simplified) Output of Excavators (simplified)

× ×
• Hourly production in m3/hr(Q) =
• Bucket Fill Factors
• q = production per cycle = heaped capacity * Swell Factor * Bucket Factor
• C = Cycle Time (seconds) = Excavation + 2*swing + Dump Material Bucket Fill Factor

Digging Depth Excavation Time in seconds Soft Clay 1-1.10

Easy Average Difficult Very Difficult Earth and Loam 0.9-1.05
0-2 m 6 9 15 26
Gravel and Sand 0.9-1.00
2-4 m 7 11 17 28
Uniform Aggregates 0.8-0.9
4m+ 8 13 19 30
Hard Clay 0.75-0.85
Loading Condition Example
Easy Sand, Sandy Soil with moisture Well Blasted Rock 0.6-0.75
Average Dry Sand, Only soil, Clay, Unscreened Gravel
Coarsely Blasted Rock 0.4-0.6
Difficult Crushed Stone, high moisture clay, Hard Clay
Very Difficult Irregular Rocks, Boulders
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

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Trenching Machines Wheel Trencher and Ladder Trencher

• Trenching machines provide relatively
fast digging, positive control of trench a) Wheel Type: This consists of a power
depth and width, reduces expensive driven wheel with buckets mounted on
it equipped with cutter teeth. The
finishing operation and labor
buckets dump the excavated soil onto
involvement. a conveyor fitted at the back to place
• Most large trenchers are crawler them on the trench sides while the
mounted to increase the stability and to machine moves.
distribute the weight over a greater area.
• Trenching machines can be of two types. b) Ladder Type: This type have more
flexibility in terms of trench depths and
– (a) wheel type &
widths. They are unsuitable for rocky
– (b) ladder type soil, collapsible soil, high water table
areas.

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Backhoe Loader VAC Excavator

To excavate
To excavate
Below Wheel
Above
level
wheel Level

It has the efficiency of a tractor, loader and hoe combined.

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

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Holland Loader Scrapers

• Scrapers are tractor pulled machines designed to dig, load, haul, dump and spread loose
material in controlled lifts.
• Loading efficiency  Excavators>>Scrapers
• Hauling efficiency  Trucks>>Scrapers

• Why Scrapers then?

• (a) Short Distance travel is economical in scraper (haul distance >100 m & <1500 m)
• (b) Ability to both load and haul
• (c) Due to availability of both tractor and loader with storage, even after breakdown of one
component, work can partially continue.
• (d) Ability to deposit loads in layers of uniform thickness.

• Production cycle consists of –

• (a) loading, (b) haul travel, (c) dumping and spreading, (d) turning, (e) return travel, (f) turning
and positioning to receive load again.

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Scraper construction & operation Scraper Types

• Bowl: It is the loading and carrying
component of the scraper. It has a cutting
edge that extends horizontally across its Single Powered Axle

front bottom edge. It is lowered for Pusher Loaded (Conventional)

loading and raised during travel.
Tandem Powered Axle

Scraper
• Apron: It is the front wall of the bowl. It is
raised during loading and unloading of Push Pull, tandem powered
axle
the material to facilitate inflow or
outflow. It is lowered during travel to
avoid spillage. Self Loading Elevating

• Ejector: It is the rear vertical wall of the

bowl. The ejector is activated and moved Auger

forward during spreading of material to

push the load outside the apron.
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

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Scraper Types - Details Scraper Types: Details

• Pusher Loaded Single Powered Axle: A tractor • Push Pull Tandem Powered Axles: This type is designed with a push block
pulling a bowl that can operate under its own mounted on the rear and a bail mounted on the front to assist other scrapers or
power or be push-assisted. This is the most be pushed by other scrapers. They are ideal for dense soil-excavating projects
common type of scraper on large earthmoving
when a dozer is not utilized for pushing. Effectively two scraper push and pull
jobs.
each other for respective loading, thereby working without any external power.

• Pusher Loaded Tandem Powered Axle: This type

has a second engine mounted in the rear and can
develop greater power. This is ideal for steeper
hauls at greater speeds. Typically cost about 30%
more than a conventional scraper.
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Scraper Types: Details Scraper Types - Details

• Auger Scrapers: Here an independent hydrostatic system powers the auger that
• Elevating Scrapers: These are self-contained loading and hauling units. The chain elevator serves as a
is located at the center of the bowl. The rotating auger lifts the material off the
loading mechanism. The extra weight of the loading mechanism is a disadvantage during the haul scraper cutting edge and carries it to the top of the load, creating a void that
cycle, but this type is ideal for short-haul situations where the ratio of haul time to load time is low. enables new material to enter the bowl. This action reduces the cutting edge
These are used generally for utility work, dressing up behind high-production spreads, or shifting resistance. These scrapers are heavier and costlier to own and operate with
material during fine-grading operations. The chain breaks the soil as it enters the bowl and is easier to respect to the other types.
discharge. These units can be push-assisted.

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

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Thank You!
Contact Me
at
ahalder@nicmar.ac.in
+91-8504017164

| Aritra Halder | Assistant Professor