Construction Equipments for civil engineering.

1. Unit No 6 (A)
Construction Equipments
a) Earth moving equipment’s
 Introduction
It is a common fact that we find a wide variety of construction machines on every construction
sites, which make the construction jobs easy, safe and quicker. Good project management in
construction must vigorously pursue the efficient utilization of labor, material and equipment.
The use of new equipment and innovative methods has made possible wholesale changes in
construction technologies in recent decades. The selection of the appropriate type and size of
construction equipment often affects the required amount of time and effort and thus the job-site
productivity of a project.
These act as a backbone in the case of huge construction projects. Proper use of the appropriate
equipment contributes to economy, quality, safety, speed and timely completion of a project.
Equipment’s are used for highway projects, irrigation, buildings, power projects etc. Almost 15-
30% of total project cost has been accounted towards equipment and machinery.
It is therefore important for site managers and construction planners to be familiar with the
characteristics of the major types of equipment most commonly used in construction.
 Advantages of utilizing the construction equipments:
 Increase the rate of output through work progress with the best effective and efficient methods.
 Reduce the overall construction costs especially for large contracts.
 Carry out activities which cannot be done manually or to do them more economically and much
faster.
 Eliminate the heavy manual work by human thus reducing fatigue and eliminates various other
hazards and health issues.
 Maintain the planned rate of production where there is a shortage of skilled or unskilled labor.
 Maintain the high quality standards often required by present-day design and specifications
(technical standards).
 Manual versus Mechanical Construction
 The construction of large projects like dams, bridges, roads, sky-scrappers, hydro-electric
stations, tunnels, etc. is much complex in nature.

2.  They involve complicated designs and huge amount of money. In order to achieve speed, safety,
efficiency and economy, use of construction equipment is quite essential. This is not possible by
using conventional manual construction methods.
 Use of mechanical equipment is advantageous where the nature of work is difficult for human
labour and speedy construction is required.
 Machines can handle tough works which are beyond the scope of human labour.
 Machines can work under adverse weather, climatic and topographical conditions which are
quite difficult for manual labour.
 Machines are more dependable in regions where local labour is not easily and economically
available.
 Use of machines may be cheaper than manual work where large quantities of construction
material are to be handled over long distances. e.g. earth moving, transportation of concrete, etc.
 Planning and scheduling can be easily done because the performance of machines can be
assessed accurately. This is difficult with manual labour.
 It is easy to supervise the control as limited number of persons (operators and cleaners only) is
working.
 In case of break-down of the machine, there may be delay in procurement of spare parts.
 Due to excessive mechanization, there are chances of unemployment, especially in countries
where abundant manpower is available.
 Factors behind the selection of construction equipment's
1. Economic Considerations
 The economic considerations such as owning costs, operating labour costs and operating fuel
costs of equipment are most important in selection of equipment.
 Besides, the resale value, the replacement costs of existing equipment, and the salvage value
associated with the equipment are also important.
2. Company-Specific
 The selection of equipment by a company may be governed by its policy on 'owning' or 'renting’.
 While emphasis on 'owning' may result in purchase of equipment keeping in mind the future
requirement of projects, the emphasis on 'renting' may lead to putting too much focus on short-
term benefits.
3. Site-Specific
 Site conditions-both ground conditions as well as climatic conditions-may affect the equipment-
selection decision.

3.  For example, the soil and profile of a site may realize that whether to go for a crawler-mounted
equipment or a wheel-mounted equipment.
 If there is a power line at or in the vicinity of site, one may go for a fixed-base kind of equipment
rather than a mobile kind of equipment.
4. Equipment-Specific
 Construction equipments come with high price tags. While it may be attractive to go for the
equipment with low initial price, it is preferable to choose for standard equipments.
 Such equipments are manufactured in large numbers by the manufacturers, and their spare parts
are easily available, which would ensure minimum downtime. Besides, they can also get good
salvage money at the time of their disposal.
5. Client And Project-Specific
 The owner/client in a certain project may have certain preferences that are not in line with the
construction company's preferred policies as far as equipment procurement is concerned.
 The schedule, quality and safety requirements demanded of a particular project may in some
cases force the company to yield to the demands of the client.
6. Manufacturer-Specific
 A construction company may prefer to buy equipment from the same manufacturer again and
again, and that too from a specific dealer.
 This may be to bring in uniformity in the equipment fleet possessed by the company or because
the company is familiar with the working style of the manufacturer and the dealer.
7. Labour Consideration
 Shortage of manpower in some situations may lead to a decision in favour of procuring
equipment that is highly automated.
 Further, the selection of equipment may be governed by the availability or non-availability of
trained manpower.
 Selection of Construction Equipment
The following points should be considered while selecting construction equipment,
 Suitability for job conditions: The equipment must meet the requirement of the work, climate
and working conditions.
 Availability of equipment: The equipment which is easily available should be selected.
 Standardization: Choice should be restricted to standard equipment. Special equipment should
be selected if job justifies its selection. Less variety of equipment should be used. More varieties
demands for more skilled operators, more spare parts requirement and more production cost.

4.  Size of equipment: Size of the equipment should be decided according to the amount of work. It
is better to use more numbers of small equipment than one large equipment. The large size
equipment may remain idle for most of the time or may work on partly, thus increasing the
production cost.
 Availability of spare parts: It is better to purchase equipment manufactured in the country. This
will reduce the cost of repairs and down-time cost as the spare parts will be available easily.
 Multi-purpose equipment: Equipment should be capable of doing more than one job.
 Use in future projects: Equipment should be useful for further projects and it should not
become obsolete.
 Operating requirements: The equipment selected should be easy to operate and maintain. It
should have lesser fuel consumption.
 Service support: After sales service support should be available in the area of project where the
equipment is being used.
 Cycle Time
 The time taken by the machine to complete on full cycle of operations is called cycle time.
 Cycle time is composed of two components, fixed time and variable time.
 Variable time is the time spent on travelling. It is a function of distance travelled and speed.
 Fixed time is the time spent for all operations other than travelling such as loading, dumping,
turning, etc.
 Correction to cycle time
 Theoretically, the machine works for 60 minutes in one working hour under ideal conditions.
Actually, at job conditions the machine works for 50 minutes or 45 minutes. Thus, the cycle time
should be corrected as,
Corrected cycle time =
 Procedure of Equipment Requirement Design
1. Estimate the quantity of work to be done (cu.m.).
2. Find working time available (hours or weeks) from the construction schedule.
3. Find average rate of production per hour required to complete the work by dividing work to be
done by time available. (cu.m/ hr.).
4. Select suitable equipment and find its cycle time. Find number of cycles per hour.
Output = machine capacity x number of cycles/hour
5. Find the number of machines required.
6. Add 10 to 30 % capacity to serve breakdowns, contingencies, etc.

5.  CLASSIFICATION OF CONSTRUCTION EQUIPMENTS
Depending on the application, construction machines are classified into various categories which
we are discussing here.
 Earth-moving equipment
 Earth-compacting equipment
 Hauling equipment
 Hoisting equipment
 Conveying equipment
 Aggregate production equipment
 Equipments used in Concrete Construction.
 Pile-driving equipment
 Earth-moving equipment
 Earthmoving may include site preparation; excavation; embankment construction; backfilling;
dredging; preparing base course, sub-base and sub-grade courses; compaction; and road
surfacing.
 In actual practice the types of equipment used and the environmental conditions will affect the
man and machine-hours required to complete a given amount of work.

6.  So Before preparing planning, it is necessary to choose the best method of operation and the type
of equipment to use.
 Each piece of equipment is specifically designed to perform certain mechanical tasks.
 Therefore, the equipment selection based on efficient operation and availability of equipment.
 Different Earthmoving Equipment’s:
 Following are the measure equipment's are used as a earthmoving equipment's:
1. Tractors,
2. Bulldozers,
3. Scrappers,
4. Power shovel,
5. Hoe
1. TRACTORS
 A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or
torque) at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or
construction.
 The durability and engine power of tractors made them very suitable for engineering tasks.
 Tractors can be fitted with engineering tools such as dozer blades, buckets, hoes, rippers, etc.
 The most common attachments for the front of a tractor are dozer blades or buckets.
 When attached to engineering tools, the tractor is called an engineering vehicle.
 Tractor converts engine power to traction power used for pulling or pushing.
 A tractor is a multi-purpose machine. Light models can be used for agricultural or small haulage
works. Heavy crawler units are used large scale earth moving works.
 Typical project applications of tractors are land clearing, ripping and towing other construction
equipment.
 Types of tractors are (i) Wheeled tractors and (ii) Crawler tractors
 Comparison between wheeled tractors and crawler tractors
 Wheeled tractors move on pneumatic tyres. Crawler tractors move on endless chain.

7.  Wheeled tractors are used for light but speedy jobs. Crawler tractors are used for heavy duty
work where more tractive force is required such as uneven and rough ground.
 Crawler tractors can easily operate in rocky conditions, whereas wheel tractors cannot work in
such conditions due to chances of damage to the rubber tyres.
 Crawler tractors need more skilled operators than wheeled tractors.
 Wheeled tractors have a speed of about 50 kmph. Crawler tractors have a speed of about 12
kmph.
 Wheeled tractors are suitable for level surface only. Crawler tractors can work on any terrain.
 Wheeled tractors cannot work in soft and wet surfaces. Crawler tractors can work on such
surface due to special tracks.
 Crawler tractors are costlier than wheeled tractors.
 Crawler tractors require more maintenance and repairs than wheeled tractors.
 Operation of wheeled tractors is easy than crawler tractors and thus, less fatigue for the operator.
 Transportation of crawler tractors over long distances is done on trailers whereas the wheeled
tractors can be self-driven over long distances.
 Performance Ratings of Tractors
The ratings of the wheeled tractors specify the engine H.P., the rim pull at different speeds in the
various gears, the total operating weight of the tractor, number and sizes of the tyres.
1. Rim pull
It is a tractive force between the rubber tyres of driving wheel and surface on which the
tyre operates. It is expressed in kg. Rim pull can be calculated as,
Pull of tractor on trailing load = Rim pull – Rolling resistance of the tractor
Rolling resistance is the resistance of a level surface to constant –velocity motion across it.
2. Drawbar pull
The ratings of crawler tractors specify the drawbar pull. The available pull which a
crawler tractor can exert on a load that is being towed is called the drawbar pull.
2 Bulldozers
Dozer is a tractor unit that has a blade attached to the machines front. It is designed to
provide tractive power for drawbar work. Dozers (track laying crawlers or wheel tractors
equipped with a blade) are perhaps the most basic and versatile items of equipment in the
construction industry. They are the standard equipment for land clearing, dozing, and assisting in
scraper loading.
They can be equipped with rear mounted winches or rippers. Crawler tractors exert low
ground-bearing pressure, which adds to their versatility. A dozer has no set volumetric capacity.

8. The amount of material the dozer moves is dependent on the quantity that will remain in front of
the blade during the push. A bulldozer is a tractor unit with a blade attached to its front end. The
blade is used to push, shear, cut and roll material ahead of the bulldozer.
Bulldozers are mounted with blades which are perpendicular to the direction of travel
they push the earth forward. Angle-dozers are mounted with blades set at an angle with the
direction of travel. They push the earth forward and to one side. Crawler dozers equipped with
special clearing blades are excellent machines for land clearing. Consistent with their purpose, as
a unit for drawbar work, they are low-center-of-gravity machines. This is a prerequisite of an
effective dozer.
The larger the difference between the lines of forces of transmission from the machine
and the line-of-resisting force, the less effective the utilization of developed power.
For long moves between projects or within a project, transport dozers on heavy trailers.
Moving them under their own power, even at slow speeds, increases track wear and shortens the
machine’s operational life.
 Types of Bulldozer
1. Crawler Bulldozer
This crawler bulldozer has traction mechanism which helps to produce force which is
supply to blade. It uses two-plate dry primary clutch, which makes the maintain easy.
The steering is hydraulically and the bulldozer can operate hydraulically.
Crawler bulldozers are powered by diesel engines, which makes the work energy
efficiency, low-pollution, high-efficiency and low-consumption.
It can be used in road, hydro-electric construction, field modification, port, mine development
and other constructions,
For soft ground work also choose crawler bulldozer was mostly use.
Different conditions can choose different ones.

9. 2. Wheeled Bulldozer
The wheeled bulldozer, which is also called wheel dozer, is a kind of commonly used
construction machinery.
The principle of the machine work is to push outfitted dozer blades by essentially tractive force,
so as to clearing and grading land or paving the roads.
These machines use a drive system of military industry technology, which is of big tractive
force, high efficiency and good performance.
It is with full hydraulic operated steering and all-wheel drive, which is easy and flexible to
operate.
Bulldozers are generally used for the following operations,
1. Clearing land of trees and bushes.
2. Opening up pilot roads through mountains.
3. Moving earth for short haul distances, up to about 100 m.
4. Spreading earth and rock fills.
5. Backfilling.
6. Construction of V-type ditches.
7. Removal of top soil.
 Dozer Blades
A heavy blade of slightly concave profile is attached in the front of the crawler tractor. It is
connected through two arms and a yoke to the tractor.
The blade is controlled by means of hydraulic cylinders. The dozer blades are available in sizes
from 2m to 7.5 m wide and 0.8 m to 1.5 m in height.
 Types of Blades
1. Straight blade (S)
It is most commonly used for general dozing and excavation. It does not have curvature in its
length. These blades are heavy duty and can be tilted thus facilitating penetration into hard
materials.

10. 2. Angle blade (A)
It is slightly curved and is fitted with sharp cutting edge. This blade is useful in cutting roads in
hills, backfilling and cutting trenches
3. Universal blade (U)
It is longer and due to side wings soil carrying capacity is more than S blade. U blade is more
suitable for handling large volumes of light loads.
4. Cushion blade (C)
It is mounted on large tractor which is used for push-loading scraper. Cushion blade is shorter
than S blade. Rubber cushions and springs in the mounting allow the dozer to absorb the impact
of contacting the scraper push block.
The size of a bulldozer is indicated by length and height of the blade, its shape and its capacity.
Working of dozer consists of lowering front blade to the ground. As the dozer move forward, it
cuts and pushes the earth collected in blade to a desired distance.
Output of Bulldozer
The production of bulldozers mainly depend upon the following factors,
 Size and condition of the bulldozer.
 Distance travelled by the bulldozer.
 Speed of operation.
 Characteristics of the soil being handled.
 Surface on which the bulldozer is operating.
 Efficiency of the bulldozer.
 Skill of the operator.
Output in bank volume/hr= loose volume handled per trip x S x x efficiency
Where, S = swell factor
t = cycle time in minutes
 Swell Factor
Loosening of earth causes an increase in volume. It is expressed as a percentage of
original undisturbed volume. The ratio of volume of original undisturbed earth to the volume of
loose earth is known as swell factor.
Loose volume handled/trip = Production per cycle
= Blade width x (Blade height)2 x Blade factor
Blade factor depends upon the type of soil and generally taken between 0.4 to 1.1 depending
upon difficult to easy doing work.
 Cycle time (minutes) =
( )
( / )
+
( )
( / )
 Factors affect output of Bull dozer
a. Efficiency of operator

11. b. Nature of soil
c. Topography of area
d. Type of equipment
e. Weather Condition
3 Scrapers
Scrapers are a type of heavy machinery used for earthmoving purpose. These machines suitable
for soft soil. Self-propelled scrapers were invented in the 1930s.
The back part of the machine is called a hopper. This hopper is lowered or raised to cut into the
ground collecting the top surface of ground.
The collected earth can be moved to place and dumped as per required height as lowering bottom
portion of the hopper.
Some scrapers work in tandem (additional equipment) with a bulldozer. Scraper is a tool or
device used for scraping i.e. to remove dirt or other unwanted matter from a surface.
In civil engineering works; scraper can be used for earthmoving applications, mining,
construction and other applications. Scrapers are work as a tractor powered and pull a bowl that holds
the soil.
The blade is mounted on the bottom of the bowl that cuts into the travel surface and the disturbed
soil flows into the bowl as the scraper moves forward. Scrapers can self-load or be assisted by another
scraper or bulldozer. The greatest advantage of scraper is the versatility.
Scrapers can be used to load and haul a wide range of material types and are economical over a wide
range of haul lengths and haul conditions. Scrapers are available with loose-heaped capacities up to 10-
15 cubic meter.

12.  Components of a Scraper
A self-propelled and motorized scraper has following components,
1. Bowl
Bowl is a pan to hold the scraped soil. It is hinged at the rear corners to the rear axle
inside the wheel. It is capable of tilting down for digging or for ejecting. The bowl size is
specified to indicate the size of the scraper.
2. Cutting edge
The bowl has a cutting edge attached at the bottom. The cutting edge is lowered into the
soil to make a shallow cut.
3. Apron
This is a wall in front of the bowl, which opens and closes to regulate the flow of the
earth in and out of the bowl.
4. Tail Gate or Ejector
It is the rear of the pan which is capable of forward and backward movement inside the
bowl.
 Scraper operation/ Working of a Scraper
A scraper performs the following operations in a cycle,
(i) Loading (digging)
(ii) Transporting (hauling)
(iii) Unloading (dumping)
A scraper is loaded by lowering the front end of the bowl until the cutting edge enters the
ground. At the same time, the front apron is raised to provide an open slot through which the earth can
flow into the bowl. As the scraper moves forward, a horizontal strip of material is forced into the bowl.

13. This is continued until the bowl is filled. Then the cutting edge is raised and the apron is lowered to
prevent spillage during the haul.
The dumping operation consists of lowering the cutting edge, raising the apron and then forcing
the material out by means of a movable ejector mounted at the rear of the bowl.
 Cycle Time of a Scraper
Cycle time for a scraper is the time required for loading, hauling to the fill location, dumping and
returning to the loading position.
Cycle time Ts = loadt + hault + dumpt + returnt + turnt
Volume a scraper is specified as either struck or heaped capacity of the bowl in cubic metres.
 Increasing Scraper Production
The scraper production can be increased by following procedures,
1. Ripping – Hard and tight soils are ripped ahead of the scraper so that they will load faster.
2. Pre-wetting the soil – Moist soil loads more easily
3. Loading downgrade – Scrapers should be loaded down-grade and in the direction of haul. This
results in faster loading and eliminates the need to turn.
4. Supervision – This will result in reduced traffic congestion and confusion of the operators.
 Output of scrapers
Output of scrapers depends upon the following factors,
(i) Size and mechanical condition of the scraper
(ii) Hauling distance
(iii) Condition of the haul surface
(iv) Characteristics of soil
(v) Efficiency of the scraper
Hourly output in bank volume =
( ) ( )
Number of scrapers required =
4 Power Shovels
Power shovels are used to excavate earth and load into dumpers. These machines excavates at or
above track (ground) level. Power shovels excavate all types of earth and loosened rock.
Power shovels may be crawler mounted or rubber- tyre mounted. Crawler – mounted power
shovels has low speed and operates on soft grounds. Rubber – tyre mounted shovels travels with higher
speed and useful for small jobs where considerable travelling is necessary and where ground is firm.

14. Power shovels are hydraulically operated. Power shovels make use of hydraulic pressure to
develop bucket penetration into the ground. An upward motion unit is known as ‘front shovel’ and
downward motion unit is called ‘hoe’.
The structure of a power shovel provide the following operations,
(i) Movement of the machine called ‘walking’.
(ii) Revolving action of the superstructure for handling loads, known as ‘swinging’.
(iii) Actual working of the bucket, known as ‘digging’.
 Front shovels
Front shovels are used for excavating above the track level and loading haul units. The most
common application of front shovel is the loading of loosened rock.
Crawler – mounted shovels have speeds of about 5 kmph.
Basic parts are – Mounting, cabin, boom, stick, bucket, cylinders.
Operation of a Front shovel
The shovel is placed in the convenient position near the face of the material to be excavated. The
bucket is lowered to the floor with the teeth pointing into the face. A crowding force is applied by
hydraulic pressure to the stick cylinder. At the same time the bucket cylinder rotates the bucket through
the face. The bucket will be filled when it reaches the top.
Size of a Front shovel
The size of a shovel is indicated by the size of the bucket, expressed in cubic metres. The
common size is 3m3
to 5m3
.
Shovel Production
A production cycle of a shovel consists of four elements,
1. Load the bucket
2. Swing the load
3. Dump the load
Cabin

15. 4. Return swing
The actual production of a shovel depends upon,
 Type of material
 Height of cut
 Angle of swing
 Size of hauling units
 Operator’s skill
 Physical condition of the shovel.
Output of Power Shovels
The production or output of a power shovel is expressed in cu.m. per hour. The capacity of
bucket is based on its heaped volume.
Production in m3
/hr Q = q x
𝟑𝟔𝟎𝟎
𝐂
𝐱 𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐜𝐲
q = production per cycle = Heaped capacity x Swell factor x Bucket factor
C = cycle time (seconds)
Efficiency Factor
 Sand, gravel, common earth – 60 %
 Clay – 50 %
 Blasted rock – 40 %
Bucket Factor
 Sand, gravel, common earth – 90 %
 Well blasted rock – 70 %
 Poorly blasted rock – 50 %
Cycle time is the time required for excavation, swing, dump and back swing.
Excavation time depends on digging depth and surface to be digged.
Swing time depends on the degree and speed of swing and the skill of the operator.
Dumping time depends upon the proper spotting of dumper and the skill of the operator.
Factors affecting output of a power shovel
1. Type of material to be excavated
2. Height or depth of cut
3. Angle of swing
4. Size of bucket
5. Mechanical condition of shovel
6. Skill of the operator
7. Capacity of hauling units and waiting time
Selection of Power Shovels
The following points should be considered while selecting a power shovel,

16. 1. Quantum of work to be done.
2. Hardness or toughness of the material to be excavated.
3. Ownership and hiring costs.
4. Depreciation.
5. Down time cost.
6. Operational expenses.
7. Size of bucket required.
8. Size of hauling units in which the excavated material is to be loaded.
Applications
 Suitable for dragging softer material.
 Can remove big size boulders with prior loosening.
 It is used in various types of jobs such as digging in gravel banks, clay pits, digging cuts in road
works, road side berms etc.
 It is very useful for excavating trenches.
 It is mostly used in the excavation for canals and depositing on the embankment without hauling
units.
 Used for excavation and removal of overburden.
5. Hoes
Hoes are also called back hoes or back shovels. The backhoe loader was invented in the UK in
1953 by JCB (J. C. Bamford).
In Britain, Ireland and India they are commonly referred to simply as JCBs due to the company
being the first manufacturer in the UK and major supplier. In the United States, they are often referred to
as ‘Backhoes’. Hoes are used to excavate below the ground on which the machine stands.
Hoes are used primarily to excavate below the natural surface of the ground on which machine
rests. Hoe is sometimes referred to as back hoe or back shovel. Hoes are used to excavate trenches and
pits for basements, and the smaller machines can handle general grading work.
Positive bucket control makes them superior to draglines in operating on close range work and
loading haul units.
Wheel mounted hydraulic hoes are available with buckets up to 1.5 cu.m. Maximum digging
depth for larger machine is about 25 ft. Hoes are not production excavation machines. They are designed
for mobility and general purpose work.

17. Crawler mounted hoes are available with buckets up to 3 cu.m. The maximum digging depth for
the larger machines is about 7.5 m. The large machines can handle 4500 kg loads at 6 m radius.
The penetration force into the ground is achieved by the stick cylinder and the bucket cylinder.
The maximum crowd force is developed when the stick cylinder operates perpendicular to the stick.
Hoe Production Rate
Hoe production (excavation)
Where,
Q = Heaped bucket capacity in cy
F = Bucket fill factor for hoe buckets
t = cycle time in seconds
E = efficiency in minutes per hour
Volume Correction = for loose volume to bank volume, 1/(1 + swell factor).
 Hoe cycles are usually of greater duration than shovels times.
 Part of reason is after making cuts, the hoe bucket must be raised above ground level to load a
haul unit or to position above a spoil pile.
 Every movement of bucket equals increased cycle time.
Cycle time
The time taken by machine to complete one full cycle of operation is called cycle time.
Cycle time is composed of two times:-
1. Fixed time:-
It is the time spend on all operations other than travelling such as loading, dumping & turning etc.
2. Variable time:-
It is the time spend on travelling. It is function of distance travelled & speed.
 Correction to cycle time:-

18. Theoretically machine works for 60min in working hours under ideal conditions but actually at site
condition machine works for 50 min or 45 min. thus cycle should be corrected as
Corrected cycle time= Theoretical cycle time/Efficiency factor
 Procedure of equipment requirement design:-
 Estimate quantity of work to be dome (M3
)
 Find working time available ( hrs or week)
 Find average rate of production from schedule per hrs required to complete the work to be done
by time available. (M3
/hrs)
 Select suitable equipment & find its cycle time. Find no. of cycles per hrs.
Output=(Machine capacity) X (No. of cycles/ hrs)
 Find no of machines required.
 Add 10 to 30% capacity to serve for breakdown, refueling, rest causes etc.
Application of Hoes
(i) Small demolitions
(ii) Digging trenches, footings and basements
(iii)In pipe laying works
(iv)Transportation of building materials for a small distance.
(v) Close trimming during excavation
(vi)The backhoe bucket can be replaced with a breaker for working on hard strata.
The factors to be considered in selecting a hoe are,
1. Maximum digging depth required
2. Working radius for digging and dumping
3. Dumping height required
4. Digging width required (for trenches)
FACTORS AFFECTING OUTPUT OF EQUIPMENT
 Class of Material
 Depth of Cut
 Angle of Swing
 Size of Bucket
 Length of Boom
 Method of Disposal –Hauling
 Size of Hauling Units
 Skill of Operator
 Physical Condition of Equipment

19.  Job Condition Factors Affecting Output of Equipment
 Cycle Time
Draglines
Dragline is a cable operated excavating machine. Draglines are used to excavate earth and load it
into hauling units or to deposit in dams, spoil banks, etc. The dragline is designed to excavate below the
level on which it stands. A dragline does not have to go into a pit for excavation. It operates near the pit.
This is advantageous when earth is removed from a ditch, canal or pit containing water.
Long boom of the dragline allows it to dig and dump over longer distances as compared to a
power shovel or a hoe. It is possible to use a dragline with a long boom to dispose off the earth in one
operation when the earth is to be deposited near the pit. This eliminates the need for hauling units, thus
reducing the cost.
For underwater works, the buckets with perforations are used to permit water to drain out from
the material. Dragline is used to excavate the loose earth and load it into hauling units such as trucks,
tractors wagons, or to deposit it in dams and spoil banks.
This will be very advantages when a earth is removed from a ditch, canal or pit containing water.
Draglines are excellent units for excavating trenches when the sides are permitted to establish there
angle of repose without shoring.
The dragline is designed to excavate below the level of the machine. A dragline usually does not
have to go into a pit or hole in order to excavate. It operates adjacent to the pit while excavating material
from the pit the bucket is lowering in to pit etc.
Frequently, it is possible to use a dragline with a long boom to dispose of the earth in longer
distance or if the material can be deposited along the canal or near the pit. This eliminates the need for
hauling units, thus reducing the cost of handling the material. It has a long light crane boom and the
bucket is loosely attached to boom through cables. It can dig and dump over larger distances than a
shovel can do. Used for digging below its track level and handling softer material.
 Types of draglines,
1. Crawler mounted draglines
2. Wheel mounted draglines
3. Truck mounted draglines
Crawler mounted draglines works at low speed of 2 kmph. They are good on soft ground. Wheel
mounted and truck mounted draglines works at high travel speeds of more than 50 kmph.
 Size of a Dragline
It is indicated by the size of the bucket, expressed in cu.m. The size varies from 1 cu.m. to 15
cu.m. Size of a bucket should be reduced when a long boom is used or when the material has high

20. specific gravity because the maximum lifting capacity of dragline is limited by the force which will tilt
the machine over.
In practice, the combined weight of the bucket and its load should produce a tilting force which
is not more than 75 % of the force required to tilt the machine.
 Basic parts and operation of a Dragline
Excavation is started by swinging the empty bucket to the digging position, while at the same
time slacking off the drag and the hoist cables. Excavation is accomplished by pulling the bucket
towards the machine while regulating the digging depth by means of the tension maintained in the hoist
cable. When the bucket is filled, the operator takes in the hoist cable while playing out the drag cable.
Hoisting, swinging and dumping makes one cycle.
Output of a Dragline
The output of a dragline is expressed in cu.m. per hour.
Output =
( ) ( . )
The output depends upon the following factors,
 Type of material
 Depth of cut
 Angle of swing
 Size of bucket
 Length of boom
 Method of disposal

21.  Capacity of hauling units, if any.
 Mechanical condition of the machine
 Skill of the operator
 Job conditions
The output of dragline is expressed in cubic metres per hour.
 Applications of Clamshell:
Used for handling loose material such as crushed stone, sand, gravel, coal etc.
Main feature is vertical lifting of material from one location to another.
Mainly used for removing material from coffer dam, sewer main holes, well foundations etc.
Used in open-cast mines to remove loose materials.
Remove the coal or phosphate from mine site.
 Limitations
The primary limitations of draglines are their boom height and boom length, which limits where
the dragline can dump the material.
Another primary limitation is their dig depth, which is limited by the length of rope the dragline
can utilize.
A dragline is most efficient excavating material below the level of their base.
While a dragline can dig above itself, it does so inefficiently and is not suitable to load piled up
material.
Clamshell
Since the shape of the bucket is like a clam fish and has hinged double shell it is named as
‘clamshell’. The clamshell has a crane boom with a specially designed bucket attached to it at the upper
end through cables. The bucket is in two halves (shells) hinged at the top. The bucket has either sharp
edge or teeth. The buckets with teeth are used for digging and the buckets with edge are used for
handling works.
The clamshell buckets are classified as heavy buckets and light buckets. Heavy duty buckets are
used for digging purpose and light-weight buckets are used for rehandling light materials like sand,
gravel, crushed stone, etc.

22.  Operation
The clamshell bucket is an attachment with a crane for vertical digging below ground level and
for placing materials at considerable height, depth, or distance.
It also uses it for moving bulk materials from stockpiles to plant bins, loading hoppers, and
conveyors. It can be used to dig loose to medium compacted soil.
 Clamshell operating procedures are as follows:
 Position and level the crane, ensuring the digging operation is as close to the radius as the
dumping operation. This prevents you from having to boom up and down, resulting in a loss of
production.
 Select the correct size and type of bucket for the crane.
 When lowering the clamshell bucket, if too much pressure is applied to the closing line brake,
the bucket will close and an excess amount of wire rope will unwind from the holding line hoist
drum. To avoid this, you should release the holding line and closing line brakes simultaneously
when lowering the open clamshell into the material for the initial bite. Engage the closing line
control lever to close the bucket. Control the digging depth by using the holding line control
lever and brake.
 If, during hoisting, the hoist line gets ahead of the closing line, the bucket will open and spill the
material. (This could also be caused by having too much wire rope on the hoist drum.) The
operator must hoist both the closing and holding lines at the same speed to keep the bucket from
opening and spilling material.
 When the clamshell bucket is raised enough to clear all obstacles, start the swing by engaging the
swing control lever. Hoisting the bucket can be performed, as it is swing to the dumping site. The
spring-loaded tag line will retard the twisting motion of the bucket if the swing is performed
smoothly.
 Dumping and unloading the clamshell is performed by keeping the holding line brake
applied while the closing line brake is released.

23.  Apply the closing line brake quickly after the load is dumped to prevent the closing line from
unwinding more wire rope than is needed to dump the material.
 After the bucket is emptied, swing the open clamshell back to the digging site. Then lower the
open bucket and repeat the cycle. The clamshell operating cycle has four steps: filling
(closing) the bucket, raising the loaded bucket, swinging, and dumping.
 The boom angle for clamshell operations should be between 40 to 60 degrees. Be careful when
working with higher boom angles, as the bucket could hit the boom.
 A clamshell attachment is not a positive digging tool. The height reached by the clamshell
depends on the length of the boom used
 The depth reached by the clamshell is limited by the length of wire rope that the hoist drum can
handle.
 For the safe lifting capacity for the clamshell, refer to the operator’s manual and the crane
capacity load chart.
 Clamshells types
 with teeth- for digging in harder type material
 without teeth - for re-handling purpose
 Clamshells are used for,
i. Accurate spot dumping of material in a confined space in a vertical plane.
ii. Removing materials from cofferdams, pier foundations, sewer manholes, etc.
iii. Lifting materials vertically from one location to another.
iv. Digging trenches.
v. Charging the materials in a bin, a silo or a stock pile.
vi. Handling materials like sand, gravel, crushed stone, etc.
 Working of a clamshell
For the purpose of digging, the bucket is lowered with shells open over the surface till it makes a
good contact with it and then it is closed. While closing, the weight of the bucket helps the teeth to dig

24. into the surface or material, thereby filling the bucket. The filled bucket is hoisted and swung to the
position where dumping is to be done. The contents are dropped by opening the bucket.
Capacity of a clamshell bucket is given in cubic metres. Clamshell buckets varies in capacity
from 0.25 cu.m. to 2 cu.m.
The factors affecting the production are,
1. Difficulty of loading the bucket
2. Size of the load
3. Height of lift
4. Angle of swing
5. Method of disposal
6. Skill of the operator
One cycle of operation consists of loading, lifting, swinging, dumping, swinging back and
lowering bucket.
Comparison between different types of equipment
Sr.no. Items of
comparison
Power
shovel
Back hoe Drag line Clam shell
1 Excavation in
hard soil or rock
Good Good Not good Poor
2 Excavation in wet
soil or mud
Poor Poor Moderately
good
Moderately
good
3 Distance between
footing and
digging
Small Small Long Long
4 Loading
efficiency
Very good Good Moderately
good
Precise but
slow
5 Footing required Close to
work
Close to pit Fairly away
from pit
Fairly away
from pit
6 Digging level Digs at or
above
footing
level
Digs below
footing
level
Digs below
footing level
Digs at or
below footing
level
7 Cycle time Short Shortly
more than
power
shovel
More than
power shovel
More than the
other
equipment
Trenchers/ Trenching Machines

25. These machines are used for digging trenches for water, gas or oil pipelines, shoulder drains on
highways, drainage ditches and sewers. They provide fast digging with better control of depths and
widths of trenches. They are usually crawler mounted. The trenching machines may be wheel type or
ladder type.
1. Wheel type Trenching Machines
Maximum cutting depth for this type is 3 m with trench width of 12 m. The excavating part of
the machine consists of a power-driven wheel on which a number of removable buckets are mounted
with cutter teeth.
The machine is operated by lowering the wheel to the desired depth, while the unit moves
forward slowly. The earth is picked up by the buckets and deposited onto the belt conveyor which
discharges the earth on either side of the trench.
These machines are suitable for trenches of shallow depths.
2. Ladder type Trenching Machines
Ladder type machines can dig 10 m deep and 3.5 m wide trenches. The excavating part of the
machine consists of two endless chains which travel along the boom. The chains are fitted with cutter
buckets provided with teeth. As the bucket travel up the underside of the boom, they bring out the earth
and deposit it on a belt conveyor which discharges it along either side of the trench.

26. Selection of Trenching Machine
The selection of trenching machine depend on,
(i) Job conditions
(ii) Depth and width of trench
(iii) Type of soil
(iv) Disposal of excavated soil
(v) Presence of ground water
Advantages of using a Trenching Machine
(i) It is faster and cheaper method of trenching.
(ii) It digs only as much as is necessary. A 10 cm pipe can be installed in a 15 cm wide slot cut
by a trencher.
(iii) It is a continuous process i.e. digging, lifting and dumping operations are continuous.
Factors affecting Selection of equipment for excavating trenches
The choice of equipment to be used in excavating a trench will depend on
1. The job condition
2. The depth and width of the trench
3. The class of soil
4. The extent to which groundwater is present
5. The width of the right of way for disposal of excavated earth.
Compactors/ Compaction Equipment
Compaction is the process by which the material particles are packed closed together through
reduction of air voids. Compaction is the process of increasing the density of a soil mass through the
application of static or dynamic force. Static forces are produced by a roller or compactor which
densifies the soil by its heavy weight.
Dynamic force uses a combination of weight and energy to produce a vibratory or tamping effect
on the soil. Compactor uses both static and dynamic forces to achieve the required density.
Soil compaction is done in order to achieve the following improvements,
1. Reduction or prevention of settlements.
2. Increased strength.
3. Improved bearing capacity.
4. Lower permeability
5. Controlled volume changes.
Compaction can be achieved by applying energy to the soil mass by following methods,
1. Impact – sharp blows.

27. 2. Pressure – static weight.
3. Vibration – shaking.
4. Kneading – rearranging.
Soil types and methods of compaction
Compaction of soil is achieved by applying energy to the soil by kneading, applying static
weight, vibration or impact.
Soil type Method of compaction adopted Type of Roller
Clay Kneading, Pressure, Impact Tamping (Sheep foot)
Silt Kneading, Pressure, Impact Tamping (Sheep foot), Pneumatic
Sand Kneading, Vibration Vibrating Smooth-wheel,
Pneumatic, Smooth static
Gravel Kneading, Vibration Vibrating Smooth-wheel,
Pneumatic, Sheep foot
Compaction is measured in terms of maximum dry density (MDD). The amount of compaction
can be controlled by the choice of compaction equipment, the thickness being compacted, the speed of
compaction and the number of passes of compaction equipment.
 Light Soil Compacting Equipments Or Manually operated vibrating plate compactors
These equipments are used for soil compacting of small areas only and where the compacting
effort needed is less.
1.Rammers:
Rammers are used for compacting small areas by providing
impact load to the soil.
2. Vibrating Plate Compactors:
Vibrating plate compactors are used for compaction of coarse
soils with 4 to 8% fines. These equipments are used for small
areas.

28. 3. Vibro Tampers:
This machine is suitable for compaction of all types of soil
by vibrations set up in a base plate through a spring activated
by an engine driven reciprocating mechanism.
4. Rammers
Rammers are used for compacting small areas by providing
impact load to the soil.
This equipment is light and can be hand or machine operated.
The base size of rammers can be 15cm x 15cm or 20cm x
20cm or more as per requirement of area.
Various compacting equipment available are,
 Smooth-wheel rollers
 Tamping rollers
 Pneumatic-tyred rollers
 Vibrating compactors
1. Smooth-wheel rollers
The diameter of front roll is around 105 cm, its width being around 100 cm , and it gives a load
of around 35-40 kg/cm width.
The diameter of rear roll is around 145 cm, its width being around 50 cm , and it gives a load of
around 70-80 kg/cm width. Self-propelled type.
Weighing from 5 to 15 tonnes.
Used for ordinary rolling work where deep compaction is not required. These rollers may have
one front and two rear wheels.
The rear wheels are being usually larger in diameter and the front one being winder. Weight of
rollers may be increased by filling water or sand or ballast in hollow cylinder. These rollers are effective
in compacting granular soils, such as sand, gravel and crushed stone.

29. 2. Tamping rollers (Sheep foot rollers)
This type of roller consists of a hollow steel drum on whose outer surface a number of projecting
steel feet are welded. The weight of the drum may be increased by adding water or sand to produce high
pressure under the feet.
As a tamping roller moves over the surface, the feet penetrate the soil to produce a kneading
action and a pressure to mix and compact the soil from the bottom to top of the layer.
3. Pneumatic-tyred rollers
These are used for compaction in earthwork. They produce more even compaction across the
rolling width than wide steel wheel smooth rollers.
These are the surface rollers which effect compaction by kneading action. These rollers are
available in weights ranging from 6 to 30 tonnes with 500 to 4000 kg per tyre and tyre pressure from 2
to 8 kg/cm2.

30. 4. Vibrating rollers (Vibratory rollers)
Vibratory rollers are available in 8 to 10 tonnes weight. Certain types of soil like sand, gravel,
etc. require a combination of pressure and vibration for effective compaction. These rollers are actuated
by an eccentric shaft which produces the vibratory action. The impacts imparted by the vibrations
produce pressure waves which set the soil particles in motion, thus producing compaction.
Vibratory rollers are available in following forms,
(i) Roller with large vibrating drum in front with two pneumatic tyred rear driving wheels. The
pneumatic tyres offer better traction in moist soils.
(ii) Roller with tandem smooth wheels, either one wheel vibrating and driven or both wheels vibrating
and driven.
(iii) Towed vibrating rollers weighing 5 to 11 tonnes are used for mass earthworks, embankments, rock
fill dams, etc.
 Output of Compactor
Output of a compactor can be expressed in two ways,
1. Surface Capacity
It is calculated neglecting the thickness of the layer. It is indicated in square metres per hour. It
considers the area of the surface compacted in one hour.

31. Q = C m2
/hr
Where,
Q = output in m2/hr
W = drum width in metres
S = average compaction speed in km/hr
P = number of passes
C = efficiency factor or site operating coefficient includes repair, inspection, breaks and other
factors affecting the efficiency. It is taken as,
0.8 under excellent conditions,
0.7 under good conditions,
0.6 under fair conditions.
Number of passes is calculated considering forward and return travel as two passes.
2. Volumetric Capacity
This gives a clear idea of the output of the roller, as it also includes the thickness of the layer. It
is expressed in cubic metres per hour.
Q = C m2
/hr
Where,
Q = output in m3/hr
W = drum width in metres
S = average compaction speed in km/hr
P = number of passes
T = layer thickness after compaction, in metres
C = efficiency factor or site operating coefficient