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CIVIL ENGINEERING

INTRODUCTION

Construction is a creation of something which will serve the purpose for which it is built. There

are many stages of a project. The first stage is to prepare plans and specifications by planning

engineers / architects. Then it passes to the stage of design and ultimately it goes to the construction

engineer. A great responsibility lies on the shoulders of construction engineer in converting plans

and specifications into a finished product at the lowest possible cost. So construction is the ultimate

objective of the project. If the construction is not carried out properly, all the beauty of planning and

all the soundness of design will mean little.

While dealing with the construction stage, selection of the most suitable equipment is a very

typical problem which is generally faced by the construction engineers or contractors. They should

keep in mind that the money spent on equipment is an investment. This investment must be

recovered during the useful life of the equipment with reasonable amount of profit. Equipment should

be purchased only when it is well established, that the equipments purchase is beneficial and is not a

losing proposition keeping in view its requirements and possible use.

STANDARD AND SPECIAL EQUIPMENT

There is no clear cut demarcation between standard equipment and special equipment. It

depends on extent of its use, availability and cost. Equipment which is standard for one may be

special equipment for other. However, a standard equipment has the following properties in general;

1. The initial investment of standard equipment is usually much less than that of special

equipment.

2. Standard equipments are easily available in the market and can be procured with short notice

period.

3. In case of breakage, the shutdown period of the equipment is comparatively very short

because replacement parts are readily available.

4. It may be economically on more than one project.

5. It has greater adaptability such as power shovels convertible into draglines.

6. Trained operators and mechanics for standard equipment are easily available.

7. It is disposed off more easily.

8. Its resale value is very high.

Because of above reasons, contractors/Engineers/Project managers are advised to purpose

standard equipments unless a project definitely and economically justifies the purchase of special

equipments. A special equipment is defined as an equipment which is manufactured for use on a

single project or for a special type of operation. Such equipment may not be suitable or economical

for use on another project. The examples of special equipments are;

i) A30 cubic meter power shovel.

ii) A canal trimmer used for final trimming of the bottom and sides of an earthen canal.

iii) A belt conveyer used for transporting materials for several kilometers.

The special equipments should be purchased when the total cost with reasonable amount of

profits is recoverable during its useful life in a project.



The example of standard equipments are 2/4 wheel tractors, diesel powered power shovel,

crawler mounted power shovel, concrete mixers, etc.

SELECTION OF CONSTRUCTION

EQUIPMENTS

Basically there are two aspects for the selection of construction equipments in a project. The

first aspect deals with the type, size and other particulars of the equipments and the second aspect

whether it is to be purchased, hired or to be procured under hire-cum-purchase arrangement, but in

all the aspects, the following factors must be taken into account before having a final choice;

I) Existing Equipments

Maximum utilization of the existing equipment should be done in order to reduce the cost of

production to the minimum. If certain type of equipment is already being used in the project, it is

desirable to have additional equipment of the same type because the existing workmen are

already acquainted with the operation of such machines and the workshop is well equipped with

the spare parts and repairing of spare parts.

II) Availability of the equipment

As far as practicable the equipment which is easily available in the market should be selected

for the purpose because any delay in delivery may increase the cost of production substantially.

III) Standard Equipment

In general the choice should be restricted to standard equipment because its delivery time is

short, trained operators are available and spare parts can be easily procured in the market,

repairing may be done easily.

IV) Special Equipment

If the project is very big, special equipment may be selected provided the economic analysis

justifies the purchase. If it is not available in the authorities to suit the job requirements.

V) Operating Cost

The most efficient and therefore the most economical equipment is one whose operating cost

is the minimum. Record of such equipment previously used should be taken as a guide for

determining its suitability and economic viability. However in absence of this guide, fresh

economic analysis should be made.

VI) Indigenous Equipment

It is always advisable to purchase equipment which is manufactured in our country because

this will decrease the repair cost and down time cost and at the same time it will be beneficial to

the nation also.

VII) Obsolescence

Obsolescence of the equipment should not be overlooked. Research and development going

on in the design of equipment should be ascertained.

VIII) Economic life

Economic life of the equipment must be analyzed and it should not be less than the useful

period of the project.

IX) Cost benefit analysis

For various alternatives, cost benefit analysis must be made and selection is based on

economic only. The equipment must pay for itself by earning more money than its cost.



X) Suitable of equipment for future

The equipment should be of versatile nature so that It can be used for other purposes which

will mean higher demand and will bring higher rescale value.

XI) Study of site condition

Topographical condition, type of soil, existing approach roads and other working conditions

must be studied before making any final decision.

XII) Size of Equipment

Size of equipment should meet the demand of work. It is better to use more than one

equipment of small size than using of one of large size.

COST OF OWNING AND OPERATING

The cost of possession of an equipment is called cost of owning to which can be added the

cost of fuel for running the equipment. It is general estimated on hourly basis. This is the amount

by which an equipment should be hired. Of course it does not include the labour cost. There are

several methods of determining the probable cost of owning and operating of a construction

equipment but there is no guarantee that similar equipment will have similar cost if used under

different conditions. Old records of the equipment used in the past maybe considered as a guide

but it must be modified as per the given situation to arrive at there alistic value. The following

factors affect the cost of owning and operating.

a) Initial cost of the equipment which consists the price of equipment, transportation cost,

loading and unloading charge and installation cost.

b) Severity of service condition under which it is to be used.

c) No. of hours it is used per year.

d) The care with which it is maintained and repaired.

e) The demand for equipment after its useful period i.e. the salvage value.

f) Useful life of equipment in years.

When detailed cost records based on past performance of equipment are not available, it

must be analyzed from the first principles. The following costs constitute the cost owning and

operating.

i) Depreciation cost

ii) Maintenance & Repair cost

iii) Investment cost

iv) Fuel or energy consumption cost

v) Lubricating oil cost

Depreciation cost, maintenance & repair cost and investment cost should be obtained separately

on yearly basic by using the appropriate methods and later on converted into hourly cost.

However, fuel/energy cost and lubrication cost is derived on the hourly basic only.

DEPRECIATION COST An expenditure that decreases in value with the passage of time must be apportioned over its

life. The term to describe this loss in value is called DEPRECIATION. In other words, Depreciation

is the loss in value of equipment resulting from wear and tear or obsolescence. The owner of the

equipment must recover the loss in value of the equipment during its useful life by way of

depreciation. There are five common methods for determining the cost of depreciation;

a) Straight of depreciation

b) Declining Balance method

c) Sum-of-the-years-digits method

d) Sinking fund method

All the five methods mentioned above have been discussed in details in article 5.6 of the



chapter Engineering Economy.

In general, the standard equipments are preferred in the construction industries. However,

special equipments also may be considered provided the economic analysis justifies its selection. So

for all equipments used in the construction, annual depreciation cost is obtained by straight line

method if the equipments do not suffer from the danger of obsolescence. Using straight line method;

annual depreciation cost of the equipment is found;

Initial value Salvage valueAnnual depreciation = Useful life of equipment (in years)

Initial value of the equipment consists; price of equipment + transpiration + loading and unloading

charge + Installation charge. At the end of the useful life, the value obtained because of disposal of

equipment may be in the term of salvage value or scrap value. ]]]]]]]]]]]]]]]

MAINTENANCE AND REPAIR COST

The annual cost of maintenance and repair is based on experience obtained from the

operation of the equipment under average conditions. The actual cost varies with the conditions

under which it is used and the care with which it is handled. It also varies with the type and quality of

equipment. The annual cost of maintenance and repair may be expressed independent of

depreciation. But in any case, it should be sufficient to meet all maintenance work including cleaning,

washing, checking of component units, instruments, ropes, adjustment of component units as well as

routine and major repairs.

Normally,

Annual maintenance and repair cost = 50 to 100% of annual

depreciation but 100% is the fair value.

INVESTMENT COST

In order to own an equipment, the owner has to spend money. So, the chance of earning the

interest on that amount is lost. In addition to it, the surance premium and the storage charge. So the

amount consisting of interest, taxes, insurance and storage is called the investment cost which must

be realized during the life of the equipment. Some equipment. Some equipment owner charges a

fixed percentage of the original cost of equipment each year equally which is much higher than it

should be. Since insurance, taxes are usually paid on the depreciated value of equipment. The

amount of interest charged also should be based in the book value of the equipment. So the realistic

value of investment cost of a particular year will be some percentage of the book value of that year.

But this process appears cumbersome, it is proper to use the average value of the equipment in

determining the average annual cost of investment.

Generally,

Annual Investment cost = 10 to 12% of the average annual cost of the equipment. The

average annual cost of the equipment may be found out by the following ways;

Case I. When there is no salvage value of the equipment.

P+P Pav= n 2 P (n+1) Pav= 2

Case II. When there is salvage value of the equipment. The average value of the equipment is the

sum of the values at the beginning of the first year and the end of the last year divided by 2.

P+ (P-S)/n+S Pav= 2 P (n+1) + S (n-1) Pav= 2n



Where P = Total original cost

Pav = Average value

n = Life in years

s = Salvage value

In both cases above, the book value is based on straight line depreciation.

FUEL OR ENERGY CONSUMPTION COST Construction equipment must require fuel in the form of gasoline oil, diesel, electrical energy

and lubricating oil which is considered as OPERATINGCOST. As the amounts consumed depend

upon type of equipment, its rated horse power, location, temperature, atmospheric pressure and the

conditions is the most significant to estimate the realistic consumption of the fuel per hour. These

working conditions of the engine are defined by engine factor i.e. the extent to which the engine will

operate at full power all the time and the time factor i.e. the actual time that the engine will operate in

one hour.

ENGINE FACTOR

As per rated horse power of the engine, the equipment is capable of developing a rated

horse power when operating at maximum output, but it is well known that the engines used in

construction industry seldom operate at the rate output, expect for short period of time. A tractor

engine may operate at maximum power when shovel engine may operate at rated HP only when it is

loading the dipper, and during the balance of the cycle the demand on the engine will be reduced

substantially, resulting in a decreased consumption of fuel.

Consider a cycle time of 20 sec. of a power shovel which consisted filling the dipper, swinging

the boom, unloading the materials in a waiting truck, and swinging back to the original position for

operating another cycle. Out of this cycle time of 20 sec. the power shovel was operating at a rated

HP only when it was filling the dipper requiring only 5sec.for the purpose and the rest of cycle time

i.e. during other 15 sec. the engine was operating at not more than half of its rated H.P.

Engine Factor;

a) Filling the dipper (5 second out of 20 second cycle time operating at full rated H.P.) = 5 x 1 =0.250

20b) Rest of cycle (15 second out of 20 second cycle time operating at half rated H.P. ) = 15 x 1 =

0.375 20 2Engineer Factor = 0.250 + 0.375 = 0.625

TIME FACTOR It is worldwide phenomenon that a driver does not operate the engine for all the sixty minutes

of an hour. He must rest for 10 to 15 minutes in an hour, during which he shuts off the engine,

therefore during this period there will be no consumption of fuel. Hence the person while estimating

the fuel consumption, he must find out the actual time that the engine will operate in an hour.

Consider power shovel operates only 45 minutes in an hour.

Time Factor = 45 = 0.75 60

OPERATING FACTOR = ENGINE FACTOR X TIME FACTOR

For above example:

Operating factor of power shovel = 0.625 x 0.75 = 0.468. Therefore the average power

generated by the engine = Operating factor x rated HP and the realistic consumption of fuel depends

upon the average power generated by the engine and is obtained by the following ways;

Fuel consumption in liter per hour

(For a gasoline engine) = Operating factor x rated HP x 0.30

Fuel consumption in liter per hour



(For a diesel engine) = Operating factor x rated HP x 0.20

A common value of operating factor for an engine during a construction equipment may be

taken as 0.6 if detailed information regarding its engine, factor and time factor are not available.

LUBRICATING OIL COST An engine must need the lubricating oil for its smooth functioning and getting more output at

minimum loss on account of frictional force in the machine. The quantity depends upon the size of the

engine, the capacity of crankcase, the condition of piston rings, and number of hours between oil

changes. It is a common practice to change oil entirely every 100 to 200 hrs.

An empirical formula may be used to estimate the quantity of lubricating oil;

Rated HP x operating factor x 0.003kg per HP hr + Cq = 0.74 kg per liter t

Where;

q= Quantity of consumed lubricating oil in liter / hr.

c = Capacity of crankcase of engine in liter.

t= No. of hours between changes.

The operating factor may be assumed as 0.6 when sufficient data is not available for the

purpose.

ECONOMIC LIFE OF CONSTRUCTION EQUIPMENT A construction equipment has two types of life estimates, viz, the economic life and the

physical life. A machine though it can be rendered usable for a long period of time (till the end of its

physical life). Through expensive maintenance and repair cost, may have smaller economic life

during which it gives maximum rate of return with the lowest possible cost per unit of production. The

economic life may be defined as the age (in years) of replacement that maximizes the profit returns

from the equipment or minimizes the cumulative hourly owning and operating cost.

Selection of the economic life of any equipment is a very typical problem which is faced by the

construction engineer and it requires the judicious analysis of the various costs of owning and

operating of the existing similar kind of equipment. If the owner replaces the equipment very soon, he

will have unnecessary capital loss whereas if he waits very long, the equipment will have exhausted

its period of economic operation.

The economic life is determined on the basis of estimates made for existing equipment

assuming that the pattern of cost and production followed by a new machine will be the same as done

by an old machine. The owner must consider all costs related to the ownership and operation of the

equipment. The cost includes;

1) Depreciation and replacement

2) Investment

3) Maintenance and repair

4) Downtime

5) Obsolescence

The hourly owning and operating cost for each year of life is estimated taking all the above

costs into account and then cumulative owning and operating cost is plotted against cumulative

operating hours (no. of years of life) and a minimum slope tangent is drawn to the resulting curve the

point of a minimum determines the economic life of the equipment.

Depreciation and replacement cost For consideration of replacement cost of the equipment, it is necessary to know the salvage

value of the similar equipment for each year of its life separately. Since the average cost of the

construction equipment has been increasing at a rate of approximately 5% per year during the past



10 years. So, the replacement cost must be increased 5% per year to accommodate the increase in

the cost of equipment.

Investment cost The investment cost is assumed to be 10 to 12% per year of the value of the equipment at

the beginning of the year.

Maintenance and Repair cost The cost of maintenance and repair cost largely varies with the condition under which the

equipment is used and the care with which it is handled. So, it is essential to keep accurate records

of these costs.

Downtime CostDowntime is the time which is lost when the equipment is undergoing repairs and adjustments. It

increases with the passage of time. If an equipment is down 5 percent of time, its availability for actual

production is 95 with an average downtime of 5%.The cost per hour for this downtime will be

0.05x5=Rs.0.25 and if the machine is used 2000 hours per year, the annual cost of downtime will be

2000xRs.0.25=Rs.500

Obsolescence costThe continuous improvements in the design of construction equipments have resulted in lower in

lower production cost. For example, if a new equip

Table7.1 SUMMARY OF CUMULATIVE COST PER HOUR

ITEM 1 Year 2

Years

3

Years

4 years 5 years 6 year

Depreciation

and replace

men cost

30.00 25.00 21.70 18.40 17.10 16.75

Investment cost 12.00 10.95 9.40 7.60 6.90 6.10

Maintenance

and repair cost

4.40 6.30 7.90 9.40 11.10 12.30

Obsolescence

cost

0.0 1.50 3.00 4.50 6.00 7.75

Cumulative

cost per hour

48.20 46.45 45.50 44.10 46.00 48.50

ECONOMIC LIFE OF EQUIPMENT=4 YEARS

Construction EquipmentsMen reduces the production cost by 5 percent when compared with the production cost for an

existing machine, the existing machine will suffer a loss in value equal to 5% and this is defined as

abso9lescence cost. During have averaged about 5% per year and it appears that future

improvements may continue at the same rate.

Initial cost of construction equipment =Rs.200, 000

No. of hours used per year=2000

Cost per hour to run and operate equipment =Rs.60

During the details analysis, the examined in determining the economic life of the machine.



ENGINEERING FUNDAMENTALS OF

EQUIPMENTSRolling Resistance

Rolling Resistance is a measure of force that must be overcome to pull or roll a vehicle

over the surface .This resistance varies considerably with the type and condition of the surface over

which a vehicle moves. Soft earth offers a higher rolling resistance than hard surface like concrete

pavement. In case of vehicle moving on wheel, the rolling resistance is affected by size, pressure and

design of the tread of tyres too. For crawler mounted vehicle, it depends on the condition and type of

the road surfaces also, A narrow-tread high-pressure tyre gives lower rolling resistance than the

broad-tread low pressure tyre on a hard surface because of the smaller area of contact between the

tyre and the surface but if the road surface is soft, the tyre will tend to sink into the earth, a broad-

tread low pressure tyre will offer a lower rolling resistance than the narrow tread high pressure tyre.

The rolling resistance also varies with the weather and soil conditions. If the earth is stable, highly

compacted, well maintained with a grader and if the moisture content is kept near the optimum value,

the rolling resistance is low as compared to concrete and asphalt.

Rolling resistance is expressed in Kg of tractive pull required to move each gross tonne over a level

surface of the specified tyre or condition.

Determination of Rolling Resistance The Rolling Resistance of a haul road can be determined by towing a truck or other vehicle

whose gross weight is known along a level section of the haul road at a uniform speed. The tow cable

is fitted with a dynamometer which measures the average tension in the cable. The ration of the

tension to the gross weight is the required rolling resistance of the haul road.

Although it is impossible to give exact values of rolling resistance for all types of haul road

and the wheels, the values given in table 7.2 are reasonably accurate and may be used for

estimating purposes.

Table 7.2 ROLLING RESISTANCE(Kg per tonne of gross weight)

Type of SurfacesSteeltyres

Crawlertype tracks

Wheel tyres

Highpressure

Lowpressure

a) Smooth concrete 20 27.5 17.5 22.5

b) Good asphalt 25-35 30-35 20-32.5 25-30

c) Earth compacted and well maintained

30-50 30-40 20-35 25-35

d) Earth, rutted, muddy,no maintenance

50-75 40-55 50-70 35-50

e) Earth poorlymaintained

100-125 70-90 90-110 75-100

f) Loose sand and gravel 140-160 80-100 130-145 110-130

g) Earth very muddyrutted and soft

175-200 100-120 150-200 140-170

Grade Resistance

Grade Resistance is a measure of the force that must be overcome to move a vehicle over

unfavorable grade (uphill).Grade assistance is a measure of the force that assists vehicle



movement on favorable grade (downhill).

Grades are generally measured in percent slope (%), which is the ration between vertical rise

or fall and the horizontal distance in which the rise of fall occurs. A 1 percent slope is one where the

surface rises or falls 1 mete vertically in a horizontal distance of 100 meter. Uphill grades are

normally referred to as averse grade usually expressed as a positive (+) percentage while downhill

grades are referred to as favorable grades expressed as a negative (-) percentage.

The effect of grade is to increase, for a plus slope, or to decrease, for a minus slope, the

required tractive effort by 10 kg per gross tonne of weight for each 1 percent of grade. While the

amount is not strictly correct for all slopes, it is sufficiently accurate for most construction equipment.

It is the physical property which is not affected by the types of equipment or the condition or type of

the road.

Total Resistance This is the combined effect of rolling resistance (wheel vehicle) and grade resistance. It is

expressed in kg.

Total resistance = Rolling resistance + Grade resistance.

Usable tractive effect= Available tractive effect Total resistance

The useable tractive effort is responsible to pull the vehicle in the given condition.

Coefficient of Traction The coefficient of traction may be defined as the factor by which the total load on a driving

tyre or track should be multiplied in order to determine the maximum possible tractive force between

the tyre or track and the surface just before slipping will occur.

Consider a truck resting on a level haul road of dry clay. The total pressure between the

driving tyres and the road surface is 400 kg and the slippage starts as soon as the tractive force

between the tyres and the surface reaches a value of 2400 kg, the coefficient of traction would be

2400/4000 = 0.60.

The coefficient of traction is affected by

i) Weight on the driving wheels or tracks

ii) Gripping action of the wheel or track, i.e. type of tread on the tyres or design of

the grouser of tracks.

iii) Ground conditions.

These variations are such that exact values cannot be given. However, the Table 7.3 gives

approximate values for the coefficient of traction between rubber tyres or the crawler tracks and the

road surfaces which are sufficiently accurate for the estimating purposes.

Surface Rubber Tires Crawler Tracks

Rough Concrete 0.80-1.00 0.45

Dry clay loam 0.50-0.70 0.90

Wet clay loam 0.40-0.50 0.70

Wet sand and gravel 0.30-0.40 0.35

Loose, dry sand 0.20-0.30 0.30

Dry snow 0.20 0.15-0.35

Ice 0.10 0.10-0.25

While purchasing a tractor, coefficient of traction must be demanded from the manufacturer,

because the energy of the equipment which is pulling a load can be converted into tractive effort only

if sufficient traction develops between tyres or tracks and the surface over which hauling is to be



done. In the absence of adequate traction, the full power of the engine can not be used and slipping

takes place.

Drawbar PullThe term drawbar pull is used in connection with a CRAWLER TRACTOR. The available pull which a

crawler tractor can exert on a load that is being towed is referred as the drawbar pull of the tractor.

The pull is expressed in kg. The performance of crawler tractors, as reported in the specifications

supplied by the manufacturer, is usually based on the assumption that the road surface has a rolling

resistance of 55 kg per tonne. If a tractor is used on a haul road whose rolling resistance is higher or

lower than 55 kg per tonne, the drawbar pull will be reduced or increased, respectively, by an amount

equal to the weight of the tractor in tonnes multiplied by the variation of the haul road over 55 kg/

tonne over tonne. If the crawler tractor is negotiating a upgrade slope, its drawbar pull will be further

reduced at the rate of 10 kg for each tonne of weight of the tractor for each 1 percent slope.

Effective drawbar pull = Available drawbar pull + Rolling resistance on a level haul surface +

grade resistance for upgrade/downgrade slope.

I. If a crawler tractor weighting 20 t moves over a level haul surface offering rolling

resistance (a) 90 kg/t (b) 45 kg/t.

Rolling Resistance to be overcome for (a) = - 20 x (90-55) kg

Rolling Resistance to be overcome for (b) = - 20 x (55-45) kg

II. Similarly, the tractor is negotiating slope (a) 45 upgrade (b) 4% downgrade

Grade Resistance for (a) = -20 x 4 x 10 Kg

Grade Resistance for (b) = +20 x 4 x 10 Kg

Rimpull Rimpull is a term used in connection with rubber tyres of wheel tractors. It defines the tractive

force between the rubber tyres of driving wheels and the surface on which the tyres operate. It is

expressed in kg and is calculated as per following condition.

Condition No. I

If the coefficient of traction is high enough that slippage is eliminated:

Maximum rimpull = 375 x HP x efficiency/ Speed in mph

(The efficiency of tractor may be taken between 0.80 and 0.85)

Condition No.II

If the coefficient of traction is such that slippage starts before its rated capacity;

Maximum rimpull = Total pressure between driving wheels and the surface x coefficient of

traction

GradabilityGradability is defined as the maximum slope, expressed as a percent, up which prime mover ( a

crawler tractor or wheel type tractor), may move at a uniform speed.

Determination of gradability of a tractor

a) Applying suitable factor of safety, the available drawbar pull of a tractor is taken not more

than 85% of the rated drawbar pull.

b) The drawbar pull of a crawler tractor, taken from the manufacturers specifications, is usually

based on rolling residence of 55 kg per tonne, any rolling resistance in excess of this amount

should be applied to the weight of the tractor.

c) The rolling resistance of a hauling unit is calculated as per the given specifications.

d) The combined rolling resistance is obtained by adding the rolling resistance of a crawler

tractor (b) and the rolling resistance of the hauling unit (c)



e) Pull available to negotiate the grade is obtained by subtracting the combined rolling

resistance (d) from the available drawbar pull (a)

f) Combined weight of tractor and its hauling unit is taken in tones.

g) Assuming 10 kg. Pull required per tonne of the combined weight per 10 grade, the gradability

of the given situation is ascertained.

EXCAVATING & TRANSPORTING

EQUIPMENTSA. TRACTOR:-

The primary purpose of tractor is to pull or push loads, and it may be unused also as mount

for many types of equipment such as bulldozer, shovel, dragline, hoe, trenchers etc.

Therefore, it is regarded as one of the most important equipments and is indispensable on

most of the construction projects whether small or big. There are sizes and types to fit

almost any job for which they are meant for.

TYPES OF TRACTORS

Tractors are divided into following types:

CRAWLER TRACTORWHEEL TRACTOR

TWO WHEEL TRACTORFOUR WHEEL TRACTOR

In selecting a tractor, several factors should be considered and some of them are enumerated as

follows:

a) The size required as per magnitude of the job.

b) The kind of job for which it is to be used like bulldozing, pulling a scraper, clearing land

etc.

c) The type of footing over which it is to operate i.e. high tractive or low tractive efficiency.

d) The firmness of haul road.

e) The smoothness of haul road.

f) The slope of haul road.

g) The length of haul.

h) The type of work it is to do after this job is completed.

CRAWLER TRACTOR If a tractor is mounted on crawler, it is called crawler tractor. A crawler track is an endless

chain consisting of steel links made of steel plats connected together by pins and bushings as shown

in fig. 7.5.

Among the construction equipments, the crawler tractor is the most basic and versatile

machine. Generally, it is used for moving heavy units on rough surface having poor traction. The

optimum pull that a crawler tractor can provide depends upon its weight and is equal to the coefficient

of traction (depending upon road surfaces) multiplied by the weight of unit, regardless of the power



supplied by the engine. Its maximum speed is limited to 10kmph while average speed lies between

4.5 to 5.6kmph. It is suited for short haul say 60 to 150m. Special advantage lies in its ability to travel

over very rough surfaces and to climb very steep grades up to 25 to 29% at a sped of 2.75kmph. A

crawler tractor has a life of 8 to 12 years (9000 to 16000hrs.) depending upon its horse power which

varies form 100 to 300 HP.

The following are the advantages claimed by crawler tractors.

i. Having more tractive effort it can operate on soft footing such as loose or muddy soil.

ii. It can operate in rocky formations where rubber tyres may be seriously damaged.

iii. It can travel over rough surfaces which may reduce the cost of maintaining haul roads.

iv. It has greater floatation because of lower pressure under the tracks.

v. Being compact and powerful, it can handle very difficult jobs.

WHEEL TRACTOR One of the basic advantages of a wheel tractor when compared with a crawler tractor lies in

its higher speed. For any earth moving project, job conditions will influence the layout of the project

and the performance of the machine working on it. But under all conditions, speed is what must be

stressed when applying the rubber tyred tractors. Sped is the biggest asset, and, when properly

used, can have an important effect on almost any earthmoving or material handling operation.

However, in order to attain a higher speed, a wheel tractor must sacrifice its pulling effort. As the

speed is increased through the selection of higher gears. The rimpull will be decreased in

approximately the same proportion. Because for a given unit whose engineer is operated at a rated

power, speed rimpul will always be constant.

Another point of a wheel tractor is that it possesses a lower coefficient of traction between

rubber tyres and some soil surfaces, the wheel tractor starts slipping before developing its rated

rimpull. Its useful life life lies between 8 to 10 yrs. (12,000 to 15,000hrs.) depending upon on its

horsepower which is generally more than 75 HP.

Among the advantages claimed by wheel tractors are as follows:

i. It can travel at higher speed (maximum speed up to 50kmph) on the job or more from

one job to another.

ii. It can give greater output where considerable traveling is necessary.

iii. It can travel over paved highways without damaging the surfaces.

iv. It can operate easily which makes the operator less fatigue.

v. A wheel tractor is very useful in the following conditions.

vi. Long push distance

vii. Fast return.

viii. Loose soil, little or no rock.

ix. Level or downhill work

x. Good underfoot conditions.

CRAWLER TRACTOR V / S WHEEL TRACTOR

The following factors should be considered when comparing crawler tractors with wheel

tractors:

1) Traction

Coefficient of traction for a crawl tractor is up to 0.9 where it is up to 0.60 for a wheel

tractor.

2) Useful rimpul

Since useful rimpull = machine weight x coefficient of traction, therefore, a crawler tractor

negotiates very heavy loads whereas a wheel tractor is useful for light loads.



3) Speed

A wheel tractor possesses speed up to 3 to 4 times higher than a crawler tractor. Where

haul distance is considerable and / or jobs are scattered at different locations, the wheel tractor

can be used more efficiently as to be compared with the crawler tractor.

4) Maneuverability

A wheel tractor has steering wheel which is easy to operate and control whilst a crawler

tractor is provided with stick control which is not easy to control. So articulated steering and good

visibility give high maneuverability to wheel tractors and better confidence to their operators.

5) Compaction

Ground pressure of wheel tractors vary from 1.25 kg/cm2 (0.125N/mm2 = 0.150 N/mm2 )

whereas the same for crawler for crawler tractor stands from 0.85kg/cm2 (0.085N/mm2 ) to 1.00

kg/ cm2 (0.1 N/mm2 ), hence crawler tractors can be effectively used on loose or muddy soil.

6) Cost

Crawler tractors are more costly initially than wheel tractors but on un-even, undulated

areas and particularly in rocky hilly areas, crawler tractors provide better service and prove

cheaper in the long run.

7) Operation and maintenance cost

Operation, maintenance and repair cost is less in wheel tractor as compared to crawler

tractor. Sometimes this cost along with under carriage cost may be the deciding factor in

selecting wheel or crawler tractors.

8) The tar and concrete pavements are liable to damage by crawler tractors while wheel

tractors are liable to slip over smooth footing.

TYPES OF WHEEL TRACTORS

There are two types of wheel tractors viz (a) Two wheel and (b) four wheel. In the two

wheel tractors, steering and driving both are done by the same wheels whereas in four wheels the

steering is done by front wheels (smaller in size) and driving is done by the rear wheels (bigger in

size). For the same power of the engine, the two wheel tractor develops more rimpull than that of four

wheels because of concentration of weight on the wheels (in case of two wheel tractors).

Among the relative advantages claimed by each type are as follows;

TWO WHEEL TRACTOR

1) Higher tractive force is available because the concentration of total load on the same

wheel.

2) Increased maneuverability because an operator has to manage the work of the steering

and driving with a skill.

3) Due to elimination of one axle, the rolling resistance is less.

4) The number of tyres to provide and maintain is only half that of four wheel type.

FOUR WHEEL TRACTOR

1) It is able to act as an independent unit when separated from the trailing unit.

2) It has got separate wheels (front) for steering purposes, so the operator feels better

confidence while driving.

3) There is less tendency to bounce on rough surfaces, so the driving is quite smooth.

4) It can be driven at higher speeds even on the rough surfaces because of the reasons

mentioned in (2) and (3).

B. BULLDOZER:-Bulldozers are very efficient excavating tools for short haul applications upto 100m and as

auxiliary machine to other construction equipments. In addition to excavating and hauling, many other

functions are also performed by the bulldozers. Therefore, they are called versatile equipments. In



many projects they may be used from the start to the completion of projects for various operations

such as;

i) Clearing land of trees and stumps including roots and of vegetation.

ii) Opening of temporary roads through rocky areas.

iii) Moving earth for haul distances up to 100m.

iv) Helping load tractor pulled scrapers.

v) Spreading and leveling earth fills.

vi) Back filling trenches.

vii) Clearing, the construction sites of debries and rubbish.

viii) Maintaining haul roads.

ix) Clearing the floors of borrows and quarry pits.

x) Stripping of the top soil that is not usable.

CLASSIFICATION OF BULLDOZERS

The bulldozers are classified on the following basis;

A) According to the direction of blades.

a) When the cutting blade is set perpendicular to the direction of travel, it is called

bulldozer. It pushes the earth forward and dump to some place.

b) When the cutting blade is set at an angle with the direction of travel, it is called angle

dozer. It pushes the earth forward and to one side, some times a v-blade.

B) According to the control of blade.

Based on the method of controlling (Lowering and rising) of blade, a bulldozer may be

classified as

i) Cable controlled bulldozer.

ii) Hydraulics controlled bulldozers.

Merit of cable controlled bulldozers.

a) Simple to install and operate.

b) Easy in repairing the controls.

c) Reduction in the danger of damaging a machine.

Merit of hydraulic controlled bulldozers.

a) Able to produce a high down pressure on the blades to force them (Blades) into the ground.

b) Able to maintain a precise setting of the position of the blade.

C) According to the mountings of a bulldozer may be classified as

i) Crawler-mounted bulldozer

ii) Wheel-mounted bulldozer.

Merits of a crawler-mounted bulldozers.

a) Able to deliver greater tractive effort especially useful when operating on loose or muddy soil.

b) Able to travel over very soft soil.

c) Able to operative in rocky formations when rubber tyres are likely to get damaged.

d) Able to travel over very rough surfaces having no haul roads.

e) Greater flotation because of low pressure under the tracks.

f) Versatile for various job conditions.



Merits of a wheel tractor bulldozer

a) Higher travel speed.

b) Elimination of hauling unit for transporting the bulldozer

c) Greater output, especially where considerable traveling is involved.

d) Less Operator fatigue.

e) Able to travel on paved highways without damaging the surfaces.

SELECTION OF BEST TYPE OF BULLDOZER

Among various types of bulldozers mentioned previously, none is superior to others under all

operating conditions. Each type has advantages under certain conditions. Therefore, it is the actual

job conditions where the bulldozer is put to work, will decide the most suitable type of bulldozer for the

purpose.

At the time of purchasing of bulldozer, the following points should be clearly specified after

examining the exact job requirements and the manufacturers limitation; engine horse power at the fly

wheel, total operating weight, speed range in various gear conditions, blade type and size, maximum

tilt position or angle position, turning radius, fuel tank capacities. In case of wheel dozers also check,

number and sizes of the tyres, wheel base, ground clearance etc.

THE OUTPUT OF BULLDOZERS

The output of a bulldozer can be defined as the bank measure volume, it handles per hour.

The output of the bulldozers depends upon following factors.

a) Size and condition of the bulldozer.

b) Distance traveled by the bulldozer.

c) Speed of operations.

d) Characteristic of soil being handled.

e) Surface on which the bulldozer is operating.

f) Efficiency of the bulldozer (blade factor).

The blade of a bulldozer has a theoretical capacity (expressed as rated mold board capacity)

which varies with the class of earth and the size of the blade. If the capacity of a blade is known, one

can approximately estimate the output of the bulldozer by determining the actual number of trips

(passes) it will make in one hour.

Output of a bulldozer in bank measure volume / hr.

Rated mold board capacity in loose volume. x Actual operating time in minutes per hour

Swell factor Time required per trip in minutes

Whereas,

Time required per trip in minutes or cycle time in minutes is given by

=D/F + D/R + G

D = Haul distance in meters.

F = Forward speed in meters / minute

R = Reverse speed in meters / minute

G = Gear shifting time in minutes (0.15 minute to 0.30 minutes)



C) POWER SHOVEL:-

Power shovel is a construction equipment whose purpose is to excavate the earth and load it

into the trucks or other pull equipment waiting nearby. They are capable of excavating all classes of

earth, except the solid rock without prior loosening.

Type of power shovel is described by its mounting. If it is mounted on crawler track, it is called

crawler-mounted power shovel, and if it is mounted on rubber tyred wheels it is referred as wheel-

mounted power shovel.

Size of power shovel is indicated by the size of dipper generally expressed in cubic meters.

They are available in size 3/8, , , 1, 1 , 1 , 2 and 2 cubic meter which come under the

category of standard power shovels. Larger size may be available on special order.

THE BASIC PARTS AND OPERATION OF A SHOVEL

The basic parts of power shovel consist the mounting (crawler track or rubber tyred wheel),

cab, boom, dipper stick, dipper and host line. These parts are illustrated in Fig. 7.6

For operation, first step is to release hoist to bring the dipper down and move the stick in a

vertical plane. Now the dipper is moved forward and downward with the cutting teeth pointing towards

the face to be excavated. The downward force is applied to the tip of the dipper through the dipper

stick. The depth of cut and angle of digging is controlled by the job conditions. When the dipper is

filled with the load, the next step is to pull out the dipper by applying the required tension through the

hoisting line and also to hoist it till he machine can be swung around for dumping. During swinging

the position of the dipper is so adjusted that it comes in most suitable dumping position. To empty the

dipper, the door is opened by unlatching it through the trip arrangement. The cycle is thus repeated

again and again.

SELECTION OF TYPE AND SIZE OF POWER SHOVEL

Best type and best size of a power shovel is decided after considering various techno-

economic factor must be considered;

a) Job location:

i) For numerous small jobs located at different places, rubber-tyred shovel will be better

choice due to its mobility.

ii) For concentration of large job at a particular location, mobility will be of less

importance, the crawler-mounted shovel will be more desirable.

b) Type of footing:

Sometimes the type of footing on which the shovel operates becomes the deciding factor. If

the ground surface is of very soft and muddy soil having large undulation, the crawler-mounted

shovel will be the only choice.

CHOICE OF SIZE

For selecting the best size of the shovel for the given job, the following factors must be

examined;

a) The cost of per cubic meter of output.

b) The job/site conditions.



a) The cost of per cubic meter of output

The best size of the shovel is one which offers the minimum cost of per cubic meter of output.

In estimating the cost per cubic meter, the following factors must be taken into account.

i) Size of job: Larger job may justify the higher cost of large size.

ii) Cost of transporting: Larger size will have higher cost of transporting.

iii) Depreciation rate: The depreciation rate for a large shovel be higher than for a small one

and the large size also may cause difficulties in its disposal.

iv) Down time cost : The cost of down time will be more for large shovels owing to increased

delays in obtaining spare parts of the large shovel.

v) Cost of wage: The cost of wages per cubic meter will be less for large shovel than for a

small one.

vi) The combined cost of drilling, blasting and excavating of rocks :Bigger size shovel should

need less expenditure on these cost as they themselves can handle bigger rocks and

thus saves the costs of drilling and blasting .

b) Job/site conditions

The following job conditions should be locked into while selecting the size of a shovel:

i) For high lifts to dump earth from basement into trucks will require long boom of a

large shovel.

ii) For excavating blasted rocks, large size dipper will easily handle bigger sizes.

iii) For excavating hard and tough bed of soil, the dipper of large shovel which can exert

greater downward pressure will be more suitable.

iv) If the project time such that it needs high hourly output, large shovel must be

preferred.

v) Size of hauling unit may determine the size of shovel. For smaller hauling unit smaller

size shovel and for larger hauling units, larger size should be used.

vi) The condition of existing highways and bridges imposing restrictions over moving

maximum load may instruct the size of the shovel.

OPTIMUM DEPTH OF CUT

The optimum depth of cut is that depth which produces the greatest output and at which the

dipper comes up with full load without excessive downward pressure and tension. This depth varies

with the type of the soil and the size of the dipper.

OUTPUT OF POWER SHOVEL

The output of power shovel is expressed in cubic meter per hour based on bank measure

volume.

The capacity of a dipper is based on struck volume but in case of certain soils the dipper may

pick-up a heaping volume which may exceed the struck volume. In every situation, the bank measure

volume of the dipper must be obtained as the average loose volume divided by 1 plus the swell

expressed as a fraction. Next, it requires the accurate estimation of one cycle time which includes

time required for digging, swinging, dumping and coming back. If no allowance is made for any lost

time;



Output of shovel = bank measure capacity of dipper x 3600/cycle time in second (m3/hr)

In general cases, Output of shovel

= loose volume of dipper X Actual time in seconds per hour x efficiency

(1 + Swell fraction) Cycle time in seconds expressed in cubic meter/hr.

Factors affecting the output of power shovel

The output of a power shovel is affected by numerous factors which are enumerated as

follows:

a) Class of material

The output of a power shovel varies with the class of materials. It is apparent from the data

given by Power Crane and Shovel Association of USA the data shows the ideal output measured in

cubic meter per 60min hour, bank measure of a 2 cum power shovel.

Moist loam or light sandy clay = 355 m3/hr

Sand and gravel = 330m3/hr

Good common earth = 300 m3/hr

Hard, tough clay = 265 m3/hr

Well blasted rock = 230 m3/hr

Wet, sticky clay = 185 m3/hr

Poorly blasted rock = 160 m3/hr

b) Depth of cut

If the depth of the face from which a shovel is excavating material is too shallow, cycle time

increases, consequently the output is reduced. If the depth of the face is greater than minimum

required to fill the dipper, the out-put is increased.

c) Angle of swing

The angle of swing of a power shovel is the horizontal angle (ex-pressed in degrees) between

the position of the dipper when it is excavating and the position when it is discharging the load. If the

angle of swing is increased the cycle time is also increased while if the angle of swing is decreased,

the cycle time is decreased. The output of shovel is inversely proportion of the cycle time. For

example if a shovel digging at optimum depth, has the angle of swing reduced from 900to 600 , the

output will be increased by 16%.

d) Job conditions

Job conditions may be classified as excellent, good, fair and poor depending upon the

situations of work site and climatic condition. These conditions greatly affect the output of the shovel.

A project may be known as having excellent job conditions when shovel operators in a large,

open pit with a firm and well drained floor and truck waiting by the side of the shovel, the ground may

be uniformly level yielding the optimum depth of cut, the haul road also not affected by climatic

conditions. In this case the output of the shovel will be the maximum.



The poor job conditions may be defined for a project of highway cut through a hill, the depth

of cut varying from zero the depth more than optimum depth. The cut being vary narrow the truck has

to keep behind the shovel having angle of swing of 180 at the same time haul road is badly affected

by climatic conditions. In this case the output of the shovel will be minimum.

e) Management conditions

The attitude of the management in establishing the conditions under which a shovel operates

will affect the output of the shovel. On the similar pattern of job conditions; management conditions

too may be excellent good, fair and poor. Excellent management conditions yield maximum output

while poor one may yield the minimum. However the following ways may be incorporated to improve

the management conditions thereby increasing the output;

Greasing and lubricating the shovel.

i) Checking the shovel parts subjected to the greater wear and tear and replacing the

worn parts.

ii) Replacing badly worn wire rope and dull dipper teeth with sharp ones.

iii) Giving a major overhaul when necessary.

iv) Keeping the pit floor clean and wide to reduce angle of swing while unloading.

v) Paying a bonus to the crew to encourage high production and providing competent

supervisor for the purpose.

vi) Paying a bonus to the crew to encourage high production and providing competent

supervisor for the purpose.

f) Size of hauling units

Size of hauling units like trucks affect the output of a shovel, for optimum output, size of

hauling units should be governed by size of a power shovel. If the shovel used is of smaller size, the

size of hauling units also must be small while for a large shovel, hauling units is of larger size.

g) Skill of Operator

If the operator of a shovel is skillful, he can judiciously apply his judgment in reducing the

angle of swing, improving job conditions, cutting the earth of the optimum depth etc. to increase the

output of a shovel.

h) Physical condition of the shovel

If the physical condition of a shovel is good, the output is increased, but if it is in bad shape, it

will be frequently subjected to wear and tear and the downtime is unnecessarily increased affecting

the output of the shovel.

METHODS OF IMPROVING THE OUTPUT OF

A POWER SHOVEL

Experience and good judgment are essential ingredients in the selection exact and correct

factors under which a power shovel has to operate. If the job planner is not able to select exactly the



correct factors, the actual output may vary from the estimated output. If the output is found to fall

below the estimated one, he should take corrective steps to increase the output and reduce the cost

of handling the materials.

METHODS OF IMPROVING THE OUTPUT OF

A POWRE SHOVEL

Experience and good judgment are essential ingredients in the selection of exact and correct factors

under which a power shovel has to operate. If the job planner is not able to select exactly the correct

factors, the actual output may vary from the estimated output. If the output is found to fall below the

estimated one, he should take corrective steps to increase the output and reduce the cost of

handling the materials.

i) Working cycle should be smooth, well balanced and well managed.

ii) Have a clear and minimum swing.

iii) Have sufficient number of hauling units to keep the shovel busy.

Avoid waiting time for the hauling unit as well as for the shovel.

iv) Load the hauling units uniformly, avoid overloading.

v) Proper positioning of shovel and hauling units for minimum time of cycle time of a

shovel.

vi) Dig the top half of the high bank first to avoid lowering of the boom in each cycle.

Then digging the next half should be taken up, this helps in reducing the cycle time.

vii) While waiting for the hauling units, do not keep shovel idle. This time should be utilized

in clearing the pit area, loosening the bank, clearing up corners, leveling the grade

etc.

viii) Keep dipper teeth sharp.

D) Dragline:-

Since the basic character of the machine is dragging the bucket against the material to be

dug, it is called as DRAGLINE. A dragline is used to excavate the earth and load it into hauling units

such as trucks or tractor pulled wagons or to deposit it into dams/embankments or spoil banks near

the pit from which it is excavated. Primarily, the functions of a dragline are same as that of a power

shovel but in some projects, a dragline has distinct advantages compared with a power shovel

because of its long light boom.

Advantages of Dragline over power shovel

i) A dragline usually does not have to go into a pit or hole for excavating the earth. It may

operate on natural firm ground. Therefore, it is more useful when the earth is removed

from a ditch, canal or pit containing water.

ii) When the excavated earth is to be deposited on nearby banks or dams, it is better to use

dragline with a long boom enough to dispose of the earth in one operation, eliminating the



need of hauling units thereby reducing the cost handling the earth.

iii) A dragline is excellent for excavating trenches without shoring.

Disadvantages of dragline over power shovel

As compared to a power shovel, the output of the dragline in terms of excavation of earth is

about 75 to 80% for the same size of bucket capacity.

Types of draglines

Draglines are of three types as given below:

i) crawler-mounted dragline

ii) Wheel mounted (self propelled) dragline

iii) Truck-mounted dragline

A crawler mounted dragline can operate on surfaces which too soft for wheel or truck

mounted dragline but its speed is as low as 2 kmph whereas wheel or truck mounted

draglines have advantages of mobility. They can travel as high as 50 kmph.

The description of a dragline

The Fig shows the basic parts of a dragline.

Excavation is started by swinging the empty bucket to the digging position at the same time slacking

off the drag and the hoist cables. Then the bucket is pulled towards the machine while the digging

depth is regulated by means of the tension maintained in the hoist cable. When the bucket is filled,

the operator takes in on the hoist line while playing

Out the drag cable. Hoisting, swinging and dumping of the loaded bucket follow in that order, and

then the cycle is repeated.

Size of dragline

The size of dragline is expressed by the size of its bucket, measured in cubic meter. Power

shovel up to a capacity of 1.9 cubic meter, can be converted into dragline, by replacing the book of

the shovel with a crane boom and substituting the dragline bucket for the shovel dipper.

Most draglines may handle more than one size bucket, depending on the length of the boom

and the class of material excavated. When the size of bucket is to be increased or decreased,

simultaneously the length of the boom should also be changed as the maximum lifting capacity of a

dragline is limited by the force which will cause of the machine . In practice the combined weight of

the bucket and its load (called capacity of dragline in kg) should produce a tilting force not greater

than 75% of the force required to tilt the machine over. A larger boom, with a smaller bucket, may be

used when it is necessary to increase the digging reach or the dumping radius.

The range of various components of a dragline illustrated in the Fig 7.8 given below in the

Table

Table Particulars of the components with reference to Fig 7.8 Range

Boom length (J)Capacity in Kg

15m to 24 m5400 to 2700



Boom angle in degree (K)Dumping radius in meter (A)Dumping height in meter (B)Maximum digging depth in (C)Digging reach (D)

20 to 4512 to 133 to 1312 to 6Depending on working conditions

OUTPUT OF DRAGLINE

The output of a dragline is expressed in cubic meter per hour bank measure. The following

factors affect the output;

i) Class of material

ii) Depth of cut

iii) Angle of swing

iv) Size and type of the bucket

v) Length of the boom

vi) Job conditions

vii) Management conditions

viii) Method of disposal or loading trucks

ix) Size of hauling units, if used

x) Skill of operator

xi) Physical conditions of the machine.

E) Clamshells:-

Clamshell is a machine having most of the characteristics of dragline and crane in common.

Digging is done like a dragline and once the bucket is filled, it works like a crane.

It consists of bucket of two halves which are hinged together at top. (Fig)

The bucket halves can be attached to the shovel-crane units or at the boom of a dragline. It

is primarily used for handing loose materials such as sand, gravel, crushed stone, coal etc. and for

removing materials from cofferdams, pier foundations, sewer-manholes sheet-lined trenches etc. It is

specially suited for vertically lifting materials from one location to another; as in charging hoppers and

overhead bins etc. The limits of vertical movement depend upon the length of the crane boom.

Since the shape of the bucket is like a clam fish and has hinged double shell, it named as

CLAMSHELL. Like bucket of a dragline, the bucket of clamshell are also classified as I) Light bucket

and ii) Heavy bucket.

Light bucket

It is primarily used for handling loose materials like sand, gravel etc. and is generally without

teeth.



Heavy Bucket

It is used for digging purpose and has long and sharp teeth. But due to its heavy weight and

more force required for closing operation, the cycle time is increased thereby the output is reduced.

F) HOE;-

Hoe is an excavating equipment of the power shovel group. Since the digging mechanism

resembles to an ordinary hoe, it is named as Hoe. But it is referred by several names such as hoe,

backhoe, back shovel and pull shovel.

The basic parts and operation of a Hoe

The basis parts a hoe have been illustrated in the Fig. The machine is placed in operation by

setting the boom at the desired angle. The dipper is moved to the desired position. The free end of

the boom is lowered down by releasing the tension in the hoist cable until the dipper teeth engages

the materials to be dug. As the cable is pulled in, the dipper is filled up. Then the boom is raised and

swung to the dumping position.

Applications of HOE

The special feature of a hoe lies in its rigidity. Thats why it is superior to the dragline of

power shovel. As the hoe is able to exert greater tooth pressure, it is commonly used in quarries

which have tough digging conditions.

In general, a hoe may be used to

a) Excavate below the natural surface of the ground on which the machine rests.

b) Dig trenches, footings or basements and general grading work which require precise

control of depths.

c) Operate on close-range work and dump into trucks.

d) Penetrate easily into toughest materials to be dug.

G) SCRAPER:-

Scraper is a machine which can scrape the ground and load it simultaneously, transport it over the

required distance, dump at the desired place and then spread the dumped material over the required

area in required level and return to the pit for the next cycle. So the scraper is self-sufficient and self

operating construction equipment designed to dig, load, dump and spread and sometimes called a

carry all. But it is not suited for (i) hard rock materials which make discharging of a scraper difficult.

BASIC PARTS OF A SCRAPER

A scraper as shown in Fig consists of the following basis parts;

i) Bowl: It is a pan to hold scraped material and is capable of tilting down for digging or ejecting.



The size of the bowl describes the size of scraper.

ii) Cutting Edge: The bowl has a cutting edge attached at the bottom to make shallow cut.

iii) Apron: This is a wall in front of the bowl which opens and closes to regulate the flow of earth.

iv) Tail gate or Ejector: It is the rear of the pan which is capable of forward and backward

movement inside the bowl.

All these parts are controlled by the hydraulic system.

TYPES OF SCRAPERS

Depending upon the type of the tractor used, scrapers are classified as

a) Crawler tractor scraper: Used for short and difficult haul.

b) Wheel tractor scraper: Used for long and easy haul.

c) Motor scraper: Having its own engine and motoring arrangement.

SIZE OF SCRAPER

The size of scraper may be specified by the struck or heaped capacity of the bowl, expressed

in cubic meter.

OUTPUT OF A SCRAPER

The output of a scraper is the bank measure volume pre hour (cubic meter/hr)

Output = Optimum loose volume per trip x S x 60/t x Efficiency.

Where S= Swell factor depending upon type of soil

T = Cycle time per trip in minutes

T = Fixed time (Loading + Dumping and turning + Accelerating+ Decelerating) + Haul time +

Return time in minutes.

FACTORS AFFECTING OUTPUT OF SCRAPERS

The output of scrapers depends upon the following main factors;

i) Size and mechanical conditions of the scraper.

ii) Characteristics of the soil to be handled by the scraper and work area.

iii) Size and conditions of borrow pit or cut.

iv) Slope of loading zone.

v) Extent of loosening material, prior to loading for hard rock.

vi) Hauling distance

vii) Condition and slope of haul road.

viii) Altitude and climatic conditions

ix) Management conditions

Scraper Vs Bulldozer

Scraper and bulldozer have the same functions in the field of constructions but is generally

seen that for every short haul distance say 50 to 100m, a bulldozer is more economical earth moving

equipment; whereas scraper is more economical when the haulage distance is more than 100m and

less than 1500 m.



H) TERNCHING MACHINES:-

(TRENCHERS)

Trenching machines or trenches are the equipments used for excavating trenches or ditches

of variable width and depth for the following utilities

i) Water/gas/oil-pipe lines

ii) Telephone/electricity cables

iii) Drainage ditches.

iv) Sewer lines

The salient features of the trenching machines over other excavating machines are asfollows;

a) Fast digging

b) Positive control over depth and width of trenches

c) Reducing expensive hand finishing to minimum

They are available in various sizes for digging trenches of varying depth and width and

usually crawler tractor mounted to increase the stability and to distribute the weight over a greater

area.

TYPES

There are two types of trenching machines

A) Wheel type trenching machine

B) Ladder-type trenching machine

WHEEL TYPE TRENCHING MACHINE

Fig 7.12 shows a wheel type trenching machine. The excavating part of the machine consists

of a power driven wheel on which are mounted a number of removal buckets, equipped with cutter

teeth. Buckets are available of varying widths.

Machine is operated by lowering of the rotating wheel to the desired depth, while the unit

moves forward slowly. The earth is picked up by the buckets and deposited onto an endless belt

conveyor, which can be adjusted to discharge the earth on either side of the trench.

The characteristics (specifications) of the smallest and largest machines of this group have

been given in the table.

Table 7.6

Sl.

No.

Description Dimension

(Small size)

Dimension

(Large size)

1. Maximum trench depth 1.6m 2.7m

2. Trench width 40cm to 75cm 100 to 150 cm

3. Approximate weight 7,000 kg 27,000 kg

4. Travel speed 0.8 to 4.5 Kmph 3.0 kmph

5. Digging speed 0.06 to 3m/minute 4 meters/minute



Suitability

If a relatively shallow and narrow trench is to be excavated in firm soil, wheel type machine is

the most suitable and generally preferred for trenches used for telephone cables, water/gas/oil pipe

etc.

LADDER TYPE TRENCHING MACHINE

The wheel type trencher is unsuitable for large sections and is therefore replaced by the

ladder type. Fig 7.13 illustrates the ladder trencher.

The excavation part of the machine consists of two endless chains, which travel along the

boom, to which are attached cutter-buckets equipped with teeth. In addition, shaft mounted side

cutters may be installed on each side of the boom to increase the width of the trench. As the buckets

travel up the underside the boom, they bring out earth and deposit it on a belt conveyer, which

discharges it along either side of the trench. When the machine moves over uneven ground, it is

possible to adjust the depth of cut.

Table 7.7 gives representatives specification of the ladder type trenching machines.

Sl.No.

Description Dimension(Small size)

Dimension(Large size)

1. Maximum trench depth 1.5m 4.5m

2. Trench width 2m 15m

3. Approximate weight 3,000kg 18,000kg

4. Travel speed 5 kmph 2.5 kmph5. Digging speed 6 meters/minute 4 meters/minute

SELECTION OF TRENCHER

The selection of type of trenching machine depends on the job conditions, depth and width of

the trench, type of soil, disposal of excavated earth and availability of ground water.

I) Hauling and Conveying Equipments HAULING EQUIPMENTS

Hauling is the movement of materials by mobile units such as road vehicle and rail

locomotives. Haulage problems involved on construction projects include transportation of the earth,

aggregate, rock, ore, coal and other material including equipments.

Road equipments for haulage mainly consist of trucks, tractors and tractor or truck driven

tailors. These units fall in two categories;

i) ON-HIGHWAY VEHICLES

ii) OFF-HIGHWAY VEHICLES

On-highway vehicles

They are designed to be used on public highways. They are used for long distance

transportation on good surface road. Such haulage is being done with trucks which may be heavy or

light, ordinary or dumpable.



J) CRANES:-

Machine for lifting and lowering a load vertically, Moving it horizontally with

the hoisting mechanism an integral part of the machine. A broad class of

construction equipment The operation of cranes can be divided by 5 steps:-

Gripping

Lifting

Moving the load from point to point

Lowering

Un-gripping

FUNCTION

Transport heavy loads and hazardous

Material in shipyard, factories, nuclear

Installations and high-building construction.

Hold & control the capacity loads

Lifting, lowering & transporting loads

TYPES OF CRANE

Classified into two major families:-

Mobile cranes

Tower cranes

MOBILE CRANES

Crawler Cranes

Telescoping - Boom Truck Mounted Cranes

Lattice Boom Truck Mounted Cranes

Rough Terrain Cranes

All Terrain Cranes

Heavy Lift Cranes

Modified Cranes For Heavy Lift

TOWER CRANES



Top Slewing [ Fixed Tower ]

Bottom Slewing [ Slewing Tower ]

MOBILE CRANES

ADVANTAGES have steering function ( the operator can steer the crane in the drive-by-wire

heavy lifts of up to 104 tons will be handled safety & fast

* using 4-rope configuration with a mechanical grab for quick & efficient

operation equipped with the new undercarriage design system DISADVANTAGES

take up more room/ large area

dont have the birds eye view

uncovered by hazard

high cost & expensive maintenance

TOWER CRANES

ADVANTAGES achieved at the expense of low lifting capacity & limited mobility

more quickly and safety

covered by hazard

provide high lifting height

have faster swing speed & line speed

good working radius

DISADVANTAGES initial high cost

difficult & take a long time to fix

continuing expensive maintenance

taking up a very limited area



HAZARD OF OPERATING CRANES electrocution hazards

over loading

turn-over (caused by turning too quickly or driving on an incline)

load instability (caused by improper loading)

driving over obstructions and pot-holes

collision with objects or pedestrians

unauthorized modifications on the industrial truck

visibility limitations

driving on soft surface

HAZARD AVOIDANCE

staying clear of crane / hoist operations

observing posted warnings

following all directions you receive from the person in charge of acrane / hoist operation

paying attention to path and swing radius of the material or bad beinglifted

avoid contact and collisions with crane / hoist equipment and avoidclose proximity to it when it is in use

aware of the location of the equipment

avoid contact with any moving parts of the equipment

CONCLUSION

From the above discussed topic it is cleared that construction equipments

are very important in construction works. But before we purchase an

equipment we should remember one thing that is Equipment should be

purchased only when it is well established, that the equipments purchase is

beneficial and is not a losing proposition keeping in view its requirements

and possible use. Basically there are two aspects for the selection of

construction equipments in a project. The first aspect deals with the type,

size and other particulars of the equipments and the second aspect whether

it is to be purchased, hired or to be procured under hire-cum-purchase

arrangement, but in all the aspects, the following factors must be taken into



account before having a final choice.

REFERENCES

1. www.constructionequipment.com

2. www.equipment/tractor.co.in

3. www.gooogle.equiphoe.com

4. www.gooogle.equipdragline.com

5. www.gooogle.equippowershovel.com

6. www.gooogle.equipcranes.com

7. www.gooogle.equiptrenchers.com

8. www.gooogle.equipscrappers.com

9. www.gooogle.equipconveybelt.com

10. myconstructionphotos.smugmug.com

11. www.freefoto.com

12. www.archive.org

13. Construction engineering equipment by purify

14. Construction management and planning by u.k shrivastav

15. Construction management by S.Seetharaman

16. www.bigoldiron.com/equipmentphotos.html

17. www.bigoldiron.com/equipmentphotos.html



18. www.maxmechgroup.net

19. www.mcepl.com

20. www.seekandsource.com/category/machinery-construction.html

Documents

Civil Engineering