Chapter 18

CHAPTERConstruction Planning, Equipment,

and Methods Sixth Edition

DRAGLINES AND CLAMSHELLS

• A. J. Clark School of Engineering •Department of Civil and Environmental Engineering

18 By

Dr. Ibrahim Assakkaf

ENCE 420 – Construction Equipment and MethodsSpring 2003

Department of Civil and Environmental Engineering

University of Maryland, College Park

CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 1

DRAGLINE, CLAMSHELLAND MAGNET CRANES

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DRAGLINES ANDCLAMSHELLS

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DRAGLINESENCE 420 ©Assakkaf

Draglines are used to excavatematerial and to load it intohauling units, such as trucks ortractor-pulled wagons, or todeposit it in levees, dams, andspoil banks near the pits fromwhich it is excavated.



The dragline is designed to excavatebelow the level of the machine.

A dragline usually does not have to gointo a pit or hole in order to excavate. Itoperates adjacent to the pit whileexcavating material from the pit bycasting its bucket. This is veryadvantageous when earth is removedfrom a ditch, canal, or pit containingwater.



Frequently, it is possible to use adragline with a long boom todispose of the earth in oneoperation if the material can bedeposited along the canal or nearthe pit. This eliminates the need forhauling units, thus reducing thecost of handling the material.


BASIC COMPONENTS OFDRAGLINE

Figure 1

Hoist cable Boom

Dump cable

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Hoist chain

Bucket

FairleadDrag cable Drag chain


TYPES OF DRAGLINESENCE 420 ©Assakkaf

Draglines may be divided intothree types:1. Crawler-mounted

2. Wheel-mounted, self-propelled

3. Truck-mounted



Crawler-mounted draglines can operateover soft ground conditions that wouldnot support wheel-or truck-mountedequipment.The travel speed of a crawler machineis very slow, frequently less than 1 mph,and it is necessary to use auxiliary,hauling equipment to transport the unitfrom one job to another.



Wheel-and track-mounted units mayhave travel speeds inexcess of 30 mph.


THE SIZE OF A DRAGLINEENCE 420 ©Assakkaf

The size of a dragline is indicatedby the size of the bucket,expressed in cubic yards (cu yd).Most draglines may handle more

than one size bucket, depending onthe length of the boom utilized andthe class and weight of the materialexcavated.



Since the maximum lifting capacityof a dragline is limited by the forcewhich will tilt the machine over, it isnecessary to reduce the size of thebucket when a long boom is usedor when the excavated material hasa high unit weight.



In practice, the combinedweight of the bucket and itsload should produce a tiltingforce that is not greater than75% of the force required totilt the machine.



A longer boom, with a smaller bucket,will be used to increase the diggingreach or the dumping radius when it isnot desirable to bring in a largermachine.

If the material is difficult to excavate, theuse of a smaller bucket, which willreduce the digging resistance, maypermit an increase in production.



Figure 2Relationship between bucketsize and boom length andangle


THE SIZEENCE 420 ©Assakkaf

Figure 3Typical Dragline Working Rangeswith Maximum Weight


OPERATION OF ADRAGLINE

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The excavating cycle is started byswinging the empty bucket to the

digging position, while at the same timeslacking off the drag-and the hoist lines.

There are separate drums on the basicunit for each of these cables so thatthey may be coordinated into a smoothoperation.



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Digging is accomplished by pullingthe bucket toward the machinewhile regulating the digging depthby means of the tension maintainedin the hoist line.

When the bucket is filled, theoperator takes in the hoist linewhile playing out the dragline.



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The bucket is so constructed that it willnot dump its contents until the drag linetension is released.

Hoisting, swinging, and dumping theloaded bucket follow in that order; thenthe cycle is repeated.An experienced operator can cast theexcavated material beyond the end ofthe boom.



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Figure 4Dragline Digging Zones


OUTPUT OF DRAGLINESENCE 420 ©Assakkaf

• The output of a dragline will vary with the followingfactors:

1. Class of material

2. Depth of cut

3. Angle of swing

4. Size and type of bucket

5. Length of boom

6. Method of disposal, casting, or loading haul units

7. Size of the hauling units, when used

8. Skill of the operator

9. Physical condition of the machine

10. Job conditions



The output of a dragline should beexpressed in bank measure cubic yards(bcy) per hour. This quantity is bestobtained from field measurements. Itmay be estimated by multiplying theaverage loose volume per bucket by thenumber of cycles per hour and dividingby 1 plus the swell factor for thematerial, expressed as a fraction.



Example:

If a 2-cu-yd bucket, excavating material whose swell is25%, will handle an average loose volume of 2.4 cu yd,the bank-measure volume will be

2.4/1.25 = 1.92 cu yd.

If the dragline can make 2 cycles per min, the outputwill be

2 x 1.92 = 3.84 bcy per min or 230 bcy per hour.



Table 1. Approximate Dragline Digging and Loading Cycles for VariousAngles of Swing


OPTIMUM DEPTH OF CUTENCE 420 ©Assakkaf

Greatest output of a dragline isexpected when it is operating at theoptimum depth of cut

The following Table (Table 2, or Table18-3 of Textbook) provides the optimumdepth of cut for various sizes of bucketsand types of materials based on usingshort-boom draglines.



Table 2. Optimum Depth of Cut and Ideal Outputs of Short-boom Draglines



Ideal outputs (bcy) of short-boomdraglines are accomplished whendigging at the optimum depth with a900 swing and no delays arepresented in the table.

The upper figure is the optimumdepth in feet and the lower numberis the ideal output in cubic yards.


EFFECT OF THE DEPTH OF CUTAND SWING ANGLE ON

DRAGLINE OUTPUT

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The table (Table 2) also gives theoptimum depth and ideal outputs inmetric units (e.g., m and m3).

The outputs of draglines providedin Table 2 (Table 18-3 of Textbook)are based on digging at optimumdepths with a swing angle of 900.


EFFECT OF THE DEPTH OFENCE 420 ©Assakkaf

CUT AND SWING ANGLE ONDRAGLINE OUTPUT

For any other depth or swing angle,the ideal output of the machinemust be adjusted by an appropriatedepth-swing factor.The effect of the depth of cut and

swing angle on dragline productionis given in the following table (Table3, or Table 18-4 of Textbook).




The percent of optimum depthof cut in the table is obtained bydividing the actual depth of cutby the optimum depth for thegiven material and bucket, thenmultiplying the result by 100.




Table 3. Factors for Depth of Cut and Angle of Swing Effect on

Dragline Production (Table 8-4 of Textbook)


Example 1ENCE 420 ©Assakkaf

A 2-cu-yd short-boom draglineis to be used to excavate hard,tough clay. The depth of cutwill be 15.4 ft, and the swingangle will be 1200. Compute theprobable production of thedragline.


Example 1 (cont’d)ENCE 420 ©Assakkaf

Optimum Depth of Cut = 11.8 ft ⇒ 195 cu-yd Ideal production (see Table 2)

Percent of Optimum Depth =15.4×100

11.8=130%

The appropriate depth-swing factor = 0.89 (by interpolation in Table 3)

The Probable Production = 195 (0.89) = 173.6 bcy per 60-min hour

The production should be corrected for normal delays (i,e., 50-min hour)

Production (corrected)=173.650 bcy

=14560 hr


EFFECT OF BUCKET SIZE ANDBOOM LENGTH ON DRAGLINEPRODUCTION

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For best operating efficiency, one shouldmatch the dragline and the bucket properly.

There are generally three types of buckets9 Light Duty, for easily dug material (i.e., sandyloam and sandy clay)

9 Medium Duty, for general excavation (I.e., clay,soft shale)

9 Heavy Duty, for mine tripping and handlingblasted rocks



Buckets are sometimes are

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perforated to allow access water todrain.

In selecting the most suitable sizeof bucket for use with a givendragline, the loose weight (in lb percu ft) should be known.



Larger buckets can increase

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production, but they may exceed therecommended safe load for adragline.

The following table (Table 4, or Table18.5 of Textbook) provides

representative capacities, weight, anddimensions for dragline buckets



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Table 4. Capacities, Weights, and Dimension of Dragline Buckets


Example 2ENCE 420 ©Assakkaf

The material to be handled has a loose weight of 90 lb per cu ft. Theuse of a 2-cu-yd medium duty bucket will be considered. The draglineis to be operated with an 80-ft boom at a 400 angle. Is the 2-cu-ydconsidered safe for the job? If not, what size bucket should be used.

Weight of Bucket = 4,825 lb (from Table 4)Weight of Material = 60 X 90 = 5,400 lb (60 cu ft from Table 4)

Combined Weight = 10,225 lb

For 80-ft boom at a 400 swing angle:Maximum Safe Load = 8,600 lb (from Figure 3)

Combined Weight (10,225 lb) > Maximum Safe Load (8600 lb) NOT OK


Example 2(cont’d)

Figure 3Typical Dragline Working Rangeswith Maximum Weight

NOTE: Figure 3 is repeated here for Example 2


Example 2 (cont’d)ENCE 420 ©Assakkaf

Try a 1½-cu-yd bucketWeight of Bucket = 3,750 lb (from Table 4)Weight of Material = 47 X 90 = 4,230 lb (47 cu ft from Table 4)

Combined Weight = 7,980 lb

For 80-ft boom at a 400 swing angle:Maximum Safe Load = 8,600 lb (from Figure 3)

Combined Weight (7,980 lb) < Maximum Safe Load (8600 lb) OK

Hence, use 1½-cu-yd bucket


CLAMSHELLSENCE 420 ©Assakkaf

Clamshells are used tohandle loose material suchas sand, gravel, and crushedstone. They are speciallysuited for lifting materialvertically.



Clamshell buckets are availablein various sizes, and in heavy-duty types for digging, medium-weight types for general-purpose work and lightweighttypes for rehandling lightmaterials.



Manufacturers supply bucketseither with removable teeth orwithout teeth.

Teeth are used in digging theharder types of materials but are

not required when a bucket is usedfor re-handling purposes.



A B

(A) Wide Re-handling Clamshell bucket(B) Heavy Duty Clamshell Bucket


CAPACITY OF CLAMSHELLBUCKETS

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The capacity of a clamshellbucket is usually given in cubicyards.

A more accurate capacity isgiven as water level, plate-line,or heaped-measure, generallyexpressed in cubic feet.



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The water-level capacity is thecapacity of the bucket if it werehung level and filled with water.The plate-line capacity indicatesthe capacity of the bucketfollowing a line along the tops ofthe clams.



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The heaped capacity is thecapacity of the bucket when it isfilled to the maximum angle ofrepose for the given material.

In specifying the heapedcapacity, the angle of repose isusually 45º.


PRODUCTION RATES FORCLAMSHELLS

Because of the variablefactors which affect the

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operations of a clamshell, itis difficult to give dependableproduction rates.


PRODUCTION RATES FORCLAMSHELLS

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The variable factors affecting operationsinclude:

9The difficulty of loading the bucket,

9The size load obtainable,9The height of lift,

9The angle of swing,

9The method of disposing of the load, and

9The experience of the operator.

Chapter 18

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