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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CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 2
DRAGLINES ANDCLAMSHELLS
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CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 3
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 4
DRAGLINESENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 5
DRAGLINESENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 6
BASIC COMPONENTS OFDRAGLINE
Figure 1
Hoist cable Boom
Dump cable
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Hoist chain
Bucket
FairleadDrag cable Drag chain
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 7
TYPES OF DRAGLINESENCE 420 ©Assakkaf
Draglines may be divided intothree types:1. Crawler-mounted
2. Wheel-mounted, self-propelled
3. Truck-mounted
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 8
TYPES OF DRAGLINESENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 9
TYPES OF DRAGLINESENCE 420 ©Assakkaf
Wheel-and track-mounted units mayhave travel speeds inexcess of 30 mph.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 10
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 11
THE SIZE OF A DRAGLINEENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 12
THE SIZE OF A DRAGLINEENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 13
THE SIZE OF A DRAGLINEENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 14
THE SIZE OF A DRAGLINEENCE 420 ©Assakkaf
Figure 2Relationship between bucketsize and boom length andangle
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 15
THE SIZEENCE 420 ©Assakkaf
Figure 3Typical Dragline Working Rangeswith Maximum Weight
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 16
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 17
OPERATION OF ADRAGLINE
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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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 18
OPERATION OF ADRAGLINE
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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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 19
OPERATION OF ADRAGLINE
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Figure 4Dragline Digging Zones
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 20
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
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 21
OUTPUT OF DRAGLINESENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 22
OUTPUT OF DRAGLINESENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 23
OUTPUT OF DRAGLINESENCE 420 ©Assakkaf
Table 1. Approximate Dragline Digging and Loading Cycles for VariousAngles of Swing
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 24
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 25
OPTIMUM DEPTH OF CUTENCE 420 ©Assakkaf
Table 2. Optimum Depth of Cut and Ideal Outputs of Short-boom Draglines
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 26
OPTIMUM DEPTH OF CUTENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 27
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 28
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).
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 29
EFFECT OF THE DEPTH OFENCE 420 ©Assakkaf
CUT AND SWING ANGLE ONDRAGLINE OUTPUT
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 30
EFFECT OF THE DEPTH OFENCE 420 ©Assakkaf
CUT AND SWING ANGLE ONDRAGLINE OUTPUT
Table 3. Factors for Depth of Cut and Angle of Swing Effect on
Dragline Production (Table 8-4 of Textbook)
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 31
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 32
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
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 33
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
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 34
EFFECT OF BUCKET SIZE ANDBOOM LENGTH ON DRAGLINEPRODUCTION
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 35
EFFECT OF BUCKET SIZE ANDBOOM LENGTH ON DRAGLINEPRODUCTION
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
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 36
EFFECT OF BUCKET SIZE ANDBOOM LENGTH ON DRAGLINEPRODUCTION
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Table 4. Capacities, Weights, and Dimension of Dragline Buckets
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 37
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
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 38
Example 2(cont’d)
Figure 3Typical Dragline Working Rangeswith Maximum Weight
NOTE: Figure 3 is repeated here for Example 2
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 39
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
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 40
CLAMSHELLSENCE 420 ©Assakkaf
Clamshells are used tohandle loose material suchas sand, gravel, and crushedstone. They are speciallysuited for lifting materialvertically.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 41
CLAMSHELLSENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 42
CLAMSHELLSENCE 420 ©Assakkaf
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 43
CLAMSHELLSENCE 420 ©Assakkaf
A B
(A) Wide Re-handling Clamshell bucket(B) Heavy Duty Clamshell Bucket
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 44
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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 45
CAPACITY OF CLAMSHELLBUCKETS
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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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 46
CAPACITY OF CLAMSHELLBUCKETS
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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.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 47
PRODUCTION RATES FORCLAMSHELLS
Because of the variablefactors which affect the
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operations of a clamshell, itis difficult to give dependableproduction rates.
CHAPTER 18. DRAGLINES AND CLAMSHELLS Slide No. 48
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.