UNIT 2 EXCAVATION EQUIPMENT-I1

Structure Introduction Objectives Power Shovels 2.2.1 Optimum Depth of Cut for Power Shovels 2.2.2 Angleof Swing of Power Shovels 2.2.3 Output of Power Shovels 2.2.4 Seleaing Type and Size of Power Shovels Hoes Draglines 2.4.1 Operatioas of a Dragline 2.4.2 Optimum Depth of Cut for Draglines 2.4.3 Angle of Swing of Draglines 2.4.4 Output of Draglines Clamshells Motor Graders Trenchers 2.7.1 Wheel-type Trenching Machines 2.7.2 Ladder-type Trenching Machines 2.7.3 Selection of Suitable Equipment fm Trenches 2.7.4 Production Rates of Trenching Machines

. 2.9 Dredges 2.10 Bulldozers

2.1 1 Tree Dozers ' 2.1 2 Rippers 2.13 Scrapers 2.13.1 Cycle Time for a Scraper 2.13.2 Number of Scrapers Served by a Pushdozer 2.13.3 Output of Scrapers 2.13.4 Increasing the Production Rates of s'crapers 2.14 Crawler vs Wheeled Equipment 2.14.1 Crawler or Track Based Equipment 2.14.2 Wheel Based Equipment 2.14.3 Relative Merits 2.15 Summary 2.16 Answers to SAQs 2.17 Further Reading

2.1 INTRODUCTION

The type of foundation to be used for any particular structure will have to'be determined at the planning stage. The type chosen will depend to a large extent on the surface or subsurface conditions encountered at the site. Soil or subsoil in its natural state is often sufficiently stable to support the foundations of light structures. Foundations for heavy structures, on the other hand, will be brought to a level with sufficient bearing strength, or to bedrock (unless the bedrock occurs at a very great depth). To build or clear a foundation, an. excavation is required, and this operation will usually be carried out by some type of power excavation equipment. Tbis unit describes the different types of excavating equipment used in construction. In this unit, various types of equipment, their application and production rates in carrying out earthwork are described. AV~Equipment Objectives By the end of th~sunit , you should be able to : understand the working of power shovels, the factors affecting their output, the procedure for selecting the type and size of shovel and calculate the production rates, understand the operations and determine the output of hoes, explain the types, size and operations of draglines, factors affecting the output of draglines and effect of size of bucket and length of boom on output of a dragline, explain the size of clamshell buckets and work out the output of clamshells, understand the operation and find the output of motor graders, differentiate between the types of trenchers and the factors affecting their selection and production, explain the types of bucket excavap and compute their production rates, differentiate between vqious types of dredges, explain the types and operatiolis of a bulldozer and determine the output of a bulldozer, explain the operations of a tree dozer, explain the use of and the method to assess output of rippers, explain the types of scrapers, the size and operations of a scraper, determine the cycle time and number of scrapers sewed by a pushdozer, output of scrapers and methods to increase production rates of scrapers, and explain the relative merits of crawler or track based equipment and wheel based equipment.

2.2 POWER SHOVELS Power shovels are used mainly to excavate earth and load into trucks or tractor-drawn wagons. 'Ihey can excavate all types of eartb except solid rock without prior loosening. They may be mounted on crawler tracks (hence called crawler-mounted shovels), in which case they have very low travel speed and give low soil pressures and so suited to soft ground. 'Ihe rubber-tyre-mounted shovels which have higher travel speeds are useful for small jobs where considerable travelling is involved and where the road surfaces and the ground are firm. The basic parts of a power shovel include the mounting, cab, boom, dipper stick and dipper (Figure 2.1 a). Other attachments to the shovel include hoe, dragline, clamshell and crane (Figure 2.1 b).

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(b) ArrrLaKnts of sbwel unit (a) Pmeudwd.

figure 21 :Power Shovel Size of Power Shovels RcavPtlm E4pipnwt-11 The size of a power shovel is denoted by the size of the dipper in m3. In measuring the size of the dipper the earth is struck even (giving "struck volume") with the contour of the dipper. This is referred to (as said above) as the struck volume, to distinguish ftom heaped volume which a dipper may pick up in loose soil. Power shovels are commonly available in dipper sizes of 0.29,0.38,0.57,0.76,0.95,1.14, 1.33, 1.53 and 1.91 m3. Operations of Shovels Positioning the shovel near the face of the earth to be excavated, the dipper is lowered to the floor of the pit, with the teeth pointing into the face. A crowding force is applied through the dipper shaft and at the same time tension is applied to the hoisting line to pull the dipper up the face of the pit. If the depth of the face (called the depth of cut) is just right, the dipper will be filled as it reaches the top of the face. If the depth is shallow it will not 6e possible to fill the dipper completely without excessive crowd in^ and hoisting tension. If the depth of cut is more than is required to fill the dipper, the dt:ptf~ of penetration of the dipper into the face must be reduced if the full face is to be excavated or to start the excavation above the floor of the pit. 2.2.1 Optimum Depth of Cut for Power Shovels The optimum depth of cut is that depth which produces the greatest output and at which the dipper comes up with a full load. The depth varies with the class of soil and the size of the dipper as shown in Table 2.1. Table 2.1 : Ideal Depths of Cut for Power Shovels In m

Class of Size of shovel Dipper, m3 Material 0.29 0.38 0.57 0.76 0.95 1.14 133 1.53 1.91 Moist loam, or 1.1 1.4 1.6 1.8 2.0 2.1 2.2 2.4 2.6 light sandy clay Sand andgravel 1.1 1.4 1.6 1.8 2.0 2.1 2.2 2.4 2.6 Good common 1.4 1.7 2.1 2.4 2.6 2.8 2.9 3.1 3.4 earth Hard,toughclay 1.8 2.1 2.4 2.7 3.0 3.3 3.5 3.7 4.0 Wet,stickyclay 1.8 2.1 2.4 2.7. 3.0 3.3 13.5 3.7 4.0

2.2.2 Angle of Swing of Power Shovels The angle of swing of a power shovel is the horizontal angle, expessed in degrees, between the position of the dipper when it is excavating and the position when it is discharging the load. The total cycle time includes , swinging fo the dumping position, dumping, and returning to the digging position. The effect of the angle of swing on the output of a shovel is given in Table 2.2. The probable output for any given depth and angle of swing is obtained by multiplying the ideal output with the factors given in Table 2.2. Table 2.2 :Conversion Factors for Depth of Cut and Angle of Swing for a Power Shovel

Percent of Angle of Swing, (degm5s) Optimum Depth 45O 60° 750 !MJO 120' 150' 180' 40 0.93 0.89 0.85 0.80 0.72 0.65 0.59 . 60 1.10 1.03 0.96 0.91 0.81 0.73 0.66 80 1.22 1.12 1.04 0.98 0.86 0.77 0.69

100 1.26 1.16 1.07 1.00 ' 0.88 0.79 0.71 120 1.20 1-11 1.03 0.97 0.86 0.77 0.70 140 1.12 1 0.97 0.91 0.81 0.73 0.66 160 1.03 0.96 0.90 0.85 0.75 0.67 0.62 Excavation Equipment 2.2.3 Output of Power Shovels The actual output of a power shovel depends on: 1) Class of Aterial 2) Depth of cut (DOC) 3) Angle of swing (AOS) 4) Job conditions 5) Management conditions 6) Size of haul units 7) .Skill of the operator 8) Physical condition of the shovel. The job and management factors have been discussed in Unit 1under Table 1.1 1.Factors for job and management conditions.'Ihble 2.3 gives the output of power shovels at optimum DOC and 90' AOS. Table 23 :Ideal Outputs of Cable Operated Power Shovels in m3/ 60 min-hr, Bank Measure

Size of Shovel Dipper, m3 Class of Material

Moist loam, or light 65 88 126 157 190 218 244 272 309 sandy clay Sand and gravel 61 84 118 153 176 206 229 252 298 Good common earth 54 73 103 134 160 183 206 229 268 Hard, tough clay 38 57 84 111 137 156 180 202 236 Wet, sticky clay 19 30 53 72 91 110 125 141 Well-blasted rock 30 46 72 95 118 137 156 175 210 I Poorlyblastedrock 11 19 38 57 73 88 107 122 149

2.2.4 Selecting Type and Size of Power Shovels If the wo* areas are scattered, the mobility of the rubber-tyre-mounted shovel is advantageous. If the work is concentrated in large jobs, mobility is less important and a crawler-mounted shovel is desirable. A crawler shovel is cheaper than a rubger tyred shovel. In selecting the size of a shovel, the two primary factors are : the cost per m of the material excavated and the job conditions undei which the shovel will operate. In estimating the cost per m3, the factors considered are: 1) The size of the job, as a larger job may justify the hlgher cost of a large shovel, 2) The cost of transporting a large shovel will be higher than a small one, 3) The depreciation rate for a large shovel may be higher than for a small one. Disposing off a large shovel at the end of a job is more difficult than a small one, 4) The cost of downtime repairs for a large shovel may be more than for a small one, due to delays in getting the parts of a large shovel, 5) The cost of drilling, blasting and excavating rock for a large shovel may be less than for a small shovel as a large machine can handle bigger rocks. This may effect some saving in drilling and blasting, and 6) The cost of wages per m3 will be less for a large shovel than a small one. The following job conditions need to be considered in selecting the size of a shovel: 1) High lifts from the working face to the haul units will require the long reach of a large shavel, 2) If blasted rock is to be excavated, ,the large sized dipper will handle bigger rocks, . 3) If the material to be excavated is hard and tough, a larger shovel will handle the material more easily, 4) If the time allotted for completing the job requires a high hourly output, a large shovel must be used, 5) If large haul units are available, then a large shovel should be used, and 6) The weight limitations and clearance of bridges and underpasses may restrict the size. Example 2.1 Determine the expected production of a power shovel given the following data: Size of bucket = 1.14 m3 Actual depth of cut = 3.15 m Actual angle of swing = 75' Class of material : sand and gravel Job and management conditions : excellent-good Working hour = 50 rnin. per hr. Solution

/ Ideal production = 206 m3 (bank)/hr. (Table 2.3) Optimum depth of cut = 2.1 m (Table 2.1) Job and management factor = 0.81 (Table 1.11) 100 Percent of actual to optimum depth of cut = 3.15 x - = 150 8 2.1 Conversion factor for DOC and AQS for a power shovel = 0.935 Fable 2.2- corresponding to 150 % and 75q Average production = 206 x 0.935 = 192.61 m3 (B)/hr. 0.81 Expected production = 50 x 192.61 x - 60

SAQ 1 i) Explain the operations of a power shovel. ii) How do you define the optimum depth of cut for a power shovel ? ill) How is "angle of swing" defined for a power shovel? iv) On what factors does the selection of type and size of a power shovel depend?

2.3 HOES

The term hoe applies to an excavating machine of the power-shovel group It is referred to by several other names, such as, backhoe, back shovel, and pull shovel. Figure 2.2 shows a typical cable operated backlpe. A power shovel is converted into a backhoe by installing a dipper stick and a dipper at the end of the shovel boom. A hoe is frequently equipped with a gooseneck boom to increase the digging depth of the machine. Hoes are used primarily to excavate below the level at which the machine rests. Ihey are adapted to dig trenches, pits and basements. Due to their rigidity they are superior to draglines in operating on close-range work hnd dumping into trucks. Because of the direct pull on the dipper, hoes may exert greaterrnth pressure than power shovels. Excavation Equipment

Figure 22 :Cable Operated Backhoe Operations of a Backhoe Figure 2.3 shows the basic parts of a cable operated backhoe. The machine is placed in operatim by setting the boom at the desired angle and pulling in the cable, while releasing the drag cable, to move the dipper to the desired position. The free end of the boom is lowered by releasing the tension in the hoist cable until the dipper teeth engage the material to be dug. As the cable is pulled in, the dipper is filled. The dipper is raised by the boom, swung and the material dumped in a truck or over a spoil bank. Hoht cable ,

Fipn 23: Bmic Parta of a Cable Operated Backhoe Output of Backhoes When a hoe is used to dig at moderate depths, the output may be as mucb as a power shovel of similar size digging in similar class of material. But, as the depth increases, the output of a hoe reduces considerably. The most effective digging action occurs when the dipper stick is at right angles to the boom. The greatest output is obtained if digging is done near the machine, because of reduced cycle time and the material rolls back into the dipper better when the dipper is pulled upward near the machine. SAQ 2 i) What are the functions of a hoe? ii) Explain the operations of a backhoe. iii) What factors affect the output of a backhoe? 2.4 DRAGLINES o Excavation Equipment-I1 Draglines are used to excavate earth and load it into haul units, such as trucks or tractor-pulled wagons, or to deposit it on spoil banks and embankments near the place from where it is excavqted. A power shovel can be converted into a dragline by replacing the dipper stick of the shovel with a crane boom and substituting a dragline bucket for the shovel dipper. Advantages of a dragline are: 1) It does not have to go into the pit to excavate, 2) It can excavate below its level and under water, 3) 'I'he trucks do not have to go into the pit nor contend with wet mud, 4) A dragline with a long boom can dispose off the earth in one operation without the need for haul units, and 5) It can excavate trenches without shoring. One disadvantage of a dragline is that its output is only 75 - 80 8 that of a powet shovel.

Draglines may be, i) crawler-mounted, ii) rubber-tyre-mounted or iii) truck-mounted. ppe (i) has speeds 1.6 kmph but can operate on soft surfaces; while types (ii) and (iii) have speeds 50 kmph but operate on hard surfaces. Size of Draglhes The size of a dragline is specified by the size of the bucket which is the same as the dipper of the Nwer shovel. Draglines may handle more than one size of bucket, depending on the class of material and the length of the boom. If the material is dficult to excavate, a smaller bucket reduces the digging resistance. 2.4.1 Operations of a Dragline The basic parts of a dragline are shown in Figure 2.4 (a). Excavation is started by swinging the empty bucket to the digging position at the same time slackening the drag and the hoist Excavation EqGrncnt cables. Excavation is done by pulling the bucket toward the machine while maintaining tension in the hoist cable. When the bucket is filled, the operator takes in the hoist cable while paying out the drag cable. Dumping is done by releasing the drag cable. Filling the bucket, hoisting, swinging and dumping of the loaded bucket, followed in that order, constitute one cycle. An experienced operator can cast the excavated material beyond the end of the boom. Since it is difficult to conlrol the accuracy in dumping from a dragline, a larger capacity of haul units is desirable to reduce the spillage. A size ratio of 5 - 6 times+he bucket capacity is recommended. Figure 2.4 (b) shows the uses of a dragline. 2.4.2 Optimum Depth of Cut for Draglines A dragline will produce its greatest output at the optimum depth of cut. Table 2.4 gives the optimum depth of cut for various sizes of buckets and classes of materials, using short boom draglines. Table 2.4 : Ideai Depths of Cut for Short-boom Draglines in m

Class of Material Size of Bucket, m3

0.29 0.38 0.57 0.76 0.95 1.14 133 1.53 1.91 Moist loam, or light sandy 1.5 1.7 1.8 2.0 2.1 2.2 2.4 2.5 2.6 clay Sand and gravel 1.5 1.7 1.8 2.0 2.1 2.2 2.4 2.5 2.6 Good common earth 1.8 2.0 2.4 2.5 2.6 2.7 2.8 3.0 3.2

Hard, tough clay 2.2 2.5 2.7 2.8 3.1 3.3 3.5 3.6 3.8 Wet, sticky clay 2.2 2.5 2.7 2.8 3.1 3.3 3.5 3.6 3.8

2.4.3 Angle of Swing of Draglines The outputs of the draglines are based on digging at optimum depths with an angle of swing of 90'. For any other depth of angle of swing the ideal output of the particular unit should be multiplied by appropriate factors given in Table 2.5. Table 2.5 : Conversion Factors for Depth of Cut and Angle of Swing for a Dragline 1 Percent of Angle of Swing (degrees) Optimum Depth 30° 45" 60' 75O 90' 120' 150° 180°

20 1.06 0.99 0.94 0.90 0.87 0.81 0.75 0.70 40 1.17 1.08 1.02 0.97 0.93 0.85 0.78 0.72 60 1.24 1.13 1.06 1.01 0.97 0.88 0.80 0.74 80 1.29 1.17 1.09 1.04 0.99 0.90 0.82 0.76

100 . 1.32 1.19 1.11 . 1.05 1.00 0.91 0.83 0.77 120 1.29 1.17 1.0 1.03 0.98 0.90 0.82 0.76 140 1.25 1.14 1.06 1.00 0.96 0.88 0.81 0.75 160 1.20 1.10 1.02 .0.97 0.93 0.85 0.79 0.73 180 1.15 1.05 0.98 0.94 0.90 0.82 0.76 0.71 200 1.10 1.00 0.94 0.90 0.87 0.79 0.73 0.69

2.4.4 Output of Draglines 1 While the effect of job and management conditions on the output of the dragline will be about the same as for a power shovel, and the job and management factors given in Table 1.11 of Unit 1 may be usedfor obtaining the probable output of draglines, the size of I bucket and length of boom have a direct effect on the output of a dragline. In selecting the size and bucket type, the draglie and bucket should be matched for best ! efficiency. Buckets are available in classes, such as light-duty, rnediumduty and , heavy-duty. Lightduty buckets are for materials that are easily dug, such as sandy loam, sandy clay, or sand. Medium-duty buckets are for general excavating service such as digging clay, soft shale or loose gravel. Heavy-duty buckets are for handling blasted rock and other abrasive materials. Buckets are often perforated to permit draining of water from the loads. In selecting the bucket size carashould be taken that the combined weight of the load and the bucket does not exceed the safe load recommended for the dragline. Other I factors affecting the output of a dragline are the same as for power shovels. Table 2.6 gives I the output of draglines for optimum DOC and 90° AOS. Table 2.6 : Ideal Outputs of Short-boom Draglines in m3/ 60 min-hr, Bank ~easure

I Size of Bucket, m3 Class of Material 0.29 038 0.57 0.76 0.95 1.14 133 1.53 1.91

Moist loam, or 53 72 99 122 149 168 187 202 233 light sandy clay Sandand gravel 49 69 95 118 141 160 180 195 225 Goodcommon 42 57 81 104 127 147 162 177 204 earth

Hard,toughclay 27 42 69 85 104 123 139 150 177 Wet, stickyclay 15 23 42 58 73 85 100 112 135

SAQ 3 i) What are the advantages and disadvantages of draglines? How are draglines classified? ii) What are the operations of a dragline? iii) What effects do depth of cut and angle of swing have on the output of draglines? How do the size of bucket and the length of boom affect the output of a dragline?

2.5 CLAMSHELLS

Clamshells are used primarily for handling loose materials such as sand, gravel, crushed stone, etc., and for removing materials from cofferdams, pier foundations, etc. They are especially suited to vertical lifting of materials from one location to another. The limit of vertical movement mybe relatively large when they are used with long crane booms. Size of Clamshell Buckets Clamshell buckets (Figure 2.5) are available in various sizes; and in heavy-duty type for digging, medium-weight type for general purpose, and light-duty type for handling light materials. Buckets may have teeth that can be easily removed or be without teeth. Teeth are used in digging harder types of materials but are not required when a bucket is rehandling materials. The capacity of a clamshell bucket is usually given in m3, and is expressed in several ways: water-level, plate-line, or heaped-measure. The water-level capacity or struck capacity are the same. The plate-line capacity indicates the capacity of the bucket following a line along the tops of the clams. The heaped capacity is the capacity of the bucket when the material is Excavation Equipment filled to the maximum angle of repose, usually taken as 45O. The deck area indicates the number of square metres covered by the bucket when fully open.

Sheaves

Figure 25 :Clamshell Bucket Output of Clamshells Because of the variable factors that affect the operations of a clamshell, it is difficult to give ! output rates that are dependable. These factors include the difficulty of loading the bucket, I I the size load obtainable, the height of lift, the angle of swing, the method of disposing the I load and the experience of the operator. Far example, if the material must be discharged into a hopper, the time required to spot the bucket over the hopper and discharge the load will be greater than when the material is discharged onto a large spoil bank. Example 2.2 A 1.5 m3rehandling type bucket, is used to transfer sand from a stockpile into a hopper, 8 m above the ground. The angle of swing will average 90'. The average speed of hoist linc is 45 m/rnin.Determine the probable output per hour. Solution Time per cycle (approx): Loading bucket = 6 sec Lifting and swinging load, 8 m 8 45m/min = 10 sec* Dumping load = 6 sec Swingipg back to stockpile = 4 sec Lost time, accelerating, etc. = 4 sec Total time = 30 sec 60 x 60 Maximum number of cycles per hour, -= 120 30 Maximum volume per hour = 120 x 1.5 = 180 m3

If the unit operates 45 .nin per hr, the probable output will be = 135 ' 3 60 per hr loose volume. -. -

+ A skilled operator should lift and swing simultaneously. If this is not possible, additional time should be allowed for swinging the load. SAQ 4 i) What are the uses of clamshell buckets? ii) What factors affect the output of clamshells?

2.6 MOTOR GRADERS A grader is primarily a device for levelling or finishing earthwork, but is also sometimes, used for mixing gravel, making windrows and trimming slopes. It is used in earth construction, making and maintaining project roads, and land reclamation. It can perform Excavation Equipment-11 operations such as grading, spreading, side-casting, road crowning, bank dressing, mixing materials, etc., through a suitable control of the blade and proper manoeuvering of the

There are two kinds of graders : towed and motorized. The towed grader is drawn with a tractor and is usually made small in size. The controls are often manual but sometimes a small petrol engine is mounted on the grader framework to operate the controls. A separate operator is required to control the grader. , The motorized grader (Figure 2.6), which is the most popular machine of this class, is a self-propulsive and fast moving machine. The machine has an arched frame converging and rased at thecfront and low at the rear where the prime mover is mounted. The blade is supported on a circle with inside gear teeth, and is capable of turning through 360'.

ETgum 26 :Motor Grader Size of Motor Graders Motor graders are powered by engines having a horse power varying from 90 to 300 metric h.p. and have speeds of 15 to 40 lanph. Operations of Motor Graders While grading the machine normally moves forward, the steering being controlled through the steering wheel. The machine is moved in low gear at a speed allowed by the depth of cut and the condition of surface, and the entire length of the road surface being graded is traversed before reversing the blade for the second cut and travelling in the'reverse gear. Alternatively, the machine is returned in high gear to start the second iut in forward motion In grader application, the top gear is used only for travel when no cutting or handling is done, and the lowest gear for abnormally heavy work, such as moving on steep grades or doing fine finishing. For other works, the intermediate gear speeds (3 to 20 krnph) are used; namely, second gear for ditching and trmming bank slopes, third gear for general road maintenance and spreading work and fourth gear for mixing and spreading earth. For nonnal grading work a speed of 10 to 15 krnph may be practical. Unnecessary tuming should be avoided as the long length of the machine makes turning in restricted areas time- consuming. It may be preferable to travel short distances in reverse gear rather than to turn for the return journey.The blade tilt and pitch should be set at a more acute angle to the ground surface for cohesive soils than for granular soils. Output of Motor Graders Production of motor graders depends upon the engine power, blade size, speed of travel, soil characteristics and operator efficiency. The output is usually expressed in units of area (m2) covered by the machine per hour. This area equals the effective width of the blade mulhplied by the average hourly speed of the motor grader during the pass. lime for acceleration and turning should be included in finding the average speed of the machine. When side-casting or grading with blade at an angle, the width actually covered by the machine should be used in finding the area. The effective width of the blade is, therefore,

Area covered by machinehour (m2) = 1000 x Effective width of blade (m) X average speed (lanph) x efficiency. Erenvnlioo Equipment A 50 min-hr is usually taken for working efficiency.

SAQ 5 i) What are the different kinds of motor graders? ii) What operations are involved in working a motor grader? iii) What factors affect the output of motor graders?

2.7 TRENCHERS

These machines dig utility trenches for water, gas and oil pipelines, telephone cables, drainage ditches and sewers. They provide fast digging, with controls of depths and widths of trenches. They can dig any type of material except rock. They are crawler-mounted to increase their stability. There are two types of trenchers: wheel-type trenching machine and ladder-type trenching machine. 2.7.1 Wheel-type Trenching Machines Figure 2.7 shows a wheeLtrenching machine. They can dig widths from 0.3 m upto 1.5 m and maximum cutting depths of the order of 2.4 m The excavating part of the machine comprises a power-driven wheel, on which are mounted a number of removable buckets equipped with cutter teeth. The machine is operated by lowering the rotating wheel to the desired depth, while the unit moves forward slowly. The earth is picked up by the buckets and deposited on a belt conveyor, which can be adjusted to discharge the earth on either' side of the trench or into a tractor-pulled wagon.

Post .

Figure 27 :Wheel-type Trending Machines Table 2.7 gives representative specifications for some wheel-type trenching machines. Table 2.7 : Representative Speciflcatiops for some Wheel-type Wenching Machines

Max. =nch Wench Engine Wheel I Travel Digging Depth width Power Speed Speed speed ( m) (4 &w) ( ds) (kmph) (dmh) 1.67 0.38$J.66 41 0.18-1.35 0.8-4.3 0.06-0.30 1.82 0.41-0.76 50 0.78-2.08 0.26-7.4 0.08-17.4 2.58 0.97-1.29 82 1.23 3.1 0.42-1 0.8

2.7.2 Ladder-type Trenching Machine The excavating part of the machine comprises cutter buckets attached to two endless chains, I, that travel along the boom As the buckets travel up the underside of the boom, they bring out earth and deposit it on a belt conveyor which discharges it along either side of the trench (Figure 2.8). As a machine moves over uneven ground, it is possible to vary the depth of cut bxr adjusting the position, but not the length, of the boom. Table 2.8 gives specifications of some ladder-type trenching nuchines. Excavation Equipment-I1

Figure 28 :Laddertype Trencher Table 2.8 : Representative Specifications for Some Ladder-type Trenching Machines

Trench Width Depth (m)

Ladder-type trenching machines have considerable flexibility with regard to trench deptks I and widths. But the machines are not suited to excavate trenches in rock or where large quantities of ground water and unstable soil prevent the walls of the trench from remaining I in place. 2.7.3 Selection of Suitable Equipment for Trenches Wheel-type trenchers are best for shallow, narrow trenches in firm soil. Ladder-type trenchers are best for deep, wide trenches in sufficiently firm soil. If the soil is rock a hoe will be the best choose. If the ground is unstable and watersaturated then a dragline, hoe or clamshell will do. If a solid sheeting is needed to hold the walls in place, then a clamshell will be the best. 2.7.4 Production Rates of Trenching Machines The factors affecting the production of trenchers are type of soil, depth and width of trench, extent of shoring required, topography, climate, vegetation, physical obstructions like boulders. Production rates may be assessed from Tables 2.7 and 2.8.

2.8 BUCKET

Bucket wheel excavators and bucket chain excavators are two main types of bucket excavators, which are most suitable for continuous digging operations where hardness of material to be excavated pennits practice of continuous digging process. However, since the Second World War the bucket wheel has to a large extent superseded the . The bucket wheel excavator (Figure 2.9), has a conical shaped digging wheel on which are mounted multiple buckets. The bucket-studded wheel revolves into the overburden face in an easy digging motion. When the buckets reach the top segment of the wheel circle, their dirt load falls onto a conveyor system that carries the material far out behind the machine. The wheeled excavator moves on four sets of crawlers like those of a large stripping shovel. Hydraulic jacks at the four comers of the base, keep the machine level. The levelling process is automatic and almost instantaneous. The design gives the machine great stability and reduces uneven wear on many parts. Propelling speedmaq~4~?.25kmpk The entire Excavation Equipment machine above the base can be swung through 360'. Swing circle diameter is about 10 m.

Figare 2.9 :Wheckd Excavator Production of Bucket Excavators Continuous excavators are usually rated in terms of theoretical output, where Qth = 6gFsS ... (2.1)

where, Qth = theoretical output, m3/hr (bank) F = capacity of a single bucket, m3 s = number of bucket discharges per minute, S = swell factor of the material being excavated. sag 6 1) What are trenchers, their ut111ty and then types'? What factors affect the production rates of Irenchcrs? ii) How are bucket excavators classitled? How is the theorekcal oulpul of a bucket excavator assessed?

2.9 DREDGES Dredging is excavation from a river bed, canal or lake generally for deepening the bed. In navigation canals, this constitutes an important operation. Dredging may be done in reservoirs to remove the accumulation of silt and sediments' to increase the storage capacity of the reservoir. This sub-aqueous excavation can be done by equipmentcalled dredges. Dredges may be classified into three classes: the dipper dredge, the ladder dredge and the suction dredge. Dipper Dredge The dipper dredge (Figure 2.10) is like an underwater shovel mounted on a floating barge and stabilbd, while digging, through a pair of spuds driven firmly into the river bed. The boom is capable of swinging through an angle of about 180'. A dipper dredge can excavate rocky soil; and can eifher deposit the material on the bank or on a floating barge. These dredges are capable of digging to a depth of 15 to 18 m ?&I- water, and have a maximum dumping range of about 30 m. Bucket sizes upto 12.25 m havz been employed and production rates 50 m3/hour/m3of bucket capacity attained.

Figure 210 :Dipper Dredge Ladder Dredge The ladder dredge (Figure 2.11) is equipped with a bucket elevator mounted on a barge. The bucket elevator functions as a digging and lifting tool. It is supported on a steel ladder and extends down to the river bed. ?he movement of the buckets which dig into the bottom of the river or stream cuts the soil and loads it into the buckets. As the bucket travels up, the soil is dumped into a hopper on the top of the elevator from where it is conveyed over a belt conveyor to the shore or to another barge. The speed of the elevator may vary from 15 to 18 mlmin and capacity of the individual bucket may give an output of about 76.5 m3/hr. This dredge is suited to soft groupd and gravel or sand only.

ere211 : Ladder Dredge Suction Dredge A suction dredge (Figure 2.12) or pump excavators as it is sometimes called, consists of a heavy duty pump mounted on a barge with the suction line supported on a ladder and

Prime Mover Tor Winches

'__--_ __------. - W"spuds - - - Excavalion Equipmmt extending into wabx upto &*river bed. The ladder usually inclines at an angle of 45O for the maximum digging depth and n hinged at the top end so that the free end can be raised or lowered with winches. The discharge line extending from the pump is supported on pontoons and ~0~ectedto another line on the bank through which the excavated material is conveyed to the desired spot. With the aid of booster pumps in the pipeline, th~smaterial can he pumped to distances of over 3.2 km and to a height of about 30 m The rapid flow of water entering the suction pipe at the lower end, loosens the soft material which is sucked into the pipe and pumped out. However, where the soil is comparatively hard, a cutter head is mounted close to the mouth of the suction pipe. This t601 is worked through a separate motor and its motion cuts and chums the material which is then sucked into the suction pip and conveyed out. The cutter has a speed of 5 to 20 rpm and is powered by a 305 metric h.p.

*

Sprocket

Trac

End Bit

Figure 213 : Crawlertractor-monated Bulldozer

Reservoir Breather Cnp Shift Lysm \ , I Steel' ""--' Shmud\ /

Axle

Fmnt Axle

Figure 214 : Wbd-tractor-mounted Bddcaer (224 kW)motor for SO cm dredge. The pump may need about 1320 metric h.p. (968 kU') for this size of dredge. The dredge is specified by the diameter of the discharge pipe. 2.10 BULEDOZERS

?be term bulldozer is broadly used to include both a bulldozer and an angle dozer.These machines may further be classified into : i) crawler-tractor-mounted (Figure 2.13), or ii) wheel-fractor-mounted (Figure 2.14). Based on the method of raising and lowering the blade, a bulldozer may be i) cable-controlled, or ii) . hYdraulically~ontrolled. Bulldozers can do many jobs on a project, like : Excavation Egoipmeat-11

I i) clearing land of timber and stumps, i ii) opening up pilot roads through mountains and rocky areas, iii) moving earth for haul distaices upto about 100 m, iv) helping load tractor-pulled scrapers, v) spreading earth fill, vi) backfilling trenches, vii) clearing construction sites of debris, I viii) maintaining haul roads, and ix) clearing the floors of borrow and quarry pits. I Bulldozers have blades mounted normal to the direction of travel, while hgle dozers have blades set at an angle to the direction of travel. The former class push the earth forward, while the latter push it forward as well as to one side. The size of a bulldozer is indicated by ) the length and height of the blade. Crawler-mounted versus Wheel-mounted Bulldozers Each type of mounting has advantages under certain conditions. Among the advantages of the crawler-mounted bulldozer, we can list the following : i) ability to deliver greater tractive effort on soft, loose or muddy soil, ii) ability to travel over muddy surfaces, iii) ability to operate in rock formations, where rubber &es may get seriously damaged, iv) ability to travel over rough surfaces, which may reduce the cost of maintaining haul roads, v) greater flotation because of lower pressures under the tracks, and vi) greater use-versatility on jobs. Among the advantages of the wheel-mounted bulldozers, we have : i) higher travel speeds on the job or from one job to another, ii) elimination of hauling equipment to transport the bulldozer to a job, iii) greater output, especially when considerable travelling is involved, iv) less operator fatigue, and v) ability to travel on paved roads without damaging the surface. Operations with a Bulldozer During the first passes of a bulldozer over a given lane most of the initial earth will spill off the ends of the blade to form a windrow on either side. After these windrows have been built up, to form a trench, further spillage reduces,or is eliminated, with an increase in output. If the earth can be pushed downhill, the output of a machine will increase substantially due to the advantage of favourable grade and the ability to float larger quantities of earth ahead of the dozer. Output of Bulldozets The output of the bulldozer and other members of the dozer family may be estimated by the formula : . Output in bank volumehour = (Loose volume handledltrip) .x S x (60/ t ) x efficiency, ... (2.2) .where, S = swell factor, and t = cycle time (time to make one trip or pass), min. 2.42 x H' x Volume of loose earth movedtrip = w for bulldozer ... (2.3) 3 Excavation Equipment

where, H = height of dozer blade, m, and W = width of dozer blade, m. 1 In these formulae, it is assumed that material will rise 10 % higher than the height of the I blade in case of bulldozers and 25 % higher in the case bull graders. The formulae may be used in average soil conditions and on level grades. The cycle time is got by adding the ti _,.d and the travel times. Fixed time includes time for loading (achieved in 6.1 to 9.1 min), and time for shifting gears for return trip, which is 0.17-0.2 rnin if shifting to higher gear is made in addition to changing forward-reverse gear (0.08-0.1 min if only a directional change is made). A turn, if involved, takes 0.25-0.33 min, and should be included in the cycle time. 1 Travel time (min) = Haul distance (m) x 0.06 / Haul speed (kmph) + Return distance (m) x 0.06 / Return speed (kmph) ...( 2.5) 1 A thumb rule suggested for output of a bulldozer is given as follows : Output in m3/hr = 25.3 x Drawbar h.p. (metric)/ dozing distance (m) ... (2.6) An angle dozer output is 10 % more than the bulldozer output as given by the rule. For example, for a 91.4 metric h.p., tractor dozer working on a dozing distance of 91 4 61 m will give the output as '25.3 x += 37.9 m3/hr. For ahgle dozer, approximate output = 37.9 x 1.1 = 41 .7 m5/hr. SAQ 7

1) What are the difltrent types of dredges 'and how does each function:' ii) What are the uses of bulldozers on a project? iii) How do crawler-mounted and wheel-mounted bulldozers compare in thelr perfor~ce? 1 iv) How is a bulldozer operated? 1 v) How is the outnut of a bulldozer estimated'?

Example 23 Determine the output of an angle dozer (make - D50A-15) with a blade width = 3.35 m, blade height = 0.855 m, forward speed = 9.4 lanph on a haul road 90 m long consisting of earth and gravel. The efficiency is 80 % and the job and management conditions are "fair-good and the working hour is 50 minihr. Solution Swell factor = 0.83 (Table 1 .l) Job and management factor = 0.69 (Table 1.11)

Volume of loose earth movedttrip =

60 Output in bank volume/hr = loose volume handled/trip x S x 7x efficiency

30 Expected output = 137.3 x 0.69 x - = 79 m3 (~)/hr. 60 1 2.11 TREE DOZERS Excavation Equipment-I1

A tree dozer is usually a heavy tractor equipped with a dozer, stumping, or V-blade and a higher push frame with longer reach which is under separate control. Trees are pushed by the upper frame (Figure 2.15) so that they lean away, and the tension enables the sturnper to drive under them readily. The.stumper is used for pushing over trees and stumps, driving under stumps to boost them out, and digging around them when necessary The V-blade casts uprooted trees to the side for disposal by other machines.

I Figure 2.15 :'Lke Dozer i 2.12 RIPPERS p Rippers are primarily used to loosen hard or tight material so that scrapers can be loaded properly or to reduce push time. Figure 2.16 shows a tractor-mounted hydraulically operated a ripper. The ripper has a number of shanks depending on the size of the tractor, the depth of penetration desired, the resistance of the material being ripped, and the degree of breakage of the material desired. If the material is to be excavated by self-loading scrapers, it should be broken into particles (usually of not more than 60 to 75 cm maximum size) that can be loaded into scrapers (described in Section 2.13). -

figure 216 :'Ractol.mounted Hydraalidy Operated Ripper Another method of classifying rippers is shown in Figure 2.17. ?be shank in (a) is attached to the tractor with a parallel-type linkage and in (b) the shank is attached with a hinge- or radial-type linkage. As the depth of penetration of the parallel-type linkage is varied, the point is kept at a constant angle, which reduces the wear and stabilizes the production. Excavation Equipment The angle of the point of hehinge-type linkage wilI vary as the depth of penetration is varied, which may be a disadvantage with some types of rock. However, hinge-type rippers are advantageous when ripping soil containing boulders.

(a) Parallel Linkage (b) Hinged Linkage

Production of Rippers Output of rippers depends upon the shape and size of the ripper tooth, number of shanks used, depth and width of ripping pass, size of tractor, characteristics of soil and average working speed of the machine. The output of a ripper is usually enough to keep 3 to 6 scrapers employed when soil is ripped before being loaded into scrapers. Volume of earth or rock ripped in one pass of the machine can be estimated from the .following formula: Bank volume tipped per pass (m3) = Length of pass (m) x spacing between ysses (m) x depth of penetration (m) x efficiency ...(2.7) Also, Production/hour (m /hr)(Bank) = (Bank volume ripped/pass) (m3) x (No. of passeshour) ...( 2.8) No. of passeshour = 601 Time for making one pass (min), and

Tiefor making- one pass (min) Length of pass ( m ) = lhm around time (min) + 0.06 x ...( 2.9 Speed of travelling (kmph) SAQ 8 i) How do tree dozers operate'! ii) What is the purpose of a ripper'? How is its production estimated?

2.13 SCRAPERS , ------Scrapers are self-operating earthmoving equipment to the extent that they can load, haul, and discharge material without depending on other equipment. If one of them breaks down, it is unnecessary to stop the job, as would be the case with a machine used exclusively for loading into haul units, for if the loader fails, the entire job must stop until repairs can be done. Figure 2.18 shows the bowl of a scraper which may be attached to the pulling or tractor unit, and hence called a towed scraper.' 'Qpes of Scrapers Excavation Equipment-I1 I There are two types of scrapers and their subdivisions are as follows: i) Crawler-tractor-pulled; and. ii) Wheel-tractor-pulled single-engine twin-engine two-bowl tandem, and elevating scraper.

:I Figure 2.18 :Scraper Bowl Crawler-tractor Scraper For relatively short haul distances the crawler-type tractor, pulling a rubbsr-tyred self-loading scraper, can move earth economically. The high drawbar pull in loading a scraper, combined with good traction, even on poor haul roads, gives the crawler tractor an advantage for short hauls. However, as the haul distance is increased, the low speed of a crawler tractor is a disadvantage compared with a wheel tractor. Unless the loading operation is difficult, a crawler tractor can load a scraper without the aid of a bulldozer. But, if there are several scraper units on a job, the increased output resulting from using a bulldozer to load the scrapers usually will justify the use of a bulldozer. Wheel-tractor Scra?er For longer haul distances the higher speed of a wheel type tractor-pulled, self-loading t scraper (Figure 2.19) will pvethe earth mbre economically than a crawler-type tractor. Although the wheel-type tractor cannot deliver as great a tractive effort in loading a scraper, the higher travel speed, which may exceed 50 kmph, will offset the disadvantage in loading when the haul distance is sufficiently long.

Rgclre 219 :Wheel-tractor Scraper Size of a Scraper The size of a scraper may be specified as the struck, or heaped capacity of the bowl in m3. Excavation Eqdpmaat The struck capacity is the volume of the material that a scraper will hold when the top of the material is struck off even with the top of the bowl.'Ihe heaped capacity is the struck volume plus the volume of eat?h above the top with slopes of 2 :1 (H :V). The capacity of a scraper (m3)in bank measure, is got by multiplying the lmevolume in the sqaper by the swell factor (see Table 1.1-Representative properties of earth and rock, Unit l).-Owing to the compacting effect on the earth in a scraper, the swell usually is less than for earth deposited into a truck by a power shovel. Tests indicate that the swell factors in Table 1.1 should be increased by 10 % for conventional scrapers. Tbus, if a conventional scraper hauls an average heaped load of 22.5 m3 of wet earth, for which the adjusted swell factor is 0.80 + 0.08 = 0.88, the bank measure volume will be 22.5 x 0.88 = 19.8 m3. Operating a Scraper A scraper is loaded (Figure 2.20) by lowering the front end of the bowl until the cutting edge, which is attached to and extends across the width of the bowl, enters the ground and, at the same time, raising the front apron to provide an open slot through which the earth

(a) Loading attiNdc.

. (d) Apron opening durlng loadiog,

(b) ~ppka&n~the cut

(e) Fihing the. cul.

F5gore 2.20 :Loading a Conventional Scraper may run into the bowl. As the scraper is pulled forward, a strip of earth is forced into the bowl. This operation is continued until the bowl is filled or until no more earth may be forced in. The cutting edge is raised and the apron is lowered to prevent spillage during the haul trip (Figure 2.21).

(aj TrewUing sttihde. (c) Bowl position. (b) Boarl~chscls*. (d) Apron and ejector position Flgwe 221 :lkvel of a Lmded Scraper The dumping operation consists in lowering the cutting edge to the desired height above the fill, raising the apron, and forcing the earth out between the blade and the apron by means of a movable ejector mounted at the rear of the bowl (Figure 2.22).

\a) Unloading attitude. /b) Bowl position. (c) Apron position for loose matedal. (d) Apron position for sticky matsdal. (8) Ejector movement

(4 ESgllre 2.22 :Unloading a Conventional Scraper The elevating scraper has horizontal slats which are operated by two endless chains, to . which the end of the slats are connected. As the scraper moves forward wlth its cutting edges digging into and loosening the earth, the slats rake the earth upward and into the bowl of the scraper. This action requires less energy than pushing earth upward through the material already in the bowl. Thus, this scraper is capable of loading without the assistance from a pusher tractor for some types of soils. Also, the pulverising action of the slats allows a more complete filling of the bowl, and it permits a more uniform spreading action on the fill. 2.13.1 Cycle Time of a Scraper The cycle time for a scraper is the time required to load, haul to the fill, dump and return to the loading position again. The cycle time includes the fixed time and the variable time. The fixed times for a scraper are given in Table 1.4 in Unit 1. The variable time depends on the distance of travel and the average speed of the vehicle. Since hauling and retuning are usually at different speed ranges, it is necessary to determine the time for each travel separately. 2.13.2 ~urntkrof Scrapers Served by a Pushdozer If wheel-type tractor-pulled scrapers are to attain their maximum hauling capacities, they need the assistance of one or more push tractors during the loading operation to reduce the loading and cycle time. Although crawler-type tractor-pulled scrapers are frequently referred to as self-loading units, it may be economically desirable to provide push tractors for them. If using a push tractor will increase the job production quite enough to more than pay the cost of the tractor, it is advantageous to use one. When using push tractors the number of pushers must match the number of scrapers. If a pusher or a scraper must wait for the other, it reduces the operating efficiency of the waiting unit as well as of the project and results in an increased production cost. The pusher cycle time includes the time required to load a scraper plus the time required to move into position to load another scraper. With the cycle times for the scraper and the pusher determined, the number of sciapers that a pusher must serve is given by :

where, N = number of scrapers served, Ts = cycle time for scraper, Tp = ,cycle time for pusher. Excavation Equipment 2.13.3 Output of Scrapers A thumb rule to determine the approximate output of a scraper has been suggested as:

where, C = struck capacity of scraper, m3 D =haul distance (one way), m.

For example, a 7.6 m3 scraper working on a 1.50 m haul may give an output - 7.6 = 95 m3 hour. - loox3.28~1.50+3 2.13.4 Increasing the Production Rates of Scrapers There are several methods of increasing the production of scrapers. These include : i) R~PP~ Tight soils will load easily if they are ripped ahead of the scraper. ii) Prewetting the Soil Some soils load more easily if they are reasonably moist. Prewetting done together with ripping, ahead of loading permits a uniform penetration of moisture into the soil. iii) Loading Downgrade When practicable, scrapers should be loaded on downgrade as the loading force is increased by 9 kg per tonne of gross weight for each 1 % of favourable grade. SAQ 9 ii Wiat are scrapers? Miat are the diflererlt rypes available? iij How is the capacity of a scraper obtained? iii) How is a scraper operated? iv) How do the cycle times of scraper and pusher help in determining [tie number of scrapers served by a pusher'! v) How will you obtain the output of a scraper'! vi) What are llie practical ways of increasing the production of scrapers?

2.14 CRAWLER Vs WHEELED EQUIPMENT

The relative merits of the two types of equipment are worth considering. Crawler or Track Based Equipment Crawler or track based equipment fit applications where maximum lugging power is the main requirement. They have maximum efficiency in limited-area operation. They are rugged machines meant to do heavy duty work where demand for tractive power is more, while the speed of movement is comparatively lower than wheeled tractors. On slippery mud, crawler tractors will do a job better than rubber tyred tractors, and crawler tractors will work effectively on rock, as sharp rock tends to damage the tyres. Wheel Based Equipment Wheel based or rubber tyred equipment is generally employed for light but speedy jobs and falls between'the crawler tractor and the truck in the scope of its applicability. In recent years, wheeled units have been designed to work on jobs which were considered the domain of crawler tractors some years ago. Wheeled Excavation Equipment-II tractor units are now available for practically all earthmoving jobs including ripping and dozing. Rubber tyred tractors find application where speed and mobility are important. When the cycle time is longer or where frequent movements from one job to another are involved, rubber tyred units are the best. Rubber tyred tractors give dependable performance with a minimum of competent, regular maintenance. Operation is easy and safe. When inspection or repairs are necessary, all parts are easily accessible and can be replaced easily atid quickly.

Rubber tyred units would be more suitable for the following job conditions: I i) large job volume, ii) increased job area, iii) eazlier completion dates to be kept, and iv) higher labour costs. Relative Merits The following are some of the important qualities of crawler or track- and rubber-tyred or wheel-based equipment: i) Wheeled units can travel faster than crawler units and have an additional advantage where travel distances are long and travel speed is important. ii) Crawler units are more compact and powerful and cati handle neavier jobs of hauling and digging as compared to wheeled units. iii) Crawler units are generally more costly than wheeled units due to expensive track system. iv) A large number of track parts subject to wear increase the operational cost of crawler units. v) Wheeled units have wheel steering control and are easily manoeuvered, white c:rawler units have stick control for steering and need greater skill in operation. vi) Crawler tracks, if moved on pavements or tarred roads, are likely to damage them unless fittzd with special shoes. vii) Transportation of crawler units over long distances is usually done on trailers due to their slow speeds of travel and to avoid excessive strain on the tracks. The wheeled units can be self-driven over long distances. viii) Wheeled units are liable to slip over very smooth surface or lose footings when increased power is applied to the wheels, while a crawler unit generally surmounts this difficulty since it moves on its own tracks and the tracks have a better grip on the ground. ix) Crawler units generally require more skill in operation, maintenance and repairs than wheeled units. SAQ 10

1) Where are crawler based equipment best suited? ii) Where are wheel based equipment kst suited? iii) What are the relative merits and demerits of crawler based and wheel based equipment?

2.15 SUMMARY

This unit describes the various types of excavation equipment, their operations and ideal production rates. The methods for determining the expe~cedproduction are illustrated by solved examples. Excavation Equipment 2.16 ANSWERS TO SAQs

Check your answers of all SAQs with respective preceding text.

2.17 FURTHER READING

1) Nichols, R.L. (1962): Moving the Earth, Galgotia Publishing House, New Delhi, 2nd ed. 2) Peurifoy, R.L.; Ledbetter,W.B. (1985): Construction Planning, Equipment & Methods, McGraw-Hill Book Co, New York, 4th ed. 3) Singh, Jagrnan (1980): Art of Earthmoving, Oxford & IBH Publishing Co., New Delhi. 4) Stubbs, F.W. (1959): Handbook of Heavy Construction, McGraw-Hill Book Co, New Yak. 5) Varrna, Mahesh (1979): Construction Equipment and its Planning and Application, Metropolitan Book Co., New Delhi, 3rd ed.