Unit 2 Excavation Equipment-11

UNIT 2 EXCAVATION EQUIPMENT-11

Structure

2.1 Introduction \ Object~ves 2.2 Power Shovels 2.3 Hoes 2.4 Draglines

\ 2.5 Clamshells 2.6 Motor Graders 2.7 Trenchers 2.8 Bucket Excavators 2.9 Dredges 2.10 Bulldozers 2.1 1 Tree Dozers 2.12 Rippers 2.13 Scrapers 2.14 Crawler vs Wheeled Equipment 2.15 Summary 2.16 Answers to SAQs

2.1 INTRODUCTION I

'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. This unit describes the different type of excavating equipment used in construction. In this unit, various types of equipment, their application and production rates in carrying out earthwork are described.

A,Rer studying this unit, 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 and draglines, a explain the size of clamshell buckets and work out the output of clamshells,

a understand the operation and find the output of motor graders, differentiate between the types of trencher and the factors affecting their selection and preduction, I 23 Construction Equipment explain the types of bucket excavators and compute their production rates, differentiate between various types of dredges, I explain the operations of a bulldozer, a tree dozer and scrapers, I explain the use of and the method to assess output of rippers, and explain the relative merits ofcrawler or track based equipment and wheel based equipment. 2.2 POWER SHOVELS Power shoveis are used mainly to excavate earth and load into trucks or tractor-drawn yagons. They can excavate all types of earth 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. The rubber-tyre-mounted shovels which have higher travel speeds are useful for small ipbs where considerable travelling is involved and where the road surfaces and the ground are firm The bask parts of pr parer shove! include the mounting, cab, boom, dipper stick and dipper (Figure 2. I(B)}, QthGr n#ochmmta to the rhoval include hoe, dragline, 'PTal?nah4ttarndarndafmifPtg%W22~)). , . " . .+ ..:. ,.... < ""... .,,..., -..*--4-.+-2 ..- s- * Size of Power ~'havels' The size of power shovels 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 from heaped volume which a dipper may pick up in loose soil. Power shovels are commonly available in dipper size of 0.29,0.38,0.57,0.76,0.95,1.14, 1.33, 1.53 and 1.91 m3.

Figure 2.1 : (a) Power Shevets Excavation Equiptnent-11

(b) Altrchmeab of shovel oaiL

Figure 2.1 : (b) Attachments of Shovel unit

Operations of Shovels

1 Positioning the shovel near the face of the earth to be excavated, the dipper is 1 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 be possible to fill the dipper completely without excessive crowding and hoisting tension. If the depth of cut is more than is required to fill the dipper, the depth of penetration of the dipper into the face must be reduced if the full face is to be excavated or to start the

L excavation above the floor of the pit. . Optimum Depth of cut for Power Shovels

ik ik ; The optimum depth of cut is that depth which produces the greatest output and at ' which the dipper comes up with a full load. Angb of Swing of Power Shovels The angle of swing of a power shovel is the horizontal angle, expressed 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 digging, swinging to the dumping position, dumping, and returning to the digging position.

Output of Power Shovels ,I The actual output of a power shovel depknds on : (a) Class of material (b) bepth of cut (DOC) (c) Angle of swing (AOS) Conetruetion Equipment (d) Job conditions (e) Management conditions (f) Size of haul units (g) Skill of the operator (h) Physical condition of the shovel. Selecting Type and Size of Power Shovels If the work areas are scattered, the mobility of the rubber-type-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 rubber tyred shovel. In selecting the size of a shovel, the two primary factors are : the cost per m3 of the material excavated and the job conditions under which the shovel will operate. In estimating the cost per m3, the factors considered are : (a) The size of the job, as a larger job may justify the higher cost of a large shovel, (b) The cost of transporting a large shovel will be higher than a small one, (c) 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, (d) 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, (e) 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 3 (f) The cost of wages per m 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 : ) (a) High lifts from the working face to the havl units will require the long reach of a large shovel, \ (b) If blasted rock is to be excavated, the large sized dipper will handle bigger rocks, (c) If the material to be excavated is hard and tou~&>a larger shovel will handle the material more easily, if (d) If the time allotted for completing the job requires a high hourly output, a large shovel must be used, (e) If large haul units are available, than a large shovel should be used, and (f) 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 : 3 Size of bucket = 1.14 m Actual depth of cut = 3.15 m Actual angle of swing = 75" Class of material : sand and gavel Job and management conditions : excellent-good Working hour = 50 min, per hr. Solution Excavation Equipment-I1 3 I [deal production = 206 m (bank)/hr. I Optimum depth of cut = 2.1 m Job and management factor = 0.8 1 100 Percent of actual to optimum depth of cut = 3.15 x - = 150% 2.1 Conversion factor for DOC and AOS for a power shovel = 0.935 3 Average production = 206 x 0.935 = 192.61 m (B)/hr.

Expected production = 50 x 192.61 x 0.81 = 130 m3 (B)/hr. 60 SAQ 1 (a) Explain the operations of a power shovel. (b) How do you define the optimum depth of cut for a power shovel? I (c) How is "angle of swing" defined for a power shovel? (d) On what factors does the selection of type and size of a power shovel depend?

I 2.3 HOES r 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 backhoe. 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 r&sThey are adapted to dig trenches, pits and basements. Due to their rigidity they are superior to draglines in operating on close-range work and dumping into trucks. Because of the direct pull on the dipper, hoes may exert greater tooth pressure than power shovels.

Figurr 22: Cable Operated Backhoe Construetion Equipment Operations of a Backhoe Figure 2.3 shows the basic parts of a cable operated backhoe. The machine is placed in operation by setting the boom at the desired angle and pulling in the hoist 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. Hoist cable -

Figure 23: Bmic Parts of a Cable Opnted Backboe Output of Backhoes When a hoe is used to dig at moderate depths, the output may be as much 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 (a) What are the functions of a hoe? (b) Explain the operations of a backhoe. (c) What factors affect the output of a backhoe?

2.4 DRAGLINES

Draglines are used to excavate earth and load it into haul units, such as trucks or tractorJpulled wagons, or to deposit it on spoil banks and embankments near the place from vhere it is excavated. A power shovel can be converted into a dragline by replacing the dipper stick of the shovel with arcane boom and substituting a dragline bucket for the shovel dipper. Advantages of a dragline are : fl (a) It does not have to go into the pit to excavate, r (b) 1tebelow its level &d under water, (c) T e trucks do not have to go into the pit nor contend with wet mud, (d) A dragline with a long boom can dispose off the earth in one operation without the need for haul units, and (e) It can excavate trenches without shoring. One disadvantage of a dragline is that its output is only 75-80% that of a power shovel. Type of Draglines Excavation Equipment-11 Draglines may be, (a) crawler-mounted, (b) rubber-tyre-mounted, or - (c) truck-mounted Type (a) has speeds 1.6 kmph but can operate on soft surfaces; while types (b) and

LA (c) have speeds 50 krnph but operate on hard surfaces. Size of Draglines The size of a dragline is specified by the size of the bucket which is the same as the dipper of the power 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 difficult to excavate, a smaller bucket reduces the digging resistance. 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 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 control 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 the bucket capacity is recommended. Figure 2.4(b) shows the uses of a dragline.

(a) Uses of the Dragline (b) Basic Parts of a Dragline

Figure 2.4 Consbuction Equipment Optimum Depth of Cut for Draglines A dragline will produce its greatest output at the optimum depth of cut. Table 2.1 gives the optimum depth of cut for various sizes of buckets and classes of material, using short boom draglines. Table 2.1 : Ideal Depths of Cut for Short-boom Draglines in m

Moist loam or

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 q.6 3.8 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 2.2. Table 2.2 : Conversion Factors for Depth of Cut and Angle of Swing for a Dragline

Output of Draglines While the effect ofjob 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 Unit 1 may be used for obtaining the probable output of draglines, the size of bucket and length of boom have a direct effect on the output of a dragline. In selecting the size and bucket type, the dragline and bucket should be matched for best efficiency. Buckets are available in classes, such as lightduty, mediumduty and heavy-duty. Light-duty buckets are for materials that are easily dug, such as sandy loam, sandy clay, or sand. Mediumduty buckets are for general excavating service such as digging clay, soft shale or loose gravel. Heavyduty buckets are for handling blasted rock and other abrasive materials. Buekets are often perforated to permit draining of water from the loads. In selecting the bucket size care should be taken that the combined weight of the load and the bucket does not exceed the safe load recommended for the dragline. Other factors affecting the Excavation Equipment-11 output of a dragline are the same as for power shocels. Table 2.3 gives the output of draglines for optimum DOC and 90"AOS. Table 2.3 : Ideal Outputs of Short-boom Draglines in m3/60 min-hr, Bank Measure L Class of Size of Bucket, m3 Material 0.29 0.38 0.57 0.76 0.95 1.14 1.33 1.53 1.91 187 202 233 -- Sandandgravel 49 69 95 118 141 160 180 195 225 Good common 42 57 81 104 127 147 162 177 204 earth 1 Hard, tough clay 27 42 69 85 104 123 139 150 177 Wet.sticky clay 15 23 42 58 73 85 100 112 135 SAQ 3 (a) What are the advantages and disadvantages of draglines? How are draglines classified? (b) What are the operations of a dragline? (c) 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 l:specially suited to vertical lifting of materials from one location to another. The limit of vertical movement maybe relatively large when they are used with long crane booms. :Size of Clamshells Buckets Clamshells buckets (Figure 2.5) are available in various sizes; and in heavyduty type for digging, medium-weight type for general purpose,md light-duty type for .L handling light materials. Buckets may have teeth that can be easily removef or they may be without teeth. Teeth are used in digging harder types of materals but are not required when a bucket is re-handling materials. I.

Figure 2.5 : Clamshell Bucket 3 1 Ceclstructios Equipmen4 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 filled to the maximum angle of repose, usually taken as 45'. The deck area indicates the number of square metres covered by the bucket when fully open. 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, the size load obtainable, the height of lift, the angle of swing, the method of disposing the load and the experience of the operator. For example, if the material must be discharged into a hopper, the time required to place the bucket over the hopper and discharge the Iqad will be greater than when the material is discharged onto a large spoil bank. Example 2.2 A 1.5 m3 re-handling 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 line is 45 mlmin. Determine the probable output per hour. Solution

Time per cycle (approx.) : Loading bucket = 6 sec.

Lifting and swinging load, 8 m @ 45mlmin = 10 sec*

Dumping load = 6 sec

Swinging back to stockpile = 4 sec

Lost time, accelerating, etc. = 4 sec Total time = 30 sec

Maximum number of cycles per hour, -60 60 - 120 30

3 Maximum volume per hour = 120 x 1.5 = 180 m

If the unit operates 45 min per hr, the probable output will be 180x 45 = 135m3 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 (a) What are the uses of clamshell buckets? 2.6 MOTOR GRADERS Excavation Equipmeat-11

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 operations such as grading, spreading, side-casting, road crowning, bank dressing, mixing materials, etc. through a suitable control of the blade and proper maneuvering of the machine. There are two kinds of graders : towed and motorised. The towed grader is drawn with a tractor and is usually made small in size. The control 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 motorised 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 raised at the front 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".

Optnting Contmls

npr~26 : Motor Grader Size of Motor Graders Motor graders are powered by engines having a horse power varying from 90 to 300 metric hp and have speeds of 15 to 40 krnph. 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 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 cut in forward motion. 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 area (mZ) covered by the machine per hour. This area equals the effective width of the blade multiplied by the average hourly speed of the grader during the pass. Time 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 ihnding the area. The effective width of the blade is, therefore, important. , . Area covered by machine/hour (mZ)= 1000 x Effective width of blade Tm> x Average speed (bph) x efficiency- 1 A 50 min-hr is usually taken for working efficiency. i Construction Equipment SAQ 5

(a) What are the different kinds of motor graders? (b) What operations are involved in working a motor grader? (c) 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. Wheel-type Trenching Machines Figure 2.7 shows a wheel-type trenching machine. Such machines 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 pickedup by the buckets and deposited on a belt conveyor, which can be adjusted to discharge theearth on either side of the trench or into a tractor-pulled wagon.

Post

Flpn 27: Wheel-tgpe lhdhgM.ebiPc - - Table 2.4 gives representative specifications for some wheel-type trenching machine. Table 2.4 : Representative Specifieafions for some Wheel-type Trenching Machine

Maximum - Trench Engine . Wheel Tr~wel Digging Trench Dqtb Width Power- Speed ' Speed Speed (m) (m) (kW) (m/s) (kmph) (m/min.) r 1.67 0.38-0.66 4 1 0.1 8-1.35 0.8-4.3 0.06-0.30

I 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 0.42-10.8 - Ladder-type Trenching Machines Excavation l3quipmerct-Fl

The excavating part of the machine comprises cutter buckets attached to two , endless chains, that travel along the boom. As the buckets travel up the underskie 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 by adjusting the position, but not the length, of the boom. Table 2.5 gives specifications of some ladder-type trenching machine?.

Figure 2.8 : Ladder-type Trencher Table 2.5 : Representative Specifications for some Ladder-type Trenching Machines Maximum Trench Engine Bucket Travel I Trench Depth I Width I Power 1 Speed tm) tm) (kw) (mls) (kmph$ (mlmin.) 1.37 0.15-0.20 3 5 1.24-2.72 1.1-5.5 0.67-6.6 2.58 0.41-0.92 41 0.48-1.14 2.2-5.1 0.15-4.2

Ladder-type trenching machines have considerable flexibility with regard to trench depths 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 in place. 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. Ifthe soil is rock a hoe will be the best choice. If the ground is unstable and water saturated then a dragIine, hoe or clamshell will do. If a solid sheeting is needed to hold the walls in place, then dclarnshell will be the best. 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 2.4 and 2.5.

2.8 iBUCKET EXCAVATORS -

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 permits practice of continuous digging process. However, since Construction Equipment the Second World War the bucket wheel excavator has. to a large extent, superseded the bucket chain excavator. 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 into a conveyor system that carries the material far out behind the machine.

Figure 2.9 : Wheeled Excavator 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 speed may be 0.25 kmph. The entire machine above the base can be swung through 360'. Swing circle diameter is about 10 m. Production of Bucket Excavators Continuous excavators are usually rated in terms of theoretical output, where Q,h=60 Fs S . . . (2.1) 3 ' \ where, Q,,,= Theoretical output, m /hr (bank), 3 F = Capacity of a single bucket, m , s = Number of bucket discharges per minute, and ' 4 S = Swell factor of the material being excavated. SAQ 6 (a) What are trenchers, their utility and their types? What factors affect the production rates of trenchers? (b)' How are bucket excavators classified? How is the theoretical output of a bucket excavator assessed?

2.9 DREDGES

Dredging is excavation from a river bed, canal or lake grarjually 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 equipment called dredges. Dredges may be Excavation Equipment-11, 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 stabilized, 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 either 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 under water, and have a maximum dumping range of about 30 m. Bucket sizes upto 12.25 m3 have been employed and production rates 50 m3/hour/m3 of bucket capacity attained.

Figure 2.10 : Dipper Dredge Ladder Dredge The ladder dredge (Figure 2.1 1) 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. The 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 sot? ground and gravel or sand only.

Slern connection

Figure 2.11 : Ladder Dredge '\

\ '\ / i' - Construction Equipment Suction Dredge I A suction *dge (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 extending into water upto the river bed. The ladder usually inclines at an angle of 45" for the maximum digging depth and is 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 connected to another line on hebank through which the excavated material is conveyed to the desired spot. With the aid of booster pumps in the pipeline, this material can be pumped to distances of over 3.2 krn 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 tool is worked through a separate motor and its motion cuts and chums the material which is then sucked into the suction pipe and conveyed out. The cutter has a speed of 5 to 20 rpm and is powered by a ?05 metric hp (224 kW) motor for 50 cm dredge. The pump may need about 1320 metric hp (968 kW) for this size of dredge. The dredge is specified by the diameter of the discharge pipe.

Prime Mover

------. ------,,------, - - '-----. -- - - -_ ----__------

Figure 2.12 : Suction Dredge

End Bit

Figure 2.13 : Crawler-tractor-mounted Bulldozer

\ 38 Excavation Equipment-I1

Exhaust Pipe Shin Levers \ Air Cleaner Steering Wh

Axle

Fmnt Axle

Figure 2.14 : Wheel-tractor-mounted Bulldozer

2.10 BULLDOZERS 1

The te,m bulldozer is broadly used to include both a bulldozer and an angle dozer. These machi 'Y s may further be classified into : r (a) crawler-tractor-mounted (Figure 2.13), or (b) wheel-tractor-mounted (Figure 2.14). Based on the method of raising and lowering the blade, a bulldozer may be (a) cablecontrolled, or (b) hydraulically-controlled. Bulldozer can do many jobs on a project, like :

(a) clearing land of timber and stumps, (b) opening up pilot roads through mountains and rocky areas, (c) moving earth for haul distances upto about 100 m, (d) helping load tractor-pulled scrapers, (e) spreading earth fil I, (f) backfilling trenches,

(g) clearing construction sites of debris, (h) maintaining haul roads, and

(i) clearing the floors of borrow and quany pits. Iklldozers have blades mounted normal to the direction of travel, while angle dozers have blades set at an angle to the direction of travel. The farmer class pushes the earth fbrward, while the latter pushes it forward as well as to one side. The size of a bulldozer is indicated by the length and height of the blade. Construction Eqbipment 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 : (a) ability to deliver greater tractive effort on soft, loose or muddy soil, (b) ability to travel over muddy surfaces, (c) ability to operate in rock formations, where rubber tyres may get seriously damaged, / (d) ability to travel over rough surfaces, which may reduce the cost of maintaining haul roads, (e) greater floatation because of lower pressures under the tracks, and (f) greater use-versatility on jobs.

--_ -. Among the advantages of the wheel-mounted bulldozers, we have : (a) higher travel speeds on the job or from one job to another, (b) elimination of hauling equipment, to t~apsp0-t,?hebulldoz It), ., Yoby +:(a)A-8 graaterbtrtput,~ia~y~hopoonsfderabla travelling is involved, (d) less operator fatigue, and (e) 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 Bulldozers The output of the bulldozer and other members of the dozer family may be estimated by the formula : Output in bank volume/hour = (Loose volumehandled/trip) x S x (4")- x efficiency . . . (2.2) - where, S = $well factor, and

t = Cycle time (time to make one trip or pass), min.

2'42 Volume of loose earth movedltrip = for bulldozer . . . (2.3) 3 3'12 - for bull grader . . . (2.4) 3

where, H = Height of dozer blade, m, and

W = Width of dozer blade, m. In these formulae, it is assumed that material will riselo% higher than the height of the 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. 40 Travel time (min) = Haul distance (m) x 0.06JHaul speed (kmph) + Return Excavation Equipmelt-il distance (m) x 0.06lReturn speed (kmph) . . . (2.5) / I A thumb rule suggested for output of a bulldozer is given as follows : Output in m5!hr = 25.3 x Drawbar hp (metric)/dozing distance (m) . . . (2.6) An angle dozer output is 10% more than the bulldozer output given by the thumb rule. -. For example, for a 9 1.4 metric hp tractor dozer working on a dozing distance of

61 m will give the output as 25.3 x %= 37.9 m3ihr. 6 1

For angle dozer. approximate output = 37.9 x 1.1 = 41.7 m3/hr . - Example 2.3 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 kmph on a haul road 90 m long consisting of earth and gravel. The efficiency is 80% and the job and I management conditions are "fair-good" and the working hour is 50 minlhr. Solution

Swell factor = 0.83 (assume)

Job and management factor = 0.69 (assume)

- 2.42 x 0.855~x 3.35 3 Volume of loose earth movedltrip = = 1.98 m I 3 loose volume handled 60 Output in bank volumelhr = x S x - x efficiency trip t

50 3 Expected output = 137.3 x 0.69 x - = 79 m (B)/hr . 60 SAQ 7 (a) What are the different types of dredges and how does each functio~? (b) What are the uses of bulldozers on a project? (c) How do crawler-mounted and wheel-mounted bulldozers compare in their performance?

2.11 TREE DOZERS

A tree dozer is usually a heavy tractor equipped with a dozer, stumper, or V-blade and a higher push frame with longer reach which is under separate control. These are pushed by the upper frame (Figure 2.15) so that they lean away, and the tension enables the Construction Equipment stumper 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 machine

Figure 2.15 : Tree Dozer 2.12 RIPPERS

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 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 2.16 : Tractor-mounted Hydraulically Operated Ripper Another method of classifying rippers is shown in Figure 2.17. ~deshank in Figure 2.1 7(a) is attached to the tractor with a parallel-type linkage and in Figure 2.17(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. The angle of the point of the hinge-type linkage will 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. Excavation Equipment-I1

F (a) Parallel Linkage (b) Hinged Linkage Figure 2.17 : Classification of Rippers 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 I the following formula :

3 Bank volume ripped per pass (m ) = Length of pass (m) x spacing between passes (m) x depth of penetration (m) x efficiency . . . (2.7) Also, Production/hour (m3/hr) (Bank) = (Bank volume rippedtpass) (m3) x (No. of passeslhour) . . . (2.8) No. of passeslhour = 60lTime for making one pass (min), and Time for making one pass (min) = Turnaround time (min) + 0.06 Length of pass (m) x , . . (2.9) Speedof travelling (kmph) SAQ 8 (a) How do tree dozers operate? (b) 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 2.1 8 shows the bowl of a scraper which may be attached, to the pulling or tractor unit, and hence called a towed scraper. Construction Equipment

Figure 2.18 : Scraper Bowl Types of Scrapers There are two types of scrapers and their sub-divisions are as follows : (a) Crawler-tractor-pulled, and (b) Wheel-tractor-pulled (i) single-engine (ii) twin-engine (iii) two-bowl tandem, and (iv) elevating scraper. Crawler-tractor Scraper For relatively short haul distances the crawler-type tractor, pulling a rubber-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 increases, the low speed of a crawler tractor is advantage 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 Scraper For longer haul distances the higher speed of a wheel type tractor-pulled, self-loading scraper (Figure 2.19) will move the earth more 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 krnph, will offset the disadvantage in loading when the haul distance is sufficiently long.

44 Figure 2.19 : Wheel-tractor Scraper

i Y ,< , 9 4, , -1 ., ' I ' 01 Size of a Scraper Excavation Equipment-I1 The size of a scraper may be specified as the struck, or heaped capacity of the bowl in m3. 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. The heaped capacity is the struck volume plus the volume of earth above the top with slopes of 2: l(H:V). The capacity of a scraper (m3) in bank measure, is got by multiplying the loose volume in the scraper by the swell factor. 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 should be increased by 10% for conventional scrapers. Thus, if a conventional scraper hauls an average heaped loadof 22.5 m3 of wet earth, for which the adjusted swell factor is 3 0.80 + 0.08 = 0.88, the bank measure volume will be 22.5 x 0.88 = 19.8 m . Operating a Scraper Brscraper 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 may run into the bowl. As the scraper is pulled forward, a strip of earth is forced into the bowl. This operation iscontinued 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).

I*) Loading artitthde.

- -- \)? JUU&~- (d) Apron opning during loadlrrg. (b) Approaching the cut.

(e) Finishing the cut.

Figure 2.20 : Loading a Conventional Scraper (a) Travelling.Attitude lc) Bowl Position

(b) Bowlany chock valve. (d) Apron and cjedor position. Fig- 2.21 : lhvcl ot a WedScmpel- 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 Material

(d) Apron Position for Sticking Material (e) Ejector Mevement Figure 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 forwafd with its cutting edges digging into and loosing 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. ~lsodhepulverising action of the slats allows a more complete filling of 46 the bowl, and it permits a more uniform spreading action on the fill. Cycle Time for a Scraper Excavation Equipment-11 The cycle time for a scraper is the time required to load, haul to the fill, damp and return to the loading position again. The cycle time includes the fixed time and the variable time. The variable time depends on the distance of travel and the average speed of the vehicle. Since hauling and returning are usually at different speed ranges, it is necessary to determine the time for each travel separately. Number of 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. Use of a push tractor will increase the job production to a level which will pay more than the cost of the tractor. Thus, 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 scrapers that a pusher must serve is given by :

where, N = Number of scrapers sewed,

Ts= Cycle time for scraper, and

Tp= Cycle time for pusher. 43utput of Scrapers A thumb rule to determine the approximate output of a scraper has been suggested as : C Output in (m3/hr.) = 100 x ... 3.280 + 3

3 where, C = Struck capacity of scraper, m , and

D = Haul distance (one yay), m. For example, a 7.6 m3 scraper working on a 1.50 m haul may give an output

llncreasing the Production Rates of Scrapers There are several methods of increasing the production of scrapers. These include : Ripping Tight soils will load easily if they are ripped ahead of the scraper. Pre-wetting the Soil Some soils load more easily if they are reasonably moist. Pre-wetting done together with ripping, ahead of loading permits a uniform penetration of moisture into the soil. Constructio~Equipment Loading Downgrade When practicable, scrapers should be loaded on downgrade as the loading force is increased by 9 kg per tonne of the gross weight for each 1% of favourable grade. SAQ 9 (a) What are scrapers? What are different types available? (b) How is the 'capacity of a scraper obtained? (c) How do the cycle times of scraper and pusher help in determining the number of scrapers served by a pusher?

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 , tractor units are now available for practically all earthmoving jobs including ripping and dozing. 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 conveniently and quickly. Rubber tyred units would be more suitable for the following job conditions (a) large job volume, (b) increased job area, (c) earlier completion dates to be kept, and (d) higher labour costs. Relative Merits The following are some of the important qualities of crawler or track- and ,i rubber-tyred or wheel-based equipment : Wheeled units can travel faster than crawler units and have an Excavation Equipment-I1 additional advantage where travel distances are long and travel speed is important. Crawler units are more compact and powerful and can handle heavier jobs of hauling and digging as compared to wheeled units. Crawler units are generally more costly than wheeled units due to- expensive track system. A large number of track parts subject to wear increase the operational cost of crawler units. Wheeled units have wheel steering control and are easily maneuvered, while crawler units have stick control for steering and need greater skill in operation. Crawler tracks, if moved on pavements or tarred roads, are likely to damage them unless fitted with special shoes. 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. 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.

(9 Crawler units generally require more skill in operation, maintenance and repairs than wheeled units. SAQ 10 (a) Where the crawler based equipment is best suited? (b) Where are wheel based equipment best suited? (c) 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 psoduction rates: The methods for determining the expected production are illustrated by solved examples.

2.16 ANSWERS TO SAQs

Refer the preceding text for all the Answers to SAQS.