(Earth moving machines: Construction and operational aspects of bulldozers, dumpers,loaders, scrapers and shovels, power a...
The cutting edge of scoop does the excavate work and the excavated material goes oncollecting in howl from the front gate....
1) The Basic Parts and Operation of a Shovel: The basic parts of a power shovel includethe mounting, cab, boom, dipper sti...
These are meant for carrying rocks, coal, minerals, aggregate and other materials inconstruction works. Dumper may be ON r...
Dumpers play important vole in dam construction, road making, mining etc. for carryingmaterials and dumping at required pl...
Types of Cranes1) Crawler-Mounted Cranes (Derrick Crane)2) Rubber - Tyre mounted or Mobile Cranes3) Portable Crane.Applica...
Fig. shows truck crane in its simplest form. It consists of a lifting boom and wire ropewith its associated winding mechan...
names like Angle dozer, tilt dozer, tree dozer and push dozer. Bull-dozer scrapes soil andgranular materials, pushes it in...
suitable ultimate strength is used for tilting the blade at required angle. The transmissionunit, engine unit etc. being s...
and to reduce heat developed clutch should be wet type. Therefore cooling oil iscirculated continuously in clutch housing ...
wheel exerts thrust on the ground while rolling over it, there will be tendency to slidingmotion or slip between the tyre ...
The constructional line diagram shows, a crawler mounted excavator. It mainly consistsof three units, namely.1) A under ca...
Motor grader is generally used for leveling spreading and finishing the work like in roadprojects. It consists of a blade ...
produces a complete coverage of surface. Usually the weight of a unit may be varied byadding ballast to suit the material ...
The compacting ability of pneumatic rollers can be known by;1) The gross weight of the unit.2) The gross weight per wheel....
The main difference between 2-wheels and 3 wheels rollers are;1) No. of wheels — 2 in case of tandem roller.2) Width — Wid...
Following fig. illustrates Towed (pulled)—type vibrating sheep’s foot roller.Sheep’s foot rollers may be towed by tractors...
same dimensions. A unit may consist of one or several drums mounted on one or morehorizontal axles. The weight of a drum m...
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Earth moving machines

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Earth moving machines

  1. 1. (Earth moving machines: Construction and operational aspects of bulldozers, dumpers,loaders, scrapers and shovels, power and capacity of earth moving machines.Construction equipment: Construction and operational aspects of mobile cranes, roadrollers, elevators and elevating graders.)Construction EquipmentsVarious construction equipments used are1. Dumpers2. Scrapers3. Power Shovels4. Motor graders5. Bulldozers6. Ripper7. Road roller8. Cranes9. Trenchers10. Wheel loadersSCRAPERSScrapers are the result of a compromise between the best loading and the best haulingmachines. Scrapers are used to scrap the ground, load it simultaneously, then transport itover a distance, dump at the desired place and then spread or layered. The ability of thesemachines to deposit their loads in uniformly thick layer will facilitate the succeedingspreading operation, On the return trips to borrow pits the cutting blades of scrapers maybe lowered enough to remove high spots, thereby assisting in maintaining the haul roads.Thus, scrapers are designed to dig, load, haul, dump and spread. Therefore sometimes itis called “Carryall.The fig. shows the self propelled wheeled type scraper, it essentially consists of a largescoop provided with cutting edge. The scoop is in the form of bucket on hollowcontainer, which is known as bowl or body. The scoop can excavate, transport and dumpthe material wherever required.
  2. 2. The cutting edge of scoop does the excavate work and the excavated material goes oncollecting in howl from the front gate. The material is transported to the site of dumpingand is taken out from the tailgate of the bowl. Then facilitate the succeeding spreadingoperations to required and uniform thick layer.Types of scrapersScrapers may be broadly classified into two main categories.They are;1) Crawler — tractor scraper2) Wheel — tractor scraper.a) Single — engineb) Twin — enginec) Two — bowl tandemd) Elevating Scrapers.Crawler — tractor scrapers are used for relatively short haul distances, pulling a rubber -tyred self - loading scraper. The high drawbar pull in loading a scraper, combined withgood traction even on poor haul roads, gives the crawler tractor an advantage for shorthauls.Wheel - tractor scrapers are used for longer haul distances and the higher speed of awheeled type tractor pulled self loading scraper will permit it to move earth moreeconomically than a crawler-type tractor.CONSTRUCTION & WORKING OF POWER SHOVELPower Shovels are used primarily to excavate earth and load it into trucks or tractorpulled wagons or onto or onto conveyor belts. They are capable of excavating all classesof earth, except solid rock, without prior loosening, like in quarries, mines in any roadprojects etc. therefore a power shovels are considered as basic tool for excavating thematerials and loading.They may be mounted on crawler tracks, in which case they are referred to as crawlermounted shovels. Such shovels have very low travel speeds. However, they may bemounted an rubber-tired wheels. Single-engine self-propelled units are powered andoperated from excavator cab. The non-self-propelled units mounted on the rear of tracks,which are referred to as truck-mounted, have separate engines for operating them. Fig.illustrates a crawler-mounted shovel.
  3. 3. 1) The Basic Parts and Operation of a Shovel: The basic parts of a power shovel includethe mounting, cab, boom, dipper stick and bucket or dipper and under carriage unit.These parts for a cable- controlled shovel.2) Power unit: It implies engine which supplies necessary power, enables to more andvarious operations to be performed by the shovel.Under carriage unit: It refers to travel assembly. It also include, steering and brakingsystem. For more details please refer “under carriage mechanism” in topic tractors.3) Hoist and loading assembly: It is used for hoisting the dipper and loading the materialinto predetermined place. It essentially consists of rigid boom and dipper stick which isstrongly built to withstand impact loading while excavation. With a shovel in the correctposition, near the face of earth to be excavated, the dipper is lowered to the floor of thepit, with the teeth pointing into the face. A crowding force is applied through the shippershaft and at the same time tension is applied to the hoisting line to pull the dipper up theface of the pit. If the depth of the face is just right, i.e. depth of cut is correctly adjusted.The dipper will be completely filled up and it is loaded to dump tracks or dumped at therequired place.To operate shovel in favorable condition i.e. economically, it will be necessary to reducethe depth of penetration of dipper face. The general operation of a hydraulicallycontrolled shovel differ from those of a cable-controlled shovel primarily in that theoperator forces are produced by pistons instead of by cables.Hence, it is clear that the applications of power shovel are1) To excavate the soils of all types except rocks without prior loosening.2) To collect and dump the material.3) To load the excavated material into dump trucks, conveyer belts etc.DUMPERSDumper is also known as Dump truck. The motor vehicle which is specially designed &constructed for carrying the heavy loads under various operations conditions can becalled as Dumpers.
  4. 4. These are meant for carrying rocks, coal, minerals, aggregate and other materials inconstruction works. Dumper may be ON road Vehicle or OFF road vehicle. ON roadDumpers generally used in normal roads such as in road construction, while OFF roadmeans, vehicle is used apart from good words, i.e. in terrains like in dam constructionmines etc.The constructional features of Dumper is similar to that heady duty truck, except a highstrength container or trolley is mounted at back side of the Cabin and Hydraulic assistedload raising and lowering facility is provided for dumping material in the trolley.Some dumpers may have 2 hydraulic cylinders and the size of rear wheel and number ofrear axles may vary with load carrying capacity and mode of operations.Suspension at front is of rigid elliptical type and at rear heavy duty leaf springs areprovided to absorb high impact loading under severe operating conditions.Container for dumper is specially constructed to withstand ill handlings. Heavy duty aircleaner, filter, share proof mountings of all instruments, dust proof electrical systems andcushion mountings for radiator may present in some dump trucks.
  5. 5. Dumpers play important vole in dam construction, road making, mining etc. for carryingmaterials and dumping at required place quickly and conveniently.CONSTRUCTION AND WORKING OF RIPPERSRipper is used for loosening the ground and for pulling up the roots, rocks etc. They playvital role in constructional works like dams, mining, road constructions etc. Rippers maybe classified into 2 types.1) Pulled type2) Tractor mounted typeLinkage used to mount ripper on a tractor:Hydraulically operated, tractor mounted ripper is found increasing use in various worksthan towed type. Fig. shows ripper using three shanks. The number of shanks useddepends on the size of the tractor, the depth of penetration desired, the resistance ofmaterial being ripped and the degree of breakage of the material.The linkage as shown is of parallel-type linkage. In this type depth of penetration isvaried. The point is kept at a constant angle, which reduces wear and stabilizes theproduction.Crawler mounted hydraulic operated ripper is preferred more because of,• In case of hard soil, the process of loosening the soil requires more “tractionpower”.• Slippages of track are not considerable.• Attachment and dis-attachment of Ripper is avoided as they may be integral.All the mechanisms included in under carriage of ripper are very similar to these crawlertractors. The ripper is actuated by hydraulic blades. The teeth of blade is replicable incase get worn.Rippers are generally preferred in road construction, dam, quarries etc.CRANESCranes are hoisting equipment used for lifting or carrying the loads and placing them atdesired place. Cranes essentially meant for lifting heavy materials and placing them ondump trucks, belt conveyors or at other required places.
  6. 6. Types of Cranes1) Crawler-Mounted Cranes (Derrick Crane)2) Rubber - Tyre mounted or Mobile Cranes3) Portable Crane.Application of CranesMain application of cranes is to lift and place heavy materials at required place. Like in1) Large building works.2) In Dam, road construction3) In quarries and mines4) In construction of bridges, industries and in shipping etc.1) Crawler-Mounted Cranes (Derrick Crane)Cranes are the hoisting equipment used for lifting the loads and placing them at desiredplace. To perform these functions cranes have mainly three motions 1) Hoisting, 2)Swinging and 3) Dumping.Fig. shows a typical Derrick crane. It mainly consists of a hoist boom which is stronglybuilt wire rope and associated lifting or winding mechanism and these are mounted on aconventional crawler tractor. The boom and cab can be rotated 3600on turn table, whichhelps the crane to place any convenient place. The Derrick crane can be used as a toecranes for the purpose of erection of high industrial and residential building of 100 meteror above they are available upto 40 tons with 25 mtr boom length and 15 mtr work radius.2) Rubber - Tyre mounted or Mobile Cranes
  7. 7. Fig. shows truck crane in its simplest form. It consists of a lifting boom and wire ropewith its associated winding mechanism. These are mounted on a truck. Wheel mountedmobile cranes are generally truck mounted and have high mobility and can travel upto 70km/hr on good roads. These are designed for long distance travel with high road speed.This crane can operated on firm grounds to increase stability. During operation triggersare used this cranes are widely used in building, constructional areas, industries, loadingand unloading of cargoes.The working principle of truck cranes is similar to that conventional truck except a craneboom and related mechanism is fitted at rear of cabin. These cranes may operate on wirerope or by hydraulic cylinders. Now-a-days hydraulic cylinder type cranes have gainedpopular.DOZERSDozers are machines designed principally for cutting and pushing the materials overrelatively short distance. Dozers are nothing but crawler tractors or track type tractor withsuitable hydraulically assisted blades, arms which is principle difference between acrawler tractor and Dozers.Dozers consist of track type tractors with front mounted blades controlled by hydrauliccylinder to vary the depth of cut and rate of leveling. Depending on the material andapplication rear mounted hydraulic blades and rippers can be fitted to loosen hardmaterial. Blades of dozers are curved and extending in front of the tractor, since in theapplication of pushing, cutting etc. needs high traction which is fulfilled by suitabletracks and rigid construction.Main areas of application of dozers generally includes in dam construction, roadconstruction in mines, to excavate the soil etc.Types of DozersThe following are the five types of Dozers.a) Bull-dozersb) Angle dozersc) Tilt dozersd) Push dozerse) Tree dozers.Following are the different types of dozers.a) Bull dozers Bull-dozer is basically pushing unit but is widely used as multi-purposeequipment and can perform large no. of operation with minor change under different
  8. 8. names like Angle dozer, tilt dozer, tree dozer and push dozer. Bull-dozer scrapes soil andgranular materials, pushes it in front of blades also leveling the excavated material.b) Angle dozers: Angle dozers are used to push its load at an angle nearly 25° to thedirection of travel of the dozer. This kind of dozers are helpful where the material ispushed down like on hill work or where the material to be collected in a long row on oneside of the line of travel of the dozer.c) Tilt dozers: Tilt type dozers are used where Blade is required to be tilted by raising oneend upto (25 cm) alone the other so as to start excavating in hard ground.d) Push dozers: It is used to push the scraper unit during digging or loading operation bymeans of rectangular plate called the pusher plate.e) Tree dozers: It is used to remove the trees and for uprooting the stems.Construction:Dozer Blades : A heavy blade of slightly concave profile in the front of the tractor,connected to frame of tractor through two arms and a yoke. The blade has replacablecutting edges which wear out with the use of Blade. The motion of blades is controlled bymeans of a suitable hydraulic cylinder arrangement.Following are the few types of blades which generally used in dozers.a) U - blade b) Straight Blade c) Land Fill Bladed) Angle Blade e) Clearing Blade f) V- blade.Method of controlling the blades of dozers:Blades of dozers can be controlled by two ways.a) Cable controlb) Hydraulic controla) Cable control: Cable controlled blades in dozers utilize a hoist unit for raising orlowering blades. Hoist unit is mounted on the front end on the radiator guard. The pusharms are tightened to the bracket outside of the track or under the cage unit. Cable with
  9. 9. suitable ultimate strength is used for tilting the blade at required angle. The transmissionunit, engine unit etc. being similar to as hydraulic controlled type dozers.b) Hydraulic control of blades Hydraulic control of blades utilizes a incompressiblehydraulic fluid, which under high pressure in the hydraulic cylinder operates the blades torequired height and direction. The important components of system include a control(direction) valve, a hydraulic pump, oil filters and suitable hose connections etc. Thedirection control valve regulates the direction of flow of oil to suitable cylinder so thatcontrol of blade at required angle can be achieved. The oil pump may be gear type orvane type which is capable of building high pressure in cylinders. Generally oil pumpsare driven by P.T.O. shaft or other suitable gear drive. Suitable cooling of hydraulic oil isrequired so as to maintain the properties arrangement (like viscosity, flash and five pointetc.) of oil constant though operation. The arrangement is shown in figure.Main Components of a DozerIn general all Dozers should be equipped with following basic parts which names theconstruction as dozers, viz.Components in Hydraulic System of a dozer1) Engine unit [power source]2) Clutch3) Transmission system.4) Control Systema) Brake System b) Steering System5) Hydraulic System.6) Track mechanism or under carriage.1) Engine unit: It is the power source for propulsion and desired operation. Usually 6-cylinder diesel engine is equipped in dozer as a power source. The engine unit beingsimilar to heavy duty operated tractors.2) Clutch: Similar to all vehicles, dozers are also equipped with clutch unit for connectingand disconnecting the power from engine to transmission unit.Clutch for dozers can be multiplate or single plate. But it should be wet type. Generallymultiplate clutch is preferable because sufficient area for friction is available for samespace and hence more power can be transmitted. To maintain properties of clutch lining
  10. 10. and to reduce heat developed clutch should be wet type. Therefore cooling oil iscirculated continuously in clutch housing at a pressure. The operation of clutch beingsimilar to conventional method i.e. clutch is disengaged by overcoming spring force.Hydraulic assisted clutch pedal may also used to reduce the power required by driver foroperation of clutch.3) Transmission system: The main function of transmission unit in dozer is to transmitthe power from engine to wheels [through differential, such that resistance of dozer isfulfilled i.e. it varies torque, speed and direction of motion as per requirement.Transmission unit in dozer may be1) Selective type gear boxa) Sliding meshb) Constant mesh gear boxc) Synchromesh type gear box.Each gear box comprises mainly i) main shaft ii) counter shaft, on which suitable gearsare arranged and output power is obtained at the end of main shaft.2) Planetary gear box and3) Hydraulic transmission.Apart from conventional gear box in some special cases [or in new versions] planetarygear box. Hydraulic transmissions are used to overcome the drawbacks fromconventional gear box.a) Gear ratio can be varied as per requirement constantly i.e. there is no fixed gear ratio.b) Wear, noise of gear box is reduced to minimum.c) Hence, less or no lubricant is desired for systems.d) Hence, systems are smooth in operation and flexible.4) Control System.Control System in dozer comprises mainlya) Steering System andb) Brake Systema) Steering System: Steering System in dozers differs from conventional steeringbecause, here steering gears and related systems are absent. Steering of vehicle [dozer]can be achieved by slowing or braking to required track and while other track remains inmotion and hence desired steering is achieved.Following are the 3 important steering mechanisms used in Dozers.a) Clutch / Brake Steering Systemb) Differential Steering Systemc) Planetary Gear Steering Systemb) Braking System: The desirable function from braking system is to slow down themotion [speed] or to stop the [vehicle] dozer within shortest possible distance and time.The distance travelled after braking and time required for complete rest depends mainlyspeed of vehicle and mass of vehicle.Hence, as mass of Dozer (vehicle) increased or is high, the brake system should be robustto absorb kinetic energy into heat energy. Here due to heat developed in braking is more,sufficient ventilation for brake is necessary. Generally, external contacting band brakesare used in dozers.5) Track mechanism or under carriage unit: Track mechanism for Dozers is very similarto track type tractors. Necessity of track for Dozer or for crawler tractor is as the driving
  11. 11. wheel exerts thrust on the ground while rolling over it, there will be tendency to slidingmotion or slip between the tyre and the ground. Now if we increases the tyre contactingarea with the ground, the slip will be reduced, but it is undesirable affects by increasingtyre size also tyre cannot work in rough terrains. In operations like reclaiming barrenland, road construction etc. Dozer requires high tractive effort with minimum possiblesize. Hence track even though it is complicated and costlier, it is sometimes or should beused under such circumstances.Main components of the Hydraulic System in dozers (or in crawler type tractor).1) Reservoir or hydraulic oil tank.2) Hydraulic pump —a) Variable displacement pumpb) Positive displacement pumpa) Gear typeb) Vane typec) Radial Piston Pump etc.3) Hydraulic valvesa) Pressure relief valve b) Direction flow control valvec) Volume control valve4) Hydraulic cylindersa) Single acting cylinder b) Double acting5) Hydraulic pipes [hose]a) High Pressure Hose b) Very high pressure HoseQ. 10. With neat sketch, describe the working of excavators.Ans : Excavators are basically digging or excavating machine used for this purpose only.These are preferred for quarries, dam projects, road construction and other related works.Excavators can be mainly two types, namely1) Crawler mounted type2) Truck mounted type.Now we shall discuss about the crawler mounted type which is becoming more popular,because,• For heavy excavating works of course, it is necessary to have more traction power. Byhaving crawler the contact area bit ground and chain (Track) is more and hence these arehaving high tractive force.• Cabin can be easily and conveniently by rotated around 360°, without affecting thetrack movement.• Hydraulic assisted system, which enables the work fast and convenient etc.
  12. 12. The constructional line diagram shows, a crawler mounted excavator. It mainly consistsof three units, namely.1) A under carriage to give mobility, this is similar to crawler tractor.2) A super structure with operation cabin mounted on a sleeve ring to travel through 360°around.3) Hydraulically articulated boom and dipper arm with bucket. Teeth at buckets can bereplaceable, which may get wear or broken with use.OperationThe machine is brought to the land or place to be excavated them boom and arm arelowered. Then Bucket is brought near the work is to be excavated. Afterwards, the bucketis pushed towards the machine to make and cut and fill with the help of hydrauliccylinder. Then the dipper arm is moved towards the machine and the boom is raised till itclears from the cutting area and now cabin is rotated to required dumping position. Thiscycle repeats for completion of work.MOTOR GRADERS
  13. 13. Motor grader is generally used for leveling spreading and finishing the work like in roadprojects. It consists of a blade supported on the frame as shown in fig. This blade used forexcavating the ground.Another blade is called scarifier is fitted ahead of the grader blade. This blade first breaksthe hard rock before the ground is excavated by grader blade. The grader is either selfpropelled or drawn by a tractor.To work with grader, place the grader where leveling is to be done. The grader blade islower and is set to move right and left as the driving unit moves forward. The scarifierblade ribs the hard ground, if any and then grader blade does the leveling and finishing ofthe uneven ground. The main application area of grader is in road construction and forleveling, spreading and finishing other similar kind of works.ROLLERSRollers are the specially constructed self propelled or pulled type machine used tocompact the earth or asphalt layer.Roller is considered as an essentially for road making machinery, it usually consists ofheavy steel or pneumatic wheels for rolling and compacting the good constructionmaterial. Generally these are self propelled with the help of diesel engines while somekind of rollers are pulled by tractors.There are many types of rollers available, which can be used according to requirement.1) 3-wheel smooth rollers.2) Sheep foot rollers.3) Pneumatic rollers.4) 2-wheel smooth roller.5) Vibrating rollers.6) Tamping rollers etc.Pneumatic Rollers:These are surface rollers which apply the principle of kneading action to effectcompaction below the surface. They may be self propelled or towed. Pneumatic rollersemploys No. of pneumatic wheels, mounted on two or more axles instead of using heavysteel wheels for compaction. They may be small or large-tyred units.The small-tired units usually have two tandem axles with four to nine tires on each axle.The rear wheels are spaced to travel over the surfaces between the front wheels, which
  14. 14. produces a complete coverage of surface. Usually the weight of a unit may be varied byadding ballast to suit the material being compacted.The large-tired rollers are available in sizes varying from 15 to 200 tons gross weight.They utilize two or more big earth-moving tyres on a single axle. The air pressure in thetyres may vary from 80 to 150 PSI. Because of the heavy and high tyre pressures, theyare capable of compacting all types of soils to greater depths.
  15. 15. The compacting ability of pneumatic rollers can be known by;1) The gross weight of the unit.2) The gross weight per wheel.3) The weight per inch of tyre width.4) The air pressure in the tyres.In recent designs for better compaction pneumatic tire rollers with variable inflationpressure are available.ApplicationThis type of rollers are considered to be most suitable for compacting non-plastic sands,fine sands, Asphalt rolling etc. like in dam, road constructional works.Smooth Wheeled RollerSmooth wheeled rollers can be two types, they are;1) 3-wheel smooth roller.2) 2-wheel smooth roller or Tandem roller.1) 3-wheel smooth roller:Fig. shows 3-wheeled smooth rollers. It mainly consists of 3-heavy constructed wheels,power plant [engine] and transmission system etc. At front side the wheel is usuallysmaller than gear wheels. The front wheel is considered as steerable wheel while rearwheels are being driving wheels.To have a good compaction the rear wheels are constructed at bigger size and heavy. Thecompacting efficiency of roller depends upon the weight exerted, width of wheel, dia. ofwheel and the type of compacting materials.The hollow drums [wheels] which may be ballasted with water or sand to increase theweight. Sometimes additional weights are also added to achieve the same. If a machine isdesignated as 8-14 tons, it means that the minimum weight of the machine only is 8 tonsand it can be ballasted to give a maximum weight of 14 tons.
  16. 16. The main difference between 2-wheels and 3 wheels rollers are;1) No. of wheels — 2 in case of tandem roller.2) Width — Width of rollers is more in tandem type.3) Capacity — 6-8 tons capacity.4) Size — Tandem type rollers are smaller compared to 3 -wheeled rollers.Remaining systems are being almost similar in operation or in working.ApplicationsThese rollers are effective in compacting granular soils, such as sand, gravel and crushedstone and they are also effective in smoothing surface of soil that have been compactedby sheep foot type rollers.Vibratory Compact RollersCertain types of soils such as sand, gravel and relatively large stones respond quite wellto compaction produced by a combination of pressure and vibration.When these materials are vibrated, the particles shift their positrons and nestle moreclosely with adjacent particles to increase the density of the mass.There are several types of vibratory compacting rollers they include.1) Vibrating sheep’s foot rollers2) Vibrating steel drum rollers3) Vibrating pneumatic-tyred rollers.4) Vibrating plates or shoes.Vibrating sheep’s-foot, steel-drum, pad-type and pneumatic tyred rollers are actuated byseparate engines mounted on the rollers or in some cases by hydraulic drives which rotatehorizontal shafts. On which one or more eccentric weights are mounted. Vibrations mayvary from 1000 to 5000 per mm. In addition to compacting the soil, the drum and pad-type rollers tend to shutter the rock particles near the surface and thus leave a relativelysmooth surface.In general, better compaction efficiencies and economy are attained by moving vibratingcompactors at relatively slow speeds. 1.5 to 2.5 mph. Slow speeds permit a greater flowof vibratory energy into the soil.Following fig. shows vibrating steel drum roller.
  17. 17. Following fig. illustrates Towed (pulled)—type vibrating sheep’s foot roller.Sheep’s foot rollers may be towed by tractors or self- propelled, consists of a hollow steeldrum on whose outer surface there are welded a no. of projected steel feet, which ondifferent pieces may be of varying lengths and cross sections or all of them may have
  18. 18. same dimensions. A unit may consist of one or several drums mounted on one or morehorizontal axles. The weight of a drum may be varied by adding water or sand to produceunit pressure under the feet upto 750 PSI or more. As the roller moves over the surface,the feet penetrate the soil to produce a kneading action and a pressure to mix and compactthe soil from the bottom to the top of the layer.Sheep’s foot rollers are quite effective in compacting clays and mixtures of sand andclay. However, they can’t compact granular soils such as sand and gravel. Also, the depthof a layer of soil to be compacted is limited to approximately the length of the feet.

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