CH-5.roller compactors.ppt

roller compactors.

1. CHAPTER- FIVE ROLLERS By: Debas D. 1 Heavy duty and Construction Equipment MEng5383 Ambo University Department of Mechanical engineering

2. Introduction A roller is a compactor vehicle used to compact soil, gravel, concrete, or asphalt in the construction work. compaction is the act of densifying the soil by pressing soil particles together into close contact, resulting in the expulsion of air and/or water from the soil mass. The result of the compactive effort is to increase the strength of an earth till or embankment. Compaction of the soil is obtained by various actions and roller machines. 2

3. Introduction Compaction of soil is attained by applying energy to soil by one of the methods given below. 1. Static Weight 2. Impact 3. Vibration 4. Kneading action 3

4. Introduction 4

5. Introduction Static Weight: Applied by smooth wheel rollers and pneumatic tyre rollers. Compaction can not reach lower strata because of internal friction of soil . So this compaction is especially good for granular soils 5

6. Introduction Impact Compaction: The equipment used for impact compaction are tamping rollers and rammers. Impact reduces the internal friction of soil and particles start moving towards voids easily. 6

7. Introduction Vibrating: Vibrating rollers and vibrating plates are used . In this system impact force penetrates down to great depth. Vibration minimizes the internal friction of particles and smaller particles move down to voids easily. 7

8. Introduction Kneading Action: In this system the compaction starts from a lower level and comes upward. Kneading action is actually the application of shear stress to soil . Sheep's foot roller (tamping rollers) and pneumatic tire rollers are used. 8

9. Types of rollers There are different types of rollers: Smooth wheeled roller Pneumatic tyre roller Sheep foot roller Vibrating and tamping roller 9

10. 1. Smooth wheeled roller Smooth wheeled rollers are of two types: Static smooth wheeled roller Vibrating smooth wheeled roller The compacting efficiency depends on weight ,width and diameter of each roller. Suitable for wide range of soil preferably granular soils such as sand, gravel, and crushed stones . It is also effective in smoothing surface of soils that have been compacted by tamping rollers 10

11. 1. Smooth wheeled roller The desirable speed and number of passes for appropriate compaction of soil depends on the type of soil and varies from location to location. In case of vibrating smooth wheeled rollers, the drums are made to vibrate by employing rotating or reciprocating mass . 11

12. Figure: Smooth wheeled roller 12

13. 2. Pneumatic tyre roller In this type number of pneumatic wheels are mounted on two or more axels under a loading platform ,pulled by tractor. In addition to the direct pressure due to rolling there is also slight kneading action. They may also be small or large tired units. The small tire units are usually have two tendon axle with 4 to 9 tires on each axels. 13

14. Pneumatic tyre roller Major advantages of Pneumatic tyre roller are the ability to control the ground contact pressure by: Altering the weights of machines, Increasing the number of wheels, Increasing the tyre width Changing the contact area of the tyre by altering the contact pressure. 14

15. Pneumatic tyre roller Figure : Pneumatic tyre roller 15

16. Pneumatic tyre roller Tyre Overlap : There is some gap between the tyres provided in front and rear tyres.This gap is filled with the movement of tyre. To achieve uniform compaction effect and avoid tyre marks, front and rear tyre are over lap. 16

17. Pneumatic tyre roller 17

18. 3.Sheep foot roller This type of roller Contains a steel drum including a number of projecting steel feet . During rolling operation the soil under the projecting feet get compacted and also considerable kneading action to the soil. When the drum rotates, the pads out of the soil they kick to the material because of their shape. They are suitable for compacting all fined grained material but is generally not suitable for use of cohesion less granular material. 18

19. Figure:Sheep foot roller 19

20. 4. Vibrating and tamping roller Vibrating roller Vibratory compactor enhance the performance of static weight machines by adding dynamic forces, usually achieved by a rotating eccentrically weighted shaft mounted inside the roller. Vibrations of vibrators arrange the particles by first disturbing even the arranged ones. Vibrators are turned off during the reversed motion of roller. 20

21. Vibrating roller 21

22. Vibrating roller 22

23. Vibrating roller Very useful for granular materials. Combination of vibration and pressure is applied. Not good for cohesive soils. They could be: Vibrating tamping rollers Vibrating steel-drum (smooth wheel) rollers Vibrating pneumatic rollers Vibrating plates or shoes (manually operated rammers ) 23

24. Main components of vibrating roller hghgfgsdfh 24

25. Principle of vibratory rollers 25 The vibration is produced by rotating the off-center weights

26. Principle of vibratory compaction : Grains of soil are effected by periodically alternating inertial forces. These forces make grain particles ‘floating ’, so ordering is progressed without friction. At vibratory compaction low amplitude high frequency excitation is used for loose so il or for deep layers. High amplitude low frequency excitation is used for cohesive soils in thin layers. Frequency of excitation should be close to characteristic frequency of the soil 26

27. Vibratory Rollers - Amplitude It is the vertical displacement of the roller drum. Amplitude of vibration is directly related to the impact force . 27

28. Vibratory Rollers - Frequency The Frequency is Drum impacts per minute 28

29. Effect of Characteristics of Vibratory Roller High amplitude and low freq uency are used to compact soft soils and to reach deeper zones while low amplitude and high frequency are used for stiff soils and shallow depth. Further High amplitude and low frequency setting is used for compaction of a thick layer whereas low amplitude and high frequency setting is used for the compaction of thin layer.

30. For example on a first pass the roller might use a high amplitude and low frequency but at the fourth pass , it sets itself with a low amplitude and high frequency . The effectiveness of compaction depends upon several factors involving interaction between the equipment and the soil being compacted. These factors include. Operating Frequency : Frequency control the number of impacts per meter between the drum and ground. Maximum compaction occurs when it vibrates near resonant frequency.

31. Effect of Frequency Fig . Effect of Frequency

32. b) Amplitude of vibration : It is the vertical displacement of the roller drum. Amplitude of vibration is directly linked to the impact force. Higher amplitude results in achieving higher thickness of compacted material at minimum number of passes , thereby improving productivity. Amplitude determines impact force Fig. Effect of Amplitude

33. C) Speed of Travel : Slow speed results in closeness of impacts , whereas high speed results in increase in the spacing of impacts. An even lower speed may be required for the initial passes. Impact Spacing Fig. Effect of Travel Speed

34. Ways of excitation: circular excitation: simple construction, single exciter unit eccentric should always rotate in , eccentric should always rotate in direction of advancing directed excitation: double exciter unit, generates both compressing and sharing forces in the soil simultaneously oscillation : the two exciter masses generate moment at the surface of the drum creating compressing and sharing forces in the soil so , so grains are ordered horizontally. Vertical force is provided by the weight of the drum 34

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36. Tamping foot roller These rollers usually have steel padded wheels and can be equipped with a small blade to help for leveling the layer. As tamping rollers moves over the surface the feet penetrate into the soil to mix and compact the soil from bottom to top of the layer. T amping foot roller is best dedicated to fine grained soils . Figure : Tamping foot roller 36

37. Output of Compactors Compacted earthwork is measured in terms of compacted volume in the fill. This can be found by multiplying the compacted area by the thickness of the compacted layer. Usually the number of passes required to attain necessary soil density is specified, and should be considered while estimating production. 37

38. Specification of rollers C aterpillar CS54B Smooth Drum Vibratory Soil Compactor 38

39. Specification of rollers 39