1. CONSTRUCTION METHODS & TECHNOLOGY
CIVL462
Lecture No: 5

2. Compacting and Finishing

3. PRINCIPLES OF COMPACTION
Compaction is the process of increasing the density of a soil by mechanically forcing the soil particles closer together, thereby expelling air from the void spaces in the soil.
Compaction should not be confused with consolidation, which is an increase in soil density of a cohesive soil resulting from the expulsion of water from the soil’s void spaces. Consolidation may require months or years to complete, whereas compaction is accomplished in a matter of hours.

4. PRINCIPLES OF COMPACTION
Compaction has been employed for centuries to improve the engineering properties of soil.
Improvements include increased bearing strength, reduced compressibility, improved volume-change characteristics, and reduced permeability.
Although the compaction principles are the same, the equipment and methods employed for compaction in building construction are usually somewhat different from those employed in heavy and highway construction.

5. PRINCIPLES OF COMPACTION
The degree of compaction that may be achieved in a particular soil depends on:
the soil’s physical and chemical properties,
the soil’s moisture content,
the compaction method employed,
the amount of compactive effort,
the thickness of the soil layer being compacted (lift thickness).
The four basic compaction forces are
static weight,
manipulation (or kneading),
impact,
vibration.

6. PRINCIPLES OF COMPACTION
Although all compactors utilize static weight to achieve compaction, most compactors combine this with one or more of the other compaction forces. For example, a plate vibrator combines static weight with vibration. Manipulation of soil under pressure to produce compaction is most effective in plastic soils.
The forces involved in impact and vibration are similar except for their frequency. Impact or tamping involves blows delivered at low frequencies, usually about 10 cycles persecond (Hz), and is most effective in plastic soils

7. Compaction equipment
Principal types of compaction equipment include tamping foot rollers, grid or mesh rollers, vibratory compactors, smooth steel drum rollers, pneumatic rollers, segmented pad rollers, and tampers or rammers.

8. Compaction equipment

9. Compaction equipment Selection of Compaction Equipment
The proper selection of compaction equipment is an important factor in obtaining the required soil density with a minimum expenditure of time and effort.
The chart in Figure provides a rough guide to the selection of compaction equipment based on soil type.

10. Compaction equipment

12. Steel cylinder roller
Two types:-
Non vibrating
Vibrating rollers

13. Steel cylinder roller Non vibrating Two types:-
Tandem (two-axle)
Three wheeled
Both types are self-propelled
Able to be ballasted (added weight) by adding water or sand to the rolls
Ballast normally required when operating the roller but may be removed when it is to be transported
Maximum effective layer compacted is 250mm

14. VIBRATING ROLLER Two major types:- Vibrating smooth drum rollers
Tractor drawn
Self-propelled
Important factors when considering vibrating rollers:-
Dynamic force- force exerted by the roller. Centrifugal force generated by a revolving eccentric shaft and total dead weight of the roller frame and drum
Frequency of vibration – no. of revolutions per minute made by the eccentric shaft
Amplitude of vibration- eccentric shaft rotates, the drum assembly moves up and down. Amplitude is the total distance the drum travels vertically.

15. Pneumatic tired rollers
Used on pavements such as sprayed or asphalt mix bitumen surfacing work
Suitable when material is cohesive, such as clays, clayey gravels or loams which is free from rock
Small, multi pneumatic roller
Heavy pneumatic roller

16. Tamping roller
Has a steel drum fitted with ‘feet’ of one type of another
Example, sheepsfoot, wedgefoot and pad foot
Compacting layer up to 250 mm
Normal compaction for clay, clayey gravel and sandy clays
Poor performance on sandy gravels
Not suitable for compact sand
Tower sheeps foot roller
Self-propelled tamping foot roller

17. Estimating Compactor Production
The following equation may be used to calculate compactor production based on compactor speed, lift thickness, and effective width of compaction. The accuracy of the result obtained will depend on the accuracy in estimating speed and lift thickness. Trial operations will usually be necessary to obtain accurate estimates of these factors.

18. Estimating Compactor Production
Typical compactor operating speeds are given in Table

19. Estimating Compactor Production
EXAMPLE Estimate the production in compacted cubic meters per hour of a self- propelled tamping foot roller under the following conditions: Average speed = 8.0 km / h Compacted lift thickness = 15.2 cm Effective roller width = 3.05 m Job efficiency = 0.75 Number of passes = 8