Roller and Compactors

7/27/2019 Roller and Compactors

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Mansoor Azam Qureshi

NUST

Islamabad


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Compactor

Compaction equipment ranges from handheldvibratory tampers (suitable for small or confinedareas) to large, self-propelled rollers and high speedcompactors (ideally suited for large, horizontalconstruction projects).

Types of Rollers

Tamping rollers and Sheepsfoot rollers Smooth-drum vibratory soil compactors

Pad-drum vibratory soil compactors

Pneumatic-tired rollers

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Smooth wheel Rollers

Widely used simple rollers

Work on static weight.

Used for compactinggranular bases, bituminouspavements



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Smooth-Drum Vibratory Soil

Compactors The smooth-drum vibratory

roller uses a vibratory action inconjunction with the ballast

weight of the drum to rearrangethe soil particles into a dense soilmass.

Vibratory compaction is veryeffective means of attaining thedesired density for cohesionless

materials. Because this roller is relatively

light, the recommendedmaximum loose-lift depth is 9inches.



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Pad-drum Vibratory Soil Compactor

These rollers are effective onsoils with up to 50% of thematerial having a PI of 5 orgreater.

The edges of the pads arerolled inward enabling them to

walk out of the lift withoutfluffing the soil.

The typical lift thickness forpadded-drum units oncohesive soil is 12 to 18 in.

These units are sometimesequipped with a leveling blade.



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Pneumatic Tired Rollers

These rollers apply the principle of kneadingaction to affect compaction below the surface.

They may be self-propelled or towed.

Pneumatics are used on small-to medium-sizesoil compaction jobs, primarily on bladedgranular base materials.

Small pneumatics are not suited for high-production, thick lift embankment compaction

projects. Pneumatic tired rollers are also used in

compacting asphalt, chip seals, recycledpavement, and base and subbase materials.



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The flexible tire surface permits conformance of the tire toslightly irregular surfaces to maintain uniform density andbearing capacity.

The rear tires are spaced to track over the uncompactedsurface left by the passage of the front tires.

The wheels may be mounted slightly out of line with theaxle, giving them a weaving action (the name "wobby

wheel") to increase the kneading action of the soil. Four parameters must be known to determine the

compacting ability of pneumatic rollers: Wheel load Tire size Tire ply Inflation pressure


Pneumatic Tired Rollers


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Vibratory PlateCompactors

Self-propelled vibratory-plate compactorsare used for compacting granular soils,

crushed aggregate, and asphalt concrete inlocations where large compactors could notoperate.

These gasoline or diesel powered units arerated by centrifugal force, exciter revolutions

per minute, depth of vibration penetration(lift), foot-per-minute travel, and area ofcoverage per hour.

Many of these compactors can be operatedeither manually as a walk-behind unit or by

remote control

Special Compactors


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Manually OperatedRammers

Gasoline-engine-driven rammers are usedfor compacting cohesive or mixed soils in

confined areas. These units range in impact from 300 to

900 foot-pounds (ft-lb) per sec at animpact rate up to 850 per min, dependingon the specific model.

Performance criteria include pounds perblow, area covered per hour, and depth ofcompaction (lift) in inches.

Rammers are self propelled in that eachblow moves them ahead slightly to contact

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Special Compactors

Special compactor provide

adequate output if

Lift thickness is minimal(usually 3 to 4 in.),

Moisture content iscarefully controlled, and

Coverage are sufficient.


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Type of Soils

To select the most appropriate type of compactionequipment, a project officer must know the characteristics,capabilities, and limitations of the different types of rollers.

Generally, tamping-foot compactors that produce high unitpressures are best for predominantly fine-grained cohesivematerials such as clays and sandy clays.

Large, steel-drum rollers are best for larger particle materials

such as gravel or cobble. Vibratory rollers are ideal for well-graded or gap-graded

materials because the shaking action causes the smallerparticles to fill voids around the larger grains.



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Suitability of Soils

Suitability ofdifferent roller for

varying soil type isshown on chart;



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Desired Soil Density



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Lift Thickness

The lift thickness to achieve required density will varywith soil and compacter characteristics.

For tamping foot rollers lift thickness should not exceedroller feet.( 2 in)

For smooth wheel rollers lift should be limited to 6 in.

For Pneumatic tired rollers lift should not be greater

than 6 in. Heavy rollers may compact lift upto 12in.



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Compaction Equipment

Equipment must suit thesite.

Must provide optimumcompaction density andproduction

Enough speed



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Example What is the estimated production rate (CCY per hour) for a tamping-

foot roller with a compaction width of 5 feet? The followinginformation was obtained from a test strip at the project:

Compacted lift thickness = 6 inches

Average speed = 6 mph

Number of passes = 5

Efficiency factor = 0.83



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Example A self-propelled tamping foot compactor will be used to compact a fill

being constructed of clay material. Field tests have shown that therequired density can be achieved with four passes of the rolleroperating at an average speed of 3 mph. The compacted lift will have athickness of 6 in. The compacting width of this machine is 7 ft. One

bank cubic yard equals 0.83 ccy. The scraper production, estimated forthe project, is 510 bcy/hr. How many rollers will be required tomaintain this production? Assume a 50-min hour efficiency.

16,3 X 7 X 3 X 6 X 50/60

Compacted cubic yards per hour = ----------------------------= 428 ccy/hr

4

428/0.83=516 bcy/hr

No of compactor = 510/516=0.99 One compactor is sufficient


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Roller and Compactors