They rely on their dead weight to compact the soil. E.g. Smooth Wheeled Rollers They are used in roadworks and have limited application in earthworks. They aim to create a smooth surface on top of embankments so as to prevent the collection of water.

They compact material by a kneading action. E.g. Pneumatic Tyred Rollers, Sheep’s Foot Rollers

Pneumatic Tyred Roller It has ability to control the ground contact pressure. They are generally used for rolling base courses, black top on roads, and fill for large earthworks in loamy soils. It is most suitable for compacting granular materials, particularly soils which have a low moisture content.

Sheep’s Foot Rollers They may be static or vibratory. Although it performs in a similar way to the pneumatic tyred roller, it is not as effective. In practice, it is difficul to ensure complete and uniform coverage of the fill when using a sheep’s foot roller. It is generally used for rolling the fill on large earthworks in cohesive soils.

Vibrating compactors apply both pressure and vibration to the ground being compacted. E.g. Vibrating Rollers and Vibrating Plates

Vibrating Rollers They are suitable for compacting granular fill such as well graded sand or gravel, uniform sand and hard rock. However, they are not suitable for cohesive soils.

Vibrating Plates They are generally used for compacting granular soils in confined space, compacting backfill material in pipe trenches and shallow foundation, but not suitable for heavy compaction.

They apply an impact force to the soil which compacts the soil.

E.g. Power Rammers and Free Fall Hammers

Power Rammers This machine is hand operate. They are suitable for compacting soil in narrow trenches and around small foundations.

Free Fall Hammers Using the free fall hammer, it is possible to compact layers of soil several metres deep. They are suitable for compacting most types of soils except uniform granular material. This method is rather slow.

The choice of compaction plant depends on the following factors:

• Material Factors
• Spatial Factors
• Plant Factors
• Legal or Contractual Factors

Materiaal factors influencing the choice of compaction plant include:

• the type of soil or rock;
• the grading (particle size) of the soil, and
• the moisture content of the soil

Large compactors have a higher output than small compactors because their rollers are wider and because they are able to compact thicker layers of fill with fewer passes. Factors need to be considered include:

• the area to be filled and compacted and its topography;
• the volume of each type of material to be compacted; and
• the length of time for which the compaction plant is required

The choice of plant or combination of plant will be determined by:

• the output rate of the plat;
• the cost of compaction, and
• the availability of the plant.

They are the specifications of the contract.