Compaction Equipment

Compaction is the process by which particles of materials are packed closely together by reducing air void content. In general the compaction is achieved by mechanical means.

1. Mechanical Forces

Mechanical forces may be applied by the following ways, viz., by rolling, by kneading, by vibration and by ramming.

(i) Rolling

In the rolling process heavy weights in the form of rollers are used to press the soil particles together. Smooth-wheeled rollers are the typical example which falls under this category.

(ii) Kneading

In the kneading process the soil while at kneading will be subjected to some pressure. Sheepsfoot roller is a typical example of this type of compaction.

(iii) Vibrations

In the vibrations process the soil particles are shaken together to form a compact mass. Vibrating rollers are typical example of compaction equipment which operate on this principle.

(iv) Ramming

In this process the soil particles are forced to move closer together by pounding action. Hand-tampers and mechanical tampers are the typical examples of compaction equipment which operate under this principle.

2. Rollers

(i) Smooth-Wheeled Rollers

These rollers are used with or without ballast and may be provided with three wheels or two wheels of equal width called tandom type. These rollers are generally used for most of the works. But these rollers are not effective in uniformly graded sand, gravel or silt and on cohesive soil with high moisture content due to poor traction.

These static rollers, also called as dead weight rollers, are diesel powered. These rollers rely on the weight only to compact the materials by passing over them. Units of 8–10 tonnes can impact a pressure of 20–40 kg per linear cm are generally in use. Rollers with weight up to 1 tonnes are used for light work.

(ii) Sheepsfoot Rollers

Sheepsfoot or Padfoot rollers are suitable for cohesive soils. These may be self-driven or tractor driven and are especially useful when the water content is on the higher side. The mass of the drum can be varied by adding ballast. For effective rolling, the lift thickness should be small and the contact pressure under the projection very high. These rollers are specially recommended for water-retaining earth works.

(iii) Pneumatic-tyred Rollers

In pneumatic-tyred rollers wheels are placed close together on two axles and placed such that the rear set of wheels overlap the lines of the front set to ensure complete coverage of the soil surface. In order to avoid the lateral displacement of soil, wide tyres with flat threads are provided. The compaction produced by these types is better than that of the smooth wheel rollers.

(iv) Tandom Compactors

Tandom compactors have two equal sized rollers and are centred in line-tandon. These rollers have smooth surface. Improvements have been made on these type of compactors as tandom vibratory compactors. Large size tandom vibratory compactors are generally preferred now-a-days as they can be used either as static compactor or as a vibratory compactor as per the requirement.