METHODS OF COMPACTION OF SOIL USED IN FIELD-ALL YOU NEED TO KNOW

METHODS OF COMPACTION OF SOIL USED IN FIELD

Compaction of soil is the pressing of soil particles close to each other by mechanical methods. Air during compaction of soil is expelled from the void space in the soil mass and therefore the mass density is increased. Compaction of soil is done to improve the engineering properties of the soil. Compaction of soil is required for the construction of earth dams, canal embankments, highways, runways and many other structures.

Soil compaction is the practice of applying mechanical compactive effort to densify a soil by reducing the void space between soil particles. Compaction occurs when particles are pressed together to reduce the space between them. Highly compacted soils contain very few spaces resulting in soil with higher unit weight. Maximum density is achieved at an optimum moisture content, or OMC, for short.

The process of compaction decreases the likelihood of settlement after a building, roadway, runway or parking lot is constructed. Settlement could result in premature pavement failure, costly maintenance or repairs.

The various equipments used in the compaction are:

Smooth wheeled roller
Sheep foot roller
Pneumatic roller
Vibratory roller
Impact rammers

Smooth wheeled rollers are of two types:

Static smooth wheeled rollers
Vibrating smooth wheeled rollers

The most suitable soils for these roller types are well-graded sand, gravel, crushed rock, asphalt etc. where crushing is required. These are used on soils that do not require great pressure for compaction. These rollers are generally used for finishing the upper surface of the soil. These rollers are not used for the compaction of uniform sands. The weight of a smooth wheel roller varies from 2 to 15 tons. In addition, these rollers cause stratification in deep layers due to non-uniform compaction.

They are used to compact well-graded coarse-grained soils for use in highway base courses and non–plastic fine-grained soils.

Sheepsfoot roller Roller:

Sheepsfoot rollers are used for compacting fine-grained soils such as heavy clays and silty clays. Sheepsfoot rollers are used for compaction of soils in dams, embankments, subgrade layers in pavements, and rail road construction projects. Sheepsfoot rollers are of static and vibratory types. Vibratory types rollers are used for compaction of all fine-grained soils and also soil with sand-gravel mixes. Generally, this roller is used for the compaction of subgrade layers in road and rail projects. Sheepsfoot rollers consist of steel drums on which projecting lugs are fixed and can apply a pressure upto 14kg/sq cm or more. Different types of lugs are namely spindle-shaped with widened base, prismatic and clubfoot type. The weight of drums can be increased as in the case of smooth wheeled rollers by ballasting with water, wet sand or by mounting steel sections. The efficiency of sheepsfoot rollers compaction can be achieved when lugs are gradual walk out of the roller lugs with successive coverage. The efficiency is affected by the pressure on the foot and coverage of ground obtained per pass. For required pressure and coverage of ground, the parameters such as gross weight of the roller, the area of each foot, the number of lugs in contact with the ground at any time, and the total number of feet per drum are considered. The compaction of soil is mainly due to feet penetrating and exerting pressure on the soil. The pressure is maximum when a foot is vertical.

Pneumatic Tyred Rollers:

Pneumatic tyred rollers are also called as rubber tyred rollers. These rollers are used for compaction of coarse grained soils with some fines. These rollers are least suitable for uniform coarse soils and rocks. Generally pneumatic tyred rollers are used in pavement subgrade works both earthwork and bituminous works. The total weight of the roller can be increased from 11.0 tonne to 25.0 tonne or more by ballasting with steel sections or other means.

Vibratory Rollers:

In vibratory rollers a vibrator mounted on a drum. These rollers are available both in the form of pneumatic tired type of smooth wheel type. In smooth wheel type, a separate motor drives an arrangement of eccentric weights to create high frequency, low amplitude and up and down oscillations of the drum.

The roller are suitable for compacting granular soils with no fines where layers up to 1 m in thickness can be contacted. If the soil contains appreciable fines, the layer thickness is to be reduced. In the pneumatic type of vibratory compactor, a separate vibrating unit is attached to the wheel axle.

The ballast box suspended separately from the axle so that it does not vibrate. These compactors are suitable for compacting granular soils with thickness of layer about 30 cm. Vibractory compactors can compact the granular soil to a very high

Impact Rammers:

Impact rammers consist of a block of iron about 3 to 5 kg wooden rod. The rammer is lifted by about 30 cm and dropped on the soil to be compacted. A mechanical rammer is operated by compressed air gasoline power. It is much heavier and weighs 30 to 150 kg.

Mechanical rammers have been used up to a weight of 1000 kg. Power controlled or manually operated impact rammers are used where the area to be compacted are small, the area is inaccessible and use of large equipment is not justified.

They are also used for compacting backfill behind retaining walls or small trenches. They can be used for all types of soils.

FACTORS AFFECTING FIELD COMPACTION OF SOIL