Different types of compaction equipment:
It is important to understand what is soil stabilization and different approaches for soil stabilization before discussing compaction equipment (rollers here).
What is soil stabilization?
Stabilization means the improvement of stability of the soil by compaction or addition of suitable admixtures.
It increases the binding properties of the soil particles. Also it improves the bearing capacity of the soil.
Methods for soil stabilization?
Soil stabilization can be achieved using different approaches. Two of the important approaches are 1) chemical stabilization 2) mechanical stabilization.
What is chemical stabilization?
Chemical stabilization is the method which involves the addition of admixtures or materials such as cement, lime and bitumen to the soil. These are often termed as a) soil-cement stabilization (b) soil-bitumen stabilization (c) soil-lime stabilization
What is mechanical stabilization?
Mechanical stabilization of soil involves compaction of soil with help of tampers, rollers and other equipment by application of weight, pressure, etc. Due to compaction density, durability and strength increases.
What is Compaction?
Compaction is densification of soil by mechanical energy. Compaction leads to decrease in volume of soil by expelling of air from partially saturated or dry soil. This is a rapid process and is carried out by means of using equipment such as rollers, tampers, etc.
What are the requirements for compaction?
Compaction is required to meet the following objectives:
- To increase the strength of the soil
- To improve the soil stability
- To reduce the permeability of soil
- To reduce the erosion of soil
- To decrease the settlement of soil
Effects of compaction on soil:
Compaction results in increased bearing capacity for the soil. The aforementioned objectives such as decrease in void ratio, decrease in permeability, increase in strength, decrease in settlement are achieved through compaction.
Methods of compaction:
Compaction is achieved with help of following loading actions/principles on soil: a) Impact loading (b) application of pressure (c) Vibration (d) Kneading
Following are few examples of compaction with rollers where different types of loading is used in the compaction process:
| Sr.No | Roller | Principle |
| 1 | Sheep foot roller | Pressure |
| 2 | Pneumatic roller | Pressure and kneading |
| 3 | Vibrating roller | Impact and vibration |
| 4 | Tamping roller | Impact and pressure |
| 5 | Rammers | Impact |
Types of rollers:
Diverse types of rollers exist for compaction of soil. Following are few of the widely used rollers.
- Cylindrical rollers
- Sheep foot rollers
- Pneumatic rollers
- Smooth wheeled rollers
- Vibratory rollers
- Grid rollers
Here’s a brief explanation of the different types of rollers mentioned for soil compaction:
- Cylindrical Rollers
- Principle of Loading: Static pressure
- Type of Pressure: Uniform static pressure across the surface
- Ballast Requirement: Can be ballasted with sand or water to increase weight
- Speed: 2-3 km/h
- Suitability: Suitable for compacting granular materials such as gravel, sand, and crushed rock
- Pressure Exerted: Moderate pressure, approximately 2-6 kg/cm²
- Use: Ideal for initial rolling on subgrades and sub-bases.
- Sheep Foot Rollers
- Principle of Loading: Pressure and kneading
- Type of Pressure: Concentrated pressure due to the protruding feet
- Ballast Requirement: Can be ballasted with water, sand, or steel sections for additional weight
- Speed: 6-10 passes at a speed of 6-10 km/h
- Suitability: Suitable for fine-grained soils such as clay and silty soils
- Pressure Exerted: 7-14 kg/cm²
- Use: Best for deep compaction and cohesive soils as it compacts soil layer by layer.
- Pneumatic Rollers
- Principle of Loading: Pressure and kneading action from pneumatic tires
- Type of Pressure: The pressure varies as it depends on the tire inflation and load
- Ballast Requirement: Can be ballasted with water, sand, or iron to achieve desired weight
- Speed: 10-25 km/h
- Suitability: Suitable for granular and fine-grained soils; often used in road construction
- Pressure Exerted: 5-25 kg/cm² depending on the inflation of tires
- Use: Provides a sealing action and good compaction on a variety of soils, from cohesive to granular.
- Smooth Wheeled Rollers
- Principle of Loading: Static pressure
- Type of Pressure: Uniform pressure across the surface
- Ballast Requirement: Can be ballasted with water or sand for increased weight
- Speed: 2-4 km/h
- Suitability: Suitable for sand, gravel, and crushed rock
- Pressure Exerted: Moderate pressure, ranging from 2-6 kg/cm²
- Use: Mainly used for finishing purposes to smooth out the surface after other types of rollers have compacted the soil.
- Vibratory Rollers
- Principle of Loading: Combination of impact and vibration
- Type of Pressure: Dynamic pressure due to vibration
- Ballast Requirement: Not usually ballasted but has adjustable weights for vibration
- Speed: 2-4 km/h, can vary based on vibration frequency
- Suitability: Suitable for granular soils like sand, gravel, and crushed stone
- Pressure Exerted: 10-40 kg/cm², with high compaction efficiency
- Use: Used for compacting non-cohesive soils at greater depths due to the vibration effect.
- Grid Rollers
- Principle of Loading: Static pressure with grid structure imparting high pressure on specific areas
- Type of Pressure: High-pressure at points of contact
- Ballast Requirement: Often filled with water or sand for increased weight
- Speed: 5-15 km/h
- Suitability: Best for compacting coarse, granular soils like crushed rock
- Pressure Exerted: 10-15 kg/cm²
- Use: Used for compacting materials that cannot be compacted with smooth rollers.