Compacted soil is a key component of a construction project. It provides dense, firm base required to support foundations, footings, pavements and slabs. When the underlying soil isn’t dense enough, excessive soil settlement may lead to structural problems such as foundation erosion, basement walls that crack and leak, slab cracks, pipes that leak and break and hence it becomes a necessity to compact the soil. 

While there is plenty of compaction machinery available in the market, finding the right machine for a project to ensure successful results is quite a hard task. 

The choice of machine depends on two major criteria: (1) The composition & properties of the soil to be compacted. (2) The expanse and amount of material to be compacted. While the first criterion determines the kind of compaction force required, the second determines the size of the machine required. 

Compaction equipment applies force to enhance soil density. Some machinery applies static force whereas a few others apply dynamic force. Soil compaction equipment is segregated into two groups. 

1. Light soil compaction equipment

These machineries are utilised for soil compacting of small regions and areas which require less compaction effort. Some of the light equipment for soil compaction are:

(a) Rammers

Rammers offer impact load to soil and are used for compacting small areas. This machine is light and can be operated easily. They are suitable for compacting cohesive soils in addition to other soils. The base size of rammers is 20cm x 20cm or 15cm x 15cm or more. For machine operated rammers, the weight varies from 30kg to 10 tonnes. The hammers with 2- 3 tonnes weights are allowed to free fall on the soil from a height of 1m to 2m for the compaction of rock fragments. 

(b) Vibrating plate compactors

Vibrating plate compactors, used in small areas, can compact coarse soils with 4 to 8% fines. The weights of these machines vary from 100 kg to 2 tonnes and have plate areas between 0.16 m2 and 1.6 m2. 

(c) Vibro tampers 

Vibro tampers, suitable for compaction of all types of soil, is used for compaction of areas in confined space. The compaction is done by setting up vibrations in a base plate via a spring activated by an engine driven reciprocating mechanism and weigh between 50 and 100 kg. 

2. Heavy soil compaction equipment 

Heavy compacting machines are used on different types of soil and in large areas. These machines are chosen based on the types of soil and its moisture content. Heavy soil compaction equipment consists of various types of machines such as: 

(a) Smooth wheeled roller

This machine is used in crushing application and on soils such as gravel, well-graded sand, asphalt, crushed rock, etc. These rollers are used for completing the upper surface of the soil and on soils which does not require high pressure for compaction. This machine is not used for compaction of uniform sands. Smooth wheeled rollers are further divided into static smooth and vibrating smooth wheeled rollers. 

The smooth wheeled rollers include 1 large steel drum in front and 2 on the rear. The total weight of these rollers ranges from 8-10 tonnes. The performance of these rollers can be improved by increasing the weight of the drum by ballasting the inner regions of drums with water or wet sand. The steel sections can also be utilised to increase the load of the drum by mounting on the steel frame that is attached to the axle. 

(b) Sheepsfoot roller 

Sheepsfoot roller is utilised for compacting fine grained soils like heavy and clays and for compaction of soils in embankments, subgrade layers in pavements, dams, and railroad construction projects. The efficiency of sheepsfoot rollers, affected by the pressure on the foot & coverage of ground, can be achieved when lugs gradual walkout of the roller lugs with successive coverage. For pressure and coverage of ground, factors such as the area of each foot, gross weight of the roller, the number of lugs in contact with the ground and the total number of feet per drum need to be considered. 

(c) Pneumatic tyred roller 

Pneumatic tyred roller is utilised for compaction of coarse grained soils with some fines. This type of roller is least suitable for rocks and uniform coarse soils. Pneumatic tyred roller used in pavement subgrade does earthwork as well as bituminous works. The roller has wheels on both axles which are staggered for compaction of soil layers with equal pressure throughout the width of the machine. 

(d) Grid roller 

Grid roller works on weathered rocks, well-graded coarse soils and is not suitable for silty clays, clayey soils, and uniform soils. The roller weight can be increased by ballasting with concrete blocks. This machine is mainly used in subgrade and subbase in road construction and  has a cylindrical heavy steel surface including a network of steel bars forming a grid with square holes. 

(e) Pad foot roller

The static pad foot roller, also known as tamping roller, weighs from 15 to 40 tonnes and its static linear drum between 30 and 80 kg/cm. The roller can operate at high speed, has high production capacity and a greater degree of compaction can be achieved. The density of soil achieved after compaction with this machine is more uniform. 

In addition to looking for suitable functions, a feature to look for when considering compaction machinery is design that minimises the transmission of machine vibrations to the operator’s arms and hands.