12-04-2023

Compactors – Introduction

Construction Equipment
• Compaction is the process of whereby material particles are considered
to pack more closely together through reduction of air voids, generally by
mechanical means.

Management • It is the process of densifying or increasing the unit weight of soil mass
through the application of static or dynamic forces, resulting in expulsion
of air and in some cases moisture.
CMT 522 • Better the compaction : Better the shear strength, density and bearing
Session 7 – Compacting Machines capacity of the respective layer.

Aritra Halder
| Aritra Halder | Assistant Professor
Assistant Professor | School of Construction

Historical development Compaction – Functions

• Primary function of compaction is to provide reasonable surface finish
and adequate load bearing capacity to the respective pavement layers.
• Compaction improves the following properties of soil –
– Improved density
• The Chinese first used – Increase in soil strength
cylindrical rollers – 1000
years ago. – Improved bearing capacity
• The romans used towed – Reduced volumetric change upon load
rollers for their road
construction. – Reduced permeability of soil.
• Britain developed steam
powered rollers in the 19th
century.
• Industrial revolution gave
rise to diesel powered
rollers in the 20th century.

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

1
 12-04-2023

Detailed Description of Different Compactors

Compactor Types Description

Types of Compactors Rammers Rammers are used for compacting small areas by providing impact load to the soil. This equipment is light and can be hand or machine operated. The base
size of rammers can be 15cm x 15cm or 20cm x 20cm or more.
For machine operated rammers, the usual weight varies from 30kg to 10 tonnes (6 lbs to 22000 lbs). These hammers with 2- 3 tonnes (4400 to 6600 lbs)
weights are allowed to free fall from a height of 1m to 2m (3ft to 7ft) on the soil for the compaction of rock fragments. Rammers are suitable for compacting
cohesive soils as well as other soils. This machine in areas with difficulty in access.
Vibrating Plate Vibrating plate compactors are used for compaction of coarse soils with 4 to 8% fines. These equipment are used for small areas. The usual weights of these
machines vary from 100 kg to 2 tonne with plate areas between 0.16 m2 and 1.6 m2.
Vibro-Tampers Vibro-tampers is used for compaction of small areas in confined space. This machine is suitable for compaction of all types of soil by vibrations set up in a base
plate through a spring activated by an engine driven reciprocating mechanism. They are usually manually guided and weigh between 50 and 100 kg (100 to
220 lbs).
Smooth Wheeled Smooth wheeled rollers are of two types: (1) Static smooth wheeled rollers & (2) Vibrating smooth wheeled rollers.
Rollers The most suitable soils for these roller type are well graded sand, gravel, crushed rock, asphalt etc. where crushing is required. These are used on soils which
does not require great pressure for compaction. These rollers are generally used for finishing the upper surface of the soil. These roller are not used for
Static Smooth Wheeled Sheep Foot Pneumatic or Rubber Tyred Vibratory Smooth Wheeled compaction of uniform sands.
The performance of smooth wheeled rollers depend on load per cm width it transfers to the soil and diameter of the drum. The load per cm width is derived
from the gross weight of the drum. The smooth wheeled rollers consists of one large steel drum in front and two steel drums on the rear. The gross weight of
these rollers is in the range of 8-10 tonnes (18000 to 22000 lbs). The other type of smooth wheel roller is called Tandem Roller, which weighs between 6-8
tonne (13000 to 18000 lbs). The performance of these rollers can be increased by increasing the increasing the weight of the drum by ballasting the inside of
drums with wet sand or water. Steel sections can also be used to increase the load of the drum by mounting on the steel frame attached with axle. The
desirable speed and number of passes for appropriate compaction of soil depends on the type of soil and varies from location to location. About 8 passes are
adequate for compacting 20 cm layer. A speed of 3-6 kmph is considered appropriate for smooth wheel rollers.
Vibrating smooth In case of vibrating smooth wheeled rollers, the drums are made to vibrate by employing rotating or reciprocating mass. These rollers are helpful from several
wheeled Rollers considerations like:-
(i) Higher compaction level can be achieved with maximum work
(ii) Compaction can be done up to greater depths
Pad Foot Grid Roller (iii) Output is many times more than conventional rollers
Vibrating Plate Although these rollers are expensive but in the long term the cost becomes economical due to their higher outputs and improved performance. The latest
Vibro- Tamper/Rammer work specifications for excavation recommends the use of vibratory rollers due to their advantage over static smooth wheeled rollers.
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Detailed Description of Different Compactors

Compactor Types Description
Sheepsfoot 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 Compaction principle
used for compaction of all fine grained soils and also soil with sand-gravel mixes. Generally this roller is used for 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 -
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 • Impact – Sharp Blow
with water, wet sand or by mounting steel sections. 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 total number of feet per drum are considered. The compaction of soil is mainly due to foots penetrating and exerting pressure on the
• Pressure – Static Weight
soil. The pressure is maximum when a foot is vertical.
• Vibrator – Shaking, rapid impact, pressure wave
Pneumatic Tyred 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
Roller least suitable for uniform coarse soils and rocks. Generally pneumatic tyred rollers are used in pavement subgrade works both earthwork and bituminous
works.
• Kneading – Manipulation or rearranging
Pneumatic rollers have wheels on both axles. These wheels are staggered for compaction of soil layers with uniform pressure throughout the width of the
roller. The factors which affects the degree of compaction are tyre inflation pressure and the area of the contact. The latest rollers have an arrangement to
inflate the tyre to the desired pressure automatically. 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. • Impact & Pressure rollers – Silt and Clay
Grid Roller Grid rollers are used for compaction of weathered rocks, well graded coarse soils. These rollers are not suitable for clayey soils, silty clays and uniform soils.
The main use of these rollers are in subgrade and sub-base in road constructions. As the name suggests, these rollers have a cylindrical heavy steel surface
• Vibratory – Gravel and Sand
consisting of a network of steel bars forming a grid with square holes. The weight of this roller can be increased by ballasting with concrete blocks. Typical
weights vary between 5.5 tonnes net and 15 tonnes ballasted. Grid rollers provide high contact pressure but little kneading action and are suitable for • Kneading – All types specially clay
compacting most coarse grained soils.

Pad Foot Roller These rollers are similar to sheepsfoot rollers with lugs of larger area than sheepsfoot rollers. The static pad foot rollers also called tamping rollers have static
weights in the range of 15 to 40 tonnes and their static linear drum loads are between 30 and 80 kg/cm. These rollers are more preferable than sheepsfoot
roller due to their high production capacity, and they are replacing sheepsfoot rollers. The degree of compaction achieved is more than sheepsfoot rollers. The
density of soil achieved after compaction with this roller is more uniform. These rollers operate at high speeds, and are capable to breaking large lumps. These
rollers also consists of leveling blades to spread the material. Pad foot or tamping rollers are best suitable for compacting cohesive soils.
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

2
 12-04-2023

Compaction Principle Soil Type vs Method of Compaction

Breakdown Intermediate Finishing Rolling Material Impact Pressure Vibration Kneading
Rolling Rolling

•Vibratory •Pneumatic •Steel wheel Gravel Poor No Good Very Good

steel wheel Tyre Rollers rollers
rollers •Speed: 2 to 4 •Speed: 3 to 7 Sand Poor No Excellent Good
•Pneumatic mph mph
Tyre Rollers
Silt Good Good Poor Excellent
•Speed: 2 to 3
mph
Clay Excellent Very Good No Good

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Principles of compaction used by various compactors Influence of soil on compaction

Compactor Type Impact Pressure Vibration Kneading • Cohesive Fine Grained Soil –
– The compaction of cohesive fine grained soil depends on
Sheep Foot/Pad Foot
X • Moisture content
• Plasticity
Tamping Foot
X X • Particle size distribution
– Suitable compactors are –
Vibrating Smooth
X X • Heavy rubber tyred compactor
• Heavy self propelled vibratory compactor
Vibrating Pad foot • Heavy towed vibratory compactor
X X
• Sheepfoot vibratory compactor
Pneumatic • Tamping foot vibratory compactor
X X

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

3
 12-04-2023

Influence of soil on compaction Influence of soil on compaction

• Non Cohesive coarse grained soil – • Fine and Coarse grained mixed soil –
– Compaction depends on – – Compaction depends on –
• Particle size distribution • Mix proportions
• Particle shape • Moisture content
• Moisture content • Particle size distribution
– Suitable compactors are – • Plasticity of the fine content
• Tandem vibratory compactor – Suitable compactors are –
• Double vibratory compactor
• For low fine content – • For high fine content –
• Towed vibratory compactor • Tandem vibratory compactor • Heavy self propelled
• Self propelled vibratory compactor • Double vibratory compactor • Heavy towed vibratory
• Rubber tyred compactor • Light towed vibratory compactor • Sheep foot vibratory
• Light self propelled vibratory compactor • Tamping foot vibratory
• Rubber tyred compactor
| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Illustrative Table
Roller Capacity - Factors
Sl. Material Thickness No. of Types of Compaction Equipment Remarks
No of Layer Passes
1 Gravel 20-30 3-5 • Vibratory Pad Foot o Foot Pr. 1.5-14 kg/sq.cm
• Net roller speed, the length of pavement that can be compacted in a unit
• Vibratory Smooth o- of time, is influenced by –
• Pneumatic o Tyre Pr. 2.5-9 kg/sq.cm – 1. The gross roller speed
• Sheep Foot o Foot Pr. 10.5-14 kg/sq.cm
– 2. The number of passes
2 Sand 20-25 3-5 • Vibratory Pad Foot o-
• Vibratory Smooth o- – 3. The number of laps
• Pneumatic o Tyre Pr. 2.5-4.5 kg/sq.cm – 4. The overlap between adjacent laps required to cover the mat width
• Smooth Static o Tandem 10-15 Ton
– S. The extension overedge
3 Silt 15-20 4-8 • Vibratory o Foot Pr. 14-28 kg/sq.cm
• Tamping Foot o- – 6. The extra passes for joints
• Pneumatic o Tyre Pr. 2.5-3.5 kg/sq.cm – 7. The non-productive travel (overrun for lap change).
• Sheep Foot o Foot Pr. 14-28 kg/sq.cm
4 Clay 10-15 4-6 • Vibratory Pad Foot o Foot Pr. 17.5-35 kg/sq.cm
• Tamping Foot o-
• Sheep Foot o Foot Pr. 17.5-35 kg/sq.cm
| Aritra Halder | Assistant Professor • Ideal number of passes for rollers is 6. | Aritra Halder | Assistant Professor

4
 12-04-2023

Factors influencing Compaction Capacity Calculations

Roller Speed
Static Weight Number of Vibratory Drums
3-4 kmph is required for high × ×
Static weight is directly With higher number of drums, density and high thickness. • 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑄 = 𝐶 × sqm/hr
proportional to the compaction requirement of passes decreases,
effect and depth effect of the roller. efficiency increases. 4+ kmph is required for low
density and less thickness. • Q = Output in sqm/hr
• C = efficiency factor (0.6-0.8)
Drum Diameter Frequency and Amplitude Frame and Drum weight relation
Best compaction is achieved at
• W = Drum width
For higher static weight roller, Heavy frame fitted close to the
drum diameter should be large.
Excessive large diameter hinders
frequencies of 25-50 Hz. drum augments the compaction
effect. Too heavy frame dampens
• S = average compaction speed (kmph)
For rocky soil, large amplitude and
compaction efficiency. high frequency is suitable. the compaction effect. • P = number of passes

Driven and Non Driven Drum

Centrifugal Force
Driven drum reduces risk of
Centrifugal force of the drum was considered to be the governing factor of
surface crack due to better control
compaction effect of rollers. Later studies proved that CF doesn’t have
of surface layer compaction and
maneuverability. direct relationship to the vibrating force transmitted to the ground.

| Aritra Halder | Assistant Professor | Aritra Halder | Assistant Professor

Capacity Calculations
× × ×
• 𝑉𝑜𝑙𝑢𝑚𝑒 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑄 = 𝐶 × cum/hr
•
•
Q = Output in cum/hr
C = efficiency factor (0.6-0.8)
Thank You!
• W = Drum width
• S = average compaction speed (kmph) Contact Me
• T = Layer thickness after compaction (m) at
ahalder@nicmar.ac.in
• P = number of passes +91-8504017164

| Aritra Halder | Assistant Professor

| Aritra Halder | Assistant Professor