The document discusses various mechanical modifications for soil density enhancement, focusing on methods like compaction and consolidation. It details different types of surface compaction equipment, including vibratory rollers, smooth wheel rollers, sheep foot rollers, pneumatic rollers, and grid rollers, explaining their characteristics and appropriate applications. Each roller type has specific features affecting their effectiveness in compaction of varied soil types.

1. UNIT-2
MECHANICAL MODIFICATIONS

2. Mechanical modifications:-
• In this, the soil density is increased by the application of mechanical
force and including compaction of surface layers by static vibratory
such as compact roller and plate vibrators.
• Densification is the process to increase the density of soil by removal
of voids through mechanical energy applications.
• Compaction means densification of an unsaturated soil by reduction in
volume of voids filled with air while the volume of solids and water
content remain the same.
• Consolidation is the process where the volume of soil mass reduced by
expulsion of water.

4. Surface compaction methods:-
Vibratory rollers
Smooth wheel rollers
Sheep foot rollers
Pneumatic or tired rollers
Grid rollers

5. Vibratory rollers:-
 This type of rollers have two smooth wheels. One is fixed
at front and other is on the back side of roller. Both
wheels are of same diameter and length as well as the
weight.
 In this roller ,vibration takes place due to the presence of
igneous rock i.e, basalt.
 During this process , rearrangement of particles occur and
hence the densification takes place and improves the
properties of granular soil.

6. Vibratory roller:-

7. Smooth wheel rollers:-
 Vibratory rollers and smooth wheel rollers are
same in characteristics and the difference is that
it has no vibrator equipment and most of smooth
wheel rollers has only one wheel on front side of
the roller.
 It is suitable for rolling of weaker aggreagrate
and rolling of subgrade etc.

8. Smooth wheel roller:-

9. Sheep foot rollers:-
 Front wheel of these rollers contains many rectangular
shaped boots of equal sizes fixed in hexagonal pattern.
 Coverage area of these rollers is less (8 to 12%).
 Compaction is done by static weight and kneading action
of respective layers.
 Contact pressure of roller is from 1200-7000 kpa.

10. Sheep foot roller:-

11. Pneumatic or tired rollers:-
 These rollers are used for general compaction as they are
effective for low cohesive soils and cohesionless soils
including gravels ,sand ,clay etc.
 In these rollers more than 2 wheels are mounted in two
rows.
 They are available in wide range of load sizes.
 The heaviest capacity is 1800kN.

12. Pneumatic or tired rollers:-

13. Grid rollers:-
 These are intermediate between the smooth roller and
sheep foot roller.
 They provide less kneading action but high contact
pressure.
 They are more suitable for coarse grained soils.
 These are not suitable for clay and sandy soils because the
clay and sandy soil particles are stuck in the grids.

14. Grid rollers:-