Explanation

Vibratory Roller: Vibratory type rollers have two smooth wheels/drums plus vibrators. One is fixed at front and or one is on rear side of vibratory roller. Vibration is to reduce air voids and to cause densification of granular soils. During vibration of soil layer, rearrangement of particles occurs due to deformation of granular soil because of oscillation of roller in a cycle.

Suitability of Compaction Equipment

Explanation:

Compaction: 

• It is process in which  soil particles are forced into a denser state by mechanical means, thus decreasing air voids and hence porosity also reduces.
• It is an instantaneous phenomenon. Commonly used equipment is rammer, roller, etc.

Consolidation: 

• It is a gradual reduction in volume of fully saturated soil due to dissipation of excess pore water pressure, set up due to an increase in effective stress.
• It is a time-dependent phenomenon.

Consolidation is believed to occur in three stages:-

a) Immediate consolidation: 

• It occurs if soil is initially partially saturated and expulsion of air and lateral expansion of soil takes place.

b) Primary consolidation: 

• It occurs due to expulsion of pore water pressure and depends on magnitude of stress increase, compressibility and thickness of soil layer.

c) Secondary consolidation: 

• It is thought to occur due to gradual readjustment of clay particles into a more stable configuration following structural disturbance caused due to decrease in void ratio. It occurs in a very long time.

Due to higher strains, flocculated structure of compacted on dry side is broken, giving rise to ultimate strength.

For same soil, effect of heavier compaction is in increase in maximum dry density. Compaction reduces voids ratio and hence re is decrease in porosity. Due to this, dry density of soil sample is increased.

Smaller rollers are having a tyre load of about 7.5kN and pressure in order of 250 kN/m².

In Standard Proctor test, layers of specimen are tested with a free fall of rammer of weight 2.5 kg or 5.5 lb with height of free fall being 12 inches or 310 mm.

The energy per volume formula is given by,
\(\frac{WhNng}{V}, \)
where, W = weight of rammer
h = free fall height
N = number of layers
n = number of blows
g = acceleration due to gravity
V = volume.
The units of energy per volume is kJ/m³.

Some of compaction tests used in laboratory is: standard and modified proctor test, Harvard Miniature compaction test, Abbot Compaction test and Jodhpur-mini compactor test.

The initial decrease of dry density at lower water content is a characteristic feature of black cotton soils, high swelling clays and fat clays. The optimum water content for such soils ranges between 20 to 25%.

The height of free fall in Abbot compaction test is 35 cm above base. For Standard Proctor test, height of free fall is 31 cm and for Modified Proctor test, height of free fall is 45.72 cm.