COMPACTION & ROLLER REQUIREMENT FOR EMBANKMENT AND SUBGRADE Compaction of soils required for different types materials for embankment and subgrade are shown here based on IS:2720 – part-8.

Following table shows the relative compaction for different soil types:

Sl. No. Type of work / material

Relative compaction as percentage of maximum laboratory dry density

1 Subgrade and earthen shoulders

Not more than 97

2 Embankment Not more than 95

Expansive clays

a) Subgrade and 500mm portion below subgrade

Not allowed 3

b) Remaining portion of embankment

Not more than 90

Selection of compaction rollers for different soil types:

Suitability of compaction roller for different types of soils Types of

compaction rollers Cohesive soils

Well graded granular and dry cohesive

soils

Uniformly graded materials

1. Smooth wheeled roller

Suitable Suitable

Suitable only if the roller is towed by tractors and the load per cm width of the roller is less than 55kg.

2. Pneumatic Suitable

Suitable when load on each wheel is more than 2 tonnes

Suitable only if the roller is towed by tractors and load on each wheel is less than 1.5 tonnes

3. Vibratory roller

Suitable only when the static load per cm width of the vibratory roller is more than 7kg.

Suitable

Suitable but when the static load per cm width of the vibratory roller is more than 12 kg, the roller should be towed by tractors.

4. Sheep foot roller

Suitable Unsuitable Unsuitable

4. Power rammer

Suitable Suitable Unsuitable

Note: For the purpose of this table, soils are grouped as follows:

1. Cohesive soils include clays upto 20% of gravel and having a moisture content not less than the value of the plastic limit minus 4.

2. Well graded granular and dry cohesive soils include clays containing more than 20% of gravel and / or having a moisture content less than the value of the plastic minus – 4, well graded sands and gravels with a uniformity coefficient exceeding 1- and all shales and clinker ash.

3. Uniformly graded material includes sands and gravels with a uniformity coefficient of 10 or less and all silt and pulverized fuel ashes. Any soil containing 80$ or more of material in the particle size range 0.06 – 0.002 mm will be regarded as silt for this purpose.

Density requirement of embankments and subgrade material:

This requirement of density of soil for embankment and subgrade is based on results obtained when tested as per IS 2720 – (Part – 8).

S. No.

Type of work Maximum laboratory

dry density (unit weight)

1. Embankments upto 3m height and not subjected to extensive flooding

Not less than 15.2 kN/m3

2. Embankments exceeding 3m height or embankments of any height subject to long period of inundation

Not less than 16.0 kN/m3

3. Subgrade and earthen shoulders / verges / backfill

Not less than 17.5 kN/m3