Void ratio, difference between compaction and consolidation

1. Q1. Define void ratio, porosity and degree of saturation.
Answer:
Void ratio:
“The ratio of the volume of voids to the volume of solids is called void ratio.”
Porosity:
“The ratio of the volume of voids to the total volume of the soil is called porosity.”
Degree of Saturation:
“The ratio of the volume of water to the total volume of void space is called degree
of saturation.”
Q2. Briefly state the difference between compaction and consolidation.
Answer:
Compaction:
 Compaction is the compression of soil by the expulsion of air from the voids
of the soil.
 It is a quick process.
 Short term loading is required.
 Loading is applied in a dynamic way.
 Any type of soil either it is cohesion or Cohesion less can be compacted.
 Degree of saturation of soil to be compacted should be less than 100%.
 Shear strength of soil increases.
 Void ratio, compressibility and permeability decreases.
 Compaction is done purposely in order to get maximum dry density of soil.
 To construct roads, earthen dams, embankments etc. compaction is useful.
Consolidation:
 Consolidation is the compressionof soil by the expulsion of water from
voids of the soil.

2.  It is a slow process.
 Long term loading is required.
 Loading is static and constant.
 Consolidation applies to cohesive soils only especially for low permeable
clay.
 Degree of saturation of soil to be consolidated should be 100%.
 Shear strength of soil increases.
 Void ratio, compressibility and permeability decreases.
 Consolidation of soil occurs naturally due to structural loads from
foundations.
 The foundation soil properties will improve over long period due to
consolidation.
Q3. State the purpose of compaction.
Answer:
 Compaction is the application of mechanical energy to a soil to rearrange the
particles and reduce the void ratio.
 The principal reason for compacting soil is to reduce subsequent settlement
under working loads.
 Compaction is intended to improve the strength and stiffness of soil.
 Compaction increases the shear strength of the soil.
Q4. Define permeability and seepage. State the name and ASTM standard
for finding "k" value for fine and coarse grained soils.
Answer:
Permeability:
“A capacity of soil to allow water passes through it is called permeability.”
Seepage:
“Flow of water through soils is called seepage.”
For Fine grained
Falling head permeability test (ASTM D5084)

3. For coarsegrained
Constant head permeability test (ASTM D2434)
THE END