SOIL MECHANICS

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• Q1: Define soil.
  Ans: The unconsolidated mineral material of earth crust is known as soil.
• Q2: Define soil mechanics.
  Ans: The branch of engineering science which enables an engineer to know the behaviour of soil under the action of Loads, water, temperature etc.
• Q3: What are the constituents of soil?
  Ans: Soil consist of four layers:

  • ➔ Litter layer (Organic matter)
  • ➔ Surface soil (Top soil with humus)
  • ➔ Subsoil
  • ➔ Bedrock (Parent rock)
• Q4: Define clay soil.
  Ans: The grain size of clay particles is less than 0.002 mm. It is composed of microscopic and sub microscopic particles of weathered rocks.
• Q5: Define silt
  Ans: It is a finer variety of soil having grain size varying from 0.002mm-0.06mm. It is found in the beds of rivers, canals etc.
• Q6: Define organic matter.
  Ans: The top most layer of soil is called organic matter or Litter layer.
• Q7: Define vegetation soil.
  Ans: Vegetative soil groups (VSG's) consist of soils having similar properties and qualities that affect their suitability for plant establishment and growth.
• Q8: What is meant by surface soil?
  Ans: It is the immediate uppermost loose layer of the earth consisting of organic matter and soil organisms suitable for plant growth.
• Q9: Define sub-soil.
  Ans: It is the layer of soil under the topsoil on the surface of the ground. Like topsoil it is composed of a variable mixture of small particles such as sand, silt and/or clay, but with a much lower percentage of organic matter and humus
• Q10: What do you know about parent rocks?
  Ans: It is the lowest layer containing unbroken rocks. It may contain more soluble compounds.
• Q11: Define alluvial soil.
  Ans: This soil is transported and is carried away by the forces of water. Solid particles get mixed up with soils of different origin.
• Q12: Define types of weathering.
  Ans: Disintegration of rocks into various forms is known as weathering. It is classified as follows:

  • ➔ Physical Weathering
  • ➔ Chemical Weathering
• Q13: What is meant by Physical Weathering?
  Ans: Physical weathering is the process in which rocks break into smaller pieces without any change in their chemical composition.
  It is also known as Mechanical Weathering.
• Q14: What is meant by Chemical Weathering?
  Ans: Chemical weathering is the process in which rocks break down due to chemical reactions that change their composition.
• Q15: What is meant by compaction?
  Ans: The process of increasing the density of a soil using force to pack the particles close together with a reduction in air voids without any significant change in the volume of water in the soil is known as compaction
• Q16: Define consolidation.
  Ans: Consolidation is a process which involves decrease in water content of a saturated soil without replacement of water by air.
• Q17: Define permeability.
  Ans: The ability of water to flow through a soil is referred to as the soil's permeability.
• Q18: Define porosity.
  Ans: Soil porosity refers to the amount of pores, or open space, between soil particles. A high porous soil has more spaces between the particles.
• Q19: Define seepage.
  Ans: The movement of water through soil into the structures is usually termed as seepage.
• Q20: Differentiate between compaction and consolidation.
  Ans: Check Answer # 13 and 14
• Q21: What are the most suitable types of soil as a backfill for the under floor?
  Ans: Coarse-grained soils, such as gravel and crushed stone, are commonly used as backfill materials.
• Q22: Define bearing capacity of soil.
  Ans: The maximum load which the soil can take per unit area without yielding or displacement is called ultimate bearing capacity of soil.
• Q23: Name the factors affecting the bearing capacity of soil.
  Ans: Following factors directly or indirectly affect the bearing capacity of soil:

  • ➔ Type of soil
  • ➔ Initial stress condition of soil
  • ➔ Location of ground water in the soil
  • ➔ Type of foundation
  • ➔ Depth & location of foundation.
  • ➔ Earthquake, floods, heavy winds etc.
• Q24: Define Atterberg limits.
  Ans: The limits which define the consistency and behavior of fine-grained soils at different water contents are called Atterberg limits.
  Atterberg limits include:

  • ➔ Liquid Limit (LL)
  • ➔ Plastic Limit (PL)
  • ➔ Shrinkage Limit (SL)
• Q25: Define Liquid Limit for soil.
  Ans: Liquid Limit (LL) is the water content at which soil changes from the plastic state to the liquid state and begins to flow like a liquid.
• Q26: Define Plastic Limit for soil.
  Ans: Plastic Limit (PL) is the water content at which soil changes from the semi-solid state to the plastic state and can be molded without cracking.
• Q27: Define Shrinkage Limit for soil.
  Ans: Shrinkage Limit (SL) is the water content at which further drying of the soil does not cause any decrease in its volume.