Geotechnical Engineering Questions and Answers

1. What is Geotechnical Engineering?

It is a broader term which includes soil mechanics, foundation engineering, rock mechanics and geology.

2. What do you know about soil formation?

The process of formation of soil is termed as “Pedogenesis”. The soil is formed due to weathering of rocks, which may be carried out either physically or chemically.

3. What is alluvial soil?

It is the soil which is deposited from suspension in running water (formed due to physical weathering. This soil is transported type of soil and formed along the banks of river.

4. Why engineers prefer coarse-grained soils to fine-grained soils for most of the civil works?

Due to following reasons

  1. These soils have less settlement
  2. Most of the settlement occurs quickly
  3. These soils also have greater bearing capacity.

5. Name the mineral present in Black cotton soil and what are the problems encountered in laying foundation on this soil.

Name of the clay mineral present in black cotton soil is “Montmorillonite”, which shows expansive property of soil. Due to this mineral, foundations laying on black cotton soils experience swelling and shrinkage problems. In this case generally under-reamed pile foundation is the best option to adopt.

6. Why void ratio is more commonly used instead of porosity?

This is due to the fact that any change in the volume of the soil mass is direct consequence of a similar change in the volume of voids while the volume of solids remains the same.

7. Mention the difference between submerged and saturated soil?

In both the conditions, soils voids are filled with water, but if buoyancy force act on soil solids, then it is called submerged soil, else it is called saturated soil.

Soil in submerged condition will be in saturated state but soil in saturated condition need not to be submerged. For example, soil mass below water table is in submerged as well as saturated condition whereas soil mass in capillary zone is in saturated condition only.

8. What is the physical significance of relative density and relative consistency of the given soil mass?

Relative density is used for coarse grained soil while the relative consistency is used for the fine grained soil.

9. For what purpose sedimentation analysis is used?

Sedimentation analysis is used for grain size distribution of fine grained soil (i.e. particle size finer than 75 micron).

10. Explain laterite soil.

It is the type of soil, which is formed due to leaching (leaching means washing out of chemical compound like siliceous compounds and accumulation of iron oxide and aluminum oxide). This soil is generally found in hilly areas having humid climate, ex – western ghat and eastern ghat.

11. What do you mean by index properties of soil?

Index properties of soils helps in classification and identification of soil. Some of the index properties of soil are water content, unit weight, specific gravity, particle size distribution, consistency of soil, thixotropy, senstivty, activity, collapsibility etc.

12. Name the methods to find out water content of soil.

Some of the methods are:

  1. Oven dry method
  2. Sand bath method
  3. Alcohol method
  4. Calcium carbide method
  5. Torsion balance method
  6. Radiation method
  7. Pycnometer method

13. Define thixotropy.

Over the period of time, soil regains a part of its lost strength on account of remoulding. This property of soil by virtue of which it regains a part of its lost strength is termed as thixotropy. Increase in strength which passage of time is due to tendency of clay soil to regain their chemical equilibrium with reorientation of water molecule in adsorbed layer.

14. Define sensitivity.

Loss of strength of soil is represented in terms of its sensitivity, which denotes degree of disturbance of sample upon remoulding. Therefore sensitivity is defined as “unconfined compressive strength of soil in its undisturbed state to unconfined compressive strength of soil in its remoulded state.