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Explanation:

• Soil can be classified according to its pH values.
• pH value from 7.0 to 7.5 is considered neutral.
• pH value over 7.5 is alkaline.
• pH value less than 7.0 is acidic.
• Soils with a pH less than 5.5 are considered strongly acidic.​​​​

• pH of the pH scale stands for the power of Hydrogen. It consists of the value from 0 to 14.
• The concept of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen in1919.
• pH scale in Chemistry is used to determine the acidity or basicity of a solution.
• pH scale indicates the concentration of Hydrogen ions in the solution. 

• Litmus, turmeric, red cabbage, China rose, etc. are some common natural indicators used widely to show the acidic or basic character of substances.

Hygroscopic water means that how much water can be held by the soil over its surface by the action adhesion forces.

Specific surface is the ratio of surface per unit volume. More surface area implies more specific surface. Clay has more surface area (more specific surface) as compared to sand since clay has smaller particles, therefore, more water can be held be clay particles over their surface. Hence, clay exhibits more hygroscopicity. 

Black cotton soil:

• Black cotton soils show swelling and shrinkage behavior on wetting and drying.
• Black Cotton Soil also consists of the excess of Montmorillonite mineral.
• These show volumetric changes with the change of atmospheric conditions.
• Black cotton soil shows swelling when moisture content increases and shrinkage behavior when moisture content decreases. 
• Under reamed piles are used for these types of soils.

As black cotton soils are expansive soils i.e having swelling and shrinkage behavior and due to this Lightly loaded structures are more susceptible to damage as a result of volume changes in the soil. Therefore these soils need to be stabilized first before loading.

Investigation says that lime is a good stabilizing agent for the construction of a road in black cotton soil.

Lime forms the bonding between the soil particles which is missing in black cotton soil and hence stabilizes.

Explanation:

Wind transported soils:

Soil particles are transported by winds. the particle size of the soil depends upon the velocity of wind. the finer particles are carried far away from the place of the formation. Soils deposited by wind are known as aeolian soil.

Loess:

It is a wind blown deposit of silt. It is generally of uniform gradation, with the particle size between 0.01 to 0.05 mm. It consists of quartz and feldspar particles, cemented with calcium carbonate or iron oxide. When wet, it becomes soft and compressible because cementing action is lost.

Glacier deposited soils:

Glaciers are large masses of ice formed by the compaction of snow. As the glaciers grow and move, they carry with them soils varying in size from fined grained to huge boulders. Drift is a general term used for the deposits made by glaciers directly or indirectly. Deposits directly made by melting of glaciers are called till.

Gravity deposited soils:

Soils can be transported through short distances under the action of gravity. Rock fragments and soil masses collected at the foot of the cliffs or steep slopes had fallen from higher elevation under the action of gravitational force. 

Colluvial soils, such as talus, have been deposited by the gravity.

Explanation:

(i) Black cotton soils have montmorillonite clay mineral which shows swelling and shrinkage behavior on wetting and drying.

(ii) Under-reamed piles are used for the structures constructed on black cotton soils or expansive soil to resist the expansive nature of the soil through the bulb provided in the piles.

(iii) Black Cotton Soil also consists of the excess of Montmorillonite mineral.

(iv) Bentonite clay shows swelling and shrinkage characteristics due to moisture content variation due to the presence of Montmorillonite mineral.

(v) Bentonite clay is also called Montmorillonite clay.

Explanation

1. Dispersive clays are a particular type of soil material in which the clay fraction erodes in the presence of water by a process of de-flocculation. This de-flocculation occurs when the interparticle forces of repulsion exceed those of attraction so that the clay particles go into suspension, and if the water is flowing, as in a crack in an earth embankment, the detached particles are carried away and piping occurs.

2. Expansive clay is clay soil that is prone to large volume changes (swelling and shrinking) that are directly related to changes in water content. Soils with a high content of expansive minerals can form deep cracks in drier seasons or years; such soils are called vertisols.

3. Varved clay is a clayey sedimentary soil, formed in glacier lakes, with visible layering.

• It is composed of two periodically repeated layers: dark (silty-clayey) and bright (silty-sandy) ones.
• During warm periods, when the glacier was melting, deposits were carried into the lake where coarser particles were deposited and composed light varves. In cold periods, when the lake was frozen, fine particles precipitate forming dark varves

Explanation:

Coefficient of Uniformity / Uniformity Coefficient:

It is defined as the ratio of D60 and D10 sieve sizes in sieve analysis of granular material.

Higher is the value of Cu larger is the range of the particle size.

\({C_u} = \frac{{{D_{60}}}}{{{D_{10}}}}\)

For uniformly graded soil, Cu = 1

For well graded sand, C_u > 6

For well graded gravel Cu > 4

Coefficient of Curvature / Curvature Coefficient:

\({C_c} = \frac{{D_{30}^2}}{{{D_{60}} \;\times \;{D_{10}}}}\)

For well graded soil, 1 < C_c < 3

For gap graded soil, 1 < Cc or Cc > 3

where

D60 = size at 60% finer by weight

D30 = size at 30% finer by weight

D10 = size at 10% finer by weight = Effective size

Concept:

As per I. S. 2386 - Part 1, a sieve size of 2 mm represents that each hole in a sieve is of 2 mm square shape.

According to the ISSC system size of coarse aggregates starts from 0.075 mm or 75 microns and ends at 80 mm.

So sieve of 4.75 mm and 10 mm are normally used for classification in coarse aggregates.

The table below shows the tabular data for different sieve suitable for different sizes of aggregates.

Explanation:

Coefficient of Curvature / Curvature Coefficient:

\({C_c} = \frac{{D_{30}^2}}{{{D_{60}} \times {D_{10}}}}\)

For well graded soil, 1 < Cc < 3

For gap graded soil, 1 < Cc or Cc > 3

where

D60 = size at 60% finer by weight

D30 = size at 30% finer by weight

D10 = size at 10% finer by weight = Effective size

Coefficient of Uniformity / Uniformity Coefficient:

It is defined as the ratio of D60 and D10 sieve sizes in the sieve analysis of granular material.

Higher is the value of Cu larger is the range of the particle size.

\({C_u} = \frac{{{D_{60}}}}{{{D_{10}}}}\)

For uniformly graded soil, Cu = 1

For well graded sand, Cu > 6

For well graded gravel Cu > 4

Explanation:

The word ‘Hydro’ means water and ‘logy’ means science.

It is the science that encompasses the study of water on the Earth’s surface and beneath the surface of the Earth, the occurrence and movement of water, the physical and chemical properties of water, and its relationship with the living and material components of the environment.

Therefore, it is the study of water moving through the earth’s surface into the atmosphere and back in its various forms.

It includes the precipitation, evaporation, surface runoff, stream flows in catchments, groundwater etc.

Explanation:

Red Soil:

• It is the largest soil group in India.
• The main parent rocks are crystalline and metamorphic rocks.
• These soils are poor, gravelly, and porous.
• They are rich, deep dark, and fertile in lower areas.
• They are acidic due to the nature of the parent rock.
• The red color is due to the presence of Iron Oxide.

Laterite soil:

• These soils are leaching intense leaching due to tropical rains.
• As heavy rains leach lime and silica, soil reach in Iron oxide and aluminum compound are left behind.
• These soils are poor in organic matter, nitrogen, phosphate, and calcium.
• Iron oxide and potash are in excess in the soil.
• Hence laterite soils are not suitable for cultivation.
• The application of manure and fertilizers makes these soils fertile for cultivation.

Black soil:

• Black soils are high compressibility, low bearing capacity, low shearing strength.
• The black color of the soil is due to the presence of titaniferous magnetite, compounds of iron and aluminum, hummus, etc.
• It riches in calcium carbonate, magnesium, potash, and lime but is poor in nitrogen and phosphorous.
• These are very fertile and soil texture.
• It is excessive retention of moisture.
• This soil is suitable for leguminous crops like cotton, citrus fruits, millets, wheat, tobacco, sugarcane.

Concept:

Fineness modulus (F.M)

It is a numerical index of fineness or grading of aggregate. It gives some idea of the average size of the aggregate. The value of fineness modulus is higher for coarse aggregate.

\({\rm{F}}.{\rm{M}} = \frac{{{\rm{Cummulative\;percentage\;of\;material\;retained\;on\;each\;sieve}}}}{{100}}\)

Classification based on Fineness modulus

Calculation:

Fineness modulus is given by

\({\rm{F}}.{\rm{M}} = \frac{{{\rm{Cummulative\;percentage\;of\;material\;retained\;on\;each\;sieve}}}}{{100}}\)

\({\rm{F}}.{\rm{M}} = \frac{{{\rm{260}}}}{{100}}=2.60\)

Hence the fineness modulus of the sand is 2.60

The correct answer is Inceptisols.

•  Inceptisols
  • Inceptisols are soils of relatively new origin and are characterized by having only the weakest appearance of horizons, or layers, produced by soil-forming factors.
  • They are the most abundant on Earth, occupying almost 22 per cent of all nonpolar continental land areas.
  • They are usually arable with appropriate control of erosion or drainage.
  • Inceptisol soil profiles give some indication of clay minerals, metal oxides, or humus accumulating in layers, but such accumulation is not sufficient to classify the soil into an order defined by characteristic surface or subsurface horizons.

• Alfisols
  • The Alfisols are soils characterized by a clay-rich horizon produced by illuviation and high base status.
  • They are moderately leached soils that have relatively high native fertility.
  • Alfisols are primarily found in temperate humid and subhumid regions of the world.
• Aridisols
  • Aridisols are CaCO3 containing soils of arid regions that exhibit subsurface horizon development.
  • They are being dry most of the year and limited leaching.
  • Aridisols contain subsurface horizons in which clays, calcium carbonate, silica, salts and or gypsum have accumulated.
• Mollisols
  • Mollisols are the soils of grassland ecosystems.
  • They are characterized by a thick, dark surface horizon.
  • This fertile surface horizon, known as a mollic epipedon, results from the long-term addition of organic materials derived from plant roots.

Concept:

Soils are generally classified in two types: Cohesive and Cohesion less soils.

Cohesive soils are soils having strong intermolecular force of attraction when water is added into them. This type of behaviour is shown by clays and silt. So, any soil having very high content of clay can be considered as cohesive soils. Cohesive soil does not crumble and can be excavated with vertical side slopes. The shear strength of these type of soils depends on inherent cohesion, friction in between them and normal stress acting on them.

Examples:  Clayey silt, Sandy clay, Silty clay, clay and organic clay.

Cohesionless soils are having no cohesion i.e. no intermolecular force of attraction when water is added into them. The shear strength of these type of soils depends on friction between particles and also normal stress acting on them.

Examples: Sand and Gravel.

The soils formed at a place may be transported to other places by agents of transportation, such as water, wind, ice and gravity.

1) Water transported Soils: Flowing water is one of the most important agents of transportation of soils. Swift running water carries a large quantity of soil either in suspension or by rolling along the bed.

The size of the soil particles carried by water depends upon the velocity.

All type of soils carried and deposited by water are known as alluvial deposits. Deposits made in lakes are called lacustrine deposits. Such deposits are laminated or varved in layers. Marine deposits are formed when the flowing water carries soils to ocean or sea.

2) Wind transported Soils: Soil particles are transported by winds. The particle size of the soil depends upon the velocity of wind. Soils deposited by wind are known as aeolian deposits.

Collapsible soil is those for which there is a decrease in volume on the addition of water. Loess is one such example. Loess is a silt deposit made by wind. These deposits have low density and high compressibility. The bearing capacity of such soils is very low.

3) Glacier-Deposited Soils: Glaciers are large masses of ice formed by the compaction of snow. As the glaciers grow and move, they carry with them soils varying in size from fine grained to huge boulders.

Drift is a general term used for the deposits made by glaciers directly or indirectly. Deposits directly made by melting of glaciers are called till. The soil carried by the melting water from the frint of a glacier is termed out-wash.

4) Gravity deposited soil: These are soils transported through short distances under the action of gravity. Colluvial soils such as talus have been deposited by the gravity. Talus consists of irregular, corase particles. It is a good source of broken rock pieces and coarse grained soils for many engineering works.

Explanation:

• The Unified Soil Classification system (USCS) is originally developed by Casagrande in 1948. The intention behind this development was to use airfield construction during World War II.
• The Unified soil classification system is almost similar to IS soil classification.

​

According to USCS,

The coarse-grained soils are classified on the basis of their grain-size distribution and the fine-grained soils on the basis of their plasticity characteristics.​

Classification of fine-grained soil:

(i) In USSC, fine-grained soils are classified on the basis of plasticity chart and compressibility.

(ii) generally, soils are considered as fine soils, when 50% or more of the total material by weight pass 75 μ sieve.

(iii) Liquid limit and plastic limit are determined for 425 μ sieve fraction and corresponding plasticity index is find out

CASE 1: Low plastic soil (Low compressibility) (LL < 35%)

CL → Low plastic inorganic soil

ML → Low plastic inorganic silt

OL → Low plastic organic clay

CASE 2: Medium Plastic soil (medium compressibility) (35% < LL < 50%)

CI → Medium plastic inorganic soil

MI → Medium plastic inorganic silt

OI → Medium plastic organic clay

CASE 3: Highly plastic soils (High compressibility) (LL > 50%)

CH → High plastic inorganic soil

MH → High plastic inorganic silt

OH → High plastic organic clay

Concept-

According to IS Classification system, the soils can be classified into 18 groups.

Soil classification using group symbols is as follows:

Explanation:

Almost all soil is derived from the disintegration of rocks. Disintegrated materials also known as sediments. 

All the soils are mainly divided into two parts-

1). Residual Soil:

• If Disintegrated materials remain over the parent rock then the soil is called Residual soil.
• Characteristics of residual soil depend on climatic conditions, natural drainage pattern, form, and extent of vegetation cover.

Example- Bentonite is a type of chemically weathered volcanic ash that is present on the parent rock from which it is formed.

2. Transported soil:

• If sediments are transported and deposited at other places then it is called transported soil.
• Sediments are transported by winds, water, glacier, etc. Some transported soils are-

Alluvial – transported in running water (rivers)

Lacustrine – Deposited by still water (lakes)

Marine – Deposited by seawater

Aeolian – Transported by wind

Glacial – Transported by ice

Colluvial – Transported by gravity

Concepts:

According to USCS, the coarse grained soils are classified on the basis of grain size distribution and fine-grained soils are classified based on plasticity.

Coarse grained soils are those having 50 % or more retained on 0.075 mm sieve. They are further divided into Gravel and Sand. They are designated as Gravel (G) if more than 50% coarse fraction is retained on 4.75 mm sieve and otherwise, they designated as Sand (S). Both Gravel and Sand are further divided into sub groups depending on the whether the soil is well graded or poorly graded (decided based on Coefficient of Uniformity and coefficient of curvature) and also based on nature of fines in them. This sub- classification is tabulated below:

Fine  grained soils are those having 50 % or more passing through 0.075 mm sieve. They are further divided into Silt (S), Clay (C) and Organic (O) based on their liquid limit and plasticity Index. They are   further divided into sub groups based on liquid limit i.e. if liquid limit is less than 50 % then they are low plasticity (L) and designated as ‘ML- Silt with Low plasticity’, ‘CL- Clay with Low plasticity’, OL- organic soils with Low plasticity’    and if liquid limit greater than 50 % they are high plasticity and designated as ‘MH- Silt with high plasticity’, ‘CH- Clay with high plasticity’, OH- organic soils with high plasticity’.

Explanation:

Properties of Aeolian soil:

1) Aeolian soil are deposited by wind action.

2) It has a uniformly graded particle.

3) The void ratio and permeability of soil is high. 

4) They are non-plastic.

5) High compressibility and high density. 

Explanation:

Almost all soil is derived from the disintegration of rocks. Disintegrated materials also known as sediments. All the soils are mainly divided into two parts-

1). Residual Soil:

If Disintegrated materials remain over the parent rock then the soil is called Residual soil. Characteristics of residual soil depend on climatic conditions, natural drainage pattern, form, and extent of vegetation cover. Example- Bentonite is a type of chemically weathered volcanic ash that is present on the parent rock from which it is formed.

2. Transported soil:

If sediments are transported and deposited at other places then it is called transported soil. Sediments are transported by winds, water, glacier, etc. Some transported soils are-

• Alluvial – transported in running water (rivers)
• Lacustrine – Deposited by still water (lakes)
• Marine – Deposited by seawater
• Aeolian – Transported by wind
• Glacial – Transported by ice
• Colluvial – Transported by gravity