MODULE-3:

Earth Surface process and Resources

Weathering, type, causes, soil insitu, drifted soil, soil profile, soil mineralogy, structure, types of soil, Black
cotton soil v/s Lateritic soil; effects of weathering on monumental rocks. Soil Horizon, Soil Classification by
Grain Size.

WEATHERING OF ROCKS

It is the breakdown of rocks into new minerals or smaller particles. Weathering is the result of
the interactions of air, water and temperature on rock surfaces and prepares the rock for erosion.
Erosion is the movement of small particles by ice, wind or water. Weathering implies decay and
change in original condition to form new minerals as a result of external processes. The disintegration
and decomposition of rocks converted to soils formed by the physical and chemical actions of
atmosphere elements. Weathering is generally a long, slow process that is continuously active on the
earth’s surface.

Types of weathering process

1. Physical weathering (Frost, Temperature)

2. Chemical weathering (Water, acid)

3. Biological weathering (Vegetation and organic matter)

1. Physical or mechanical weathering process:-A single block is broken gradually into numerous
small irregular fragments and then into much smaller fragments either by frost or thermalaction.

i. Block disintegration occurs due to regular arrangement of atoms in a rock due to this the individual
blocks are obtained.

ii. Granular disintegration occurs due to irregular arrangement of atoms due to which small grains
are obtained.

a. Frost action:- When rain water is trapped in joints, pores, cracks, fractures; then the water
freezes and expands during low temperature (during night time). This will gradually lead to partial
or total disintegration of the rock into small pieces forming angular or sub-angular fragments.

b. Thermal action:-The temperature difference between day-time and night-time is very high in
arid and semi-arid regions. Expansion on heating followed by contraction on cooling, and repeated
expansion of the same rock body gradually breaks into smaller pieces due to stress and thermal
effects.

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c. Spheroidal weathering:- It is a combination of mechanical and chemical weathering process due
to which the rounded boulders are produced. Water can penetrate more easily along 3D networks of
joints and fractures. These joints & fractures are weathered inwards to form cubes like pieces. The rate
of weathering will be greatest along the corners of each cube, followed by the edges, and finally the
faces of the cubes. As a result the cube will weather into a spherical shape, with unweathered portion at
the centre& weathered rock in the periphery referred as spheroidal weathering.

d. Exfoliation: Concentric shells of weathering

may form in the peripheral region of a rock mass
and get separated from the rock. These thin shells
of weathered rock are separated by stresses that
result from changes in volume of the minerals that
occur as a result of the formation of new minerals.

2. Chemical weathering: Water, oxygen and weak acids are the main agent responsible for chemical
weathering. These react with surface part of rocks to form a new mineral and become stable. Any
excess ions left over from the chemical reactions are carried away in the acidic water. These helps in
cementing newly deposited minerals such as calcite or quartz.

a. Water: Chemical weathering is most intense in areas that have abundant water. Different minerals
weather at different rates that are climate dependent. Ferromagnesian minerals breakdown quickly but
quartz is very resistant to weathering.

b. Acids: Acids are chemical compounds that decompose in water to release hydrogen atoms.
Hydrogen atoms frequently substitute for other elements in mineral structures, breaking them down to
form new minerals that contain the hydrogen atoms. The most abundant natural acid is carbonic acid,
a weak acid that consist of dissolved carbon-dioxide in water. Other acids that can affect the
formation of minerals in the near surface weathering environment are organic acids derived from
plant and humus material.

c. Leaching: Ions are removed by dissolution into water.

d. Oxidation: Since free oxygen (O2) is more common near the Earth’s surface, it may react with
minerals to change the oxidation state of an ion. This is more common in Fe (iron) bearing minerals,
since Fe can have several oxidation states, Fe, Fe+2,Fe+3.

3. Biological weathering: Plant roots can extend into fractures and grow, causing expansion of the
fracture and eventually can break rock. Plants can penetrate into the ground just a few meters whereas
microorganisms can penetrate to a greater than of 10-25 mts. Animals burrowing or moving through
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cracks can break rock.

WEATHERING EFFECTS ON CIVIL ENGINEERING PROJECTS

Most civil engineering works are located close to the surface where the ground mass is
affected by the weathering. The rate of weathering depends on climatic conditions, rock mass, the
type of rock mass (mineral composition), strength of rock, presence of joints, faults, shear zones and
other discontinuities. The weathering process varies from rocks to rocks and place to place. Hence,
such rocks and places need special attention and focus.

 Weathering happens over large amounts of time and is usually a contributor to structural failures.
 Weathering takes place in all environments but is most intense in hot, wet climates where it may
be expected to extend to great depths.
 Himalayan rocks may be significantly affected for their strength once the rock mass is saturated
during snowfall conditions and highly prone to chemical attacks.
 The weathering of soft rocks is one of the primary causes of slope failure and shallow landslide in
hilly areas during monsoon seasons.
 Due to continuous impact of weathering on building materials, the rock blocks, materials between
the rock blocks and soil grains gradually weakens and affects the civil structures.
 Dissolution in 50 years can erode chemical materials of around ½ to 5 mm, in which fraction of
mm enough to reduce (shear) strength showing its negative influence on civil structures.
 Weathering in road projects can cause cracks in pavements or even more worsen allowing water
into the pavement structure overtime.
 Intense weathering in reinforced concrete can contribute to structural failure when reinforcement
is exposed to the elements in unsealed cracks.
 Rocks containing joints and fractures should be investigated thoroughly for long term use.
 Soft and weathered rock mass conditions are subjected to mine blasting and seismicity.
 By reducing the strength of hard rock like granite can be a lot softer when exposed to weathering
conditions.
 The thickness of weathered zone keeps on increasing with time.
 This thickness of the weathered zone gradually increases the weathering process in the newly
exposed surface.

SOIL MECHANICS

It is the upper most layer of the earth surface typically consisting of a mixture of organic
remains, clay and rock particles. Soil is one of the valuable resources without which no agriculture,
forestry and construction can be done. It is the end product of weathering rocks modified by physical
and chemical interaction with organic material, rainwater and organisms over time.

SOIL IN-SITU: FORMATION OF SOIL: It takes several million years to form a thin layer of
soil. The formation particularly depends upon the physic-chemical properties of the parent rock,
intensity and duration of weathering, climatic and other parameters. Climatic conditions are important
factors affecting both the rate for physical and chemical weathering of the parent material.
1. Time: Most of the soils of the world have taken more than 10,000 years to form the current state
of soils. Rock disintegrates due to the addition of organic matter, exposure to moisture and other

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 environmental factors forming younger soils. Gradually these soils may change from one type to
another and settles in deeper below the surface with time.
2. Parental materials: The parental material determines the chemical and physical characteristics of
the soils which vary from place to place. Rate of soil forming in hard rock takes much time when
comparing to soft rocks. Most soil parent materials were rocks at some time in their history.
3. Precipitation: Precipitation is the most important among the climatic factors. As it percolates and
moves from one part of the parent material to another. It carries substances in solution form and
re-deposits in another part causing soil formation.
4. Temperature: High temperature favors rapid decomposition of organic matter and increase
microbial activities in soil. Temperature thus controls the rate of chemical and biological
reactions taking place in the parent material causing soil formation.
5. Topography and relief: Topography is the undulations of a land surface in relations with slope of
the natural features. These features highly determine the types of soils formed within a region.
Soils formed on higher elevations, sloping areas, groundwater table and surface run-off are being
largely drained. This changes in the time of soil formation processes.
6. Organisms (living things including man, plants and animals): All living organisms play an
active role in the soil formation processes. Organisms including fungi, bacteria, animals, humans,
and vegetations impact on the physical and chemical environments of the soils. Micro-organisms
encourage acidic conditions which change the soils chemistry and eventually determine the kind
of soil formation process that occur. Microbial activities also decompose organic matter and
recycle them in the soil. Larger animals including burrowing animals and earthworms mix the soil
and alter its physical characteristics.

Soil Profile: A vertical section of the soil through all of its horizons and extending into the parent
material. A cross-sectional view beneath the surface reveals the soil types and weathered &
unweathered rocks that make up the soil profile. The profile will be most helpful in deriving the
parent material, slope, native vegetation, weathering, and climate.

There are five horizons encountered based on their appearance, composition and origin.
i. ‘O’ horizon: It is largely dominated by fresh or partly decomposed Organic matter formed in
upper part of the soil. These are commonly seen in forest areas in which plants and animal residue
can be recognized through naked eye. It is often black or dark brown in color due to organic
content. It is the layer in which the roots of small grass are found.
i. ‘A’ horizon: It is the topmost soil cover formed by
inorganic matter, although it may contain up to 30%
organic matter. Typically, the A horizons are made of
sand, silt and clay with high amounts of organic
matter. This layer is most vulnerable to wind and
water erosion and also known as the rootzone.
ii. ‘B’ horizon: It is encountered just beneath the ‘A’
horizon and primarily made up of clay, small pieces of
weathered rock and minerals. It may contain high
concentrations of silicate, clay, iron, aluminum and
carbonates. It is the layer in which the roots of big
treesexist.
iv. ‘C’ horizon: It is mainly made up of broken bedrock
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 and no organic material. This is the first horizon where
weathering of soils occurs.
v. ‘R’ horizon: A mass of rock such as granite, basalt, quartzite, limestone or sandstone that forms
the parent material for some soils. This is not soil and is located under the C horizon.

SOIL MINERALOGY:

Minerals are natural inorganic compounds with definite physical, chemical, and crystalline
properties. They can be classified into primary (chemically unaltered) or secondary (chemically altered)
minerals, silicates and non-silicates, crystalline and noncrystalline minerals. Silicate minerals dominate in
most soils. Other major soil mineral groups include: sulfides, oxides and hydroxides, halides, sulfates,
carbonates and phosphates.

The most common methods used for soil mineral characterization include x-ray diffraction,
thermal, elemental, and optical analyses. Through these techniques unique mineral features, which are
essential in predicting their impact on the overall soil behaviour, are identified and quantified. Most
primary minerals undergo structural and chemical alterations (weathering) driven by physical, chemical,
and biological gradients. These processes cause redistribution of primary and secondary soil minerals
resulting in a soil profile which is consistent with the surrounding climatic and topographic setting.

Soil minerals play also a significant role in dictating the suitability and behavior of the soil for
various land uses. They provide physical support for plants, contribute to soil structural formation, are
sources of many plant nutrients, and can act as sorbents for several environmental pollutants. Therefore,
having a good grasp of soil mineralogy is essential to understanding many facets of land use, including
misuse, and is often a key to solving specific environmental problems.

Soil minerals are also referred to as primary and secondary minerals. Primary minerals have not
experienced significant chemical or structural alteration since their crystallization within igneous or
metamorphic rocks or their deposition in sedimentary rocks. They are inherited from the parent material,
and are usually found in the sand and silt fraction of soils.

Common primary minerals in soil environments include: silicates, oxides of iron (Fe), zircon (Zr)
and titanium (Ti), and phosphates (P). Secondary minerals are re-crystallized or transformed products of
the chemical breakdown and/or alteration of primary minerals under ambient conditions. Secondary
minerals are mainly found in the clay and fine-silt fractions because the particle size of primary minerals
usually decreases during weathering. Typical secondary minerals found in soils include alumino-silicates,
oxides and hydroxides, carbonates, sulfates, and amorphous minerals.

Mineral occurrences in soil environments are the result of inheritance from parent materials,
precipitation from soil solution (neoformation), or alteration of existing minerals into new phases
(diagenesis). Climatic changes have a paramount effect in these processes and in the overall distribution
of minerals in soils of different regions, different soil horizons, and even different soil fractions.
Therefore, the mineralogical composition of an individual soil is determined mostly by the make-up of the
parent material(s), and the intensity and duration of the weathering regime.

SOIL STRUCTURE

Soil conditions and characteristics such as water movement, heat transfer, aeration, and porosity
are much influenced by structure. In fact, the important physical changes imposed by the farmer in
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ploughing, cultivating, draining, liming, and manuring his land are structural rather than textural.

Definition: The arrangement and organization of primary and secondary particles in a soil mass is known
as soil structure. Soil structure controls the amount of water and air present in soil. Plant roots and
germinating seeds require sufficient air and oxygen for respiration. Bacterial activities also depend upon
the supply of water and air in the soil.

Formation of soil structure: Soil particles may be present either as single individual grains or as
aggregate i.e. group of particles bound together into granules or compound particles. These granules or
compound particles are known as secondary particles. A majority of particles in a sandy or silty soil are
present as single individual grains while in clayey soil they are present in granulated condition. The
individual particles are usually solid, while the aggregates are not solid but they possess a porous or
spongy character. Most soils are mixture of single grain and compound particle. Soils, which predominate
with single grains are said to be structureless, while those possess majority of secondary particles are said
to be aggregate, granulated or crumb structure.

Structure of a soil is the arrangement of the constituent particles in the soil matrix that contains
voids, fissures and cracks. Soil structure depends on many factors such as shape, size, mineral
composition, orientation of the grains, the relation of soil-water in their ionic components, and the
interactive forces among the particles. Coarse grained particles when clean and dry do not possess
plasticity and cohesion, soil containing these particles cannot form stable structure. In moist sands,
however, the contact pressure developed by capillary water ring may provide the necessary bonding to
create stable structure. However, when the grains become dry, the structure again breaks down. Gravity
and surface forces are the main forces that play an active part on soil particles in developing the soil
structure. Gravitational force is operative only in soil containing coarse grained particles. In small
particles, surface forces are effective in most of the soil types. There are three types of soil structures (a)
Single-grain structure; (b) Flocculated and dispersed structure; and (c) Honeycomb structure.

Single-grain structure: The particle shape is spheres, and mainly present in gravels and sand. The
loosest and densest packaging of this structure is shown in the figure. The void ratio for the loosest
state is 0.91, and that of the densest state is 0.35.

Flocculated soil structure: It is mainly found in clays and formed when there is a net attractive force
between different particles. The orientation of this type of structure is an edge to face as shown in the
figure. It has very high shear strength, low compressibility and high permeability.
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Dispersed structure: It occurs in remoulded clays. The orientation in this type of structure is face to face
as shown in the figure. The shear strength and permeability are very low but have high compressibility
strength. This formation of this type of structure occurs when there is net repulsive force.

Honey – comb structure: This type of structure is present in fine sands or silts. When we use this
type of structure for construction, the structure collapses and large deformation takes place under
vibrations and shocks.

SOIL CLASSIFICATION:
Soils have been classified on the basis of methods based on Pedologists, geographers, geologists, and civil
engineers. Each classification differs from the other, depending on the purpose of utilization of soils.
Here the geological and the civil engineering classification of soils are described.

Geological Classification of Soils: Engineering geologists use their knowledge of geology for the
analysis of the parent rock materials and the effects of the soil forming process. According to the mode of
formation and the agencies involved, soils may be classified into two types: (1) Soil In-situ and (2) Drifted
Soil.

(1) Soil In-situ: This type is again subclassified into two groups namely, Residual soil and Cumulose
soil.
(A) Residual Soil: These soils are formed above the original parent rock material where they are
found. They show all the characteristic features of the original rock. Lateritic soil is the best
example of a residual soil.
(B) Cumulose Soil: This soil type is formed mostly due to the accumulation of organic matter, for
example – peat. These soils are formed in waterlogged conditions – lakes, estuaries, river
beds, deltaic regions, etc.,
(2) Drifted Soil: These soils are formed far away from the original parent rocks. They drift from the
place of origin to the site of deposition by means of various geological agents such as slopes of the
area, rivers, glaciers, wind, lake, marine and volcanic activities. Drifted soils are classified on the
basis of drifting agents and are grouped into the following types: (a) Colluvial soils (b) Alluvial
soil (c) Glacial soils (d) Aeolian soils (e) Lacustrine soil.
(a) Colluvial Soil: These soils are formed from the rock materials that accumulate at the base of
the steep mountains by the action of gravity. Thus, they are stony in nature. Very few
mountain plants can grow on it.
(b) Alluvial Soil: These soils are very fertile because they are formed by the action of rivers and
are confined to river basins. The Indo-Gangetic alluvium plains belong to this type.
(c) Glacial Soil: These soils are transported and deposited by glacial action. Rock fragments,
which are formed under the glacial action show angularity with striations. These soils are not
fertile.
(d) Aeolin Soil: These soils are formed due to the wind action. They consist mainly of silt and
clay. Some are fertile.
(e) Lacustrine Soil: These soils are formed at the bottom of the lake beds. Rivers and glaciers
bring the sediments and silts which get deposited in the lakes. When the lakes dry up,
lacustrine soils are formed.

Engineering Classification of Soils: The engineering classification of soils is based on their material and
mechanical properties. A civil engineer normally deals with soil as a building material. A number of
classifications have been proposed. Soils may be classified by the Wentworth Scale, the Attenberg, the
Casagrande or the Unified Soil Classification system. Soil investigation and classification are done to
evaluate the sol in terms of its bearing power. The Indian Standard was therefore published in 1958,
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which classified soils into three divisions: (a) coarse-grained soils (b) fine-grained soils (c) highly organic,
a common basis for soil classification.

Wentworth Attenberg Casagrande

Grade Size Grade Size Grade Size
Pebble sieve >2 mm Gravel >2 mm Gravel ‘G’ 7.6 cm No.4
0.48 cm
Sand, very 2-1 mm Sand Coarse 2-0.6 mm S and ‘S’ No.4-10 sieve
coarse coarse
Coarse 1-0.5 mm Medium 0.6-0.2 mm Medium No.10-40 sieve
Medium 0.5-0.25 mm Fine 0.2-0.06 mm Fine No.40-200 sieve
0.074 mm
Fine 0.25-0.125 mm Silt - Coarse 0.06-0.02 mm Silt ‘M’ >2 mm
Very fine 0.125-0.06 mm Medium 0.02-0.06 mm Clay ‘C’ <2 00
Silt 0.06-0.002 Fine 0.006-0.002 mm
Clay <0.002 mm Clay <0.002 mm

TYPES OF SOIL:
Based on scientific work, this classification of Soil Types in India is based on parameters such as time,
topography, source of origin, natural factors, climatic conditions and biological factors. It is widely accepted
throughout the world. There are a huge variety of types of soil in India. Some of the major soil types are mentioned
below:
1. Alluvial soil
2. Red soil
3. Black / Regur soil
4. Arid / Desert soil
5. Laterite soil
6. Saline and Alkaline Soil
7. Peaty and Marshy soil
8. Forest soil
9. Sub-mountain soil
10. Snowfields.

Alluvial Soil: Alluvial Soil in India is the most widespread soil in the Northern region of India. Deposition of
materials by sea and river is called alluvium, and the soil formed due to the alluvium deposition is called alluvial
soil. • The Alluvial soil comprises 40% of the total soil in the country. This type of soil is mainly found in the Indo-
Ganga and Brahmaputra plain, i.e. the whole northern plain and in some parts of the river basin in the south and
some plateau region.

Laterite Soil: Laterite is a clayey rock or soil formed under high temperature and high rainfall and with an
alternate dry and wet period. An interesting feature about Laterite soil is that it is called the monsoon soil as after
the rain lime and silica get washed away and the soil left behind is rich in iron oxide and aluminium with a small
percentage of manganese and titanium ultimately leads to the formation of Laterite soil. Minerals like potash and
iron oxide are abundant in the laterite soil, whereas the organic matter phosphate, calcium and nitrogen are highly
deficient in the soil. Laterites are two types: viz., primary and secondary. Primary laterites are found in the original
rock materials from which they are derived. These rocks are generally formed at the high elevated portions at
hillocks while secondary laterites are formed due to the sedimentary deposits. These rocks show no relation with
the original parental materials. This type of soil is unsuitable for agriculture due to the high content of acidity and
inability to retain moisture.

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Red Soil: Red soil is also known as yellow soil. These soils are red in colour due to the high concentration of Iron
Oxide. It covers about the total land area of 18% of the country. Red soils develop on granite and geneses rocks
under low rainfall conditions, i.e. due to weathering of the metamorphic rocks. The red soil is best for crops like
wheat, tobacco, oil seed, millets, and cotton. Red Soil is friable and medium fertile and found mainly in the
Western Ghats, some parts of Odisha, Chhattisgarh, Tamil Nadu, and South-eastern Karnataka. It is also found in
North-eastern and South-eastern Madhya Pradesh, Jharkhand and the Hills and Plateaus of North-east India.
During monsoon or when the red soil is in its hydrated form, then it appears in yellow colour. The soil is red due to
the excessive presence of iron in Metamorphic and crystalline rocks.

Black Soil: Black soil is also called black cotton soil as it is the best-suited soil for cotton crops. The regur or black
soils have developed extensively upon the Lava Plateaus of Maharashtra, Gujarat, Madhya Pradesh, and mainly
Malwa and are formed due to volcanic activities. Black cotton covers a total land area of 15% of the country. Black
soil can be found in the states of Andhra Pradesh, Tamil Nadu Maharashtra, Gujarat, Madhya Pradesh etc. As the
same name, the colour of the soil is black but varies from black to grey. • The black soil is rich in minerals like Iron
lime magnesium aluminium and potassium but it lacks phosphorus nitrogen and organic matter. Apart from cotton
other cash crops like pulses, castor, tobacco, sugarcane citrus fruits and linseed are cultivated in black soil.

Mountain Soil: As the name says mountain soil is the soil that is found in hilly areas. Also, the texture of the
mountain soil may vary from region to region. The characteristics of this type of soil are changed according to the
altitudes. The mountain soil is loamy and silty in the valleys and coarse-grained on the upper slopes. The soil found
in the lower valleys is highly fertile in nature and is also known as forest soil. In the snowy areas of the Himalayan
range, the soil is acidic in nature and has much lesser humus as compared to the plain areas.

Saline Soil: Saline soil is also called alkaline soil because it has a higher percentage of potassium magnesium and
sodium and therefore is very infertile in nature. The presence of excess salt in the soil is due to the poor drainage
and dry climate in the region. • Since the soil has a higher percentage of sodium in it therefore it lacks nitrogen and
calcium. Saline soil can be found in the Sundarban area of West Bengal, the Rann of Kutch Western Gujarat deltas
of the eastern coast. Saline soil can be used to grow leguminous crops.

Peaty and Marshy Soil: Marshy soil can be found in the reasons which receive rich rainfall. Since they are highly
moisturized in soil and are rich in water content the Marshy soil is very rich in humus and organic matter. Marshy
soils are dense in nature due to the presence of water and appear black in colour. This type of soil can be found in
the states of Bihar, Bengal, Tamil nadu, and Odisha. Crops like paddy rice cassava maze and fruits like Cranberries
and sweet potatoes are grown in the Marshy soil.

Desert Soil: Desert soil is found mainly in the state of Rajasthan and covers a total land of 4.42% of the country. In
the absence of sufficient wash by rainwater, soils have become saline and rather unfit for cultivation. In spite of that
cultivation can be carried on with the help of modern irrigation. The colour of desert soil may vary from brown to
Red and vice-versa. Desert soil is saline in nature because the salt content in the soil is very high in it. Desert soil
is rich in phosphate but lacks nitrogen. The kankar layers are created which is caused of the presence of higher
calcium concentration in the soil which lowers the soil horizons. This kankar layer prevents the water from
penetrating deep. So when water is supplied by irrigation methods, the moisture of the soil is available for long-
term plant development.

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 Black cotton soil v/s Lateritic soil
Following are the points of difference between Black Soil and Laterite Soil:

Black Soil (Regur Soil) Laterite Soil

Regur Soil is the local name given to the Black The soil which has come into existence because of
Soil, Cotton has grown abundantly in it. So it is the leaching processes in the heavy rainfall areas of
also called Cotton Soil. This soil has come into tropical India is called Laterite Soil.
existence by the solidification of lava spread over
large areas during volcanic activities.
The soil is very fertile and there is no need for It is less fertile. Only grass grows in it abundantly.
manuring.
During the dry season, it develops cracks and This soil neither develops cracks in the dry season
during rains it becomes sticky. nor is sticky during the wet season.
It is clayey and there are no visible crystals in it. It is heavily crystalline.
It is capable of maintaining moisture for long It lacks moisture.
periods.
Soil nutrients are found in abundance. Calcium It lacks lime, phosphorous and nitrogen. Soda and
carbonate, magnesium carbonate and iron contents Potash are not, at all, found in it.
are found in it in large quantities.
Deccan trap is known for Regur Soil. Maharashtra, The Eastern parts of Peninsular India abound in
Gujarat and M.P. dominate in this soil. Laterite Soil. It is found in patches. Some regions
of Meghalaya also have Laterite Soil.

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 Effects of weathering on monumental rocks
Various physicochemical factors contribute to the degradation of the monument. The degradation manifests
itself into various forms which can be broadly classified into: 1. Structural deterioration. 2. Deterioration of execute
fine carvings.

Structural Deterioration: Structural deterioration deals with damage of the structure as a whole. It is generally
caused due to factors like disturbances or instability in the main foundation of the structure and growth of plants on
the monuments. Disturbance or Instability in the foundation is generally caused by the subsidence and unequal
settlement of the structure due to loose soils and natural calamities like earthquakes, floods etc. Growth of plants in
the joints of the structure should be attended to as the growing plant expands its size thus widening the joints
consequently developing cracks in the structure.

Deterioration of execute fine carvings: Deterioration of execute fine carvings is a weathering phenomenon and
hence be further classified into physical weathering and chemical weathering.

Physical weathering: is caused by parameters such as water, temperature variations, salt laden winds etc.

Water: It acts as a good solvent and transporting agent. Capillary rise of salt solutions from ground into the stone
surface gives rise to crystallization of the salts within the stone pore. The increase in volume of the crystallized salt
builds up stress and thus ruptures the rock. Contact of the stone surface leads to loss of stone minerals leaving the
stone surface more porous and rough. At sub-zero temperatures, the water within the pores can freeze and expand to
about 9% thus leading to rupturing of the stone.

Air: Strong winds laden with sand particles have an abrasive action on the monumental stone surface. It also acts as
a transporting agent for the dust, micro flora, pollen micro soot etc.

Temperature: It is an ever existing factor accompanying almost all processes and bearing on several properties. A
rock is a poor conductor of heat and hence the differential thermal expansion between the surface and the crust
leads to exfoliation and micro cracks.

Chemical Weathering: occurs because rocks and minerals are seldom in equilibrium with near surface
environment. The general reaction Primary minerals + Attacking solution → Secondary minerals+Leaching
solution The nature of the secondary mineral formed and the type of geochemical process involved depends on
(1) The nature of the mineral subject to weathering
(2) The nature of the attacking agent

Depending on the nature of the attacking agents the reactions have been classified as Hydrolysis, Acidolysis,
Alkynolysis, and Oxidation etc. The attacking agents which are mainly the acidic gasses could be either natural or
anthropogenic. Carbon dioxide finds its origin both from the nature as well as through man-made sources. Other
highly acidic gasses such as NOx and SO2 and alkaline agents like NH3 are mostly anthropogenic in nature. The
nature of weathering taking place on the stone monument and the attacking agent can be identified using various
analytical methods, which include both classical as well as instrumental techniques, can be used to identify the
agents responsible for the damage caused. The subsequent step is the conservation of the monument, which
involves cleaning and preservation.

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 Soil Classification by Grain Size:

COARSE GRAINED SOILS: Relative proportions of the different grain sizes have significant
influence on the engineering behaviour of a coarse grained soil. Other major factors that influence the
geotechnical characteristics of a coarse grained soil are the density of packing of the soil grains and the
shape of the soil grains. The grain size distribution of a coarse grained soil is generally determined
through sieve analysis, where the soil sample is passed through a stack of sieves and the percentages
passing different sizes of sieves are noted.

FINE GRAINED SOILS: While the gravels, sands and silts are equi-dimensional (same order of
magnitude in all three directions), clay particles are like plates or needles. Their surfaces are electrically
charged due to a charge imbalance between the cations and anions within the atomic structure. The
microstructure or microfabric of the clay depends on the mineralogy of the clay and the valence,
concentration and the type of the cations present in the pore water.
Atterberg Limits: The consistency (degree of firmness. i.e., soft, firm, stiff) of a fine grained soil varies
significantly with the water content. As the water content of a fine grained soil is increased gradually from
0%, it goes through different consistencies, namely, brittle solid, semi-solid, plastic and liquid states.
Atterberg limits are the border line water contents between two such states. They were developed in early
1900’s by a Swedish soil scientist A. Atterberg, working in ceramics industry. Later, K.Terzaghi (in late
1920’s) and A. Casagrande (early 1930’s) modified them to suit geotechnical works.

Size of soil components (IS 460 – 1962):

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 MODULE-3: Earth Surface process and Resources

Weathering, type, causes, soil in-situ, drifted soil, soil profile, soil mineralogy, structure,
types of soil, Black cotton soil v/s Lateritic soil; effects of weathering on monumental
rocks. Soil Horizon, Soil Classification by Grain Size .

QUESTION BANK:
1) What is meant by weathering of rocks? Describe in detail the factors and types of
rock weathering. Discuss the weathering pattern of rocks in civil engineering.
2) Describe in detail the physical, chemical and biological weathering of rocks. Add
a detailed note on weathering products and its role in civil engineering.
3) Write notes on the following:
1) Thermal weathering b) Mechanical weathering c) Chemical weathering
4) What is meant by biological weathering of rocks?
5) Describe the drainage pattern and the parameters of drainage and its development.
6) What is Soil? Explain the Soil Profile and their formation.
7) Explain the Geological Classification of soil.
8) Explain the Engineering Classification of soil.
9) Add a note on soil mineralogy and soil structure
10) List the types of soil and explain in brief.
11) Differentiate the Black cotton soil v/s Lateritic soil
12) How do you understand the effects of weathering on monumental rocks.
13) Explain the Soil Classification by Grain Size.

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