assignment for water influence different behaviours of soil

1. WATER INFLUENCES DIFFERENT BEHAVIOURS
OF SOIL
(Assignment submitted for partial fulfillment of course CE501, CIVIL ENGINEERING….ENGINEERING
BEHAVIOUR OF SOIL MECHANICS)
SUBMITTED BY INDRANIL BANERJEE
ENROLLMENT NO-CEM18005
DEPARTMENT OF CIVIL ENGINEERING
TEZPUR UNIVERSITY
1ST
SEMISTER, AUTUMN 2018

2. INTRODUCTION
In soils, water is a major driver of biogeochemical processes. Chemical reactions that control
soil formation and weathering reactions occur almost exclusively in liquid water. water is the
diffusive medium that mediates the movement of gases, solutes, and particles in soils. Water
regulates the transfer of heat, thereby helping buffer soil temperature. Biologically, microbes
require water in soil pores to metabolically function. Additionally, the availability of water is
considered to be one of the most important factors for the growth of crops and other plants in
this article, we explore how the molecular structure, chemical properties and physical properties
of water control the functioning of soils.
MOLECULAR STRUCTUREOF WATER

3. The molecular properties of water result in many of its unique and familiar qualities. Individually,
water molecules consist of two hydrogen atoms attached by covalent bonds to
a tetrahedral oxygen atom, resulting in a bent molecule with a 104º angle between hydrogen
atoms. The molecule has a permanent dipole moment, with a positive charge (δ+
) residing on
the hydrogen atoms and a negative charge (δ-
) on the oxygen atom.
Water has many physical and chemical properties that result from its molecular structure. The
polar nature of the molecule helps to explain its high dielectric constant and its ionic
dissociation, which result in its ability to separate the charges on ions and dissolve polar
solids. The cohesive nature that stems from “water molecules” intermolecular attraction results
in abnormally high surface tension, heat capacity, heat of vaporization, and boiling point.
The ordering of water molecules upon freezing results in a high heat of fusion and reduction
of density for the solid phase.these properties are critical to understanding the chemistry and
physics of water in soils.
Property Molecular Rationale Significance
High dielectric
constant
Dipole moment allow s w ater to stabilize solutes
w ithboth positive and negative charges
Excellent solvent for polar and charged species
Ionic dissociation
Water readily splits into protons and hydroxide ions
due to the polarity of the molecule
Acid-base chemistry of aqueous solutions is
facilitated by this property
Expansion upon
freezing
Ordering molecules in crystalline solid results in more
void space than in the liquid phase
Ice floats; freezing occurs at the top of a w ater
body
High boiling point
Adhesion of molecules hinders transformation to gas
phase
Water is a liquid at common temperatures
High heat capacity
Strong interactions betw een molecules require a large
energetic input to change temperature
Temperature is buffered against small changes
in thermal energy
High heat of
vaporization
Adhesion of molecules requires a large thermal input
to cause transformation to gas phase
Temperature is additionally buffered at
environmentally extreme temperatures
High heat of
fusion
Ordering of molecules upon freezing results in
significant release of thermal energy
Temperature is additionally buffered at
environmentally extreme temperatures
High surface
tension
Molecules have cooperative interactions that cause
cohesion at interfaces
Causes formation of drops and capillary
behavior
Important properties of w ater and their relationship to its molecular structure.
BEHAVIOUR OF SOILS IN THE PRESENCE OF
WATER

6. CHEMICAL PROPERTIES OF WATER AND
BEHAVIOR IN SOILS
The chemical properties of water behavior in the environment and control many
processes occurring in soils as the aqueous phase interacts with organisms, mineral
surfaces, and air spaces. As a result of its nonlinear structure and dipole moment water
has a high dielectric constant. which is a measure of a substance's ability to minimize
the force of attraction between oppositely charged species. Water's dielectric constant,
which is significantly higher than that of the solid and gaseous components of soil
(dielectric constants of ~2-5 and 1, respectively), is often utilized in electromagnetic
measurement approaches to determine soil water content. This unique property of
water also makes it a powerful solvent, allowing it to readily dissolve ionic solids. Water
acts to dissipate the attractive force of ions by forming solvation spheres around them.
The polar nature of the water molecules allow them to surround and stabilize the
charges of both anions and cations, preventing their association.
Consider the dissolution of potassium chloride (KCl), a common potassium source in
chemical fertilizers. When combined with water, the ionic solid dissolves:
KCl(s) + (m+n)H2O(l) ↔ [K(H2O)m]+(aq) + [Cl(H2O)n]-(aq)
where m and n represent the numbers of water molecules within each solvation sphere
— numbers that are functions of the charge, size, concentration, and chemical
properties of the ions in solution. Although KCl is quite soluble and readily dissolves, the
extent to which other soil minerals dissolve or precipitate is variable, depending on the
specific mineral properties and the soil solution chemistry. Water's ability to enhance
dissolution or prevent precipitation impacts a range of processes and properties in soils,
including mineral weathering, soil salinity, and soil fertility.

7. Another particularly important chemical property of water that impacts processes
occurring within the soil solution is that it is amphoteric, meaning that it can act as
either an acid or a base (IUPAC 1997). Due to its polarity, water readily
undergoes ionic dissociation into protons and hydroxide ions:
H2O(l) ↔ H+(aq) + OH-(aq) (1)
Accordingly, when it reacts with a strong base, water acts as an acid, releasing protons:
H2O(l) + NH3 ↔ NH4+(aq) + OH-(aq) (2)
When it reacts with a strong acid, water acts as a base, accepting protons:
H2O(l) + HCl ↔ H3O+(aq) + Cl-(aq) (3)
The amphoteric behavior of water facilitates the acid-base chemistry and dictates the
potential pH range of aqueous solutions, thereby imparting soil pH — a "master
variable" of soils that influences soil formation, plant growth, and environmental quality.
The ability of water to stabilize charged species in solution allows it to support the flow
of electrons in soils. As such, water helps mediate oxidation and reduction reactions
within the soil solution. Water itself may participate in these processes, and it is a
product of cellular respiration in soils. In aerobic soils, water is produced from the
oxidation of carbon in organic matter (here notated as CH2O) for energy production by
microorganisms:
CH2O(s) + O2(g) → CO2(g) + H2O(l) (4)
In the above reaction, the transfer of electrons reduces the oxidation state of oxygen in
O2 (0) to that of water (-2). Particularly in anaerobic soils, carbon oxidation may also be
coupled to reduction of chemical species other than O2. The specific respiration
processes in soils are governed by thermodynamics and reaction kinetics but occur
within the soil solution or at the mineral-solution interface. These are important
processes that govern microbial community structure, soil mineralogy, soil solution
chemistry , and pollutant fate and transport.
Consider the dissolution of potassium chloride (KCl), a common potassium source in
chemical fertilizers. When combined with water, the ionic solid dissolves:

8. KCl(s) + (m+n)H2O(l) ↔ [K(H2O)m]+(aq) + [Cl(H2O)n]-(aq)
where m and n represent the numbers of water molecules within each solvation sphere
— numbers that are functions of the charge, size, concentration, and chemical
properties of the ions in solution. Although KCl is quite soluble and readily dissolves, the
extent to which other soil minerals dissolve or precipitate is variable, depending on the
specific mineral properties and the soil solution chemistry. Water's ability to enhance
dissolution or prevent precipitation impacts a range of processes and properties in soils,
including mineral weathering, soil salinity, and soil fertility.
Another particularly important chemical property of water that impacts processes
occurring within the soil solution is that it is amphoteric, meaning that it can act as
either an acid or a base (IUPAC 1997). Due to its polarity, water readily
undergoes ionic dissociation into protons and hydroxide ions:
H2O(l) ↔ H+(aq) + OH-(aq) (1)
Accordingly, when it reacts with a strong base, water acts as an acid, releasing protons:
H2O(l) + NH3 ↔ NH4+(aq) + OH-(aq) (2)
When it reacts with a strong acid, water acts as a base, accepting protons:
H2O(l) + HCl ↔ H3O+(aq) + Cl-(aq) (3)
The amphoteric behavior of water facilitates the acid-base chemistry and dictates the
potential pH range of aqueous solutions, thereby imparting soil pH — a "master
variable" of soils that influences soil formation, plant growth, and environmental quality.
The ability of water to stabilize charged species in solution allows it to support the flow
of electrons in soils. As such, water helps mediate oxidation and reduction reactions
within the soil solution. Water itself may participate in these processes, and it is a
product of cellular respiration in soils. In aerobic soils, water is produced from the
oxidation of carbon in organic matter (here notated as CH2O) for energy production by
microorganisms:
CH2O(s) + O2(g) → CO2(g) + H2O(l) (4)
In the above reaction, the transfer of electrons reduces the oxidation state of oxygen in
O2 (0) to that of water (-2). Particularly in anaerobic soils, carbon oxidation may also be
coupled to reduction of chemical species other than O2. The specific respiration
processes in soils are governed by thermodynamics and reaction kinetics but occur
within the soil solution or at the mineral-solution interface.
PHYSICAL PROPERTIES OF WATER AND
BEHAVIOR IN SOILS
Liquid water is a component of the three-phase (solid, liquid, gas) soil system, possibly
occupying 50% or more of the total soil volume under saturated conditions. Even under
relatively dry conditions, water held at large tensions within soil pores occupies
approximately 5–10% of the soil volume. Liquid water is held in soil under tension
arising from the adhesive and cohesive forces associated with water's molecular
structure. The capacity of water to be held in soil pores via cohesion and adhesion
partially controls water storage and redistribution in the hydrologic cycle.

9. The interaction between water and the soil solid matrix is often visualized with a
capillary tube model. Liquid water at the water-gas interface exhibits a meniscus. The
inward pull of liquid water molecules from hydrogen bonding (cohesion) is unbalanced
at the liquid-gas interface, which is referred to as surface tension.

10. In combination with the polar attraction of water molecules for a wet table soil solid
matrix (adhesion to the capillary tube wall), this cohesion creates concave curvature.
Water rises in the tube to reach equilibrium between the attractive upward force at the
interface and the weight of water pulling downward on the meniscus.
CAPILLARY RISE:
The capillary action or tension, which holds water in the soil, is most important to plant growth.
Smaller pores hold water with more tension (negative pressure) than larger pores. As soil dries,
the tension of the remaining water increases.
In the same way that water moves upwards through a tube against the force of gravity; water
moves upwards through soil pores, or the spaces between soilparticles. The height to which
the water rises is dependent upon pore size. As a result, the smaller the soil pores, the higher
the capillary rise

11. CONSOLIDATION
When a soil layer is subjected to vertical stress, volume change can take place through
rearrangement of soil grains, and some amount of grain fracture may also take place. The volume of
soil grains remains constant, so change in total volume is due to change in volume of water. In
saturated soils, this can happen only if water is pushed out of the voids. The movement of water
takes time and is controlled by the permeability of the soil and the locations of free draining
boundary surfaces.
It is necessary to determine both the magnitude of volume change (or the settlement) and the time
required for the volume change to occur. The magnitude of settlement is dependent on the
magnitude of applied stress, thickness of the soil layer, and the compressibility of the soil.
When soil is loaded undrained, the pore pressure increases. As the excess pore pressure dissipates
and water leaves the soil, settlement takes place. This process takes time, and the rate of settlement
decreases over time. In coarse soils (sands and gravels), volume change occurs immediately as
pore pressures are dissipated rapidly due to high permeability. In fine soils (silts and clays), slow
seepage occurs due to low permeability.
DILATANCY
Dilatancy is the volume change observed in granular materials when they are subjected to
shear deformations. ... A sample of a material is called dilative if its volume increases with
increasing shear and contractive if the volume decreases with increasing shear. Dilatancy is a
common feature of the soils and sands.
The amount of dilation depends strongly on the density of the soil. In general, the
denser the soil the greater the amount of volume expansion under shear.

12. In the time of dilatancy negative pore water pressure developed which causes the
increases of effective stress.
When the effective stress increases shear strength of soil also increases.
FLUCTUATIONS IN GROUNDWATER LEVEL
If the water level is below ground level and if water level decreases the
effective stress increases. If the unit wt of water is γw and the height
decreases is h then effective stress will increases by hγw. With the increases of
effective stress the shear strength of soil also increases.

13. COMPACTION
Compaction is the application of mechanical energy to a soil so as to rearrange its particles and
reduce the void ratio.
It is applied to improve the properties of an existing soil or in the process of placing fill such as in the
construction of embankments, road bases, runways, earth dams, and reinforced earth walls.
Compaction is also used to prepare a level surface during construction of buildings. There is usually
no change in the water content and in the size of the individual soil particles.
The objectives of compaction are:
 To increase soil shear strength and therefore its bearing capacity.
 To reduce subsequent settlement under working loads.
 To reduce soil permeability making it more difficult for water to flow through.
SWELLING
A soil will react very differently depending on the amount of water it has absorbed. One can
differentiate between four broad hydrous states: dry, moist, plastic and liquid. Each hydrous state
has a corresponding application. These will be dependent on a number of factors linked not only
to the nature of the soil and the building system used, but also to the broader context (whether
the region is arid or not, traditions, skills, etc.).

14. BULKING OF SAND
Bulking of sand refers to the volume expansion of fine aggregates (sand)
for consuming of moisture. Whenever dry sand interacts with moisture a thin
film is conformed around the sand particles that forces them to get aside from
each other. These outcomes in expanding the volume of sand.
Bulking increases gradually with moisture content and the increase in
volume may reach ~35% by volume at 5% – 6% moisture content by
weight. It then decreases down to zero, when the quantity of water
becomes more than ~25% (as if they are fully compacted.
The Bulking increases with fineness of sand, because of large surface area
contributed by fine particles for the same volume contribution.

15. REFFERENCE :
1) https://www.ctahr.hawaii.edu/mauisoil/a_comp03.aspx
2) https://nptel.ac.in/courses/105103097/37
3) https://www.google.co.in/search?safe=active&rlz=1C1CHBF_enIN822IN822&biw=1366&bih=60
8&ei=9SIIXIXDJ8K5rQGzmIe4CQ&q=SWELLING+IN+SOIL&oq=SWELLING+IN+SOIL&gs_l=psy-
ab.12...0.0..200138...0.0..0.0.0.......0......gws-wiz.uflrSxtxuq0
4) https://www.google.co.in/search?safe=active&rlz=1C1CHBF_enIN822IN822&biw=1366&bih=60
8&ei=Yx8IXLO1B4vFvQT-
3oHACA&q=fluctuation+of+groundwater+table+IN+SOIL&oq=fluctuation+of+groundwater+table
+IN+SOIL&gs_l=psy-ab.3..33i160.17091.21616..23040...0.0..0.238.1324.0j7j1......0....1..gws-
wiz.......0i71j0i22i30j33i22i29i30.K2aixOY0p9Y
5) https://www.google.co.in/search?safe=active&rlz=1C1CHBF_enIN822IN822&q=what+is+dilatan
cy+of+soil&sa=X&ved=2ahUKEwimlYzWrInfAhUIinAKHT5lD5MQ1QIoAHoECAQQAQ&biw=1366&
bih=608
6) http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0hdl--00-0----0-10-0---0---0direct-10---4-------
0-1l--11-en-50---20-about---00-0-1-00-0--4----0-0-11-10-0utfZz-8-
00&cl=CL1.3&d=HASH01cf0835ed104fa479c5cc9b.4.4&gt=1