Chapter - 4Chapter - 4

Flow Of Water Flow Of Water Through SoilThrough Soil

Er Raju Sharma (Lecturer) Er Raju Sharma (Lecturer)

Department - civil engineeringDepartment - civil engineering

(yamuna polytechnic for engineering(yamuna polytechnic for engineering))

YamunanagarYamunanagar

Permeability and its conceptPermeability and its concept

The property of soil which permit the The property of soil which permit the flow of water through it is called the flow of water through it is called the permeabilitypermeability

In other words, permeability is the In other words, permeability is the ease with which water flow through ease with which water flow through the soilthe soil

A soil is called pervious, when water can A soil is called pervious, when water can flow through it easilyflow through it easily

A soil is called impervious when water A soil is called impervious when water cannot flow through it easilycannot flow through it easily

The permeability of one The permeability of one soil varies from the other because the soil varies from the other because the size , cross section and orientation of the size , cross section and orientation of the interstices is different in different soil interstices is different in different soil

Gravels are highly permeable while Gravels are highly permeable while stiff clay is the least permeable and stiff clay is the least permeable and hence such a clay may be termed as hence such a clay may be termed as impermeable soil. it is because a impermeable soil. it is because a completely impervious soil do not completely impervious soil do not exist in nature ,so a soil is termed as exist in nature ,so a soil is termed as impervious when the permeablity is impervious when the permeablity is extremely lowextremely low

Importance of permeablityImportance of permeablity

Permeablity is a very important Permeablity is a very important engineering property of soils. The engineering property of soils. The knowledge of permeablity is knowledge of permeablity is essential for solving different essential for solving different engineering problems few of which engineering problems few of which enlisted below.enlisted below.

To calculate the rate of settlement of To calculate the rate of settlement of building and other structurebuilding and other structure

To determine yield of wellTo determine yield of well

To analyses seepage through dams and To analyses seepage through dams and leveeslevees

To design the filter required to prevent soil To design the filter required to prevent soil piping in hydraulic structurepiping in hydraulic structure

To study losses from irrigation canalTo study losses from irrigation canal

To solve the problems of water To solve the problems of water logging in certain areas by logging in certain areas by constructing suitable under drains for constructing suitable under drains for lowering the water table.lowering the water table.

To study stability of slopes and To study stability of slopes and drainage of soildrainage of soil

Factor affecting permeablityFactor affecting permeablity The following factor affect the The following factor affect the

permeablity of soilpermeablity of soil

1.Void ratio1.Void ratio2.Partical size2.Partical size3.Structure and stratification of soil3.Structure and stratification of soil4.Shape of practical4.Shape of practical5.Temprature5.Temprature6.Degree of saturation6.Degree of saturation

1. 1. Void Ratio:Void Ratio: Greater the void ratio, Greater the void ratio, higher is the value of coefficient of higher is the value of coefficient of permeability. approximately k ~ e².permeability. approximately k ~ e².

The plot between e The plot between e and k is a straight line. however it may be and k is a straight line. however it may be noted that the clay which have largest noted that the clay which have largest void ratio are almost impervious. This is void ratio are almost impervious. This is due to the fact that individual void holes in due to the fact that individual void holes in clays are extremely small through which clays are extremely small through which water cannot pass easilywater cannot pass easily

Particle SizeParticle Size:-Particle size for fine :-Particle size for fine grained soils ,the structural grained soils ,the structural arrangement of soil mass affects the arrangement of soil mass affects the coefficient of permeability. for the coefficient of permeability. for the same void ratio, the permeability of same void ratio, the permeability of soil is more in case of flocculated soil is more in case of flocculated structure as compare to that of structure as compare to that of dispersed structuredispersed structure

Shape of particleShape of particle: The permeability of a : The permeability of a coarse grained soil also depend upon the coarse grained soil also depend upon the shape of the particle. The angular particle shape of the particle. The angular particle are less permeable as compare to rounded are less permeable as compare to rounded particleparticle

TemperatureTemperature: The coefficient of : The coefficient of permeability increases with increase in permeability increases with increase in temperature due to reduction in viscositytemperature due to reduction in viscosity

Degree of saturationDegree of saturation: The coefficient of : The coefficient of permeability of a fully saturated soil is permeability of a fully saturated soil is more as compare to partially saturated soilmore as compare to partially saturated soil

Water impuritiesWater impurities: Presences of any foreign : Presences of any foreign matter in water reduces the permeability matter in water reduces the permeability of soil as it has a tendency to plug the of soil as it has a tendency to plug the flow of water passageflow of water passage

Comparison of permeability of different Comparison of permeability of different soils as per BISsoils as per BIS

s. nos. no Permeability in cm/secPermeability in cm/sec Soil classificationSoil classification

11 Less than .0001Less than .0001 imperviousimpervious

22 Greater then .0001and Greater then .0001and less than.10less than.10

Semi imperviousSemi impervious

33 Greater than 0.10Greater than 0.10 perviouspervious

Hydraulic gradient:Hydraulic gradient: It is defined as It is defined as the loss of head (h) per unit length of the loss of head (h) per unit length of flow of water through the soil. it is flow of water through the soil. it is denoted by i.denoted by i.

Darcy lawDarcy law: for a laminar flow in : for a laminar flow in soils, the velocity of flow (v) is soils, the velocity of flow (v) is proportional to its hydraulic gradient. proportional to its hydraulic gradient. (I)(I)

Darcy LawDarcy Law

v~iv~i

v=k.iv=k.i

where k is a constant, known as where k is a constant, known as coefficient of permeabilitycoefficient of permeability

The equation v=ki is known as Darcy's The equation v=ki is known as Darcy's equationequation

coefficient of permeabilitycoefficient of permeability v =ki v =ki i =v/ki =v/kIf i =1 If i =1 thenthen k=v k=vSo coefficient of permeability k is defined as the average So coefficient of permeability k is defined as the average

velocity of flow through the total cross sectional area of soil velocity of flow through the total cross sectional area of soil under unit hydraulic gradientunder unit hydraulic gradient

Units of k is same as velocity unit m/sUnits of k is same as velocity unit m/s

Er Raju Sharma (Lecturer) Er Raju Sharma (Lecturer) Department - civil Department - civil

engineering engineering (yamuna polytechnic for (yamuna polytechnic for

engineeringengineering)) YamunanagarYamunanagar