Classification of Surveying

Primary Divisions in Surveying

1) Plane Surveying

It is the type of surveying where the mean surface of the earth is considered as a plane. In such surveying a line joining any two stations is considered to be straight. The triangle formed by any three points is considered as a plane triangle and the angles of the triangle are considered as plain angles. For small areas less than 250 km2 plane surveying can safely be used. For most engineering projects such as canal, railway, highway, building, pipeline, constructions, etc. this type of surveying is used. It is worth noting that the difference between an arc distance of 18.5 km and the subtended chord lying in the earth’s surface is 7mm. Also, the sum of the angles of a plane triangle and the sum of the angles in a spherical triangle differ by 1 second for a triangle on the earth’s surface having an area of 196 km2.

2) Geodetic Surveying

The geodetic Surveying is that type of surveying in which the curvature of the earth is taken into account. It is generally extended over larger areas (Example: a state or country). The line joining any two stations is considered as curved line. The triangle formed by any three points is considered to be spherical and the angles of the triangle are considered to be spherical angles. Geodetic surveying is conducted by the Survey of India Department and is carried out for a larger area exceeding 250 km2. Geodetic surveying is concerned with determining the size and shape of the earth and it also provides a high-accuracy framework for the control of lower order surveys. The highest standards of accuracy are necessary.

Difference between Plain Surveying and Geodetic Surveying

Plain Surveying	Geodetic Surveying
The earth surface is considered as    plain surface.	The earth surface is considered as      curved surface.
The curvature of the earth is ignored.	The curvature of earth is taken into account.
Line joining any two stations is considered to be straight.	The line joining any two stations is considered as curved.
The triangle formed by any three points is considered as plain.	The triangle formed by any three points is considered as spherical.
The angles of triangle are considered as plain angles.	The angles of the triangle are considered as spherical angles.
Carried out for a small area < 250 km2	Carried out for a small area > 250 km2
Survey accuracy is low	Survey accuracy is high
Plane surveying uses normal instruments like chain, measuring tape,  theodolite etc.	Geodetic surveying uses more precise instruments and modern technology like GPS.

Surveying is classified based on various criteria including the instruments used, purpose, the area surveyed and the method used.

I) Classification based on the surface and the area to be surveyed

1) Land Survey 

Land surveys are done for objects on the surface of the earth. Land surveying is the art of establishing or re-establishing corners, lines, boundaries and monuments of property/land based upon recorded documents, historical evidence and present standards of practice. It helps in preparation of topographical maps, planning and estimation of project works, locating boundary lines, etc.

2) Marine or Hydrographic Survey (Hydro-Survey)

Marine or hydrographic survey deals with bodies of water for purpose of navigation, tidal monitoring, water supply, harbour works or for determination of mean sea level. The work consists in measurement of discharge of streams, making topographic survey of shores and banks, taking and locating soundings to determine the depth of water and observing the fluctuations of the ocean tide.

3) Astronomical Survey

Astronomical survey uses the observations of the heavenly bodies (sun, moon, stars etc) to fix the absolute locations of places on the surface of the earth. It also determines the azimuth, latitude, longitude and time.

Land survey is classified into the following.

a) Topographic survey

This survey is for depicting the natural features like hills, valleys, mountains, rivers etc and manmade features like roads, houses, settlements, etc on the surface of the earth. These are surveys where the physical features on the earth are measured and maps/plans prepared to show their relative positions both horizontally and vertically.

b) Cadastral Survey

It is used to determining property boundaries including those of fields, houses, plots of land, etc. These are surveys undertaken to define and record the boundary of properties, legislative area and even countries. It may be almost entirely topographical where features define boundaries with the topographical details appearing on ordinary survey maps.

c) Engineering Survey

It is used to acquire the required data for the planning, design and execution of engineering projects like roads, bridges, canals, dams, railways, buildings, etc. These are surveys undertaken to provide special information for construction of civil engineering and building projects. This

survey supply details for a particular engineering schemes and could include setting out of the work on the ground and dimensional control on such schemes.

d) City Survey

The surveys involve the construction and development of towns including roads, drainage, water supply, sewage, street network, etc.

II) Classification on the basis of purpose

1) Engineering survey

This type of surveying helps to analyze the field data for engineering works such as the construction of roads, railways, sewage pipelines etc.

2) Military survey

This type of surveying helps the military services like the army, navy etc to determine the location of strategic importance. Through this surveying, it can provide maps of broader areas. Since it uses advanced technologies like remote sensing, GIS and GPS, the precise field details are obtained.

3) Mine surveying

In the mine surveying method, underground and surface surveying is done. Mine surveying is done for fixing the positions and directions of the underground structures.

4) Geological survey

Geological survey helps in the study of earth composition. It helps to determine the arrangement of different strata on the earth. Geological surveying is very important for projects like dams and bridges etc.

5) Archaeological survey

Archeological survey is carried out to discover and map ancient/relies of antiquity.

6) Control survey

Control survey uses geodetic methods to establish widely spaced vertical and horizontal control points.

III) Classification Based on Instruments Used

1) Chain surveying

Generally linear measurements are taken with a chain and tape. But in chain surveying, no angular measurements are taken. The main instrument in chain surveying is a metallic chain. The principle of chain surveying is triangulation. Chain surveying is suitable for small areas with level grounds. It is a relatively simple and inexpensive method that is often used for small-scale surveys and for preliminary surveys for larger projects. Chain surveying is not suitable for areas with sloped ground or highly undulated areas. It is also known as “tape surveying.” The chain surveying uses instruments such as chains, arrows, pegs, ranging rods, etc.

2) Compass surveying

In compass surveying both the linear and angular measurements are taken. Horizontal angles are measured with a compass (prismatic or surveyors compass) and linear measurements are taken with tape or a chain. Compass surveying is suitable for small areas with level ground. The compass surveying is not suitable for areas with high magnetic influence. It is often used in conjunction with chain surveying or tape surveying.

Compass surveying is mostly used in the early stages of a survey project, for reconnaissance and layout of the different survey lines. It is a relatively simple and inexpensive method, but it does have a few limitations, such as being affected by local magnetic attraction and thus so not providing accurate measurements over long distances. It is also known as “directional surveying” or “bearing surveying.”

3) Theodolite surveying

The theodolite survey is generally used in triangulation and traversing. It is one of the precise methods of surveying. Theodolite is called a universal instrument in surveying because of its various capabilities. The theodolite can be used for measuring horizontal angles, vertical angles, deflection angles, magnetic bearings, horizontal distance between two points, vertical height of an object, ranging a line, difference of elevation between various points etc.

4) Plane table surveying

It is a method of land surveying that uses a flat board, called a plane table, to prepare a map of an area by plotting the points directly on that board. Fieldwork and plotting are done simultaneously in this method. This method is the most rapid method of surveying. The principle of the plane table survey is parallelism. In this method, there is no possibility of overlooking any object or measurement as the plotting is done in the field. This method of surveying does not provide the most accurate results. Mostly preferable in magnetic areas where compass surveying is not possible. Also, we can check errors and mistakes using check lines. The instruments for plane table surveying are plane table, alidade, plumbing fork, plumb bob, spirit level, compass, etc.

5) Levelling

In Levelling the relative vertical height and vertical distance of different points are measured. The relative position of different points is also calculated in leveling. The auto-level and graduated staff are the main instruments in leveling.

6) Tacheometric surveying

A tachometer is a transit theodolite fitted with a stadia diaphragm and anallactic lens. In this type of surveying the horizontal distance and vertical distances are obtained by taking only angular measurements. The chaining is completely eliminated in tacheometric surveying. This method is adopted for areas with highly undulated areas.

7) Photographic surveying

In this type of surveying aerial photographs are taken by aerial methods, then they are plotted in the office.

8) Electromagnetic Distance Measurement (EDM) surveying

Distance measured using the propagation, reflection and reception of radio or light waves.

9) Total-station surveying

Total station combines EDMs and electronic data collectors, reads and records horizontal and vertical angles, along with slope distances.

10) Satellite-based surveying

Remote sensing and Global Positioning System (GPS) are used to detect and take measurements.

IV) Classification based on the method used

1) Triangulation Survey

In the triangulation method of surveying method the entire surveying area is initially divided into a network of triangles. Lines are first run round the perimeter of the plot, then the details fixed in relation to the established lines. This process is called triangulation. The triangle is preferred as it is the only shape that can completely over an irregularly shaped area with minimum space left. There are two types of triangles in surveying.

a) Well-conditioned triangle

Triangle having all the angles is more than 30 degrees and less than 120 degrees.

b) Ill-conditioned triangle

If any of the angles is less than 30 degrees or greater than 120 degrees, the triangle is called an ill-conditioned triangle.

In triangulation surveying, the well-condition triangles are preferred.

2) Traverse survey

Traverse surveying is a type of surveying in which we connect the survey lines to form a framework. The length can be measured either using the directly or indirectly method. So for the direct method of measurement, we use tapes and for the indirect method, we use Electronic Distance measurement. In traverse surveying, if the bearing and distance of a place of a known point is known, it is possible to establish the position of that point on the ground. From this point, the bearing and distances of other surrounding points may be established. There are two types of traverse surveying that is performed.

a) Closed Traverse

When a series of connected lines forms a closed circuit, i.e. when the finishing point coincides with the starting point of a survey, it is called as a ‘closed traverse’.

Closed Traverse

b) Open Traverse

When a sequence of connected lines extends along a general direction and does not return to the starting point, it is known as ‘open traverse’ or (unclosed traverse).

Open Traverse

3) Tacheometric survey

Taacheometric surveying is angular surveying in which horizontal and vertical distance are calculated from the angular measurements. It is a convenient surveying method. Tacheometric surveying uses transit theodolite with a stadia diaphragm for taking measurements. This method is preferable when a direct method of surveying is not possible.

4) Photogrammetric survey

It is a surveying type that uses photographs for making measurements. We can prepare maps, 3D diagrams from these photographs. These are mostly to study the wild life and to make virtual models of historical structures. Photogrammetric surveys cover a large area for surveying and they are less time-consuming.

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History and Scope of Fluid Mechanics

Fluid mechanics has a history of erratically occurring early achievements, then an intermediate era of steady fundamental discoveries in the eighteenth and nineteenth centuries, leading to the twenty-first-century era of “modern practice,”. Ancient civilizations had enough knowledge to solve certain flow problems. Sailing ships with oars and irrigation systems were both known in prehistoric times.

Archimedes (285–212 B.C.) formulated the laws of buoyancy and applied them to floating and submerged bodies, actually deriving a form of the differential calculus as part of the analysis. The Romans built extensive aqueduct systems in the fourth century B.C. but left no records showing any quantitative knowledge of design principles.

Then Leonardo da Vinci (1452–1519) stated the equation of conservation of mass in one-dimensional steady flow. Leonardo was an excellent experimentalist and his notes contain accurate descriptions of waves, jets, hydraulic jumps, eddy formation and both low-drag (streamlined) and high-drag (parachute) designs. A Frenchman, Edme Mariotte (1620–1684), built the first wind tunnel and tested models in it. Problems involving the momentum of fluids could finally be analyzed after Isaac Newton (1642–1727) postulated his laws of motion and the law of viscosity of the linear fluids. The theory first yielded to the assumption of a “perfect” or frictionless fluid, and eighteenth-century mathematicians (Daniel Bernoulli, Leonhard Euler, Jean d’Alembert, Joseph-Louis Lagrange and Pierre-Simon Laplace) produced many solutions of frictionless-flow problems.

Euler developed both the differential equations of motion and their integrated form, now called the Bernoulli equation. D’Alembert used them to show his famous paradox: that a body immersed in a frictionless fluid has zero drag. These results amounted to overkill, since perfect-fluid assumptions have very limited application in practice and most engineering flows are dominated by the effects of viscosity. Engineers began to reject what they regarded as a totally unrealistic theory and developed the science of hydraulics, relying almost entirely on experiment. Such experimentalists as Chezy, Pitot, Borda, Weber, Francis, Hagen, Poiseuille, Darcy, Manning, Bazin, and Weisbach produced data on a variety of flows such as open channels, ship resistance, pipe flows, waves and turbines.

At the end of the nineteenth century, unification between experimental hydraulics and theoretical hydrodynamics finally began. William Froude (1810–1879) and his son Robert (1846–1924) developed laws of model testing, Lord Rayleigh (1842–1919) proposed the technique of dimensional analysis and Osborne Reynolds (1842–1912) published the classic pipe experiment in 1883, which showed the importance of the dimensionless Reynolds number named after him. Meanwhile, viscous-flow theory was available but unexploited, since Navier (1785–1836) and Stokes (1819–1903) had successfully added Newtonian viscous terms to the equations of motion. The resulting Navier-Stokes equations were too difficult to analyze for arbitrary flows.

In 1904, a German engineer, Ludwig Prandtl (1875–1953), published the most important paper ever written on fluid mechanics. Prandtl pointed out that fluid flows with small viscosity, such as water flows and airflows, can be divided into a thin viscous layer, or boundary layer, near solid surfaces and interfaces, patched onto a nearly in viscid outer layer, where the Euler and Bernoulli equations apply. Boundary-layer theory has proved to be a very important tool in modern flow analysis. The twentieth century foundations for the present state of the art in fluid mechanics were laid in a series of broad-based experiments and theories by Prandtl and his two chief friendly competitors, Theodore von Kármán (1881–1963) and Sir Geoffrey I. Taylor (1886–1975).

The second half of the twentieth century introduced a new tool: Computational Fluid Dynamics (CFD). Commercial digital computers became available in the 1950s and personal computers in the 1970s, bringing CFD into adulthood. Presently, with increases in computer speed and memory, almost any laminar flow can be modeled accurately. Turbulent flow is still calculated with empirical models, but Direct Numerical Simulation is possible for low Reynolds numbers.

Since the earth is 75 percent covered with water and 100 percent covered with air, the scope of fluid mechanics is vast and touches nearly every human endeavor. The sciences of meteorology, physical oceanography and hydrology are concerned with naturally occurring fluid flows. All transportation problems involve fluid motion with well-developed specialties in aerodynamics of aircraft and rockets and in naval hydrodynamics of ships and submarines. Almost all our electric energy is developed either from water flow or from steam flow through turbine generators. All combustion problems involve fluid motion as do the more classic problems of irrigation, flood control, water supply, sewage disposal, projectile motion and oil and gas pipelines.

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System of Units and Measurement

Measurement 

Measurement is defined as the action of associating numerical with their possible physical quantities and phenomena. Measurement is a technique in which the properties of an object are determined by comparing them to a standard quantity. Also, measurement is the essential metric to express any quantity of objects, things and events. 

Unit 

Unit is defined as the physical quantity which is measured in terms of the chosen standards of measurement. The unit of a specified physical quantity can be considered as an arbitrarily chosen standard that can be used to estimate the quantities belonging to similar measurements. The units are well accepted and recognized by the people and well within all guidelines. 

System of Units 

The system of units is the complete set of units, both fundamental units and derived units, for all kinds of physical quantities. Each system is named with reference to fundamental units on which it is based. The common system of units utilized in mechanics is as follows. 

1) F.P.S or Foot-Pound System 

The F.P.S. system is a variant of the non-metric system, widely used in the states of the U.S. before the global audience universally accepted the S.I system. It uses the foot as the unit of measurement of length, and pound as the unit of mass and second as the unit of time. 

2) C.G.S or Centimeter-Gram-Second System 

The C.G.S. system is a metric system of measurement. This system uses centimeter, gram and second as the three basic units for length, mass and time respectively. 

3) M.K.S or Meter-Kilogram-Second System 

The fundamental units of length, mass and time are meter, kilogram and second respectively.

Fundamental Units

Every quantity is measured in terms of some internationally accepted units, called fundamental units. All the physical quantities in mechanics are expressed in terms of three fundamental quantities, i.e. Length, Mass and Time. 

1) Mass 

The fundamental property of all material things to resist any change in momentum is referred to as mass. It is independent of the object’s temperature, pressure or position in space. The downward force produced when a mass is in a gravitational field is referred to as weight. The metric units of mass are grams and kilograms, and both are mass units. The mass of an object can also include the total number of electrons, protons and neutrons, which an object contains.

2) Length 

Length is defined as the measurement or extent of something from end to end. The length of any object can be found in either way such as using a scale (i.e., ruler) or measuring tape. 

3) Time 

It is a concept for ordering the flow of events. Time is the change or the interval over which change occurs. It is impossible to know that time has passed unless something changes. It can be measured in terms of seconds, minutes, hours, days, weeks, months and years.

S.I. System of Units

In the year 1960, the Eleventh General Conference of Weights and Measures introduced the International System of Units. The International Standard Organization (ISO) and the International Electrochemical Commission endorsed the system in 1962. In October 1971 a replacement of the metric system of units was done with a new system called Systeme Internationale d’ Unites, International System of Units (S.I. Units).

Fundamental SI Units

Fundamental Quantity	SI Unit	Symbol
Length	Meter	M
Mass	Kilogram	kg
Time	Second	s
Electric Current	Ampere	A
Temperature	Kelvin	K
Luminous Intensity	Candela	cd
Amount of Substance	Mole	mol

Two supplementary units on the SI system are Radian and Steradian.

Quantity	SI Unit	Symbol
Plane Angle	Radian	rad
Solid Angle	Steradian	sr

1) Radian 

It is the unit of a plane angle. One radian is equivalent to an angle subtended at the center of a circle by an arc of length equal to the radius of the circle. 

Fig. 1 Radian

2) Steradian 

It is the unit of solid angle. One steradian is the solid angle subtended at the centre of a sphere, by the surface of a sphere which is equal in area to the square of its radius.

Fig. 2 Steradian

Properties of Fundamental Units 

Any standard unit should have the following properties. 

• Consistency or invariability 
• Availability or reproducibility 
• Imperishability or permanency 
• Convenience and acceptability

Derived Units

The units which are derived from the basic fundamental units are said to be derived units. These units are used to measure the physical quantities but the fact that these can be further resolved into simpler units or the fundamental units.

Quantity	Derived Unit	Symbol
Force	Newton	N
Moment	Newton-meter	Nm
Work	Joule	J
Power	Watt	W
Velocity	Meter per second	m/s
Pressure	Pascal or Newton per square meter	Pa or N/m2

Definition of Fundamental Units

1) Meter (m)

It is the unit of length. One meter is the distance traveled by light through a vacuum in 1/299,792,458 (3.33564095 x 10^-9) of a second. The meter was originally defined as one ten-millionth (0.0000001 or 10^-7) of the distance around the earth's surface, as measured in a great circle passing through Paris, France, from the geographic North Pole to the equator.

Fig. 3 A bar of platinum - iridium metre kept at a temperature of 0º C

2) Kilogram (kg)

It is the unit of mass. The value of the kilogram is now based on the Planck constant, which is 6.62607015 × 10^-34 Js. Prior to 2018, the kilogram was defined as the mass of a specific international prototype made of platinum-iridium and kept at BIPM (The International Bureau of Weights and Measures (Bureau International des Poids et Mesures)) headquarters. Before that, the kilogram was defined as the mass of one liter (10^-3 cubic meters) of pure water.

Fig. 4 The standard platinum - iridium is kept at the International Bureau of Weights and Measures in France

3) Second (s)

It is the unit of time. One second is the time that elapses during 9.192631770 periods of the radiation produced by the transition between two hyperfine levels of the Cesium-133 atom in an unperturbed ground state. It is also the time required for light to travel 299,792,458 (2.99792458 x 10^8) meters through a vacuum.

4) Kelvin (K)

It is the unit of thermodynamic temperature. The value of the Kelvin is now based on the Boltzmann constant, which is 1.380649 × 10^-23 J/K-1. Prior to 2018, a Kelvin was considered equal to 1/273.16 (3.6609 x 10^-3) of the thermodynamic temperature of the triple point of pure water (H2O).

5) Ampere (A)

It is the unit of electric current. The value of the ampere is now based on the elementary charge, which is 1/1.602176634 × 10^-19 times the elementary charge per second. Prior to 2018, the ampere was based on the force between two current carrying conductors that fixed the value of vacuum magnetic permeability at 4π × 10^−7 H m−1.

6) Candela (cd)

It is the unit of luminous intensity. The value of the candela is now based on the luminous efficacy of monochromatic radiation of frequency 540 × 1014 Hz, which is 683 lm/W. Prior to 2018, the candela was the measure of electromagnetic radiation, in a specified direction, that had an intensity of 1/683 (1.46 x 10^-3) watt per steradian at a frequency of 540 terahertz (5.40 x 10^14 hertz).

7) Mole (mol)

It is the unit of an amount of substance. The value of the mole is based on the Avogadro constant, which is 6.02214076 x 10^23 mol−1. One mole has exactly 6.022169 x 10^23 elementary entities.

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Common Applications of Fluids

Fluids are used in a wide range of applications, often playing a vital role, without which, these applications will just cease to exist. The important thing to note is that most of the crucial applications of fluids are for generation of electricity or power. In hydroelectric power plants and automobiles, fluids are directly used to generate power or electricity. In thermal and nuclear power plants, fluids are indirectly used for generation of power, and still they are the dominant parts of these applications. It is not an overstatement to say that without fluids, the progress of the human race would stop. Some of the major applications are:

1) Hydroelectric Power Plants

In hydroelectric power plants, water is used to generate electricity on a large-scale basis. Water stored in the dam possesses potential energy, which is converted into the electrical energy in the power generation unit of the plant. Hydroelectric power plants are one of the major suppliers of power throughout the world. In some countries power requirements are fulfilled entirely by these plants. The discharged water from dams can be used for irrigation purpose also.

2) Hydraulic machines

Machines that operate on a fluid like water and oil are called hydraulic machines. The fluid has the capacity to lift heavy loads and exert extremely high pressures. Some hydraulic machines are used to perform various machining operations. In most of these machines, oil is used as the fluid. The oil is passed through the hydraulic motor which transfers large amounts of energy to the fluid. This high energy fluid enters the piston and cylinder arrangement where it can be used to lift heavy loads or apply large forces.

3) Automobiles

No automobile can run without fluid. Fluids perform three crucial operations in automobiles: generation of power, lubrication and cooling of the engine. Petrol or diesel generates provide power to combustion in the engine. This is commonly referred to as fuel. Oil is used for the lubrication of the engine and the gearbox and also various other moving parts of the vehicle. In larger automobiles like cars, busses and trucks, water is used for cooling the engine.

4) Refrigerators and Air Conditioners

This is another important area where fluids play a crucial role. In refrigerators and air-conditioners, the fluids are known as refrigerants. The refrigerant absorbs the heat from whatever is being kept in the chiller or evaporator, which is at a low temperature, and delivers that heat to the atmosphere, which is at a high temperature. In air conditioners, the refrigerant absorbs room heat and throws it in to the atmosphere, thereby keeping the room cool. The entire operation of refrigerators and air-conditioners depends on the use of a refrigerant.

5) Thermal Power Plants

In thermal power plants, water is used as the working fluid. After getting heated in a boiler, water is converted into superheated steam which is passes through the blades of turbines, thus rotating them. The shaft of the turbine rotates in the generator, where electricity is produced. Thermal power plants are one of the major suppliers of power in various parts of the world, and water working as the fluid is their most important component.

6) Nuclear power plants

Water is again a crucial power plant component. Here it is both the working fluid and a coolant. In some nuclear power plants, heat produced within the nuclear reactor is used to directly heat water, which is converted into steam. This steam is passed through the turbines similar to thermal power plants, rotating turbine blades to generate power. This is an application of water as the working fluid.

In other nuclear power plants, the heat from nuclear reactors is not used to generate steam directly. Heat is first used to heat the water, which acts as the coolant. This coolant then transfers the heat to a secondary coolant or the working fluid, which is again water and it is passed through the turbine to generate electricity.

7) Fluids as a Renewable Energy Source

There are number of fluids that are being used as a renewable energy source. Air or wind is one of the most popular sources of renewable energy. Wind is used for generation of electricity on a small as well as large scale basis. Water is used in tidal power plants to generate electricity on a small scale basis. Ocean waves are used to rotate turbine blades within the power generation unit. Bio diesel, a type of the vegetable oil, is used as a fuel for vehicles along with traditional diesel.

8) Operating Various Instruments

Compressed air is used for the operation of various types of instruments and automatic valves. These valves can be activated and deactivated by applying the pressure of compressed air. The pneumatic tools which work on compressed air are used for various applications like grinding, screwing and unscrewing various machinery parts etc.

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Ingredients of Ordinary Concrete

Concrete is a heterogeneous composite material consisting of cement, water, fine aggregates and coarse aggregates. Aggregates occupy about 60 to 80 percent of the volume of concrete. The paste which is formed from cement and water constitutes 20 to 40 percent of the total volume. Concrete is one of the most frequently used building materials. The quality of the concrete is greatly depending upon the quality of paste, which in turn, is dependent upon the ratio of water to cement content used. To get quality concrete due attention should be paid in choosing the constituents, in mixing them in correct proportions, in mixing the concrete in correct manner and finally in using it properly followed by proper curing.

The ingredient of concrete can be classified in to two groups active group such as cement and water, inactive group such as fine and coarse aggregate.

Fine Aggregate

The particle that passes through 4.75 mm sieve and retain on 0.075 mm sieve is known as fine aggregate. The surface area of fine aggregates is higher. The voids between the coarse aggregate are filled up by fine aggregate. It reduces the cost of the concrete and increase the workability of concrete. The main characteristics of fine aggregate which affect in the properties of concrete is bulking. The phenomenon of increase in sand volume due to the increase of moisture content i.e. called Bulking of sand. The main causes of bulking of sand are the moisture content in the sand and it makes thin films around sand particles. Hence, each particle exerts pressure. Thus they move away from each other causing increasing in volume.

The bulking of the aggregates are dependent on two factors; the fineness of the aggregates and percentage moisture content. A fully saturated fine aggregate does not show any bulking. Thus when the sand contains sufficient moisture 12-20%, it occupies the same volume as when it was dry. The percentage of bulking is inversely proportional to the size of the fine aggregates. Hence, finer the sand more is bulking.

Coarse Aggregate

The particles that are retained on the 4.75 mm sieve are called coarse aggregate. Use of the largest maximum size of coarse aggregate permits a reduction in cement and water requirements. Using aggregates larger than the maximum size of coarse aggregates permitted can result in interlock and form arches or obstructions within a concrete form. That allows the area below to become a void, or at best, to become filled with finer particles of sand and cement only and results in a weakened area. Size of aggregate shall depend upon the type of work and the reinforcement. Size of aggregate should be less than the distance between two consecutive steel bars in RCC.

The main characteristics of fine aggregate which affect in the properties of concrete is crushing strength of aggregate. The crushing strength of aggregate defines as the resistance of aggregate to the compressive load. The compressive strength of concrete is depending on the strength of aggregate.

Cement

Cement is the most important ingredient of concrete act as a binding material having both adhesive and cohesive properties. Cement binds the coarse and fine aggregate by filling the voids and chemically reacting with water. It contains about 10% of the volume of concrete mix. The type of cement to be selected for concrete is based on the factors like type of work, site condition, transportation time etc. The different types of cement are ordinary portland cement (OPC), portland slag cement, portland pozzolana cement, white cement, sulphate resisting cement, low heat cement, rapid hardening cement, quick setting cement, blast furnace slag cement, high alumina cement, colored cement, expansive cement etc.

Water

Water is an important ingredient of concrete without which concrete cannot be manufactured. Water in concrete making is used for mixing, washing aggregate and curing. In general, water which is acceptable for drinking purpose is suitable for making the concrete. The main harmful substance in water for concrete is salt which is present in sea water. The salts present in sea water reduce the strength of concrete, but sometimes it has to be used when there is no alternative. Sea water contains up to 3.5% salt and has tendency to decrease the strength 10% - 20% of the concrete. There is more chance of causes of dampness and surface efflorescence in building.

Admixtures 

Admixtures are optional in concrete. This is used for the special purposes like to increase or decrease the initial or final setting time of the concrete, workability of concrete etc. Admixtures are used in special cases only. Type of admixtures used in concrete includes accelerators, retarders, water-reducing agents, super plasticizers, air entraining agents etc. The proportion of all the ingredients of concrete is considered as per grade of the concrete or as per mix design of concrete.

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Soil and Soil Mechanics

The word “Soil” is derived from the Latin word “solum” which, according to Webster’s dictionary, means ‘the upper layer of the earth that may be dug or plowed specifically, the loose surface material of the earth in which plants grow’. The term ‘Soil’ has different meanings in different scientific fields. To an agricultural scientist, it means ‘‘the loose material on the earth’s crust consisting of disintegrated rock with an admixture of organic matter, which supports plant life’’. To a geologist, it means the disintegrated rock material which has/has not been transported from the place of origin.

But, to a civil engineer, the term ‘soil’ means, the loose unconsolidated inorganic material on the earth’s crust produced by the disintegration of rocks, overlying hard rock with or without organic matter. Foundations of all structures have to be placed on or in such soil, which is the primary reason for its engineering behaviour.

In general, soils are formed by weathering of rocks. The formation of soil happens over a very long period of time. The physical properties of soil are dictated primarily by the minerals that constitute the soil particles and, hence, the rock from which it is derived. The mineral grains that form the solid phase of a soil aggregate are the product of rock weathering. The size of the individual grains varies over a wide range. Many of the physical properties of soil are dictated by the size, shape and chemical composition of the grains.

Soils are formed over thousands of years through the weathering of parent rocks, which can be igneous, sedimentary or metamorphic rocks. Igneous rocks (e.g., granite) are formed by the cooling of magma (underground) or lava (above the ground). Sedimentary rocks (e.g., limestone, shale) are formed by gradual deposition of fine soil grains over a long period. Metamorphic rocks (e.g., marble) are formed by altering igneous or sedimentary rocks by pressure or temperature or both. Soils are quite different from other engineering materials, which makes them interesting and at the same time challenging.

Soil Mechanics

Karl Terzaghi (an Austrian geotechnical engineer, and geologist known as the "father of soil mechanics and geotechnical engineering) defined Soil Mechanics as follows:

“Soil Mechanics is the application of the laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks regardless of whether or not they contain an admixture of organic constituents.”

The term Soil Mechanics is now accepted quite generally to designate that discipline of engineering science which deals with the properties and behavior of soil as a structural material. All structures have to be built on soils. The application of the principles of soil mechanics to the design and construction of foundations for various structures is known as ‘‘Foundation Engineering’’. ‘‘Geotechnical Engineering’’ may be considered to include both soil mechanics and foundation engineering.

History and Development of Soil Mechanics

The use of soil for engineering purposes dates back to prehistoric times. Soil was used not only for foundations but also as construction material for embankments. The knowledge was empirical in nature and was based on trial and error, and experience. The hanging gardens of Babylon were supported by huge retaining walls, the construction of which should have required some knowledge of earth pressures. The large public buildings, harbours, aqueducts, bridges, roads and sanitary works of Romans certainly indicate some knowledge of the engineering behaviour of soil. This has been evident from the writings of Vitruvius, the Roman Engineer in the first century, B.C. Mansar and Viswakarma, in India, wrote books on ‘construction science’ during the medieval period.

The Leaning Tower of Pisa, Italy, built between 1174 and 1350 A.D., is a glaring example of a lack of sufficient knowledge of the behaviour of compressible soil, in those days. Coulomb, a French Engineer, published his wedge theory of earth pressure in 1776, which is the first major contribution to the scientific study of soil behaviour. He was the first to introduce the concept of shearing resistance of the soil as composed of the two components— cohesion and internal friction. Poncelet, Culmann and Rebhann were the other men who extended the work of Coulomb. D’ Arcy and Stokes were notable for their laws for the flow of water through soil and settlement of a solid particle in liquid medium, respectively. These laws are still valid and play an important role in soil mechanics.

Rankine gave his theory of earth pressure in 1857; he did not consider cohesion, although he knew of its existence. Boussinesq, in 1885, gave his theory of stress distribution in an elastic medium under a point load on the surface. Mohr, in 1871, gave a graphical representation of the state of stress at a point, called ‘Mohr’s Circle of Stress’. This has an extensive application in the strength theories applicable to soil. Atterberg, a Swedish soil scientist, gave in 1911 the concept of ‘consistency limits’ for a soil. This made possible the understanding of the physical properties of soil.

The Swedish method of slices for slope stability analysis was developed by Fellenius in 1926. He was the chairman of the Swedish Geotechnical Commission. Prandtl gave his theory of plastic equilibrium in 1920 which became the basis for the development of various theories of bearing capacity. Terzaghi gave his theory of consolidation in 1923 which became an important development in soil mechanics. He also published, in 1925, the first treatise on Soil Mechanics, a term coined by him. Thus, he is regarded as the Father of modern soil mechanics’. Later on, R.R. Proctor and A. Casagrande and a host of others were responsible for the development of the subject as a full-fledged discipline.

Application of Soil Mechanics

1) Foundations

The loads from any structure have to be ultimately transmitted to a soil through the foundation for the structure. Thus, the foundation is an important part of a structure, the type and details of which can be decided upon only with the knowledge and application of the principles of soil mechanics. A foundation is termed shallow foundation when it transmitted the load to upper strata of earth. A foundation is called deep foundation when the load is transmitted to strata at considerable depth below the ground surface. Pile foundation is a type of deep foundation.

Shallow Foundation

Deep Foundation

2) Earth-Retaining Structures

When sufficient space is not available for a mass of soil to spread and form a safe slope, a structure is required to retain the soil. An earth retaining structure is also required to keep the soil at different levels on its either side. The retaining structure may be rigid retaining wall or a sheet pile which is relatively flexible. Such as retaining walls can be designed and constructed only by using the principles of soil mechanics and the concept of ‘soil-structure interaction’.

Retaining Wall

Sheet Pile

3) Stability of Slopes

If soil surface is not horizontal, there is a component of weight of the soil which tends to move it downward and thus causes instability of slope. The slopes may be natural or man-made. Soil engineering provides the methods for checking the stability of slopes.

Embankment Slope

4) Underground structures

The design and construction of underground structures, such as tunnels and conduits, require evaluation of forces exerted by the soil on these structures.

Tunnel

5) Pavement Design

Pavement Design may consist of the design of flexible or rigid pavements. Flexible pavements depend more on the subgrade soil for transmitting the traffic loads. Problems peculiar to the design of pavements are the effect of repetitive loading, swelling and shrinkage of sub-soil and frost action. Consideration of these and other factors in the efficient design of a pavement is a must and one cannot do without the knowledge of soil mechanics.

Pavement

6) Excavations, Embankments and Dams

Excavations require the knowledge of slope stability analysis; deep excavations may need temporary supports such as ‘timbering’ or ‘bracing’, the design of which requires knowledge of soil mechanics. Likewise the construction of embankments and earth dams where soil itself is used as the construction material requires a thorough knowledge of the engineering behaviour of soil especially in the presence of water.

Earth Dam

7) Miscellaneous Soil

The geotechnical engineer has sometimes to tackle miscellaneous problems related with soil. Such as soil heave, soil subsidence, frost heave, shrinkage and swelling of soils.

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