SURVEYINGSURVEYING

Neeraj KhareNeeraj Khare

Associate Professor / WorksAssociate Professor / Works

SURVEYING :- We will discussSURVEYING :- We will discuss

CHAPTERCHAPTER PeriodsPeriods

Concepts of surveying,Concepts of surveying, 11

LevellingLevelling,, 11

Surveying with theodolite,Surveying with theodolite, 22

Familarisation with modern survey Familarisation with modern survey equipments,equipments,

22

Curve layout,Curve layout, 11

Field practices.Field practices. 66

CONCEPTS CONCEPTS OF OF

SURVEYINGSURVEYING

SURVEYINGSURVEYINGPreamblePreamble

Surveying is involved in a project from Surveying is involved in a project from conceptual stage to construction and conceptual stage to construction and afterwards in maintenance also. afterwards in maintenance also. Depending on the stage at which Depending on the stage at which surveying is carried out it can be called.surveying is carried out it can be called.i) Pre i) Pre construction construction surveysurvey

Feasibility survey (RECT Feasibility survey (RECT & PECT )& PECT )

ii) Construction ii) Construction surveysurvey

To maintain alignment and To maintain alignment and Geometry control during Geometry control during construction. (FLS and construction. (FLS and other )other )

iii) Post iii) Post constructionconstruction

Maintenance surveyMaintenance survey

Definition of Survey :Definition of Survey : Operation of Operation of making such measurements that the making such measurements that the relative position of various features, relative position of various features, natural or Artificial on the surface of natural or Artificial on the surface of the earth can be exhibited in their the earth can be exhibited in their correct Horizontal and vertical correct Horizontal and vertical relationship.relationship.

Normally determining position in Normally determining position in Horizontal plane is called surveying.Horizontal plane is called surveying.

Determining relative heights or depth Determining relative heights or depth is called levelling.is called levelling.

PurposePurpose : : The main object of surveying is the The main object of surveying is the preparation of maps or plans which are the preparation of maps or plans which are the basis in planning and design of engineering basis in planning and design of engineering project such as route location of railway line, project such as route location of railway line, roads and water supply scheme.roads and water supply scheme.Basic Principles in SurveyingBasic Principles in Surveying : : Ruling principle Ruling principle of survey is :of survey is :i) i) “ to work from whole to part”.“ to work from whole to part”. For surveying For surveying Establish control points with high precision by Establish control points with high precision by use of Triangulation and precise levelling. Area use of Triangulation and precise levelling. Area is further divided into triangle, which are is further divided into triangle, which are surveyed with less accuracy.surveyed with less accuracy.ii) to fix the position of new stations byii) to fix the position of new stations by at-at-least twoleast two independent processes – By linear independent processes – By linear and Angularand Angular

Classification of SurveysClassification of Surveys : : Surveying is divided into Surveying is divided into two main categories-two main categories-i) Geodetic Surveyi) Geodetic Surveyii) Plane surveyii) Plane survey

i) Geodetic Survey :-i) Geodetic Survey :- When survey extends over a When survey extends over a large areas more than 200 sq. km. and degree of large areas more than 200 sq. km. and degree of accuracy is also great. The curvature of earth is also accuracy is also great. The curvature of earth is also taken into account. Geodetic survey is used to provide taken into account. Geodetic survey is used to provide control points to which small surveys can be connected.control points to which small surveys can be connected.

ii) Plane Survey :-ii) Plane Survey :- For small projects covering Area For small projects covering Area less than 200 sq.km. Earth curvature is not counted for less than 200 sq.km. Earth curvature is not counted for in distances. Earth surface is considered as plane. in distances. Earth surface is considered as plane. (Angular error of 1” in 200 sq. km. area by assuming (Angular error of 1” in 200 sq. km. area by assuming plane).plane).

A) Classification based upon equipment usedA) Classification based upon equipment used::

i) Chain surveyi) Chain surveyii) Compass surveyii) Compass surveyiii) Theodolite surveyiii) Theodolite surveyiv) Plane Table surveyiv) Plane Table surveyv) Tachometric surveyv) Tachometric surveyvi) Aerial Photographic Surveyvi) Aerial Photographic Surveyvi) Remote sensing.vi) Remote sensing.Vii) Hydrographic survey.Vii) Hydrographic survey.

B) Based upon Method Employed :B) Based upon Method Employed :i) Triangulation :i) Triangulation : Control points are established through a net- Control points are established through a net-work of triangles.work of triangles.

ii) Traversing:ii) Traversing: Scheme of control points consisting of a series of Scheme of control points consisting of a series of connected lines.connected lines.

iii) Trilateration:iii) Trilateration: Distances are measured for exercising the Distances are measured for exercising the control.control.

LEVELLINGLEVELLING

Levelling :Levelling :The art of determining relative altitudes The art of determining relative altitudes of points on the surface of the earth of of points on the surface of the earth of beneath the surface of earth is called beneath the surface of earth is called LEVELLING.LEVELLING.

For execution of Engineering Projects it is For execution of Engineering Projects it is very necessary to determine elevations of very necessary to determine elevations of different points along the alignment of different points along the alignment of proposed project.proposed project.

Other applications are :Other applications are :i) Taking rail levels existing before track renewals to i) Taking rail levels existing before track renewals to finalise final rail level profile including vertical curves.finalise final rail level profile including vertical curves.ii) Initial ground levels for earthwork calculations.ii) Initial ground levels for earthwork calculations.iii) Levels for measurement of earthwork.iii) Levels for measurement of earthwork.iv) Measurement of ballast etc.iv) Measurement of ballast etc.

Terms used in Levelling –Terms used in Levelling –a) DATUM – a) DATUM – or Datum plane is an arbitrarily assumed or Datum plane is an arbitrarily assumed level surface or line with reference to which level of level surface or line with reference to which level of other line or surface are calculated.other line or surface are calculated.

b) REDUCED LEVEL (RL) –b) REDUCED LEVEL (RL) – Height or depth of a Height or depth of a point above or below the assumed datum is called point above or below the assumed datum is called Reduced level.Reduced level.c) BENCH MARK –c) BENCH MARK – (BM) – (BM) – B.M. is a fixed reference B.M. is a fixed reference point of known elevation. It may be of the following point of known elevation. It may be of the following types.types.i) GTS Bench mark (i) GTS Bench mark (Geodetic Triangulation Survey) :Geodetic Triangulation Survey) :

These Bench marks are established by national These Bench marks are established by national agency like Survey of India. They are established agency like Survey of India. They are established with highest precision. Their position and elevation with highest precision. Their position and elevation above MSL is given in a special catalogue known as above MSL is given in a special catalogue known as GTS Maps ( 100 km. interval).GTS Maps ( 100 km. interval).

ii) ii) Permanent Bench Mark :Permanent Bench Mark : They are fixed They are fixed points of reference establish with reference to GTS points of reference establish with reference to GTS Bench mark (10 km. interval).Bench mark (10 km. interval).

iii) Arbitrary Bench mark :iii) Arbitrary Bench mark : These are These are reference points whose elevations are arbitrarily reference points whose elevations are arbitrarily assumed. In most of Engineering projects, the assumed. In most of Engineering projects, the difference in elevation is more important than their difference in elevation is more important than their reduced levels with reference to MSL as given in a reduced levels with reference to MSL as given in a special catalogue known as GTS Maps ( 100 Km. special catalogue known as GTS Maps ( 100 Km. interval).interval).

d)d)Mean Sea Level (M.S.L.) :Mean Sea Level (M.S.L.) : M.S.L. is obtained by M.S.L. is obtained by making hourly observations of the tides at any place making hourly observations of the tides at any place over a period of 19 years. MSL adopted by Survey of over a period of 19 years. MSL adopted by Survey of India is now Bombay which was Karachi earlier.India is now Bombay which was Karachi earlier.

e) Level Surface :e) Level Surface : The surface which is parallel to The surface which is parallel to the mean sphereoidal surface of the earth is known as the mean sphereoidal surface of the earth is known as level surface.level surface.

ff) Line of Collimation :) Line of Collimation : It is the line joining the It is the line joining the intersection of the cross hair and the optical center of intersection of the cross hair and the optical center of the objective and its extensions, it is also called line of the objective and its extensions, it is also called line of sight or collimation.sight or collimation.

g)g) Height of Instrument (HI) :Height of Instrument (HI) : The elevation of the line The elevation of the line of sight with respect to assumed datum is known as of sight with respect to assumed datum is known as HI.HI.

h) Back sight : (B.S.) -h) Back sight : (B.S.) - The first sight taken on a The first sight taken on a levelling staff held at a point of known elevation. B.S. levelling staff held at a point of known elevation. B.S. enables the surveyor to obtain HI +sight i.e. Height of enables the surveyor to obtain HI +sight i.e. Height of Instrument or line of sight.Instrument or line of sight.i) Fore Sight : (F.S.) –i) Fore Sight : (F.S.) – It is the last staff reading taken It is the last staff reading taken from a setting of the level. It is also termed as minus from a setting of the level. It is also termed as minus sight.sight.Fore sight is the sight taken on a levelling staff held at Fore sight is the sight taken on a levelling staff held at a point of unknown elevation to ascertain the amount a point of unknown elevation to ascertain the amount by which the point is above or below the line of sight. by which the point is above or below the line of sight. This is also called minus sight as the foresight reading This is also called minus sight as the foresight reading is always subtracted from height of Instrument.is always subtracted from height of Instrument.

k) Change Point (CP) :k) Change Point (CP) : The point on which The point on which both the foresight and back sight are taken both the foresight and back sight are taken during the operation of levelling is called during the operation of levelling is called change point.change point.

l) Intermediate Sight (IS) :l) Intermediate Sight (IS) :The foresight taken on a levelling staff held The foresight taken on a levelling staff held at a point between two turning points, to at a point between two turning points, to determine the elevation of that point, is determine the elevation of that point, is known as intermediate sight.known as intermediate sight.

It may be noted that for one setting of a level, It may be noted that for one setting of a level, there will be only one back sight and one there will be only one back sight and one foresight but there can be any number of foresight but there can be any number of intermediate sights.intermediate sights.

Type of Levelling Equipments:Type of Levelling Equipments:i) i) Dumpy levelDumpy levelii) Tilting levelii) Tilting leveliii) Automatic leveliii) Automatic leveliv) Digital Auto leveliv) Digital Auto level

Dumpy level Dumpy level It is simple compact It is simple compact and stable. The and stable. The telescope is rigidly telescope is rigidly fixed to its support fixed to its support therefore cannot be therefore cannot be rotated about its rotated about its longitudinal axis. A longitudinal axis. A long bubble tube is long bubble tube is attached to the top attached to the top of telescope. Dumpy of telescope. Dumpy literally means short literally means short and thick.and thick.

Tilting level Tilting level It consists of a It consists of a telescope telescope attached with attached with a level tube a level tube which can be which can be tilted within tilted within few degrees in few degrees in vertical plane vertical plane by a tilting by a tilting screw.screw.

The main peculiarity of this The main peculiarity of this level is that the vertical axis level is that the vertical axis need not be truly vertical, since need not be truly vertical, since the line of collimation is not the line of collimation is not perpendicular to it. The line of perpendicular to it. The line of collimation, is, however, made collimation, is, however, made horizontal for each pointing of horizontal for each pointing of telescope by means of tilting telescope by means of tilting screw. It is mainly designed for screw. It is mainly designed for precise levelling work.precise levelling work.

The Automatic levelThe Automatic level

The Automatic The Automatic levellevel

The Automatic level :The Automatic level : Also Also termed as self aligning leveltermed as self aligning level. . The fundamental difference between The fundamental difference between automatic and the classic spirit level is automatic and the classic spirit level is that in the former the line of sight is no that in the former the line of sight is no longer levelled manually using a tubular longer levelled manually using a tubular spirit level, but is levelled automatically spirit level, but is levelled automatically within a certain tilt range. This is within a certain tilt range. This is achieved by compensator in the telescope.achieved by compensator in the telescope.

Advantage of automatic levelAdvantage of automatic leveli)i) Much simpler to use Much simpler to useii) ii) High precisionHigh precision – Mean elevation error – Mean elevation error on staff graduated to 5mm division varies on staff graduated to 5mm division varies between +0.5 to 0.8 mm per km of forward between +0.5 to 0.8 mm per km of forward and backward levelling.and backward levelling.iii) iii) High speedHigh speed : For fly levelling the : For fly levelling the progress achieved by various level-wise progress achieved by various level-wise compared.compared.

Type of level D(m) 20m 40 60 80 100 120Type of level D(m) 20m 40 60 80 100 120Automatic level speed 1.2 2 2.4 2.5 2.6 2.7Automatic level speed 1.2 2 2.4 2.5 2.6 2.7 S(Km/hr) S(Km/hr)Tilting level speed 0.6 1.1 1.5 1.7 1.8 1.9Tilting level speed 0.6 1.1 1.5 1.7 1.8 1.9 S(Km/hr) S(Km/hr)

S = Speed of levelling in km/hr.S = Speed of levelling in km/hr.D = Sighting distance in meter.D = Sighting distance in meter.The speed of Dumpy level is about 25% lower than The speed of Dumpy level is about 25% lower than tilting level.tilting level.iv)iv) Freedom from errorsFreedom from errors – Accuracy is increased by – Accuracy is increased by

an an erecterect telescope image. telescope image.

v) Range of applicationv) Range of application – level can be used on – level can be used on medium and large sized projects and setting bench medium and large sized projects and setting bench marks.marks.

Basic components of level :Basic components of level :1. Telescope1. Telescope – to provide a line of sight – to provide a line of sight

2. Level Tube2. Level Tube – to make line of sight horizontal – to make line of sight horizontal

3. Levelling head3. Levelling head – to bring the bubble of tube level – to bring the bubble of tube level at the centre of its run.at the centre of its run.4. Tripod4. Tripod – to support the above three parts of the – to support the above three parts of the level.level.1. TELESCOPE1. TELESCOPE : : Telescope is an optical Telescope is an optical instrument used for magnifying and viewing the instrument used for magnifying and viewing the images of distant objects. It consists of two lenses. images of distant objects. It consists of two lenses. The lens fitted near the eye is called the eye piece and The lens fitted near the eye is called the eye piece and the other fitted at the end near to the object is called the other fitted at the end near to the object is called the objective lens.the objective lens.

The objective provides a real inverted image The objective provides a real inverted image infront of the eye piece at a distance lesser than infront of the eye piece at a distance lesser than its focal distance.its focal distance.Two essential conditions are involved. : Two essential conditions are involved. : i) The real image of the object, must be formed.i) The real image of the object, must be formed.Ii) the plane of image must coincide with that of Ii) the plane of image must coincide with that of cross hairs.cross hairs.Focusing of Telescope : Focusing of Telescope : The operation of The operation of obtaining a clear image of the object in the plane obtaining a clear image of the object in the plane of cross hairs is known as focusing.of cross hairs is known as focusing.

1. Diaphram :1. Diaphram : A frame carrying cross hairs usually A frame carrying cross hairs usually made of either silk thread or platinum wire and placed at made of either silk thread or platinum wire and placed at the plane at which vertical image of the object is formed the plane at which vertical image of the object is formed by the objective.by the objective. Vertical hair of the diaphram enables the surveyor to Vertical hair of the diaphram enables the surveyor to check the verticality of levelling staff whereas horizontal check the verticality of levelling staff whereas horizontal hairs are used to read the staff graduations.hairs are used to read the staff graduations.

2.Level Tube :2.Level Tube : Also known as Bubble Tube consists of Also known as Bubble Tube consists of a glass tube placed in a brass tube which is sealed with a glass tube placed in a brass tube which is sealed with plaster of paris. The whole of the interior surface or the plaster of paris. The whole of the interior surface or the upper half is accurately ground so that its longitudinal upper half is accurately ground so that its longitudinal section, is an arc of a circle. Level tube is filled with section, is an arc of a circle. Level tube is filled with either or alcohol, the remaining space is occupied by an either or alcohol, the remaining space is occupied by an air bubble. The centre of air bubble always rest at the air bubble. The centre of air bubble always rest at the highest point of the tube.highest point of the tube.

Outer surface of the bubble tube is graduated Outer surface of the bubble tube is graduated in both the directions from the centre.in both the directions from the centre.

The line tangential to the circular are at its The line tangential to the circular are at its highest point i.e. the middle of tube is called highest point i.e. the middle of tube is called the axis of bubble tube. When the bubble is the axis of bubble tube. When the bubble is central the axis of bubble becomes Horizontal.central the axis of bubble becomes Horizontal.

The level tube is attached on the top of The level tube is attached on the top of Telescope by means of capstan headed nuts.Telescope by means of capstan headed nuts.

3.3.Levelling head :Levelling head : Levelling head generally Levelling head generally consists of two parallel plates with 3 foot consists of two parallel plates with 3 foot screws. Upper plate is known as Tribrach and screws. Upper plate is known as Tribrach and lower plate is trivet which can be screwed on to lower plate is trivet which can be screwed on to the tripod. Levelling head has to perform 3 the tripod. Levelling head has to perform 3 distant functions :distant functions :

i) to support the telescopei) to support the telescopeii) to attach the level to the tripodii) to attach the level to the tripodiii) to provide a means for level (foot screws)iii) to provide a means for level (foot screws)

Adjustment of level :Adjustment of level :i) Temporarily Adjustments – i) Temporarily Adjustments – adjustments which adjustments which are made for every setting of a level.are made for every setting of a level.ii) Permanent adjustments- ii) Permanent adjustments- required if some error is required if some error is there in instrument. there in instrument. i) Temporary Adjustments : i) Temporary Adjustments : includesincludes

a) setting up the levela) setting up the levelb) levelling upb) levelling upc) elimination of parallaxc) elimination of parallax

a) Setting up the level :a) Setting up the level : This operation includes This operation includes fixing the instrument on the tripod and also fixing the instrument on the tripod and also approximate levelling by leg adjustment.approximate levelling by leg adjustment.

b) Levelling up :b) Levelling up : Accurate levelling is done with the Accurate levelling is done with the help of foot screws and by using plate levels. The object help of foot screws and by using plate levels. The object of levelling up the instrument is to make its vertical axis of levelling up the instrument is to make its vertical axis truly vertical.truly vertical.

c) Elimination of parallax :c) Elimination of parallax : If the image formed by If the image formed by the objective does not lie in the plane of the cross hairs, the objective does not lie in the plane of the cross hairs, there will be a shift in the image due to shift of the eye. there will be a shift in the image due to shift of the eye. Such displacement of image is termed as parallax. Such displacement of image is termed as parallax. Parallax is removed in two stages.Parallax is removed in two stages.1) 1) Focusing the eye for distinct vision of cross hairs.Focusing the eye for distinct vision of cross hairs.2) Focusing the objective so that image is formed in the 2) Focusing the objective so that image is formed in the plane of cross hairs.plane of cross hairs.

Principles of levelling :Principles of levelling :a) Simple levelling : a) Simple levelling : The operation of The operation of levelling for determining the difference in levelling for determining the difference in elevation, if not too great between two elevation, if not too great between two points visible from single position of the points visible from single position of the level is known as simple levelling.level is known as simple levelling.

PROCEDURE : PROCEDURE : Following steps are Following steps are involved.involved.

1.1.Level the instrument correctly.Level the instrument correctly.2. Direct the telescope towards the staff held2. Direct the telescope towards the staff held3. Take the reading of Central, horizontal hair of the 3. Take the reading of Central, horizontal hair of the diaphram, where it appears to cut the staff ensuring diaphram, where it appears to cut the staff ensuring that the bubble is central.that the bubble is central.4. Send the staff to next point4. Send the staff to next point5. Direct the telescope towards C and focus it again5. Direct the telescope towards C and focus it again6. Check up the bubble if central, if not bring it to the 6. Check up the bubble if central, if not bring it to the Central position by the foot screw nearest to the Central position by the foot screw nearest to the telescope.telescope.7. Take the reading of Central Horizontal cross hair.7. Take the reading of Central Horizontal cross hair.

b) Differential levelling or fly levelling :b) Differential levelling or fly levelling : This method is used in order to find the This method is used in order to find the difference in elevation between two points.difference in elevation between two points.i) If they are too far aparti) If they are too far apartii) if the difference in elevation between them is ii) if the difference in elevation between them is too great.too great.iii) If there are obstacles intervening. In such iii) If there are obstacles intervening. In such case it is necessary to set up the level in several case it is necessary to set up the level in several positions and to work in series of stages.positions and to work in series of stages.

The difference of level of the points A&B is equal The difference of level of the points A&B is equal to the algebraic sum of these difference between to the algebraic sum of these difference between the sum of back sights and sum of the fore sights the sum of back sights and sum of the fore sights i.e. i.e. ΣΣ BS - BS - ΣΣ FS FS

Booking and reduction of the levels may be done Booking and reduction of the levels may be done by following 2 methods.by following 2 methods.i) Rise and fall methodi) Rise and fall methodii) Height of collimation methodii) Height of collimation method

RISE AND FALL METHOD –RISE AND FALL METHOD –

In this method, the difference of level between two In this method, the difference of level between two consecutive points for each setting of the instrument is consecutive points for each setting of the instrument is obtained by comparing their staff readings.obtained by comparing their staff readings.

The difference between their staff readings The difference between their staff readings indicates a rise if back sight is more than foresight and a indicates a rise if back sight is more than foresight and a fall if it is less than foresight.fall if it is less than foresight.

The Rise and Fall worked out for all the points The Rise and Fall worked out for all the points given the vertical distances of each point relative to the given the vertical distances of each point relative to the proceeding one.proceeding one.

If the RL of the Back staff point is known, then RL If the RL of the Back staff point is known, then RL of the following staff point may be obtained by adding its of the following staff point may be obtained by adding its rise or substracting fall from the RL of preceding point.rise or substracting fall from the RL of preceding point.

Height of Collimation Method:Height of Collimation Method:In this method Height of Instrument In this method Height of Instrument

(H.I.) is calculated for each setting of the (H.I.) is calculated for each setting of the instrument by adding the back sight (B.S.) to instrument by adding the back sight (B.S.) to the elevation of B.M.the elevation of B.M.

Height of instrument (H.I.) = R.L. of the Height of instrument (H.I.) = R.L. of the plane of collimation plane of collimation

= R.L. of B.M.+B.S. = R.L. of B.M.+B.S.

RL of a point = H.I. – FSRL of a point = H.I. – FSOr = H.I. – IS Or = H.I. – IS

- After every back sight, there may be many - After every back sight, there may be many intermediate sights but there must be only one intermediate sights but there must be only one foresight.foresight.- The B.S. & F.S. forms the two ends of one - The B.S. & F.S. forms the two ends of one stage in levelling.stage in levelling.- Levelling should always commence from a - Levelling should always commence from a permanent B.M. and end on a permanent B.M.permanent B.M. and end on a permanent B.M.

HI method of RL calculation

Stn

Reading

HI RL RemarksBS IS FS

TBM 1.265     101.265 100.000

TBM no 1 on parapet of well near Ch. 1000m

P1   1.390     99.875  

P2   0.850     100.415  

P3   2.255     99.010  

P4   1.640     99.625  

CP1 1.220 1.350 101.135 99.915

Change point on found. Of El pole

    1.350     99.785  

    1.275     99.860  

      1.135   100.000Closed on same

TBM1

Rise -Fall method of RL calculation

Stn

Reading

Rise Fall RL RemarksBS IS FS

TBM 1.265         100.000TBM no 1

….

P1   1.390     0.125 99.875  

P2   0.850   0.540   100.415  

P3   2.255     1.405 99.010  

P4   1.640   0.615   99.625  

CP1 1.220 1.350 0.290   99.915

Change point ….

    1.350     0.130 99.785  

    1.275   0.075   99.860  

      1.135 0.140   100.000

Closed on same TBM1