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SURVEYINGSURVEYING--11

UNITUNIT -- 11

Introduction & Chain surveyingIntroduction & Chain surveying

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SynopsisSynopsis

DefinitionDefinition PrinciplesPrinciples ClassificationClassification

ScalesScales Field &Office workField &Office work Conventional signsConventional signs Survey instrumentsSurvey instruments

Well conditioned triangleWell conditioned triangle Ranging & ChainingRanging & Chaining Errors in chainingErrors in chaining

Chain surveyingChain surveyingSetting perpendicularSetting perpendicular

Instruments used forInstruments used for

setting out right anglessetting out right angles

ObstaclesObstacles

TraversingTraversing

MethodsMethodsChain traversingChain traversing

PlottingPlotting

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DefinitionDefinition

Surveying is the art of determining the relative position of pointsSurveying is the art of determining the relative position of points

on, above or beneath the earth surface by means of direct oron, above or beneath the earth surface by means of direct or

indirect measurements of distance, direction & elevation.indirect measurements of distance, direction & elevation.

PrinciplesPrinciples

Location of a point by measurement from two points of reference.Location of a point by measurement from two points of reference.

Working from whole to partWorking from whole to part

Plane or GeodeticPlane or Geodetic

Fix control points (higher precision) & minor control pointsFix control points (higher precision) & minor control points

(less precision).(less precision).

Its control error.Its control error.

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P

Q

P

Q

R

R

S

90

PR,QR- measured

R-plotted by swinging two arcsprinciples Used- chain surveying

RS-dropped in PQ ,PS & RS measuredR plotted using set square

This principle used for defining details.

QR, angle PQR measured

R- plotted by protractor

Principles used - Traversing

P

Q

R

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P

Q

R

PR & QR not measured

Angle PQR & RQP measured

R plotted by protractor

Principle used Triangulation

Used in very extensive work

P

Q

R

Angle RQP , distance PR measured

R plotted by protractor

Principles used Traversing

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Artificial features of roads, railways, canals,

towns & villages.

Cadastral surveys calculation of land area& also made to fix the boundaries of

municipalities & of state & Federal jurisdictions.

City surveys construction of streets, water

supply system, sewers.

Classification

Classification based upon nature of field survey.1.Land surveying

Topographical surveys- natural features of

rivers, streams, lakes, woods, hills etc.

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Classification based on object of survey1.Engineering surveys - roads, reservoirs

2.Military surveys - for determiningpoints of strategic importance.

3.Mine surveys - for exploring mineralwealth.

4.Archaeological surveys for unearthing relics ofantiquity.

3.Astronomical surveys observation toheavenly bodies such as sun & any fixed star.

2.Marine or Hydrographic surveys - dealswith water bodies for purpose of navigation, water

supply, harbour works.

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Classification based on instruments usedClassification based on instruments used

Chain surveyChain survey

Tacheometric surveyTacheometric survey Theodolite surveyTheodolite survey Traverse surveyTraverse survey

Triangulation surveyTriangulation survey

Plane table surveyPlane table surveyPhotogrammetric surveyPhotogrammetric surveyAerial surveyAerial survey

Scales

Area surveyed is vast so plans are made to some

scale.

Scale is the fixed ratio that every distance on the

plan bears with corresponding distance on the ground.

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Methods

Engineers Scale 1cm = 10m

Representative Fraction 1/1000

Graphical Scale

Types

Plain scale It is possible to measure two

dimensions only. Eg : miles & furlongs

Diagonal scale - It is possible to measure three

dimensions. Eg : meters, centimetres, decimetres

Vernier scale - It is a device for measuring

fractional part of one of the smallest division.

Scale of chords To measure angle.

Also called

numerical

scales

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Field work & Office work

Surveyor work divided into three parts.

Field work Measurement of angles & distances &

keeping of a record of what has been done in form of

field notes.

Office work Drafting, computing & designing

Care & Adjustment of instruments

It requires experience in handling the equipments

used in the in the field. The many surveying instrumentsare very delicate & must be handled with great care

since there are many parts of instruments which if once

impaired can not be restored their original efficiency.

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Conventional SignsDifference features on the ground are represented by

difference symbols. This symbols are called asconventional signs.

Pine tree Ford Church

Sand pit Railway Stations

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Survey Instruments for chaining1.Chain or Tape 5. Arrows

2. Pegs 6. Ranging rods3. Offset rods 7. Plasterers laths & Whites

4.Plumb bob

Chain

Mild steel, every one metre one ring, brass handle.

Types of chains

Metric chains tallies for every 5,10,20,30 meters

Gunters or surveyors chain 66ft ,100 links

Engineers chains 100ft,100 links

Revenue chain 33ft,16 links (cadastral)

Steel band or Band chain 20 to 30 metre

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TapesIt is used for accurate measurement

Tapes classification

Cloth or Linen Tape Steel Tape

Metallic Tape Invar Tape

Arrows

Arrows or marking pins are made of stout steel wire.

Length 25 to 50 cm (commonly 40cm) , Diameter 50mm

10 arrows supplied with a chain.

Pegswooden pegs are used to mark the positions of the stations or

terminal points of survey line.

15cm long,2.5cm or 3cm square

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Ranging Rods

Length 2 to3 meter

Rod should have white, red or yellow flags

Ranging poles similar to ranging rods & 4 to 8m ht

Offset Rods

It is similar to ranging rods. They are round wooden rods.Length 3m

Butt Rods

Used for measuring offsets.

It is used by building surveyors or architects.

Length 1m

The rod is painted black.

Feet & Inches marked out with White & Red paint.

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Plasterers laths

Made of soft wood.

Length to 1mWhites Pieces of sharpened thin sticks

Used in cross sectioning or in temporary marking

of contour pointsPlumb bob

It is required to transfer the points to the ground.

It is used in centering aid in theodolites, compassplane table & other surveying instruments.

Also used to make ranging poles vertical.

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Well conditioned triangle or Well connected

triangle

Well condition triangle should satisfy the followingConditions.

1. The magnitude of angles in each individual triangle(>30 &

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Ranging

While survey line length is measured 20m,30m wecan use chain or tape but if it extends it is difficult tomeasure. So that intermediate points are establishedbetween the two points.

The process of fixing or establishing suchintermediate points called ranging.

There are two types of ranging:1. Direct ranging It is done when

two ends of survey lines are intervisible.

2. Indirect or reciprocal ranging It is resorted whenboth ends of the survey lines are not intervisible.

AB

P

A

AM N

B

A BM N

M1 N1

M2 N2

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Chaining

Two chain men required to measure length.

1.Follower Zero end or real end.2.Leader - Holding forward handle.

Errors due to incorrect chain

L = true length L' = incorrect length of chain

1. Correction to measure length

l = l' (L'/L) l = true length l' = measured length

2. Correction to area

A = A'(L'/L) A' = measured area of the ground

A = true area of the ground

3. Correction to volume

V = V'(L'/L) V = true volume

V' = measured volume

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Errors in chaining

1.Errorneous length of chain or tape cumulative + or

2.Bad ranging cumulative +3.Tape not stretched horizontally cumulative +

4.Tape not stretched tight & straight,

but both ends in line cumulative +

5. Error due to temperature cumulative + or

6. Variation in pull compensating

7. Errors due to sag cumulative +

8. Error in marking tape lengths compensating

9. Disturbing arrows after they are set blunder

10.Errors in reading the tape mistake

11.Incorrect counting of tape lengths blunder

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Chain surveying

Chain surveying is the type of surveying in whichonly linear measurements are made in field.

Setting perpendicular

The point or object is located by measurement of adistance & angle from a point on chain line. When theangle of offset is 90 it is called perpendicular offset.

When the angle of offset is other than 90 is obliqueset.

A B

R

P S

R

Q

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Instrument for setting out right angles

Cross staff

1.Open cross staff

2.French cross staff

3.Adjustable cross staff

Optical square

Site squareObstacles in chaining

Obstacles to ranging

Obstacles to chaining

Obstacles to chaining & ranging

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TraversingTraversing is the type of surveying in which a number

of connected survey lines form a frame work &

directions, length of survey lines are measured.Closed traverse

Lines form a circuit which ends at starting point.

Open traverse

Circuit ends elsewhere.Methods of traversing

Chain traversing

Chain & Compass traversing (loose needle method)

Transit tape traversing

By fast needle method

By measurement of angle between lines

Plane table traversing

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Chain traversing

Chain & Tape is used to do the work

No angle measuring instruments used

Directions of the lines are fixed by linearmeasurements. The angles fixed by linearmeasurements are known as chain angles.

This method is unsuitable for accurate work.

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Plotting

Plotting is done by two methods:

Angle & distance methods By protractor

By tangent of angle

By chord of angle

Co-ordinate methodThis method is more practical & accurate.

Balancing the traverse

Following are methods of adjusting the traverse:

Bowditchs method

Transit method

Graphical method

Axis method