Leveling 1

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Surveying & Measurement

Levelling


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Levelling

The general term applied to any of the

various processes by which elevations of

points or differences in elevation are

determined.


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Levelling

To measure the difference in height (H)

between two points and !" vertical rods are

set up at each of these two points and a level

somewhere between them. The height difference between and ! is the

difference between the rod (staff) readings.


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#nce the elevation of a point is

determined" that point can be used for

determining the elevations of other points.


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Some $efinitions (%)

Levelling surveying operation carried out todetermine the elevation of points or to find the differencein elevation of points

Spirit Level/Engineers Level surveying instrumentused to carry out levelling

Backshot (BS) sighting with a level bac' to a pointof 'nown elevation

Foreshot (FS) sighting with a level to determine theelevation of a point

Turning Point point at which you have establishedan elevation with S and on which you will subseuentlyta'e a !S

Intermediate Shot foreshot to a point at which youwant to 'now the elevation but which will not be used asa turning point


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Some $efinitions (*)

Peg Test Surveying operation carried out to determineif the levelling bubble and telescope line+of+sight areparallel

Elevation o Instrument (EI) ,levation of the

telescope cross+hairs Balancing shots ttempt when doing a levelling

survey to 'eep the lengths of S and !S at any giveninstrument setup as close as possible.

!losure Error $ifference in elevation determined fromthe levelling survey and the 'nown elevation of abenchmar'.


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The -se of Levelling

To design highways" railroads" canals" sewers"

water supply systems etc" having grade lines

that best conform the eisting topography"

To lay out construction pro/ects according toplanned elevations"

To calculate volume of earthwor's and other

materials"

To investigate drainage characteristics of an

area" etc.


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The ,uipments 0

1od (Staff) (%)


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The ,uipments 0

1od (Staff) (*)

2hiladelphia 1od (front)

2hiladelphia 1od (rear)

$ouble faced levelling

rod


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The ,uipments 0

1od Level and Tripod


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3arrying and Setting -p a Level

lways carry it in the container.

Screw the head snugly on the tripod.

or bull eye4s bubble" alternately turn one screw

and then the other two.

#n side+hill setups" place one leg on the uphill

side and other two on the down hill side.

-se hand level to chec' for proper height of thesetup before precisely levelling the instrument.

vial


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2ond !ubble

5hen pond bubble is centred the instrument4sstanding ais is approimately vertical.

The compensators in the instrument ta'e overand ad/ust the optical Line of 3ollimation so that

it is hori6ontal. 5hen the instrument is rotated the

compensators ensure that a hori"ontal plane ocollimationis swept out.


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#utomatic Levels

fter the pond bubble

is manually centered"an automatic

compensator levels the

line of sight" and 'eepsit level.


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utomatic Level


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,+type Levelling Staff (%)


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,+type Levelling Staff (*)

%.788%.7%8%.7*8%.798

%.79*


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,+type Levelling Staff (9)

%.%88%.%%8

%.%*8%.%98

%.%99


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3ommon ,rror Sources

Level rod not vertical

Levelling rod not fully etended or

incorrect length

Level instrument not level

:nstrument out of ad/ustment

,nvironment + wind and heat


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,limination of 2aralla

2aralla is the apparent movement of the

image produced by movement of the

observer


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Types of Levelling =ets

#pen leveling nets

3losed loop leveling nets

height

kno$n


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Types of Level>ng =ets

3losed lin' or closed connecting leveling nets

Leveling between two points is performed in two

steps0 forward (HAB) and bac'ward (HBA).

The height differences"HAB

andHBA

shouldbe theoretically eual.

HAB - HBA d

height

kno$n

height

kno$n


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HPC MethodHeight of the Plane of Collimation Method

:t consists in finding the elevation of the

plane of collimation for every set up of the

instrument and then obtaining the reduced

levels (1L) of point with reference to therespective plane of collimation.

The ?23 method is generally used in

profile levelling and in setting out levels forconstructional wor'.


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Same staff position as last reading

therefore the same row =ew staff position therefore a new row

?23 @ 1educed Level (1L) A !S

1L @ ?23 + S

1L @ ?23 + :S


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!L%SE&'L%%P LEELI* !%+P,T#TI%

!ollimation +ethod

-od -eadings (m)Bench+arks

&istance(m) BS IS FS

!ollimation.eight

.eights !orrected.eights (m)

/

*

9

B

C

D

E

F

/

B8

F8

E8

C8

D8

E8

FB

B*

*.%BE

%.D%9

%.8E7

9.BC*

8.9%B

8.*E%

*.EBC

8.DF*

8.B7%

*.9%*

8.*FD

8.%E7

9.C7F

%.8C*

%.B*9

*.7C9

%*F.D*%

%*7.EB9

%*F.C%8

%9%.DED

%9%.F%%

%*F.BFB

%98.%EE

%*7.B9D

%*D.BEB

%*F.%98+%

%*E.B9%+*

%*F.**B

+9

%9%.B7E+B

%*F.*%9+C

%*E.B9*+D

%*F.ECB+F

%*D.BF9+7

/012343

%*F.%*7

%*E.B*7

%*F.**%

%9%.B79

%*F.*8F

%*E.B*D

%*F.EBD

/012343

L @ B7D m !S@%*.989 %*D.BF9 G %*D.BEB @ 8.887 m

3hec' 0 !S+ S @%*.989 G %*.*7B @ 8. @ 8.887m


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!alculation checks

S + !S @ %st 1L + Last 1L

:S A S A (1Ls ecept first)@ (each ?23 number of applications)

!heck +isclosure

llowable Misclosure @ H C= mm. (I1ule of ThumbI)

5hen calculations are chec'ed andif the misclosure is allowable

$istribute the misclosure.

Simple check

Full check


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1ise and all Method

:t consist in determining the difference of levelbetween consecutive points by comparing eachpoint after the first with that immediatelypreceding it.

The difference between their staff readingindicates a rise or a fall according as the staffreading at the point is smaller or greater thanthat preceding point.

The 1L of each point is then found by addingrise or subtracting fall to or from the 1L.

The 1 method provides complete chec' on :S.

:t is commonly used for differential levelling.


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!L%SE&'L%%P LEELI* !%+P,T#TI%

-ise 5 Fall +ethod-od -eadings (m) &. (m)Bench

+arks

&istance

(m) BS IS FS -ise (6) Fall (')

.eights (m)

/

*

9

B

C

D

E

F

/

B8

F8

E8

C8

D8

E8

FB

B*

*.%BE

%.D%9

%.8E7

9.BC*

8.9%B

8.*E%

*.EBC

8.DF*

8.B7%

*.9%*

8.*FD

8.%E7

9.C7F

%.8C*

%.B*9

*.7C9

%.DCD+%

8.E79+%

9.*E9

+%

%.9**+*

8.D77+%

9.*FB+%

8.EF%+%

*.*E%+%

/012343

%*F.%*7

%*E.B*7

%*F.**%

%9%.B79

%*F.*8F

%*E.B*D

%*F.EBD

/012343

L @ B7D m !S@%*.989 S@%*.*7B @ E.8BB @ E.89C

3hec' 0 !S+ S @%*.989 G %*.*7B @ 8.887 1:S,+ LL @ E.8BB + E.89C @ 8.887


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1ise and all Method


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1ise and all Method

all @ S + !S

all @ :S + !S

1ise @ !S + S1L @ 2revious 1L A 1ise

1L @ 2revious 1L + all


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3ollimation ,rrorTwo 2eg Test

The trueheight difference" hT

The visi7leheight difference" h

S%@ S

%4A and

S*@ S

*

4 A

?ori6ontal

Line of sight

!

d

S%

S%4

S*

S*4

L J *

L

L J *

hT @ S%4 + S*4

@ S% + S*h

h @ S%4+ S*4 @hT

h @ (S%4A ) + (S*4 A )

Since the instrument

is the same distancefrom both staff

positions and the

errors are eual

and cancel out.


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?ori6ontal

!

S9

S94

SB

SB4

L J %8L

:f =#T then the error is @

The visi7leheight difference!ut the trueheight difference

:f h @ hT then the instrument is #K

(S% + S*) + (S9 + SB) J L mm J m

h @ S9 + SBhT @ S% + S*


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2lace two pegs about L @ 98m (to B8m) apart. Set up level midway between the two pegs. 1ead staff on each peg" and calculate true

height difference . Move level about L J %8 @ 9m (or Bm) beyond

one of the pegs. 1ead staff on each peg again" and calculate

height difference.

3ollimation ,rror" @ difference in the differencesand is epressed as a number of mm per L m


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cceptable errors -ren and 2rice %mm per *8m 5impey Bmm per C8m

Test should be carried out regularly.


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?ori6ontal

Line of sight

!

d

S%S*

L J *

L

L J *

?ori6ontal

!

S9

SB

L J %8L

3ollimation error" @ (S% + S*) + (S9 + SB) J L" mmJm


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2834 m 249 m

2:38 m

02;09 m

# t$o peg test gave the ollo$ing results

Leveling 1

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