lecture 02 differential levelling

8/19/2019 Lecture 02 Differential Levelling

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BRAE 239 – Engineering SurveyingBRAE 239 – Engineering Surveying

Homework “A” Due

1/5/2016 Differential Leveling 2

Definitions

• Leveling is used for

Design of improvements

Layout of construction projects

Volume Calculations

Mapping

Monitoring of earth movement


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Definitions

• Datum - vertical A level surface taken as a surface of reference

o NGVD29 – National Geodetic Vertical Datum of 1929

o NAVD88 – North American Vertical Datum of 1988

o Tidal

o Local

o Assumed

• Elevation The vertical distance from the datum

• Benchmark A permanent object, having a marked point whose elevation relative

to a specific datum is known


Definitions

• Level loop or Level Circuit

The process in leveling of completing a “loop” by always starting on a

point of known elevation and always terminating on a point with a

known elevation

Often can be the same point for both the start and end.


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Field Note keeping


Field

Note

keeping


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Field Note keeping

• Once the loop is completed you need to Perform a Math Check

o ElevStarting + ∑BS - ∑FS = ELEVEnding

Determine Error of Closure

o |MeasureEndElev – KnownEndElev|

Determine Allowable Error

D0.0014 A.E.


Field

Note

keeping


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Rod Readings


Rod

Readings

0.01’

0.01’

1 Foot Marker

0.1’ Marker0.05’ Marker

Rod Reading = 7.24’


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Rod Readings


Field

Procedures


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Field Procedures


Field

Procedures


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Field Procedures

• Set the level up equidistant between backsight &foresight

± 30 feet

You do not need to be in line between both points

Make sure you can see both pointso Check with hand level

Do NOT Set up on the Asphalt

• Set the level no further then 150 feet from either

backsight or foresight


Field

Procedures

• Before moving the level

Make sure you have all the readings needed from your

current location

o Backsight

First reading after setup

o Foresight

Second reading after setup

Make sure the rod stays at the foresighto This will be your next Backsight Reading


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Field Procedures

• When moving

Keep the level upright

• When using a Turning Point Spike

Set the Spike so it is solid in the Ground

Set the rod on top of the Spike when reading the rod

Leave something by the spike so you can find it


Field

Procedures

• Always Turn through a point

This means after you take a foresight reading on a pointo You move the level before you take your backsight reading

• Check your Error of closure in the field

Make sure it meets the allowable error

If noto Run each section of the loop and check to see if that solves the

problem


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Lab 03

• You will be workingover at the Sportsfield Area

• You will determinethe elevations ofPoints C & D foryour Crew NumberYou will start on

Benchmark SF-1oElevation 322.42’

First go to the “D”Point

Then go to C point

Finally close backon SF-1


Field

Procedures

• ShowNorth

General Area

Location of MonumentsoMonument is any relatively permanentobject that you measure to

Description of MonumentsoWhat physically is the monument

Swing Ties to MonumentsoTwo distance ties

To the nearest 0.10’

Tie out Both “D” and “C”Monuments


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Lab 03

• Party Chiefs You will need to check out on the Equipment card

o Field Box

o Automatic Level

o Tripod

o Philadelphia Rod

Put your party No, Date (January 5, 2016), and your name

• Crews make sure you have Equipment

Note keepers field book o Note the Serial Number of the Level in your books

Lab instructions

Calculator

• The Room will be locked up

No one gets in untilo I get back from the field

So there is no reason to rush

lecture 02 differential levelling

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