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Transferring Datums PowerPoint PPT Presentation


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Transferring Datums. Temporary Bench Mark (TBM). Temporary Bench Mark (TBM) from which levels are taken. A Temporary Bench Mark (TBM) is a known height point from which all levels are taken. The TBM can be related to an Ordnance Survey Bench Mark. . The TBM can be surrounded by concrete

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Transferring Datums

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Transferring Datums


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Temporary Bench Mark (TBM)

Temporary Bench Mark

(TBM) from which levels are taken

A Temporary Bench Mark (TBM)

is a known height point from which

all levels are taken.

The TBM can be related to an

Ordnance Survey Bench Mark.

The TBM can be surrounded by concrete

and a timber enclosure for protection.


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Ordnance Survey Bench Mark

Level taken from here

Ordnance Survey Bench Mark – datum which marks the height above mean sea level at Newlyn in Cornwall.

These datum's are established by the

Government Survey Office and are

usually permanently marked on public

building, bridges etc.


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Example of Ordnance Survey Bench Mark


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A Datum peg is a level point that is established in relation to a

Temporary Bench Mark.

The datum is a level reference point for the building activities, a few are shown

below.

Datum peg at

DPC level

DPC

Oversite

concrete

level

Foundation

concrete level

Invert level


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Transferring Datums

Using Straight Edge and Level


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A

Mark the position of the level

on the straight edge to ensure

it remains in the same

position.

B

X

Drive a peg (X) in the lengths of the straight

away from the datum and level.


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B

X

A

Y

To maintain accuracy the spirit level

and straight edge should be reversed at each intermediate

leveling point as seen point B on the straight edge remains on peg X and

A swings round to peg Y.


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A

B

A


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Any inaccuracies in the level and straight edge are corrected by reversal

of the level and straight edge as illustrated below.

TBM

Peg 1

Peg 2

Peg 3

Peg 4

Datum Level


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