Levelling-Intro

7/27/2019 Levelling-Intro

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3a. LEVELLING

Rauf Rasam

[email protected]

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OUTLINE

Levelling When do we level?

Definitions/Terminology

Levelling Instrumentation

Method of Levelling

Rules for Levelling

Levelling Procedures (Two peg test, reducing levels

using rise and fall method)


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What is levelling?

A measurement process whereby the relative

dif ference in heigh tbetween two or more points

can be determined

Difference in heightH=BS-FS

BS FS

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When do we level?

Typical examples include : To establish new vertical control (BM or TBM)

To determine the heights of discrete points

To provide spot heights or contours on a plan

To provide data for road cross-sections or volumes ofearthworks

To provide a level or inclined plane in the setting out of

construction works To prepare a layout map for engineering work (e.g. Water

supply, road, sanitary or drainage.

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Definitions

direction of gravity

level surface

Earth SurfaceA

B

Datum = M.S.L

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Vertical line

Reduced level


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Definitions (cont.)

BS FS

CP

BS FS

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BMFixed mark of known RL

TBM


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Definitions (cont.)

Level surface

A curved surface

The direction of gravity is always perpendicular to a

level surface

Horizontal Plane

A horizontalplane will be tangent to a levelsurface

Over short distances (


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Definitions (cont.)

Datum

A reference surface to which the heights of all points

in a survey or on a site are referred

Datum in Malaysia is Mean Sea Level

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Definitions (cont.)

Reduced Level (RL) The height of a point above/below the datum

Benchmark (BM)

A stable reference point of known RL

Usually used as the starting and finishing point when

levelling

Temporary Bench Mark (TBM)

A point placed (e.g. peg, nail, spike) to provide atemporary reference point

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Definitions (cont.)

Backsight (BS) Always the first reading from a new instrument station

Foresight (FS)

Always the last reading from the current instrument

station

Intermediate sight (IS)

Any sighting that is not a backsight or foresight

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Definitions (cont.)

Change point (CP) Location of the staff when the level is moved

Change points should be...

Stable

Well defined

Recoverable

e.g.

sharp rock, nail, change plate, etc...

Parallax

-Imperfect focusing due to the image move up/down

relative to cross-hairs/plane of diaphragm

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Levelling Instruments

Level (e.g. dumpy, wye, tilting, automatic/auto &digital)

Tripod

Levelling Staff

Levelling Staff bubble

50 m tape measure (sometimes)

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Levelling Instruments (cont.)

Eyepiece

Circular bubble

Focusing skru

Object lens

Base plateTangent screw

Levelling staff

Auto level

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Cross hair in adiaphgram of level


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Method of levelling

Barometric levelling Atmospheric Pressures

Trigonometric levelling

Compute by vertical angle and horizontal angle

Also called stadia levelling Direct levelling

Level and levelling staff

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Reading an E-face staff

0.315

0.342

0.364

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Rules for levelling

Always commence and finish a level run on aBenchmark (BM or TBM)

Keep foresight and backsight distances as equal as

possible

Keep lines of sight short (normally < 50m)

Never read below 0.5m on a staff (refraction)

Use stable, well defined change points

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Procedures

Setting Up Instrument

Levelling up

Eliminate of errors (parallax, collimation)

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1. Temporary Adjustment/ Levelling Adjustment

Setting/Levelling Up Instruments (Observation)

Taking & booking the staff readings Calculating and adjusting/reducting reduced

levels

2. Fieldwork/Labworks


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Procedures/ Levelling Adjustment

Identifies whether the level has a collimation error

Allows the collimation error to be determined

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Levelling Adjustment: Two peg test


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Two-peg test (Cont.)

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Procedures/ Fieldwork/Labworks

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Setting/Levelling Up Instruments (Observation)


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Procedures/ Fieldwork/Labworks

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Taking & booking the staff readings


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A sample loop

BM A

CP 1

CP 2

CP 3

Kerb

Post

Kerb

Setup 1

Setup 2

Setup 3

Setup 4

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Booking the observations

BM A

CP 1

CP 2

CP 3

Kerb

Post

Kerb

Setup 1

Back Inter Fore Point

BM A

CP 1

1.32

3.98

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BM A

CP 1

CP 2

CP 3

Kerb

Post

Kerb

Setup 1

Setup 2


1.32 BM A

3.98 CP 1

Kerb

Post

CP 2

2.56

1.25

3.65

0.67

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BM A

CP 1

CP 2

CP 3

Kerb

Post

Kerb

Setup 1

Setup 2

Setup 3


1.32 BM A

2.56 3.98 CP 1

1.25 Kerb

3.65 Post

0.67 CP 2

KerbCP 3

3.49

2.58

1.54

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BM A

CP 1

CP 2

CP 3

Kerb

Post

Kerb

Setup 1

Setup 4

Setup 2

Setup 3


1.32 BM A

2.56 3.98 CP 1

1.25 Kerb

3.65 Post

3.49 0.67 CP 2

2.58 Kerb1.54 CP 3

BM A

2.64

3.79

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Reducing levels (Rise and Fall)

Back Inter Fore Rise Fall RL Comment

1.32 50.00 BM A

2.56 3.98 CP 1

1.25 Kerb3.65 Post

3.49 0.67 CP 2

2.58 Kerb

2.64 1.54 CP 3

3.79 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 Kerb3.65 Post

3.49 0.67 CP 2

2.58 Kerb

2.64 1.54 CP 3

3.79 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 Post

3.49 0.67 CP 2

2.58 Kerb

2.64 1.54 CP 3

3.79 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 CP 2

2.58 Kerb

2.64 1.54 CP 3

3.79 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 Kerb

2.64 1.54 CP 3

3.79 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 CP 3

3.79 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 1.15 50.03 BM A

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 1.15 50.03 BM A

10.01 9.98

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 1.15 50.03 BM A

10.01 9.98

(0.03)

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 1.15 50.03 BM A

10.01 9.98 6.24 6.21

(0.03)

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 1.15 50.03 BM A

10.01 9.98 6.24 6.21

(0.03) (0.03)

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 1.15 50.03 BM A

10.01 9.98 6.24 6.21

(0.03) (0.03) (0.03)

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1.32 50.00 BM A

2.56 3.98 2.66 47.34 CP 1

1.25 1.31 48.65 Kerb3.65 2.40 46.25 Post

3.49 0.67 2.98 49.23 CP 2

2.58 0.91 50.14 Kerb

2.64 1.54 1.04 51.18 CP 3

3.79 1.15 50.03 BM A

10.01 9.98 6.24 6.21

(0 03) (0 03) (0 03)

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Levelling-Intro

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