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TABLE OF CONTENT

NO. TOPIC PAGE

1. INTRODUCTION TO LEVELLING

1.1 Definition of Levelling

1.2 Uses of Levelling

1.3 Definition of terms used in Levelling

1.4 Methods of Levelling

2 - 9

2. OBJECTIVES 10

3. APPARATUS USED 11 - 13

4. LEVELLING FIELDWORK 14

5. FIELD DATA 15 - 16

6. ADJUSTED FIELD DATA 17 - 18

7 TWO PEG TEST 19

8. DISCUSSION 20

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INTRODUCTION TO LEVELLING

1.1 DEFINITION OF LEVELLING

Levelling is the process of finding the relative height of different points on, above, or below the

surface.

It is the measurement of geodetic height using an optical levelling instrument and a level staff or

rod having a numbered scale.

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1.2 USES OF LEVELLING

Levelling acts as a referencing point to find out and make sure the vertical stability of the points

with respect to reference point or known as the benchmarks in its immediate vicinity.

It can be the connection to GPS reference points by connecting the points to reference stations

in global coordinate system via GPS to find out its regional stability and to separate sea level

rise from vertical crustal motion.

The point of mean sea level is connected to the national levelling network to define vertical

datum for national surveying and mapping, the connection to the network will allow all points to

be connected to each other and provides information on spatial variations in mean sea level.

Levelling can be used to design highways, railroads, canals, sewers, water supply systems, to

lay out construction projects according to planned elevations, to calculate volume of earthworks

and other materials and to investigate drainage characteristics of an area.

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1.3 DEFINITION OF TERMS USED IN LEVELLING

Level surface: A surface in which any point is perpendicular to the direction of the force

towards the pull of gravity. It can also refer to any surface which is parallel to the mean

spheroidal surface of the earth.

Level line: A line lying on a level surface in which normal to the plumb line at all points.

Level datum: An arbitrary level surface which refer to elevations. There are two types of datum,

the ordnance datum and an assumed datum.

● Ordnance datum (O.D.): Heights that are shown on Ordnance Survey (O.S.) referring

to the maps. Datum line is the mean sea level (MSL).

● Assumed datum: Established by giving a benchmark an assumed value to which all

heights and levels in the local area will be reduced.

Horizontal plane: A plane point that is tangent to the level surface at that particular point in

which perpendicular to the plumb line through that point.

Horizontal line: A straight line that is tangent to a point at a level line in which perpendicular to

the plumb line.

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Vertical plane: A plane containing a vertical line.

Vertical line: Commonly defined by a plumb line. It is a line normal to a point at the level line.

Elevation: Vertical distance above or below an arbitrarily assumed level surface or datum of a

point on or near the surface of the earth.

Mean sea level (MSL): The average height of the sea for all stages of the tides. It is derived by

averaging the hourly tide heights over a long period of 19 years at any particular place.

Bench mark (BM): A definite and permanent accessible point of known height above a datum

to which the height of other points can be referred.

Temporary benchmark (T.B.M.): A bench-mark set up by the surveyor himself for his own use

for a particular task.

Reduced level: Height or depth of any point above or below any datum. It is denoted as R.L.

Line of collimation: Intersection line of cross hairs of diaphragm to the optical centre of object

glass and its continuation. It is also known as line of sight.

Height of instrument: Vertical distance of collimation with respect to datum.

Back-sight (B.S.): First staff reading taken after the set-up of instrument. It is a staff reading

taken at a known elevation.

Foresight (F.S.): Last staff reading taken denoting the shifting of the instrument.

Intermediate sight (I.S.): Staff reading taken on a point in which elevation is to be determined.

It is the staff reading between back-sight and foresight.

Change point (C.P.): An arbitrary point which enables the levelling to continue from a new

instrument position. It is also denoted as turning point (T.P.).

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1.4 METHODS OF LEVELLING

Height of Collimation Method

This method consists of discovering the elevation of the plane of collimation (H.I.) for every set

up of the instrument and to obtain the reduced level of point to with reference to the respective

plane of collimation.

It is generally used in profile levelling and in setting out levels for constructional work.

Rules of booking

a. The survey starts from a known level which is the Ordnance Bench Mark (OBM) or a

Temporary Bench Mark (TBM). This is to obtain the first reading from the instrument

position which is the back sight.

b. The height of collimation is the addition of the back sight and reduced level, entered on

the same line.

c. An intermediate sight will occur between the back sight and foresight.

d. Foresight is the last reading from an instrument position.

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e. In order to get the next reduced level, the foresight or intermediate sight is subtracted

from the height of collimation, entered on the same line as the foresight or intermediate

sight.

f. When the instrument is moved to a new position, the height of collimation change.

g. A new height of collimation is given entered on the same line for every back sight.

h. All readings referring to the same point on the ground are entered on the same line.

In brief,

Heights of collimation (H. of C.) = Reduced Level (R.L.) + Back-sight (B.S.)

Reduced Level (R.L.) = Heights of collimation (H. of C.) - Foresight (F.S.)

Reduced Level (R.L.) = Heights of collimation (H. of C.) - Intermediate sight (I.S.)

Calculation checks,

Simple Check

Σ F.S. - Σ B.S. = First R.L. - Last R.L.

Full check

Σ I.S. + Σ F.S. + Σ (R.L. except the first) = Σ (each H. of C. x number of applications)

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Rise and Fall Method

This method consists in finding the difference of level between consecutive points by comparing

each point after the first with that immediately preceding it. The reduced level (R.L.) is found by

adding rise of subtracting fall to or from the preceding reduced level itself (R.L.).

It is commonly used for differential levelling.

Rules of booking

a. The first and last reduced level is on an Ordnance Bench Mark (OBM) or a Temporary

Bench Mark (TBM)

b. There is a rise when the first staff reading is larger than the second staff reading in any

consecutive pair of staff readings.

c. There is a fall when the first staff reading is less than the second staff reading in any

consecutive pair of staff readings.

d. In order to obtain the new reduced level, add the rise and subtract the fall from the

preceding reduced level entering on the same line as the rise or fall.

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In brief,

Fall (F) = Foresight (F.S.) – Back-sight (B.S.)

Fall (F) = Intermediate sight (I.S.) – Back-sight (B.S.)

Rise (R) = Back-sight (B.S.) - Foresight (F.S.)

Reduced Level (R.L.) = Precede Reduced Level + Rise (R)

Reduced Level (R.L.) = Precede Reduced Level - Fall (F)

Calculation checks,

Σ B.S. - Σ F.S. = Σ R - Σ F = Last R.L. - First R.L.

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OBJECTIVES

To give meaning as a basis for the proper knowledge of levelling.

To understand the ways of using levelling.

To determine the elevations of given points with respect to an assumed reference line

called datum.

To establish point at required elevation respect to datum

To measure the difference in height (ΔH) between two points, A and B, where

vertical rods are set up at each of these two points and a level between them.

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APPARATUS USED

Auto Level

An auto level, also known as a dumpy level or builder’s auto level is a professional levelling tool

used by contractors, builders, land surveying professionals, or the engineer who demands

accurate levelling every time. It is an optical measuring device used to establish a horizontal

plane. Auto level sets up fast, it is easy to use, and save time and money on every jobs.

The auto level has a compensator mechanism that uses a combination of fixed prisms or

mirrors and a moving prism suspended on a pendulum to give a horizontal reference. When

correctly set up the compensator will ensure that the ray of light through the centre of the

reticule is exactly horizontal.

Plumb bob

A plumb bob or a plummet is a weight with a pointed tip on the bottom that is suspended from a

string and used as a vertical reference line. This instrument used in surveying to sight a point on

the ground that is not readily visible. They are used to set the instrument exactly over a fixed

datum marker, prior to taking fresh readings.

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Tripod

To set up the tripod so that it is secure, the head is approximately level and the instrument

telescope will be at the eye level.

Each leg of a tripod is adjustable for length. The legs are locked by a lever clamp (left) or screw

(right). Once the legs have been set to the correct length it is important that the locking lever or

screw is tight.

Tripod Head has a polished level surface for the instrument to stand on. The tripod screw is

captive and mounted on a movable bracket to allow the instrument to be centred over a station

if necessary.

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Levelling Staff

The levelling staff is simply a large ruler, available in lengths of 3, 4, or 5 metres and usually

made of aluminium with telescopic sections. The levelling staff is sectional so that can be

adjusted in length to allow for easy storage and transport. The sections have locking buttons to

ensure accurate length is maintained.

The “E” pattern is designed to make it easy to read a small section of the scale when see

through a telescope.

Staff bubble

The staff bubble is an attachment for the levelling staff. It has to ensure that the bubble is in the

centre of the black circle which makes sure that the levelling staff is vertical and not tilted.

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LEVELLING FIELDWORK

Location: Taylor’s University Lakeside campus staff car park

Source: https://times.taylors.edu.my/pluginfile.php/2423365/mod_resource/content/1/Field-Work%20Assignment1.pdf

https://times.taylors.edu.my/pluginfile.php/2423365/mod_resource/content/1/Field-Work%20Assignment1.pdf

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FIELD DATA


BS IS FS HEIGHT OF COLLIMATION

REDUCED LEVEL

1.338 101.338 100.000

1.367 3.668 99.037 97.670

1.310 97.727

1.259 1.352 98.944 97.685

1.516 1.381 99.079 97.563

1.320 1.305 99.094 97.774

1.258 1.258 99.094 97.836

1.240 1.482 98.852 97.612

1.244 1.128 98.968 97.724

3.572 1.252 101.288 97.716

1.289 99.999

1.280 100.008

14.114 14.106 100.008

14.106 100.000

0.008 0.008

Acceptance Mis-closure: 12+/- √k

k = Number of set ups

12+/-√9 = +/- 36mm

Therefore, the levelling is acceptable

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BS IS FS RISE FALL REDUCED LEVEL

1.338 100.000

1.367 3.668 2.330 97.670

1.310 0.057 97.727

1.259 1.352 0.042 97.685

1.516 1.381 0.122 97.563

1.320 1.305 0.211 97.774

1.258 1.258 0.062 97.836

1.240 1.482 0.224 97.612

1.244 1.128 0.112 97.724

3.572 1.252 0.008 97.716

1.289 2.283 99.999

1.280 0.009 100.008

14.114 14.106 2.734 2.726 100.008

14.106 2.726 100.000

0.008 0.008 0.008

Acceptance Mis-closure: 12+/- √k

k = Number of set ups

12+/-√9 = +/- 36mm

Therefore, the levelling is acceptable

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ADJUSTED FIELD DATA

BS IS FS HEIGHT OF COLLIMATION

REDUCED LEVEL

ADJUSTMENT FINAL REDUCED

LEVEL

1.338 101.338 100.000 100.000

1.367 3.668 99.037 97.670 -0.0009 97.669

1.310 97.727 -0.0018 97.668

1.259 1.352 98.944 97.685 -0.0018 97.683

1.516 1.381 99.079 97.563 -0.0027 97.560

1.320 1.305 99.094 97.774 -0.0036 97.770

1.258 1.258 99.094 97.836 -0.0045 97.832

1.240 1.482 98.852 97.612 -0.0054 97.607

1.244 1.128 98.968 97.724 -0.0063 97.718

3.572 1.252 101.288 97.716 -0.0072 97.709

1.289 99.999 -0.0080 99.991

1.280 100.008 -0.0080 100.000

14.114 14.106 100.008

14.106 100.000

0.008 0.008


Arith. checked

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BS IS FS RISE FALL REDUCED LEVEL

ADJUSTMENT FINAL REDUCED LEVEL

1.338 100.000 100.000

1.367 3.668 2.330 97.670 -0.0009 97.669

1.310 0.057 97.727 -0.0018 97.668

1.259 1.352 0.042 97.685 -0.0018 97.683

1.516 1.381 0.122 97.563 -0.0027 97.560

1.320 1.305 0.211 97.774 -0.0036 97.770

1.258 1.258 0.062 97.836 -0.0045 97.832

1.240 1.482 0.224 97.612 -0.0054 97.607

1.244 1.128 0.112 97.724 -0.0063 97.718

3.572 1.252 0.008 97.716 -0.0072 97.709

1.289 2.283 99.999 -0.0080 99.991

1.280 0.009 100.008 -0.0080 100.000

14.114 14.106 2.734 2.726 100.008

14.106 2.726 100.000

0.008 0.008 0.008 Arith. checked

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TWO PEG TEST

Solution:

Instrument midway between point A and B:

RLA1 = 1.256

RLB1 = 1.258

True difference in level BA - 1.258 – 1.256 = 0.002m

From 1m away from A point:

RLA2 = 1.261

RLB2 = 1.261

Apparent difference in level BA - 1.261 – 1.261 = 0m

Since the apparent difference is less than the true difference in level, the line of

collimation is depressed by

0.002m – 0m = 0.002m over 30m

Angle of depression = tan-1 (0.002/30)

= 00’00’14”

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DISCUSSION

In this fieldwork we were required to measure the reduced level of 10 locations around

the Staff Parking at Taylor’s University Lakeside Campus. We started out by assuming a R.L of

100.000m AOD at a lamp post labelled BM 101. Aside from this assumed R.L, we need to

calculate the R.L of the other 10 other locations that was given to us, so we need to take our

equipment around. Making sure to mark down each R.L.

One of the difficulties we faced was trying to make sure the bubble was place in the

middle perfectly. So there will not be any errors. As we were taking down the measurement, we

did not have many intermediate sights, only 2 and most of it is back-sight and foresight.

Once the readings were taken, we used one method to calculate the reduced level,

which is Collimation Method. We arrived at a mis-closure of 0.008m, which was in the

acceptable error range. We then distributed the error to arrive at our final reduced level

readings.

Overall, this is a very new experience for us handling surveying instruments. It really

helps us understand more about the condition as well as widen our horizon. This was a really

fun and interesting assignment.

site surveying leveling

Education