Notes Engineering Survey

8/16/2019 Notes Engineering Survey

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Prof. Dr.-Ing. John Bosco Kyalo KiemaUniversity of Nairobi

Email: [email protected]

by

Engineering SurveyingII


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Course Outline

Introduction. Horizontal Control; traverse

observation, calculation and adjustment. Vertical

control: Levelling and contouring. Applications in

highway drainage and setting out works. Area and

volumes. Mass haul diagram. Practicals: field

surveying.


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Exam CourseWork

CAT PassMark

Total

70 20 10 50 100

Course Assessment


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References

1. Awange, J.L., and Kiema, J.B.K. (2013). Environmental Geoinformatics: Monitoring and Management . Springer Verlag.

2. Bannister, A., Raymond, S., and Baker, R. (1998). Surveying . Pitmans

ELBS. 7th Ed.

3. Irvine and Macclennan (2006). Surveying for Construction . McGraw, C.

5th Ed.,

4. Schofield, W. and Breach, M. (2007). Engineering Surveying.

Butterworth-Heinemann, UK. 6th Ed.

5. Uren and Price. (2010). Surveying for Engineers. Macmillan Press Ltd.

5th Ed.

6. Wolf, P, R., and Ghilani, C.D., (2006). Elementary Surveying: An

Introduction to Geomatics . Pearson Prentice Hall. New Jersey. 11 Ed.


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Course Assignment/Term Paper

Using suitable examples discuss the role of

Geoinformatics in the monitoring and management ofenvironmental pollution.


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Lecture Outline

Part 2: Traversing

Overview of Control Surveys

Concept of Traversing Traverse Computation

Accuracy of Traversing

Part 1: Background

Basic Principle of Surveying

Datum Concept

Tenets of Survey Practice

Part 3: Vertical Control

Introduction and Definitions

Principle of Levelling Sources of Errors

Applications of Levelling

Part 4: Earthworks

Computation of Areas and Volumes

Mass Haul Diagrams


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Part 1: Background


Datum Concept



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1) Working from the “whole to the part”. First

provide control using methods with higher

accuracy followed by detail mapping usinglower accuracy and cheaper methods.

2) Always perform independent checks. Make

more observations than the basic minimumneeded.

3) Specifications and accuracy required.


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Datum ConceptBasic problem in Surveying is to determine the position

(measure) of features on Earth’s curved surface and

map (coordinate) them for diverse purposes often onto

a plane.

Datum refers to a plane or surface to which positions

and elevations of points are referenced.

Ellipsoid is reference surface in geodetic surveys.

Best fitting ellipsoid is selected.For heighting the most commonly adopted datum is

the Mean Sea Level. This is taken with data from

coastal tide gauges over several years.


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Datum Concept (2)

Relationship between the Earth’s Surface, Geoid, and Ellipsoid


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Complete in shortest possible time.

Complete at the least possible cost.

Complete according to client instruction(s) and

survey manual specifications.

Complete using instrumentation of appropriate

accuracy.


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Part 2: Traversing

Horizontal Control Surveys

Concept of Traversing Traverse Computation



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In line with the Principle of Surveying a control

survey provides a framework of survey points,whose relative positions are known to

prescribed degrees of accuracy.

The areas covered by these points may extend

over a whole country and form the basis for the

national maps of that country.

Alternatively the area may be relatively small,

encompassing a construction site for which alarge-scale plan is required. Although the areas

covered in construction are usually quite small,

the accuracy may be required to a very high

order.

Horizontal Control Surveys


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Horizontal Control Surveys (2)

Hence control networks provide a referenceframework of points for:

(1) Topographic mapping and large-scale plan

production.(2) Dimensional control of construction work.

(3) Deformation surveys for all manner of structures,

both new and old.

(4) The extension and densification of existing controlnetworks.


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Horizontal Control Surveys (3)Techniques used in the provision of horizontal controlsurveys include:

(1) Traversing

(2) Triangulation Classical methods

(3) Trilateration

(4) Triangulateration Modern approaches

(5) Satellite position fixing (Global Navigation Satellite

Systems)

(6) Inertial position fixing

(7) Continuously Operating Reference Stations (CORS).

Whilst the above systems establish a network ofpoints, single points may be fixed by intersection

and/or resection.


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Since the advent of EDM equipment, traversinghas emerged as the most popular method ofestablishing control networks not only inengineering surveying but also in geodetic work.Traverse networks are, to a large extent, freeof the limitations imposed on the other systemsand have the following advantages:

(1) Much less reconnaissance and organizationrequired in establishing a single line of easily

accessible stations compared with the laying outof well-conditioned geometric figures.

(2) The limitations imposed on the other systems bytopographic conditions do not apply to

traversing.

Concept of Traversing


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Concept of Traversing (2)

(3) The extent of observations to only two stationsat a time is relatively small and flexiblecompared with the extensive angular and/orlinear observations at stations in the other

systems. It is thus much easier to organize.(4) Traverse networks are free of the strength of

figure considerations so characteristic oftriangular systems. Thus once again the

organizational requirements are reduced.(5) Scale error does not accrue as in triangulation,

whilst the use of longer sides, easily measuredwith EDM equipment, reduces azimuth swing

errors.


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(6) Traverse stations can usually be chosen so as tobe easily accessible, as well as convenient for

the subsequent densification of lower order

control.

(7) Traversing permits the control to closely follow

the route of a highway, pipeline or tunnel, etc.,

with the minimum number of stations.

From the logistical point of view, traversing isfar superior to the other classical horizontal

control methods and offers at least equivalent

accuracy.

Concept of Traversing (3)


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Definition of TraversingTraversing is a surveying technique used to

determine the planimetric positions (Easting andNorthing: EB and NB below) of control points orsetting out points using measured angles anddistances (DAB and Q below).

EB=EA+ΔEAB= EA+ DABsin Q

NB=NA+ΔNAB= NA+ DABcosQ


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In traversing, the relative position of control

points is fixed by measuring the horizontal angleat each point, subtended by the adjacent

stations, and the horizontal distance between

consecutive pairs of stations.The liability of a traverse to undetected error

makes it essential that there should be some

external check on its accuracy. Hence, the

traverse needs to commence from and connectinto known points of greater accuracy than the

traverse.

Types of Traverses


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Types of Traverses (2)

In this way, the error vector of misclosure can

be quantified and distributed throughout thenetwork, to produce geometric correctness. Sucha traverse is called a ‘link’ traverse.The link traverse has certain advantages over

the remaining types, in that systematic error indistance measurement and orientation are clearlyrevealed by the error vector.Alternatively, the error vector can be obtained

by completing the traverse back to its startingorigin. Such a traverse is called a ‘polygonal’ or‘loop’ traverse.


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a) Link traverse b) Loop traverse (oriented)

d) Open (free) traverse

c) Loop traverse (independent)


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Both the ‘link’ and ‘polygonal’ traverses aregenerally referred to as ‘closed’ traverses.

The third type of traverse is the ‘free’ or

‘open’ traverse, which does not close back onto

any known point and which therefore has no wayof detecting or quantifying the errors.

Open traverses are not recommended due to

the lack of checks. Nevertheless, it is

frequently utilized in mining and tunnelling work

because of the physical restriction on closure.



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Field Procedure

Reconnaissance is a vitally important part of anysurvey project. Its purpose here is to decide

the best location for the traverse points.

In the first instance the points should be

intervisible from the point of view of traverseobservations.

If the purpose of the control network is the

location of topographic detail only, then they

should be positioned to afford the best view of

the terrain, thereby ensuring that the maximum

amount of detail can be surveyed from each

point.


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Field Procedure (2)If the traverse is to be used for setting out

e.g., the centre-line of a road, then thestations should be sited to afford the best

positions for setting out the intersection points

(IPs) and tangent points (TPs), to provide

accurate location.

The distance between stations should be kept as

long as possible to minimize effect of centring

errors.Finally, as cost is always important, the scheme

should be one that can be completed in the

minimum of time, with the minimum of

personnel.


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Sources of Errors

The sources of error in traversing include:

(1) Errors in the observation of horizontal and vertical

angles (angular error).

(2) Errors in the measurement of distance (linear

error).

(3) Errors in the accurate centring of the instrument

and targets, directly over the survey point

(centring error).


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Traverse Computation

Using the data given below, compute the

coordinates of various points in the following

traverse.

Apply Bowditch rule to distribute the

misclosure.


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Station Observations Station Observations

At Tr29 At Tr37

Tr28 97

11

10

Tr36 179

02

59

Tr10 279

15

11

Tr42 21

54

58

Tr36 52

15

03

At Tr42

At Tr36 Tr37 201

54

58

Tr29 232

15

03

Tr43 234

55

58

Tr37 359

02

59

Tr41 120

32

05

Traverse Computation (2)


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Traverse Computation (3)

Traverse Distances: Datum Bearings:Tr29 – Tr36: 78.959m Tr29 – Tr28: 97

11

10

Tr36 – Tr37: 68.589m Tr10 – Tr29: 99

15

25

Tr37 – Tr42: 62.019m Tr42 – Tr43: 234

56

07

Tr42 – Tr41: 120

31

34

Datum Coordinates:

Station N (Metres) E

Tr29 78 674.77 92 174.20Tr42 78 849.21 92 258.63


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Bearing Sheet

Station Observations OrientationCorrection

ProvisionalBearing Misclosure FinalBearing

At Tr29

Tr28

Tr10

Tr36

At Tr36

Tr29

Tr37

At Tr37

Tr36Tr42

At Tr42

Tr37

Tr43

Tr41

97 11 10

279

15

11

52

15

03

232

15

03

359

02

59

179

02

59

21 54 58

201 54 58

234

55

58

120 32 05

00

+14

+07

+07

+07

+07

52

15

10

232

15

10

359

03

06

179

03

06

21 55 05

201 55 05

234

56

05

120

32

12

-05

-09

-14

-18

+02

-38

97 11 10

279

15

25

52

15

05

359

02

57

21 54 51

234

56

07

120

31

34


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Computation of Coordinates

ΔN (m) ΔE N (metres) ETr29 – Tr36 Tr29:+78 674.77 +92 174.20

52

15

05

+48.339 +62.433

78.959m -0.01 -0.01

Tr36 – Tr37 Tr36:+78 723.10 +92 236.62359 02 57 +68.580 -1.138

68.589m -0.01 0.00

Tr37 – Tr42 Tr37:+78 791.67 +92 235.48

21 54 51 +57.538 +23.14762.019m 0.00 0.00

Tr42:+78 849.21 +92 258.63


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ΔN (m) ΔE

By Datum: 174.440 84.430

By Traverse: 174.456 84.442

Misclosure: -0.016 -0.012

Length of Traverse = 209.567m

Accuracy = Sqrt{(-0.016)2+(-0.012)2 }/209.567 = 1 in 13,000

(approx)

Computation of Coordinates (2)


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Traversing is generally more accurate thanclassical triangulation and trilateration.Due to the weak geometry of a traverse, itgenerally has only three degrees of freedom (that

is three redundant observations), it is difficult toarrive at an estimate of accuracy.Although there have been many attempts toproduce equations defining the accuracy of a

traverse, at the present time the best approach isa strength analysis using variance–covariancematrices from a least squares adjustment.


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Blunders in the observed data

Blunders or mistakes in the measurement of theangles, results in gross angular misclosure.Provided it is only a single blunder it can easily belocated.In the case of an angle, the traverse can be computed

forward from X (Figure) and then backwards from Y .The point which has the same co-ordinates in eachcase, is where the blunder occurred and the angle mustbe re-observed.

Figure: Detection ofangular traverse blunder


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Blunders in the observed data (2)

In the case of a blunder in measuring distance,the incorrect leg is the one whose bearing is

similar to the bearing of the error vector.

If there are several legs with similar bearings themethod fails.

Again the incorrect leg must be re-measured.


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Part 3: Vertical Control

Introduction and Definitions

Principle of Levelling

Sources of Errors Applications of Levelling


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The process of determining elevations (heights)

of points of interest above or below a referencedatum or differences in elevations.For most practical applications only thedifference in elevation between points ofinterest and not absolute heights is oftenrequired.Used in all aspects of surveying, particularly forengineering surveys, route surveys, construction,etc.

Different methods may be used for estimatingheights or height differences including;differential levelling, barometric heighting,trigonometric heighting, gravimetry andsatellite positioning etc.

Overview of Levelling


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a) Differential levelling: basic idea involves obtaining of heightdifference between points by measuring their vertical distancefrom a horizontal line of sight.

b) Trigonometric heighting: method is generally used indetermination of elevation differences of lower accuracy thanspirit levelling. It is useful where it is very difficult (or

impossible) for differential levelling to be undertaken (e.g.towers, spires, mountain ranges etc).

c) Barometric heighting: method consists of reading air pressuredifferences from which elevation differences are computed.

d) Gravimetry: by measuring the gravitational potential variation

between different points it is possible to correlate this todifferences in heights.d) Satellite Positioning: method is poised for extensive use in the

future with its only drawback being the determination of theseparation between the geoid and ellipsoid in areas of interest.

Comparison of Various Heighting Methods


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a) Differential Levelling b) Trigonometric heighting

c) Barometer d) Gravimeters


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e) Satellite Heighting


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A horizontal line is a line that

is tangential to the level lineat a particular point. Hence a

horizontal line is perpendicular

to the direction of gravity.

Levelling Line and Horizontal Line

A level line is a line that is

normal to the direction of

gravity as shown by a plumbline

at any point. A level line iscurved by virtue of the shape

of the Earth. Hence, a level

line is a line in which all points

are the same height.


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Basic Concept


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Datum: A level surface to which elevations of points may

be referenced. The most commonly adopted datum is theMean Sea Level (MSL).Reduced level: The elevation (above or below) of a pointin relation to the Datum.Benchmark (BM): A permanent monument or feature for

which elevation is known. BMs are built on stable rock.

Three (3) types of benchmarks can be distinguished:1) Fundamental benchmarks (FBMs): Very stable concrete structures

most often built into rock forming part of the primary levelling

network.2) Ordinary benchmarks: Concrete points or marks on rocks, culverts,

bridges etc constructed between FBMs.

3) Temporary benchmarks (TBMs): Stable points established in the course

of a survey between established benchmarks, which may be some

distance away.

Datums, Reduced Levels and Benchmarks


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A (curved) surface orthogonal to the plumb line

everywhere.

More correctly an equipotential surface for which

gravitational potential is constant.

A still body of water unaffected by tides is a good

analogy.

They are not equidistant apart, but converge and diverge

due to changes in density.

Level Surface


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Vertical Line

The direction of gravity

Therefore the direction indicated by a plumb

line

In general it deviates from a line emanating

from the geometric centre of the Earth

In reality it is curved, but this can be

neglected in small plane surveys


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Horizontal Plane

A plane tangent to a level surface (orthogonal

to the plumb line).

The collimation axis (line of sight) of a levelling

instrument that is in correct adjustment, once

levelled, defines a horizontal plane as the

instrument is rotated.


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Levelling Instruments

Level, Tripod, staff and tape

Change plate.


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Level and reading of staff


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Level and reading of staff

Staffs of a variety of lengths andgraduation styles made from avariety of materials (wood,aluminium, fibreglass) exist.The alternate metre lengths are inblack and red on a white

background.Majority of staffs are telescopicor socketed in three sections foreasy carrying.Graduations can take various formswith E-pattern type popular. Thesmallest graduation on the staff is0.01 m, with readings estimated tothe nearest millimetre.As the staff must be held verticalduring observation it should be

fitted with a circular bubble.


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Types of Levels


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Examples of Levels


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Examples of Levels

NA2000 Digital level with

coded levelling staff


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Two Peg Test

This test is often conducted before using a level for any

levelling exercise.

The purpose of the test is find out to if the line of

collimation is parallel to the bubbles tube axis.Collimation error occurs if the line of sight is not truly

horizontal when the bubble is centred. The line of sight

may be inclined either upwards or downwards from

the horizontal.


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Levelling Procedure

A horizontal line of sight is established using some

form of levelling mechanism:

Spirit level tube

Swinging pendulumA graduated staff is read through the telescope of

the level.

The elevation of points can be established by first

reading the staff on a bench mark.

The staff is then moved to the desired point, the

level is turned and the staff is read again.


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Levelling Procedure (2)

The reading at the benchmark is called the backsight

(BS)

The reading taken after turning the instrument and

moving the staff is the foresight (FS)


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Levelling Procedure (4)

Two note reduction methods for calculating elevations

from the BS and FS observations exist.

Each use only two equations for the computations.

Height of Collimation method HC = Elev + BS

Elev = HC – FS

Rise and Fall method Rise (or Fall) = BS – FS

Elev = Previous Elev + Rise (or Fall)

A Fall is simply a negative Rise


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Rise and Fall

Check: ∑BS - ∑ FS = ∑ Rise - ∑ Fall = RLlast - RLFirst


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Height of Collimation

Check: ∑BS - ∑ FS = RLlast - RLFirst

Applied when points of interest can be seen


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Acceptable Misclosures

Maximum acceptable misclosure depends on class oflevelling and specifications for the particular survey.

As a guideline the following figures give an indication of

misclosures for various classes:

Precise levelling:

4

K

2nd order levelling: 8K

3rd order levelling:

12

K.

Ordinary levelling falls into this category. On roughground, allowance may be made for misclosures of up to

30K (Where K is the total distance levelled in

kilometres).


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Precise Levelling

This class of levelling requires further refinement tofield technique and instrumentation to that applied inordinary levelling.The accuracy requirements for this class of levellingare more stringent than for ordinary levelling.Typical rules governing field technique for preciselevelling include:

1) Backsights and foresights are made equal in length,two staffs being used.

2) Readings are made to one particular staff at eachsetup, and there being an even number of set ups.Readings are made to all three hairs of the reticuleat each set up and a special format for booking ofreadings used.


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Precise Levelling (2)

3) All lines of levels to be run twice in oppositedirections, the runs being made on different days

with different change points.

4) All change points made on special footplates.

5) Staff readings below 0.5m level to be avoided.6) Special staffs with invar strip and a bubble to be

used.

7) Only levels designed for precise levelling (or

comparable accuracy) should be used (e.g. with

parallel plate micrometer).

8) If the standards in the regulations for allowable

error are not complied with, the work is repeated.


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Sources of Errors

Equipment errors

(a) Collimation error

(b) Compensator not working

(c) Parallax

(d) Defective staff

(e) Defective Tripod


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Sources of Errors (2)

Field or on-sight errors (Gross error sources)(a) Staff reading error.

(b) Unstable change point.

(c) Non vertical staff.

(d) Booking error

(e) Instrument not level

(f) Handling the instrument and tripod

Effect of curvature and refraction(a) Earth curvature.

(b) Vertical collimation error in the instrument.

(c) Temperature relation expansion in the staff.


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How to Reduce Errors

Levelling should start and finish at known Bench Mark.

Where possible, all sight lengths should be below 50m.

The staff must be held vertically.

BS and FS must be kept equal for each instrument

position.

Rise and Fall method should be used when heighting

controls.

HCM should be used when setting out.

For Automatic levels, staff readings should be booked

immediately they are observed.


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Establishing vertical control.To establish heights of points during

constructions – setting out levels.

For contouring purposes.

For road cross section, longitudinal

sections/profiles or volumes of

Earthwork in civil engineering works.

For provision of levels of inclined surface

during construction.

Applications of levelling


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Estimation of areas and volumes is basic to

most engineering schemes such as route

alignment, reservoirs, tunnels, etc.

Excavation and hauling of material is the

most significant and costly aspect of the

work, on which profit or loss may depend.

Areas may be required in connection withthe purchase or sale of land, with the

subdivision of land or with the grading of

land.

Overview

( )


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Earthwork volumes are estimated to:

i) enable route alignment to be located at such

lines and levels that cut and fill are balanced

as far as practicable;

ii) to enable contract estimates of time and

cost to be made for proposed work;

iii) to form the basis of payment for workcarried out.

Overview (2)


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Areas

a) Trapezoidal rule

Area (A) = w(h1 + h2

b) Simpson’s rule

V l


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Many volumes encountered in civil engineering appear, atfirst glance, to be rather complex in shape.Generally, estimation of volumes can be divided intocomputation of volumes for prisms, wedges or pyramids.

(1) Prism

The two ends of the prism (Figure 9.17) are equal andparallel, the resulting sides thus being parallelograms.Volume = AL

Volumes

(2) WedgeVolume of wedge (Figure 9.18)= L/6 (sum of parallel edges × vertical height of base)= L/6 [(a + b + c) × h] (9.7a)

when a = b = c: V = AL/2


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