Surveying 3B chapter 1 PDF

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Introduction to Surveying 3B...

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SURVEYING 3B 2015 UNIVERSITY OF JOHANNESBURG SURVEYING FOR CIVIL ENGINEERS SURVEYING 3B CHAPTER 1 TABLE OF CONTENTS

Page

1.

Introduction

2

1.1

Reconnaissance and choice of control points

3

1.2

Qualities and functions of a surveyor

4

1.3

Description of surveying

4

1.4

Description of leveling

4

1.5

Classification of surveying

4

1.5.1 Topographic surveying

4-5

1.5.2 Engineering surveying

5

1.5.3 Mine surveying

5

1.5.4 Hydrographic surveying

5

1.5.5 Cadastral surveying

5

1.5.6 Geodetic surveying

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1.6 Surveying units 1.6.1 Linear 1.6.1.1 The Cape-foot 1.6.1.2 The English-foot 1.6.1.3 The metre

6 6 6 6 6

1.6.2 Area 1.6.3 Volume

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1.7 1.7.1 1.7.2 1.7.3 1.8 1.8.1 1.8.2 1.8.3

7 7 7 7 7 7 7 7

List of units Length Area Volume Units of angular measurements Radians Sexagesimal angles Centesimal angles

1.9 Basic mathematics 1.9.1 Mental arithmetic

8 8

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1.

Introduction As civil engineering students you are prepared to operate within the full wide spectrum of civil engineering. You have therefore, in the view of the writer, currently knowledge of a wide variety of al the disciplines within civil engineering but you are actually master of none. It is only in post graduate studies where you will most probably make your own informed choice to specialize in any one civil engineering discipline. Civil engineering mostly revolves around the design and construction of structures and within the design we can branch out in the following types of structures: • Brick and or wood housing structures • Large high rise concrete structures • Large and small dam structures; o Earth fill dam wall structures o Concrete and re-enforced concrete dam wall structures • Irrigation Canal structures • Geometric design of road or rail structures including bridges and culverts • Power line design and construction In all of these designs and constructions the engineer cannot operate on his / her own in a vacuum. Engineers need a team of experts in other fields to work together as a team, such as architects, geotechnical experts, surveyors, mechanical, electrical and other experts. In your training and studies you will however have to study some of the principles of these directions to be able to understand their roles and language to be able to effectively communicate with them in the workplace. After all this is said and done it must be clear that all these other disciplines are support services to the civil engineering industry. It is hoped that this will eliminate some of the resistance and questions why you have to study surveying. We do not want to – nor is it our intention to make surveyors out of you. In designing any one of the structures mentioned above the surveyor will play a role right from the initiation phase up to the finalisation of the project. It is not expected from you as engineer to actually do the survey work on site, although it may at some times be necessary for the engineer to carry out minor surveying measurements to check or if there is no surveyor present and the work cannot be stopped. •

•

•

•

If you do not know the surveying principles needed for the specific task / project you will not be able to effectively design the structure that it is practically constructible (light castles). At the same time you will at some stage in your development have to become involved in the bill of quantities and costing of the different components that contribute to the final cost of the project. How will you write surveying specifications in setting up tender documents and or know whether the quoted prices are in line – too low – or too high if you know nothing about what is expected from the surveyor. All the same arguments are applicable to all the other support services that you have to know enough about

A lot of problems and costly results were encountered in the past when some engineers did not properly budget for the costs of surveying on a project. Some money then had to be scraped from 2 © JN WIESNER & JIP BISSCHOFF 2014

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other sources resulting in a situation where the required qualified surveyors could not be afforded. This resulted in appointing what we call “plastic surveyors” and eventually high financial losses because of mistakes due to lack of training and the correct knowledge. Currently legislation does not require that engineering surveyors have to register with PLATO, the surveying statuary body, to operate in surveying. Therefore many untrained, poorly skilled persons give themselves out in practice as surveyors. When you appoint a surveyor on any project always make sure that he / she is registered with PLATO, looking after the interests of and protecting the public against poor workmanship and malpractices. Engineers should preferably also ensure that the surveyor is registered with SAGI, the surveying institute looking at the interests of the surveyor. It is very easy to get money from somewhere to buy a GPS receiver nowadays but this “computerised” instrument is a very patient fast idiot. It basically works on the principle of “see button, push button” and will almost always give an answer, but if you do not have the background knowledge you will not know if it is a correct and or usable result? If you want to pay monkey money you will get baboons and get boo – boo results. Remember the good engineers’ motto: When in doubt call a registered surveyor! 1.2

Reconnaissance and choice of control points (will be fully discussed during the lecture)

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1.2 QUALITIES AND FUNCTIONS OF A SURVEYOR. ➢ His / her knowledge of surveying (theory and practical) must be good. ➢ A surveyor must be absolutely honest. ➢ Checks should be arranged wherever possible on linear, angular or height measurements. Never assume anything as correct unless it is checked thoroughly, preferably by means of an independent check. ➢ Since no measurement can ever be absolutely accurate, surveys are usually described as being to a certain degree of accuracy. A surveyor must aim for a degree of accuracy suited to the particular job at hand. ➢ A surveyor must be trustworthy. ➢ A surveyor must have good judgment, ➢ A surveyor must display initiative and tackle every task with perseverance ➢ A surveyor must be thorough and only satisfied with a task after thorough completion. ➢

Concentration and care must be maintained. At all times think clearly and reason without prejudice.

The best surveyor is not always the very accurate one, but the one who aims for a degree of accuracy suited to the particular job, without waste of precious and costly time. It is very often necessary to measure very accurate, such as distances to an accuracy of 1:10 000 and this could only be obtained by working methodically. 1.3

Description of surveying Surveying is the determination in the field of the relative positions and elevations of existing objects, the size and form of any portion of the earth’s surface and the plotting of the measured data on a plan or map. 1.4 Description of leveling Leveling is the determination of the relative heights of different points on the earth’s surface. There are four types of measurements necessary to fix a point: (i) Horizontal distances (ii) Vertical distances (iii) Horizontal angles (ii) Vertical angles 1.5 Classification of surveying Surveying is classified in 6 different types of surveys namely: 1.5.1 Topographic surveying Topographic surveys are those that are made for the purpose of representing the threedimensional relations of the earth’s surface on maps or models. The features shown include such natural objects as hills, valleys, streams, lakes, relief of the ground surface etc., and the works of man such as buildings, roads, railways, cultivation, towns and villages. The problem encountered is that we see hills and valleys as high and low points. In order to show this on a flat piece of paper (plan) we use contour lines. A Contour is a continuous line joining all points of the same relative height.

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20 15 10 5 0 CROSS SECTION OF A TWO HILLS AND A VALEY

PRESENTATION OF THE CONTOUR LINES (as seen from the top) 1.5.2

Engineering surveying Engineering survey is any survey work done in preparation of or in conjunction with the execution of Civil Engineering works such as mass concrete or earth fill dams, canals, pipelines, tunnels, roads, railways, bridges, power-stations, power-lines and construction of high-rise buildings.

1.5.3

Mine surveying Mine surveys are the same as engineering surveys but only in connection with underground or opencast mining operations. Mine Survey work entails the determination of the: (i)

Extent of present work.

(ii)

Relative position of all underground workings and the surface.

(iii)

As well as to fix the positions and directions of tunnels and shafts.

1.5.4

Hydrographic surveying Hydrographic survey comprises the operations necessary to map the shorelines of bodies of water; to chart the bottom areas of streams, dams, lakes, harbours and coastal waters; to measure the flow of streams. This includes the determination of Mean Sea Level, which is done over a long period of time, to get the mean between low and high tide.

1.5.5

Cadastral surveying Cadastral Surveys comprise any survey operations for subdivision of land and the preparation of plans showing and defining legal property boundaries. The registration of the boundaries and ownership of property at the Deeds offices may only be signed off and done by a registered “Land Surveyor”. Presently, under the new Survey Act, new SA University 5

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graduates may register as a Professional Surveyor: Cadastral and no longer call themselves Land Surveyors. 1.5.6 Geodetic surveying The plans submitted to the Survey Generals and Deeds offices must show the form, area and measurements of the property. If any landowner wants to sell a portion of the property it must be surveyed and a new plan drawn of the sub-division, new boundaries fixed and the area stated. Individual Cadastral surveys cover such a small part of the earth’s surface that curvature of the earth can be ignored. Therefore the survey operations are called Plane Surveying Geodetic surveying is surveys of such a wide extent that the earth’s curvature cannot be ignored. Geodetic surveying is done to determine the form and extent of the earth or part thereof. Because it is of such a wide extent it cannot be done with a tape alone. Trigonometrical beacons were constructed on suitable hills to form a series / network of triangles. The operations involved was to accurately measure a baseline between 8 to 16 Kilometres in length in a suitable location and a series of well conditioned triangles, of which the inner angles are determined very accurately, are extended (Baseline Extension). With one side and two inner angles of the first triangle known, all the other sides’ lengths can be calculated and coordinates of all the beacons of the series are calculated. Coordinate lists compiled and supplied by the Department of Trigonometric surveys, for use by all surveyors. In modern days with GPS equipment the use and application of Trig beacons are not such a major necessity anymore, but they are still necessary to initialise GPS equipment before and during survey operations, in the control process to make the survey fit in with the whole. 1.6 Surveying units 1.6.1 Linear 1.6.1.1 The Cape-foot: Cadastral- and Geodetic surveys were previously done in this unit. The Cape-foot is a bit longer than the English-foot. 1.6.1.2 The English-foot: All types of survey in South Africa were previously done in this unit, usually to one or two decimal places. 1.6.1.3 The Meter: All surveys, horizontal and vertical, must now be done in this unit in South Africa. Previously it was only used in Southwest Africa (Namibia). 1.6.2.

Area The accepted units are the Square Kilometre (Km2), the hectare (ha) and the square meter (m2). All of these may be used in surveying as appropriate. Previously areas were measured in Square cape-feet, Square English-feet, Morgen and Acres. 10 000 m2 = 1 ha 1 000 000 m2 = 1 Km2 100 ha = 1 Km2

1.6.3 1.6.3.1

Volume Cubic Metres (m3): Quantities of materials such as excavations, rock, sand etc. are expressed in this unit. 1.6.3.2 Litre: Liquid volumes are stated in litres (l) 1 litre = 0,001 m3 1 litre = 1000 ml

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1.6.3.3

Morgen Eng-ft or Acre Eng-ft: The volumes of irrigation dams and lakes were expressed in these units. It represents the volume of water to cover an acre or morgen respectively to a depth of 1 foot. Now it is expressed in millions of cubic metres (106 m3).

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1.7 1.7.1

LIST OF UNITS LENGTH 1 Mile = 1,609344 Km 1 yard = 0,9144 m 1 Feet = 0,304797265 m 1 inch = 25,4 mm 1 C-feet = 0,31485557516 m

1Km = 0,6214 mile 1 m = 1,094 yard 1 m = 3,28084 Feet 1 m = 3,176059 Cape-Feet 1 mm= 0,0393701 inch

1 Cape-Feet = 1,033 Eng-Feet 1 Chain = 66 Ft = 7,9 inch π = 3,141593 1 furlong = 220 yards 1.7.2 AREA 1 ha = 1,167499 Morgen 1 Morgen = 0,856532 ha 2 2 1 Km = 0,3861 mile 1 Mile2 = 2,589990 Km2 1 ha = 2,471 Acre 1 Acre = 0,404686 ha Side of a morgen = 92,549m = 101,2139 yard 1 Morgen = 2,116540 Acres 1 Morgen = 92196,4896 Sq Eng Feet 1 Acre = 0,47246718 Morgen 1 Morgen = 600 Cape Rood 1 Morgen = 86400 Sq Cape-feet 1 Acre = 43560 sq Eng-ft = 40821,3 sq Cape-feet 1 Sq mile = 640 Acres 1.7.3 VOLUME Cusecs: One cusec represents a cubic foot per second. Thus the quantity of water flowing past a point in one second is measured in cusecs. 1 cusec = 1 cubic Eng-ft water flowing for 1 sec 1 cusec-hour = 22400 Imperial Gallons 1 Acre-ft = 271300 Imperial Gallons 1 Morgen-ft = 574300 Imperial Gallons 2 1 cub yd = 0,764555 m 1 morgen-ft = 2610,71001 m3 1 Acre-ft = 1233,48001 m3 1.8 UNITS OF ANGULAR MEASUREMENTS 1.8.1 Radians A radian is the angle subtended at the centre of a circle by a curve length equal to the radius of the circle The circumference of a circle = 2πR 2R One revolution = 360° = Radians = 2π Radians R 360 = 57° 17’ 44,8” = 206265 seconds 1 Radian = 2 Curve  length Arc     An angle in Radians = Radians R R Curve length  206265 An angle in seconds = R Arc x 206265 Seconds   R 1.8.2 Sexagesimal angles The practical unit of angular measurement in South Africa will continue to be the degree and its sub-divisions, the minute and the second. 1 Degree = 60 minutes 1 minute = 60 seconds 360 degrees = 1 revolution 1 degree = 0,0175 Radians 1 Radian = 57,29 degrees 1 Radian = 206264,8 seconds 1.8.3 Centesimal angles 8 © JN WIESNER & JIP BISSCHOFF 2014

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In Europe the Centesimal system is used where the circle is divided into 400 grads. Take note that most photogrammetric stereo plotters operates on the centesimal system. 1.9 Basic mathematics 1.9.1 Mental arithmetic A surveyor must be able to evaluate measured and calculated data. He/she must develop the ability to analyse the data in order to determine whether the results are acceptable or have to be rejected. If the measured and or calculated data must be rejected it can only be done based on scientific proven grounds. Therefore it is of the utmost importance that a good surveyor must before accepting any calculated answer, should have a good idea of the expected magnitude and sign of any calculated result, even before using the calculator. Take care not to become a slave of the calculator. Rather make the calculator your slave. A calculator is only a fast idiot. It can do involved calculations very fast and will always supply an answer. It does not have the ability to think and can only perform whatever you tell him to do. If you key in wrong data, or keying in correct data wrongly, it will still supply an answer but it will be a totally wrong answer. You can only be his master if you develop the ability through mental arithmetic to anticipate the expected answer. Then only will you be able to question the answer and redo the calculation without the detrimental loss of time and money. A good surveyor does not always directly run back to the field to redo measurements that was found, by evaluation, to be un-acceptable. By analyzing the task or problem it can most of the times be determined where the incorrect measurement or calculation was made. Then it is necessary to go out to redo only that measurement. You can only develop this analytical ability and sharpen it if you in the first instance develop a solid knowledge and understanding of the theory on the relevant task and secondly one learns by application of the mathematical principles to be able to analyze. By quickly doing small mental arithmetic calculations the process can always be speeded up. In order to prepare you for this and to sharpen your abilities on evaluation and analysis we will regularly do mental arithmetic exercises in the class. We will even sometimes do more involved calculations without a calculator, where you will only have to give your expected answers in magnitude and sign

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