Building Site Surveying and Set Out
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Topics in module
1. Surveying laws and geometry
2. Survey plans, bearings and set out
3. Measuring equipment
4. Leveling devices, tools and instruments
5. Using your level and level books
6. Grid levels, areas and volumes
7. Plotting and calculating grades
Topic 1. Surveying laws and geometry
Contents
The laws relating to surveying
· Surveyors and survey qualifications
· Cadastral surveying
· Survey marks
Geometry revisited
· The measurement of angles
· Right-angled triangles and Pythagoras’s theorem
· Triangles without a right angle
· Triangles and building sites
Learning outcomes
On completion of this section you will:
• know the various Acts of parliament which affect building setting-out
• know which areas of surveying require the services of a practicing Registered Surveyor
• be able to identify various survey marks
• be able to calculate missing values in a right-angled triangle and use trigonometrical ratios to calculate oblique triangles
• be able to use these triangles as an aid in setting out buildings.
Introduction
Setting out for building construction requires some knowledge of basic surveying. Part of this section is devoted to a brief introduction to land surveying in Australia.
Surveying has been described as the second-oldest profession. About 5000 years ago, surveyors were in great demand in Egypt to mark out the corners of each farm allotment following the annual flooding of the land by the River Nile. This was most important, because the Pharaohs based taxation on the area of land owned and the estimated yield from that area of land.
In the Book of Genesis in the Bible, Moses exhorted the Israelites, ‘Thou shalt not remove thy neighbour’s corner mark’. Just 2000 years ago the Roman agrimensor (agri- for land and mensor for measurer) was in great demand to set out villages, roads and aqueducts.
In Australia, surveying is one of the very few professions which are controlled by government statute. There are laws for the qualifications of surveyors, laws as to the type of surveying which only surveyors can carry out, the type of marks which are placed and even the dimensions of these marks.
The laws relating to surveying
As mentioned in the introduction, there are several Acts of parliament or parliamentary statutes which affect the practice of land surveying in Australia. Each state has its own specific laws.
Here are some of those laws which apply specifically to NSW.
The principal Act of parliament which controls the practice of land surveying is the Surveyors Act, which sets out:
• the academic qualifications required for registration as a surveyor
• the types of surveys which only a Registered Surveyor can carry out
• the types of survey marks which are used to define a parcel of land
• the dimensions of these marks.
Some other acts of parliament which have a bearing on surveying are the Local Government Act, the Real Property Act and the Survey Coordination Act.
Surveyors and survey qualifications
Within any surveying organisation there are three levels:
• Registered Surveyor
• Survey technician
• Survey field hand.
Of course these three levels are not clearly defined and there are ‘grey’ areas in between each level. There are also other support staff such as clerical workers, draftspeople and so on.
Table 1: Three levels of surveyors’ qualifications
The Surveyors Act specifies that any firm or business setting up as land surveyors must have Registered Surveyors as its principals.
Registered surveyors
For registration as a surveyor by the Board of Surveyors, the candidate must have a degree in surveying from a recognised university. On completion of the degree, the candidate must then complete two years as an articled pupil to a Registered Surveyor. On completion of the two years, the candidate then must pass a practical and oral examination set by the Board of Surveyors. This final examination carries over five days.
Each year in the Government Gazette, the Board of Surveyors publishes a list of all surveyors who are registered.
Technician surveyors
Technician surveyors are those who have completed a degree at the university and have not for various reasons bothered with registration, or have completed a surveying course through TAFE (Surveying Certificate or Surveying Diploma). There are some technicians without qualification, who through skill and expertise are competent to use surveying equipment and carry out the necessary calculations.
Survey field hand
The survey field hand is the equivalent of the surveyor’s labourer—the one who has to scramble over fences, is chased by savage guard dogs, confronts irate property owners and invariably has to cut a line through the thickest patch of blackberry bush within kilometres!
Cadastral surveying
The term cadastral simply means boundary surveying. The Surveyors Act states that cadastral surveys must be carried out by a Registered Surveyor or by a survey technician under the immediate supervision of a Registered Surveyor.
This part of the Act is very important because it means that only Registered Surveyors or technicians under immediate supervision can mark out the corners of a property or define the location of a boundary.
The two types of boundary survey which are of concern to us are surveys for property identification and surveys to mark property boundaries.
Surveys for property identification
The boundaries of a property are located but not necessarily marked. The survey identifies that the land which is the subject of the survey agrees with the description of the land given on the title documents. Any improvements on the property are usually related to the property boundaries, and the survey report also shows any restrictions on the title by way of easements or covenants, and also any encroachments on the land or by the land on adjoining property.
Surveys to mark property boundaries
In this case the corners of the property are marked, and sometimes, depending on the length of the boundary or nature of the boundary, line marks are placed along the boundary. Additional line marks may also be placed at the request of the client as an aid to building setting-out.
There are other types of surveys defined by the Act which are used for the definition of boundaries. These are surveys to create new titles or to amend existing property titles. An example is a subdivision survey where new allotments are created.
It is important to note that cadastral or boundary surveys are the only surveys which are specified by the Surveyors Act requiring supervision by a Registered Surveyor.
Survey marks
Marking corners
The Surveyors Act specifies the type of marks to be used for marking corners, angles and line marks on property boundaries. For example in NSW, for an urban holding, the dimensions of the peg marking a corner should be 75 mm by 50 mm and 450 mm long. These pegs are driven into the ground leaving only 75 mm of the top of the peg above ground. The actual corner is marked on the top of the peg by a clout.
Each state has its own standard for survey marks. Become familiar with the type of mark used m your state to ensure that you do not become confused when setting out a building and use the wrong marks.
Where it is not possible to place a peg (for example, where the boundary is fenced), the corner is marked by a galvanised clout or by a spring-head roofing nail. In rock, the corner is marked by a drill-hole in the rock, with wings cut in the rock indicating the direction of the boundary lines.
For rural allotments in NSW, the corners are marked by pegs 75 mm by 75 mm, with trenches or a line of stones two meters long on each side of the peg to indicate the direction of the boundaries. These are called Lock spits. The centre of the peg is taken as the actual corner.
Figure 1 shows some of the different types of marks used for marking property boundaries.
Other survey marks
There are many other marks specified by law which surveyors place when carrying out surveys for new subdivisions or for redefinition of a land title. Some of these are called permanent marks, reference marks and state survey marks.
Reference marks can take the form of a drill and wing similar to the drill hole and wings which indicate a property corner. Take
care if the mark appears to be ‘off-line’ to the rest of the boundary marks.
There are also two pegs which are used to mark points which are not corners of properties. First there is the ‘dumpy’ peg. This is a short peg the head of which is much smaller than the property corner peg.
Note that dumpy pegs are never used to mark property corners. These pegs are not described in the Surveyors Act. The uses to which these pegs are used are to mark corners of buildings, centre lines of pipelines, centre lines of roads and driveways, and anything else not related to property boundaries. By the same token, survey pegs described by the Surveyors Act are never used for anything else but property corners. This is to avoid confusion about marks.
Indicator pegs are used to indicate the location of a dumpy peg, because dumpy pegs are driven so that the top of the peg is flush with the ground. Indicator pegs are 50 mm by 20 mm and a length sufficient so that the top of the indicator will show above the paspalum or other grass which will hide the location of the dumpy.
One final point before we leave survey marks: just as Moses could call down fire and brimstone on anyone who removed his neighbour’s corner mark, the Board of Surveyors has power under the provisions of the Surveyors Act to impose penalties on anyone who willfully removes or disturbs a survey mark. Not quite fire and brimstone, but a heavy fine, and the miscreant also has to pay for the replacement of the mark in its correct position.
Geometry revisited
This is not going to be a detailed or heavy exposé on the proof of theorems with which you may have battled at school. We will look at some very basic formulae and the application of the formulae to solve right-angled triangles. Many surveying calculations are based on simple right-angled triangles.
Before we delve into triangles, there is one area for which clarification is needed, the measurement of angles.
The measurement of angles
You may recall that a degree is divided into 60 minutes (‘) and each minute is divided into 60 seconds (”). One second is one three-thousand-six-hundredth of one degree (‘1/3600°). This may seem a very minuscule fraction, but surveyors are used to working down to fractions of this size. In fact, the Surveyors Act states that all angles shall be shown to the nearest five seconds.
Converting degrees, minutes and seconds into decimals
Unfortunately calculators cannot work directly in degrees, minutes and seconds. We need to convert these fractions of angles into decimals of a degree.
Scientific calculators have a built-in function key which allows you to enter degrees, minutes and seconds, and this key will then convert them into decimals.
Before you reach for your calculator to see how this function key works, here is the simple routine to convert angles to decimal degrees:
minutes seconds
Unfortunately all calculator manufacturers seem to have their own ideas how the angle-conversion function key should work. Refer to the handbook which came with your calculator to find out how your particular machine works.
Whichever way your machine requires the entry of angles, remember you must always convert angles from degrees, minutes and seconds to decimal degrees before carrying out any mathematical operation of the angles.
SSmall fractions of degrees
We have already mentioned small fractions of degrees. These small fractions also carry over when you convert to decimals. For example, one minute = 0.0166667 in decimal degrees. One minute and 5 seconds = 0.0180556 decimal degrees.
You can see that there is a substantial difference in the third decimal place. Your calculator will work to 7 or 8 places so always show all these places. Do not round off to four places. You will introduce errors.
One final point when working with angles, always show high-order zeros for minutes and seconds. That is 5 minutes is always shown as 05’ and not 5’.3 minutes and 5 seconds is shown as 03’OS”. This is to avoid the possibility of errors.
Check your progress 1
Work through these problems. Convert the following angles to decimal degrees: show your answers to seven decimal places.
1. 15°08’30” _____________________________
2. 63°27’55” _____________________________
3. 41°03’45” ___________________________
4. 88°57’05” _____________________________
5. 3°O1’50” _____________________________
6. 19°33’lO” ___________________________
7. 71°O8’25” _____________________________
8. 57°46’SO” _____________________________
9. 31°12’20” ___________________________
10. 29°55’05” _____________________________
Right-angled triangles and
Pythagoras’s theorem
Pythagoras’s theorem
Pythagoras’s theorem states that the square on the hypotenuse of a right-angled triangle is equal to the sum of the squares on the other two sides.
Useful formulae
Let’s have a look at a right-angled triangle and break this sentence down into simple, easy-to-remember formulae.
The hypotenuse of any triangle is the longest side.
Now let’s try an example.
Figure 4: A right-angled triangle
In this triangle we are given two sides and require to determine the length of the third side.
a2 =b2+c2
=42 32
= 16 + 9
=25
a=√25=5
This is the classic 3:4:5 triangle and as you can see, the calculations are quite simple. Remember, if you are given the hypotenuse (the longest side) and one other side, the rule is to subtract and not add.
Check your progress 2
Figure 5 shows six different right-angled triangles each with the value of one side missing. In each case calculate the missing value.
Figure 5: Right-angled triangles with missing values
Sine, cosine and tangent
Unfortunately the calculation of a missing side from two other sides is only part of the story. As you may have gathered from the previous pages, angles play an important part in the solution of triangles for missing values.