IAN HUMBY TEACHING. List of Hand-Outs. Levelling

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1 IAN HUMBY TEACHING List of Hand-Outs Levelling 6-1 Equipment List (Levelling) 11-1 to 11-3 Introduction to Levelling 11-4 Levelling Terminology 12-1 to 12-2 Measuring Height Change by Basic Methods 13-1 to 13-2 The Optical Level 13-3 Using an Optical Level (a) 13-4 to 13-5 Using an Optical Level (b) 14-1 Levelling Booking Sheet 15-1 to 15-3 Setting up an Optical Level 16-1 Zip Level 17-1 to 17-2 The Laser Level 17-3 Using a Laser Level

2 Equipment List Site Work (Levelling) Ian Humby 6-1 Get Geared-Up! All, or most, of the following items will be required for a Levels Survey, although some of the items already listed for carrying out a Garden Survey will have dual usage. If you can see yourself doing a lot of your own surveys (if, for example, you plan on not using a Land Surveyor or if you only plan on taking on smaller gardens that you can survey yourself), you would be advised to purchase the best equipment, within reason, that you can afford. Also, if you look after the equipment it should last for years. Basic Levelling Equipment Water Level. Various water levels are available ranging in price from about Hand-Held Level. These are in the price range of Hammer and Pegs. Pieces of timber or straight edges (~1-2m long). Spirit Level. Graduated Ranging Poles. (These can be used instead of a levelling staff and also for marking out grids). Note book etc. Precise Levelling Equipment Automatic Level Instrument. A basic Levelling kit (consisting of a Level, a tripod and a staff) can be bought from as little as Laser Level Instrument. (Including tripod and staff) for about 600. Zip Level. From about 880. This list is not necessarily complete every Garden Designer will have his or her own preferences but it should at least give an idea of some of the items of equipment required. Where do I get all this stuff? Most, if not all, of the above equipment can be obtained from a specialist supplier like York Survey Supplies at (The author has no connection with this company, but has used them extensively over many years).

3 Introduction to Levelling Ian Humby 11-1 Why are Levels so important? Few gardens are perfectly flat and level. The Garden Designer will often need to take into account changes of level within the garden as part of the design process. Some designs may need very little levelling information and in these instances a very basic, and approximate, level survey may be all that is required. Other designs may be more complicated and require more thorough and precise levelling techniques to be employed. Examples of this may be when steps need to be built up a slope; or if retaining walls or terracing is required; or if flat areas are going to be created within a sloping garden. You will always have to have a survey drawing of the garden before adding height information. This survey may be your own, or supplied by others (and checked as correct by you!). Some Designers may add the height information straight onto the original survey drawing, others may use a copy or an overlay of the survey, in order to keep the information separate and clearly visible. It is obvious that if the original survey has been completed to a reasonably large scale on a large sheet of paper there should be enough room to add the levels straight onto the drawing. The positions at which levels are taken must be accurately marked onto the drawing so that the correct level information is in its correct place on the survey. Some Terminology A Level Value at a point is the height of that point relative to another point. It is expressed figuratively in metres (or feet) on the survey drawing and marked at its correct point by a small symbol, usually a cross (+ or x). All levels must be related to a Level Datum. This Datum is given a height value from which all other levels within the survey are related. It is important that the chosen Datum is something solid, relatively permanent and well defined that can be referred to at some time in the future (for example by the groundworks contractors, or by the Garden Designer needing to survey additional parts of the garden at a later date). Within a garden a Level Datum could be a manhole cover, a door step or the DPC (damp proof course). You may also come across surveys that have been related to Ordnance Survey (OS) Datum. This is a Level Datum adopted by the OS to which all their mapping heights are related and which equates roughly to sea level. So, a survey related to OS Datum is effectively giving heights related to sea level. Anyone can relate a survey to OS Datum by levelling to a local OS Benchmark,

4 Ian Humby 11-2 the location and height of which can be taken from Large Scale (1:1250/1:2500) OS Super Plans. A Level Grid is a grid across an open area of garden, with equal spacings between the vertical and horizontal lines. These spacings will be of sufficient distance apart so that levels taken at the intersections will give a good representation of the slope of the ground. It is therefore obvious that on steep or varied slopes the grid may need to be closer than on gentle slopes. A grid can be marked out using Ranging Poles, bean sticks or pegs. The grid must of course be positioned onto the surveyed drawing so that the level information is in the correct place. Contours are lines drawn on a map or plan that represent a common level or height. A decent Contour plot can be calculated from Levels taken on a Level Grid. (See the attached diagram for further explanations). Levels are usually best recorded as absolute levels in relation to the Level Datum. In other words if the Datum is given a level of 10.00m a feature may have a level of 10.52m (i.e. 0.52m above the Datum). An alternative method is to record the Levels as relative values to the datum in the above example the Datum would be 10.00m and the feature would be recorded as +0.52m. Some Designers may choose to give the Level Datum a value of 0.00m. All levels above this datum will therefore automatically show the difference in height between the datum and the point. However this means that any features below the Datum will have a negative value and this could lead to possible errors in height change calculations between negative and positive figures. In effect, a Level Datum can be given any value. Values of 10.00m or 50.00m make for easy calculating; a value of m will mean that many level values will have extra digits to write and fit into the survey drawing. Try to avoid awkward values that will be difficult to use at a later stage. You may hear the term Level Survey used by architects or builders. This is basically another word for a Land Survey, Topographical Survey, or Site Survey as this type of survey will nearly always have level information recorded. Get it Right! As with carrying out the Plan Survey all design work involving changes of level will be based on the collected level information, so it really does pay to get it right. Any mistakes made now could have serious consequences at a later stage of the design or construction process.

5 Ian Humby 11-3 There are several different ways to measure height change all are dependent on the accuracy required, the number of levels needed and the equipment available. These methods will be dealt with in detail a little later. Bring in a Professional! It must be remembered that most Garden Designers will only have basic methods and equipment to help them in carrying out Level Surveys. In certain instances therefore, it may prove very cost-effective to call in the services of a professional Land Surveyor. Land Surveyors have specialist laser theodolites, software and methods to carry out quite complicated surveys. They should be able to give level values at all relevant points and features, as well as all changes in slope. Most Land Surveyors should be able to produce, either within the cost of the survey or for a small additional fee, a decent contour plot. Land Surveyor s work is usually produced nowadays in CAD (computer aided drawing) software with results presented by plotters on A0 or A1 sheets. Large, odd-shaped, complicated or very sloping gardens may therefore all need to be left to the services of a Land Surveyor, who for a usually quite reasonable price can produce drawings quicker, cheaper and more accurately than a Garden designer working on his or her own with just tape measures and ranging poles! Unfortunately the standards of Land Surveyors (or to use the modern term Geomatics Surveyor ) can be very varied, as in most professions. It is probably best to use one who has been personally recommended to you; a call to the Royal Institution of Surveyors (RICS) can help in getting a Chartered Land Surveyor in your area who would be backed up by a Professional organisation.

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9 Ian Humby 13-1 An Optical Level, Tripod and Staff Side View of an Optical Level Top View of an Optical Level

10 1. Gun Sight 2. Circular Bubble 3. Levelling Footscrew 4. Base Plate 5. Objective Lens 6. Focusing knob 7. Horizontal Slow Motion Knob 8. Horizontal Circle Window (not all instruments) 9. Horizontal Circle Setting Ring 10. Reticle Adjusting Screw Cover 11. Eyepiece Ian Humby 13-2

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12 Levelling Notes (Read these notes in conjunction with the attached sketch pg 13-3) Ian Humby ) Hold the staff on a point of known level (or a Level Datum). This is Point A on the diagram and has been given a value of m. In other words the level value of this mark is m above our Datum of zero. 2) Set up the Level at a convenient location (X) that can see both Points A and B. 3) Level the instrument, using the instructions provided with the instrument (or see pages 15-1 to 15-3). The line of sight will now be in the Horizontal. This is shown by a dashed line on the sketch. 4) Take a reading back to the Staff at A this reading is called a Back Sight (BS1 on the sketch). The example shows a reading of ) Now add this Back Sight to the level of Point A. (i.e = ). This value of is now the accepted level value of the centre of the instrument at X (which is shown by the dashed line on the sketch). This is called the Height of Collimation. 6) Do not move the instrument. Move the staff to the next point at which a level is required (Point B on the sketch). If you want to transfer levels around a site or round a corner then this Point B must be a solid fixed point (like our Level Datum) you could use an Inspection Cover, a rock, concrete, a nail etc. 7) Swing the instrument around and take a reading to the Staff at B this reading is called a Fore Sight (FS1 on the sketch). The example shows a reading of 2.000m. 8) Now subtract this Fore Sight from the instrument level at Point X. (i.e = 9.500). This value of is now the accepted level value of the point at B (and is directly related to the level at Point A i.e. Point B is 0.500m below Point A). 9) Leave the Staff at Point B. 10) Move the instrument to another convenient location (Y) that can see both Points B and C. 11) Take a reading back to the Staff at B this reading is called a Back Sight (BS2 on the sketch). The example shows a reading of ) Now add this Back Sight to the level of Point B. (i.e = ). This value of is now the accepted level value of the centre of the instrument at Y (which is shown by the dashed line on the sketch). 13) Do not move the instrument. Move the staff to the next point at which a level is required (Point C on the sketch). Again, if you want to transfer levels around a site or round a corner then this Point C must be a solid fixed point as in 6) above). 14) Swing the instrument around and take a reading to the Staff at C this reading is called a Fore Sight (FS2 on the sketch). The example shows a reading of 2.500m. 15) Now subtract this Fore Sight from the instrument level at Point Y. (i.e = 8.750). This value of is now the accepted level value of the point at C (and is still directly related to the level at Point A i.e. Point C is 1.250m below Point A).

13 Ian Humby 13-5 Repeat Steps around the site for as many instrument set-ups as is required. It is highly recommended that levels are transferred using these procedures so that the last Fore Sight finishes back on the starting Datum Point. The calculated Datum Level should then be exactly the same, or very close to, the original starting value. This will show if any reading error has been made. At any instrument set-up (like X and Y) you can take as many levels to as many other points as is needed. Each reading must be subtracted from the level value of the instrument at that point. (For example, from X all readings would be subtracted from ; from Y subtract all readings from ). These are called Intermediate Readings. It is useful to make up a form on which to record levelling information. The example is set out below and a separate blank sheet is attached (see pg 14-1). Point Back Inter Fore Ht of Reduced Sight Sight Sight Collimation Level A B C

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18 Ian Humby 16-1 A Zip Level The Zip Level is an extremely simple, weather-proof, one-man, Levelling system with its only possible drawback being its relatively high purchase cost. This instrument uses a patented gas/liquid system along a cable. This is connected to the base unit and can quickly and accurately measure level differences over distances of up to 50m with a height range of about 6m above and below the base unit. Line-of-sight is not required and accuracy is not affected by the distance away from the base unit. There are many functions within the unit the manual that comes with the instrument is very clearly written.

19 Ian Humby 17-1 A Laser Level The Laser Level is a simple, weather-proof, one-man, Levelling system which, although pricier than an Optical Level, is cheaper than a Zip Level. It does have limitations on measuring levels over a large height range but this would not affect the majority of Garden Designers. Setting up a Laser Level Decide where to set up the instrument. In a simple, open garden this will be around the centre of the area in a position from which the staff will be visible from the instrument when it is placed on the Bench Mark and on all the points that need to be levelled. You do not need to know the instrument position within the site itself. Set the tripod up, ideally with all three legs at 120 to each other, so that the tripod head is roughly flat (use a brick course on the nearby house as a check). Place the instrument box on a flat surface and take the instrument out of its box, ensuring that its position within the box is noted so that you know how it will go back in at the end of the work! Place the instrument onto the tripod head and screw it firmly on. Release the compensator clamp and switch the instrument on. The instrument should self-level but can only do so within a set range. If an audible signal is heard the tripod should be re-levelled. Most laser levels have various types and speeds of rotating laser which can be chosen by referring to the supplied instruction manual.

20 Ian Humby 17-2 Using a Laser Level The mathematics and use of a Laser Level are almost entirely the same as with an Optical Level. (Read these notes in conjunction with the attached sketch pg 17-3). 1) Hold the staff (with receiver firmly attached) on a point of known level (or a Level Datum). This is Point A on the diagram and has been given a value of m. In other words the level value of this mark is m above our Datum of zero. 2) Move the receiver up or down until the audible signal tells you that the receiver is receiving the laser. Tighten the receiver and read the staff. This reading is called a Back Sight (BS1 on the sketch). The example shows a reading of ) Now add this Back Sight to the level of Point A. (i.e = ). This value of is now the accepted level value of the centre of the laser at X (which is shown by the dashed line on the sketch). This is called the Height of Collimation. 4) Do not move the instrument. Move the staff to the next point at which a level is required (Point B on the sketch) and move the receiver up or down until the audible signal is acquired. Read the staff. This reading is called an Intermediate Sight (IS1 on the sketch). The example shows a reading of 2.000m. 5) Now subtract this Intermediate Sight from the instrument level at Point X. (i.e = 9.500). This value of is now the accepted level value of the point at B (and is directly related to the level at Point A i.e. Point B is 0.500m below Point A). 6) Continue around the sight repeating at every point at which a level is required. Each Intermediate value is subtracted from the Instrument Height of Collimation to get the Reduced Level.

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