SURVEYING EQUIPMENT AND LEVEL SET-UPThe opposite figure shows a LEICA Level packages.
Make sure the surveying equipment you will borrow is reliable and in good working order.
To ensure this a two peck test must be carried out each time you borrow a level.
Surveying instruments that you need to complete your projects, can be borrowed from the following persons:
For carrying out your project work you need to borrow the following equipment:
Additional equipment is needed for some other projects and the lecturer will inform you what you need to do this exercises.
The following information is extracted from 'LEICA NA720 User Manual'.
There are different types (Leica, Sokkia, Wild) of levels you can borrow. The level opposite is a Leica NA720. Most level instruments have an automatic horizontal adjustment of the line of sight. Levels are supplied in a case in which the instrument can be shock proof stored. All survey levels operate in a similar way. The function and operation of levels is explained using the Leica 720 which is the most available instrument in the storerooms.
The metric staff has major numbered graduations in meters and tenths of meters (there is a tiny decimal point between the numbers). Our staves have an ''E'' shape mark (or its mirror image) with horizontal spaces between them of 10 mm.
When viewed through an instrument's telescope, the observer can easily visually interpolate a 10 mm mark to a quarter of its height, giving a reading accuracy of 2.5 mm. On one side of the rod, the colours of the markings alternate between red and black with each meter of length.
The Black arrows indicates where to push to extend the staff to its full length.
The figure below shows three different staff readings:
It is easy to read (b) and (c) because the cross-hair is exactly on a mark division. The reading for (a) is between 1.630 and 1.640. To assess the mm reading you have to estimate where the position of the cross-hair is. For (a) the reading is 1.636. The millimeter reading is to be estimated and can very between ± 1 mm.
reading (a) is 1.636 (b) is exactly 1.500 and (c) is 1.580
There are a wide range of spirit levels to meet the varying requirements of specific jobs. The majority of those used on construction work are made of powder coated aluminum or die cast construction. The length varies from 800 mm to 2000 mm. Spirit levels are very handy for short distance levelling (depending on the spirit level up to 2 metres and with straight edge up to approximate 5 metres). The straight edge is used if the the points to be levelled exceed the length of the spirit level.
The line level has been designed and made with two small hooks to hold it on a line as shown in the figure above. A line level is a level designed to hang on a string line. The level must hung in the center of the string and each ''leg'' of the string line extends the levels plane.
The line level is a simple surveying instrument which can be used to lay out contours and gradients, and also to assist measuring horizontal distances at slope.
An old device but a simple instrument for measuring the level differences of two points. This level, is illustrated in the opposite figure. The two levelling staffs are of the same length with a graduated tape attached to each stave. The tube is filled with water. The ends of the tube are fitted with rubber stoppers to prevent loss of water. The total length of tube defines the range of the instrument.
A 'straight edge' in conjunction with a spirit level and tape measure can be used to establish a gradient. The straight edge is usually 3 to 5 metres long and set horizontally with the aid of a spirit level. This method should be used for the measurement of gradients which continue only for short distances, e.g. to calculate the horizontal distance shown in plan-views. The figure below shows how a gradient for the ground profile is found.
Distinguish between a horizontal distance and a slope distance. All distances should be measured 'horizontally'. Do not measure along slopes. Sag (tape are not supported for its length will sag under the influence of gravity) and to a lesser extent temperature may have an effect on the distance measurement also. To reduce the sag break tape measurement into shorter lengths.
The sum of horizontal lengths (L1 & L2) equals the horizontal distance of the slope from A to C. Remember the horizontal distance is always shorter than the measurement on the slope.
For an accurate measurement, the tape should be held horizontal and straight with a specified tension applied to it.
Slopes - Gradient calculations
A slope is the steepness, incline, gradient, or grade of a straight line, and it is defined as the ratio of the "rise" divided by the "run" between two points on a line. The gradient of a straight line shows how steep a straight line is. The slope of a line in the plane containing the y (rise) and x (run) axes may be represented as:
Here are the calculation example of the figures shown in the "Straight edge" section
(a) Gradient 200 : 3000 = 1 : x x = 15 Gradient = 1 :15
(b) Decimal fraction 200/3000 = 0.066666 Fraction = 0.0667
(c) Percentage multiply decimal fraction by 100
0.06666 × 100 = 0.06666 Percentage = 6.667%
(d) Angle in degree inverse tan-function rise over run (tan-1 function on calculator)
tan a = 200/3000 = 0.06666 a = 3.814°
For measuring a distance we use steel or fibre glass tapes as shown in the opposite figure. They are available in 30 metre and 50 metre length.
A more sophisticated method is to use the Electronic Distance Measuring (EDM).
We will not use this method. EDM devices use electromagnetic waves, infrared waves, or lasers to measure distances precisely.
Approximate (fairly accurate) distance measurement method is 'pacing' or using the 'stadia lines' on the reticle of the level
Don't try to pace out one metre with every step. Walk casually over 50 or better 100 metre counting the number of steps. Work out the length of a casual step and use this instead. The longer the walking distance the more accurate is the step measurement.
If it takes you 65 steps to walk 50 metres; then your step is 50/65 = 0.77 metre. If you would waked 39 steps, then the distance is 39 x 0.77 = 30 m.
The stadia lines on the reticle can be used for simple distance measurement. The distances intercepted on the vertically-held rod between two stadia hairs seen in the eyepiece gives the distance. Just multiply the difference on the rod between the top and bottom stadia lines by 100* as shown in the figure below.
In the example above the distance between the top and bottom stadia hair is 62 mm. Therefore, the distance to the staff is 62 × 100 = 6200 mm or 6,2 metres.
* The 100 figure should be checked before beginning any survey by measuring the known distance with a tape.
Surveyors usually use total stations for land surveying. A total stations is a combination of an electronic theodolite (transit), and electronic distance measuring device (EDM).