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LEVEL SET-UP

SURVEYING EQUIPMENT AND LEVEL SET-UP

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SURVEYING EQUIPMENT AND LEVEL SET-UP

The 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:

Equipment

For carrying out your project work you need to borrow the following equipment:

  • Level
  • Tripod
  • Staff (5 metre)
    		•

  • Staff bubble
  • Measuring tape (50 metre)
  • Wooden pegs (if needed)
    		•

    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’.

    Level types
    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.

    1. Endless drive (both sides)
    2. Bubble level (to check horizontal plane)
    3. Mirror to view bubble level
    4. Base plate (sits on tripod)
    5. Footscrew (to adjust the horizontal plane)
    6. Eyepiece (focus adjustment
    7. Knurled ring (for horizontal circle reading)
    8. Objective
    9. Course aiming devise
    10. Focusing knob (turn until staff reading is clearly visible)
    11. Window for digital angle reading (see 7)

    Setting up the tripod



    1. Loosen screws of tripod legs, pull out to required length and tighten screws.
    2. In order to guarantee a firm foothold sufficiently press the tripod legs into the ground. When pressing the legs into the ground note that the force must be applied along the legs.
    3. Check all screws and bolts for correct fit.

    When setting up the tripod pay attention to a horizontal position of the tripod plate. Minor inclinations of the tripod can be corrected with the footscrews of the tribrach.
    1. Place level onto tripod head. Tighten central fixing screw of tripod.
    2. Turn footscrews A and B simultaneously in opposite directions until bubble is in the centre (on the imaginary “T“).
    3. Turn the instrument 90° and then turn the foot screw C until bubble is centred.
    If you want to centre an instrument over a ground point:

      1. Attach plumb bob and arrange the tripod in such way that the plummet is over the point.
      2. For fine adjustment loosen central fixing screw slightly and shift instrument parallel on tripod until the plummet is exactly over the point.
      3. Tighten central fixing screw.

    Focusing telescope

  • Aim telescope against a bright background (e.g. white paper).

  • Turn eyepiece until reticule is sharp-focused and deep black. Now the eyepiece is adapted to your eye.

  • Aim telescope on staff using the coarse aiming device.

  • Turn focusing knob until image of staff is sharply focused.
    		•
    Levelling staffs (rods) and accessories

    There are many types of staffs, with names that identify the form of the graduations and other characteristics. Staffs can be one piece, but most of them are sectional and adjust the length by telescoping..

    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.
                                                                    
    Staff readings
    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
    Spirit & line levels

    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.
    Plumb bobs
      A plumb-bob or a plummet is a weight with a pointed tip on the bottom that is suspended from a string and used as a vertical reference line. This instrument has been used since the time of the ancient Egyptians by bricklayers, masons, and carpenters to ensure that their constructions are “plumb”, or perfectly upright. It may also be used in surveying to sight a point on the ground that is not readily visible. Small plumb bobs are often included in the kits of various instruments such as levels and theodolites. They are used to set the instrument exactly over a fixed datum marker, prior to taking fresh readings. In conjunction with the line-level the can also be used to assist the horizontal measurement on slopes.
    Water level
    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.
    Straight edge
    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:

    (a) gradient      (1:50;  1:2)
    (b) percentage  ( 2%; 50%)    		 (c) decimal fraction  (0.02;      0.5)
    (d) angle                  (1.146°;  26.565°) 

    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°

    Distance measurement methods
    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
    Pacing
    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.
    Example
    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.
    Stadia lines
    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).
    Other accessories

    Optical square

    Range Pole

    		 Opticle Square and Range Poles are used in surveying course No W5939

    Change Plate – a small flat metal plate with a raised point in the centre that is used to support the staff on the ground. The plate is firmly embedded into the ground to stop the staff from subsiding.
    There are various types of staff bubbles available to assist in keeping the staff in an upright position.
    You will need pegs or stakes and hammer for Project 4 (Grid points for RL’s) All can be borrowed from the surveying department.

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