10/23/2018. Ishik University / Sulaimani. Architecture Department. Surveying ARCH 224 CHAPTER -3- Level and Leveling LEVEL AND LEVELING

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1 Ishik University - Sulaimani Architecture Department Surveying ARCH 224 CHAPTER -3- Level and Leveling 1 CHAPTER -3- LEVEL AND LEVELING 2 1

2 CONTENTS 1. Level instrument 2. Bubble 3. Tripod 4. Definitions 5. Reading a staff 6. Rules for levelling 7. Booking the observations 8. Loop misclosure (Error) 9. Adjusting the misclose 10. Applications of levelling 11. Field Notes 12. Procedure of leveling 13. Errors in levelling 14. Types of leveling 3 1. Level instrument 2

1. Base Plate 2. Horizontal Circle 3. Eyepiece 4. Circular Bubble 5. Sighting Pointer 6. Objective Lens 7. Focusing Knob 8. Fine Motion Drive 9. Footscrew 10.

3 1. Base Plate 2. Horizontal Circle 3. Eyepiece 4. Circular Bubble 5. Sighting Pointer 6. Objective Lens 7. Focusing Knob 8. Fine Motion Drive 9. Footscrew 10. Bubble Mirror Level instrument 5 BASIC COMPONENTS OF LEVEL: 1. Telescope to provide a line of sight 2. Level Tube to make line of sight horizontal 3. Levelling head to bring the bubble of tube level at the centre of its run. 4. Tripod to support the above three parts of the level. 6 3

4 7 Leveling of the instrument is done to make the vertical axis of the instrument truly vertical. It is achieved by carrying out the following steps: Step 1: The level tube is brought parallel to any two of the foot screws, by rotating the upper part of the instrument. Step 2: The bubble is brought to the centre of the level tube by rotating both the foot screws either inward or outward. (The bubble moves in the same direction as the left thumb.) Step 3: The level tube is then brought over the third foot screw again by rotating the upper part of the instrument. Step 4: The bubble is then again brought to the centre of the level tube by rotating the third foot screw either inward or outward. 4

5 Level Instrument 2. Bubble When bubble is centred the instrument s standing axis is approximately vertical. The compensators in the instrument take over and adjust the optical Line of Collimation so that it is horizontal (hopefully). 10 5

6 Keep the pole upright Any tilt will disturb your readings Tripod From easy to sit to ops, this is high 12 6

7 Tripod stand :- is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object. TRIPOD STAND 13 What is levelling? A measurement process whereby the difference in height between two or more points can be determined. BS FS Difference in height H=BS-FS 14 7

8 When do we level? Typical examples include : To establish new vertical control (BM or TBM) To determine the heights of discrete points To provide spot heights or contours on a plan To provide data for road cross-sections or volumes of earthworks To provide a level or inclined plane in the setting out of construction works Definitions 1. Datum line (M.S.L.) :-Is the level (line), which are attributed to it points levels on the surface of the Earth. Which is the average sea level. 2. Reduced level (R.L) :- Is the high point from datum line. Or height or depth of a point above or below the assumed datum. 3. Benchmark (B.M.) :- Are fixed points information site and attributed placed in different places until you start racing them when conducting settlement. Or is a fixed reference point of known elevation. It may be of the following types; 4. Level Surface :- A level surface is a surface, all points of which are normal to the pull of gravity. I.e. a line at right angles to the string line on a freely suspended plumb bob. The open sea provides a good example of a level surface. 8

9 a. GTS Bench mark (Geodetic Triangulation Survey): These Bench marks are established by national agency like Survey of India. They are established with highest precision. Their position and elevation above MSL is given in a special catalogue known as GTS Maps ( 100 km. interval). b. Permanent Bench Mark : They are fixed points of reference establish with reference to GTS Bench mark (10 km. interval). c. Arbitrary Bench mark : These are reference points whose elevations are arbitrarily assumed. In most of Engineering projects, the difference in elevation is more important than their reduced levels with reference to MSL as given in a special catalogue known as GTS Maps ( 100 Km. interval) Back sight (B.S.) :- Is the first reading taken after placing the device in any position so that we see the greatest possible number of points required to find the elevation. 6. Change Point (CP) :- The point on which both the foresight and back sight are taken during the operation of levelling is called change point. 7. Fore sight (F.S) :- Is the last reading taken before the transfer device. 8. Intermediate sight (I.S.) :- Is reading taken between the back sight and fore sight reading. 9. Elevation of line of sight (H.I) :- Is the imaginary vertical level determined by the line of sight to the amount of increase or decrease for sea level (Height of Instrument). 9

10 Measures height differences between points. Leveling rods Line of sight Back sight Fore sight

11 Definitions (cont.) direction of gravity horizontal surface level surface limit of practical coincidence (~100 m) 21 Benchmarks 11

12 5. Reading a Staff Read the [m], [dm] & [cm] Estimate the [mm] Check yourself for frequent used numbers (2/3) or (7/8) 23 Finding the Target Most telescopes have a targeting system along the top of the barrel (similar to a rifle target finder). The telescope should be aimed at the staff using this targeting system prior to trying to find the staff through the eyepiece. Staff Target finder (Look at this and beyond towards staff) Eye-piece Staff Target finder (In line with staff) Eye-piece MOVE TELESCOPE UNTIL TRIANGLE APPEARS OVER STAFF Telescope Telescope 24 12

13 Reading an E-face staff Leveling staff Leveling Staff :-Is a wooden or metal ruler one side runway to meters and centimeters. And is a ruler of solid wood 2, 3, 4, 5 meters in length and usually 4 meters

31 6. Rules for levelling Always commence and

$5m on a staff (refraction) Use stable, well$

16 31 6. Rules for levelling Always commence and finish a level run on a Benchmark (BM or TBM) Keep foresight and backsight distances as equal as possible Keep lines of sight short (normally < 50m) Never read below 0.5m on a staff (refraction) Use stable, well defined change points 32 16

17 A sample loop Setup 4 BM A CP 3 Kerb Setup 1 Kerb Setup 3 Setup 2 CP 1 Post CP Booking the observations Setup 1 BM A Kerb Kerb CP 3 Back Inter Fore Point 1.32 BM A 3.98 CP 1 CP 1 Post CP

18 Booking the observations BM A CP 3 Back Inter Fore Point 1.32 BM A Setup 1 Kerb Kerb Setup CP 1 Kerb Post 0.67 CP 2 CP 1 Post CP 2 35 Booking the observations BM A Setup 1 Kerb CP 1 CP 3 Kerb Setup 2 Post Back Inter Fore Point 1.32 BM A CP 1 Setup Kerb 3.65 Post CP Kerb 1.54 CP 3 CP

19 Booking the observations Setup 4 BM A Setup 1 Kerb CP 1 CP 3 Kerb Setup 2 Post Back Inter Fore Point 1.32 BM A CP 1 Setup Kerb 3.65 Post CP Kerb CP BM A CP 2 37 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb 3.65 Post CP Kerb CP BM A 38 19

20 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb 3.65 Post CP Kerb CP BM A 39 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb 3.65 Post CP Kerb CP BM A 40 20

21 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A 41 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A 42 21

22 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A 43 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A 44 22

23 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A 45 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A

24 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A (0.03) 47 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A (0.03) 48 24

25 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A (0.03) (0.03) 49 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A (0.03) (0.03) (0.03) 50 25

26 Reducing levels (Rise and Fall) Back Inter Fore Rise Fall RL Comment BM A CP Kerb Post CP Kerb CP BM A (0.03) (0.03) (0.03) (Error) Loop misclosure (Error) Misclosure (Error) The amount by which the measured height (RL measured ) differs from the known height (RL known ) of the starting and finishing benchmarks Misclosure (Error) = RL measured RL known Error = = 0.03 m or Error = Back Fore = = 0.03 m Error = Rise Fall = = 0.03 m 52 26

27 An acceptable misclose? Small misclosures in closed level loops are expected because of the accumulation of errors If the misclosure is small, it can be adjusted If the misclosure is large, the loop (or part of it) must be repeated Misclosures can also result from errors in published BM levels and from BM instability 53 Testing the misclose The amount of misclosure we are prepared to accept depends on the accuracy we are hoping to achieve For routine levelling, the third order levelling standard is adopted misclosure 12 k mm where k is the length of the loop in km 54 27

28 Continuing the example The misclosure is +30 mm (0.03 m) The length of the loop is 0.7 km The misclosure limit is 12 (0.7) = ±10 mm The misclosure of +30 mm is too big The loop must be repeated (or find the error) Adjusting the misclose Adjustment is carried out to ensure that the measured and known RLs of the closing benchmark agree The misclosure is linearly distributed according to the number of set-ups The adjustment per set-up for the example is Correction=(-0.03/4) 56 28

29 Adjusting the misclose Measured RL Point Correction Corrected RL BM A CP Kerb Post CP Kerb CP BM A 57 Adjusting the misclose Measured RL Point Correction Corrected RL BM A CP Kerb Post CP Kerb CP BM A =1*(-0.03/4) 58 29

30 Adjusting the misclose Measured RL Point Correction Corrected RL BM A CP Kerb Post CP Kerb CP BM A =2*(-0.03/4) 59 Adjusting the misclose Measured RL Point Correction Corrected RL BM A CP Kerb Post CP Kerb CP BM A =3*(-0.03/4) 60 30

31 Adjusting the misclose Measured RL Point Correction Corrected RL BM A CP Kerb Post CP Kerb CP =4*(-0.03/4) BM A Adjusting the misclose Measured RL Point Correction Corrected RL BM A CP Kerb Post CP Kerb CP BM A

32 10. Applications of levelling Point heights (relative to a datum) Height differences (independent of datum) Longitudinal sections and cross sections Data for volume calculations Contouring Setting out 63 Establishing a new point New point Benchmark RL NEW RL BM Datum 64 32

33 Measuring height differences H 3 H 2 Benchmark H 1 RL BM Datum 65 Profiles and cross-sections Benchmark RL BM Datum 66 33

34 11. Field Notes S2 New Benchmark NB1 New Benchmark NB2 Back Inter Fore Point TH NB1 NB2 NB1 TH Tidal Hut TH S Procedure of leveling 1. The instrument must be check before use! 2. The instrument and level must be stable settled-up 3. The bubble tube must be leveled before the reading Beware of sun exposure (will wander) Ensure the instruments pendulum is in-limit 4. The instrument must be set up in the middle between two staffs Prevents curvature effects If impossible, use the same distances, but opposite for the next readings 5. You must not use the parallax screw between the backsight and foresight readings 68 34

35 6. Readings must be taken cm above the ground Surface refractions Beware also of temperature gradients (inside/outside buildings). 7. Staff should be set up vertically 8. A change plate should be used 9. Leveling must be done in two opposite directions but the same line (beware of gravity gradients) 10. Staff should be calibrated, especially if INVAR 11. Be careful when crossing rivers (large water surfaces) Use same-time (mutual) observations Repeat it during different times of the day Errors in levelling Collimation Parallax Change point instability Instrument instability Staff instability Benchmark instability Refraction Staff reading and interpolation errors Staff verticality Instrument shading Temperature on staff Booking errors (e.g. using just 1 benchmark) Earth curvature Magnetic field effects on auto level 70 35

36 a. Collimation Error Line of Collimation Imaginary line that passes through leveling instrument at Cross Hairs 71 Collimation Error 72 36

37 b. Parallax Error When using an optical instrument both the image and cross hairs can be focused- if either is imprecisely focused, the cross hairs will appear to move with respect to the object focused, if one moves one's head horizontally in front of the eyepiece. 73 Parallax Error 74 37

38 c. Curvature of the Earth Due to the curvature of the Earth, the line of sight at the instrument will deviate from a horizontal line as one moves away from the level Types of Levelling 1) Simple levelling 2) Differential levelling 3) Fly levelling 4) Profile levelling 5) Cross sectional levelling 6) Reciprocal levelling 76 38

39 1. Simple levelling:- When the difference in the elevation of two nearby points is required then simple levelling is performed Differential levelling:- Performed when the final point is very far from the initial point

3. Fly levelling Performed when the work site is very far away from the bench mark. The surveyor starts by taking BS at BM and proceed towards worksite till he finds a suitable place for temporary BM.

40 3. Fly levelling Performed when the work site is very far away from the bench mark. The surveyor starts by taking BS at BM and proceed towards worksite till he finds a suitable place for temporary BM. All works are done with respect to temporary BM. At the end of the day the surveyor comes back to original BM. This is called fly levelling Profile levelling:- Profile levelling, which yields elevations at definite points along a reference line, provides the needed data for designing facilities such as highways, railroads, transmission lines. Reduced levels at various points at regular interval along the line is calculated. After getting the RL of various points the profile is drawn. Normally vertical scale is much larger than horizontal scale for the clear view of the profile

41 5. Reciprocal levelling:- When levelling across river is required then this method is applied to get rid of various errors

42 References 1. H.U. MINING ENGINEERING DEPARTMENT MAD 256 SURVEYING 2. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov

MAD 256 SURVEYING APRIL. Levelling. Güneş Ertunç, PhD Assist. Prof

MAD 256 SURVEYING APRIL. Levelling. Güneş Ertunç, PhD Assist. Prof MAD 256 SURVEYING APRIL 10 Levelling Güneş Ertunç, PhD Assist. Prof gertunc@hacettepe.edu.tr What is Levelling? A measurement process whereby the difference in height between two or more points can be