Surveying and levelling

Description of surveying and levelling equipment

1. WELCOME

2. SURVEYING AND LEVELLING SWCE152 3(1+2)

3. Surveying Surveying is an art of determining the relative position of points on ,above or beneath the surface of the earth by means of direct or indirect points by Predetermined angular and linear measurements. It is the art of determination of horizontal distances, differences in elevation, directions, angles, locations, areas and volumes on or near the surface of the earth.

4. Objectives of surveying: (plan or map) Classification of surveying (Geodetic surveying, Plane surveying) Classification based upon the nature of the field survey Land Surveying Topographical surveys: Cadastral Surveys: City surveys : Marine or Hydrographic survey: Astronomical Survey: Classification based on the object of survey Engineering survey: Military survey: Mine Survey: Geological survey: Archaeological survey:

5. CLASSIFICATION BASED ON INSTRUMENTS USED ( 1) Chain survey   (2) Theodolite survey   (3) Traverse survey   (4) Triangulation survey   (5) Tacheometric survey   (6) Plane table survey   (7) Photogrammetric survey   (8) Aerial survey

6. Uses of surveys The engineer must be thoroughly familiar with the principles and practice of surveying, Since all engineering and construction projects extending over large areas, such as highways, railways, irrigation, water supply, etc. are based upon elaborate and complete surveys. In all engineering projects the preparation of accurate plans and sections is the first necessity

7. PRINCIPLES OF SURVEYING : Working from whole to part To fix the position of new stations by at least two independent processes.

8. Units of measurement- (Basic units of length, area and volume) British Units 12 inches = 1 foot 3 feet = I Yard 5 1/2 yards = I rod, pole 4 rods = 1 chain 10 chains = 1 furlong 8 furlongs = I mile 100 links = I chain= 66 feet 6 feet = I fathom 120 fathoms = 1 cable length 6080 feet = 1 nautical mile Metric Units 10 millimeters = I centimeter 10 centimeters = I decimeter 10 decimeters = 1 meter 10 meters = I decameter 10 decameters = I hectormeter 10 hectometers = I kilometer 1852 meters = 1 mile 144 sq. inches = 1 sq. foot 9 sq. feet = I sq. Yard 30 1/4 sq yards = I sq. rod, pole 40 sq. rods = 1 rood 4 roods = 1 acre 640 acres = I sq. mile 484 sq. yards = I sq. chain l0 sq. chains = I acre 100 sq. millimeters = I sq. centimeter 100 sq. centimeters = I sq. decimeter 100 sq. decimeters = 1 sq. meter 100 sq. meters = I are or I sq. decameter 100 ares = I hectare or I sq. hectometer 100 hectares = I sq. kilometer British Units 1728 cu. inches= I cu. foot 27 cu. feet = I cu. yards Metric Units 1000 cu. millimeters = I cu.centimeters 1000 cu. centimeters = I cu. decimeters 1000 cu. decimeters = I cu. Meters

9. PRECISION IN SURVEYING : The degree of precision required in survey mainly depends upon the purpose of the survey. Before commencing work, the Surveyor must, therefore, consider the following factors: The purpose of the survey, (ii) the degree of precision required for the purpose, (iii) the nature and extent of the country, (iv) the sources of error (v) the time available for both field and office work, and (vi) The cost of the survey. WORK OF THE SURVEYOR The work of the surveyor may be divided into three parts: ( i ) Field work, (ii) Office work, and (iii) Care and maintenance of the instruments.

10. Field work : The field work consists of Measuring distances and angles, Locating the details, Recording the field notes, Determining the relative altitudes of points, and Setting out boundaries, buildings, roads, culverts, and bridges, etc. Office work : The office work consists of The preparation of plans and sections from the data collected in the field, Computations of areas and volumes, Design of structures Care and adjustments of instruments:

11. Measurement of distance There are two main methods of determining distance: (1) Direct and (2) Competitive. Pacing : Passometer : Pedometer: Odometer : Speedometer : Perambulator : Chaining :

12. Chains: The chain (fig.) is composed of 100 or 150 pieces of galvanized mild steel wire 4mm in diameter called links. The ends of each link are bent into a loop and connected together by means of three oval rings which afford flexibility to the chain and make it less liable to become kinked. The following are various types of chains in common use: (1) Metric chains : (20,30m ,&5m, tallies@1m small brass rings) (2) Gunter's chain or Surveyor's chain: (66ft,100 links,0.6ft or 7.92 inches, 10GC=1furlong& 80 GC=1mile) (3) Engineer's chain :(100ft, 100links each link 1ft every 10links brass tag) (4) Revenue chain : (33ft, 16 links each links 2 1/6ft long) (5) Steel band or band chain :(20,30m long&16mm wide)

13. Measuring Tapes- Instrument for chain survey: Tapes are made of various materials and are, therefore, divided into five classes: Cloth or linen tape: Metric Woven Metallic tape : ( 2,5,10,20,30,&50m. The tape is made of yarn and metal wire in the warp and only yarn in the weft.) (3) Metric Steel tape :(1,2,10,30,50m. ( The tape is of steel or stainless steel, or may be provided with vinyl coating.) (4) Invar tape : For work of the highest precision, the invar tape is generally used as in measurement of base lines in triangulation and in city work. It is made of an alloy of steel and nickel. It is 6 mm wide and may be obtained in lengths of 30 m, 50 m and 100 m. (5) Synthetic tape: The tapes are manufactured of glass fiber having a PVC coating. They are graduated every l0 mm and figured every 100 mm whose meter figures are shown in red at every meter. The tapes maintain their lengths well and are convenient for measuring short lengths.

14. Instruments for marking stations- The instruments used for marking stations are as fallows. Chain or tape Arrows Pegs Ranging rods Offset rods Plasterer’s laths Whites Plumb bob

15. Ranging Out Survey Lines : Direct Ranging- Indirect Ranging-Reciprocal ranging ,

16. Indirect Ranging-Reciprocal ranging

17. Folding and unfolding of chain: Unfolding the Chain : Method of chaining : Reading the Chain : Folding the Chain : Degree of Accuracy in Chaining : The limits of error under different conditions are as fallows. For ordinary measurements with a steel band on flat ground with careful work – 1 in 2000 For ordinary measurements with a carefully tested chain on fairly level ground and with reasonable care – 1 in 1000 Under average conditions -- 1 in 500 For measurements over rough or somewhat hilly ground --1 in 250

18. Chain surveying or Chain Triangulation ( i ) The ground is fairly level and open with simple details. (ii) Plans are required on a large scale such as those of estates, fields, etc. (iii) The area is small in extent A triangle is said to be well conditioned or well proportioned when it contains no angle smaller than 30 and greater than 120 Base line : The longest of the chain lines used in making a survey is generally regarded as the base line. Check line : also termed as a proof line, is a line joining the apex of a triangle to some fixed point on the side opposite or a line joining some fixed Points on any two sides of a triangle. Tie Line : a line joining some fixed points referred to as tie stations on the main survey lines. A tie line usually fulfils a dual purpose,

19. Equipment : Reconnaissance : Marking Stations : Reference Sketches: Running Survey Lines : Booking Field Notes : OFFSETS Oblique offsets : Number of Offsets : Field work in chain triangulation

20. Cross Staff survey-types of cross staffs There are three forms of cross staff, namely Open Cross staff : It consists of two parts ( i ) the head and (ii) the leg. The head is simply a wooden block octagonal or round about 15 cm side or diameter and 4 cm deep with two fine saw cuts at right angles to each others. French Cross staff : It consists of an octagonal brass tube with slits on all eight sides. These are used for setting out right angles. Which are at 45 to those previously mentioned, for setting out angles of 45 . Adjustable Cross staff : It consists of a brass cylindrical tube about 8 cm in diameter and 10 cm deep, and is divided in the centre.

21. OPTICAL SQUARE : The optical square is used for the same purpose as a cross staff, but it is more accurate. It consists of a circular metal box about 5cm. in diameter and l.25 cm deep. It works on the principle of “If there are two plane mirrors whose reflecting surfaces make a given angle with each other and if a ray of light in a plane perpendicular to the planes of both mirrors is reflected successively from both

22. Obstacles in Chaining : Various obstacles or obstructions such as woods, hills, ponds, rivers, buildings, etc., are continually met with in chaining. Various obstacles may be classified as Chaining Free, vision obstructed: (2) Chaining obstructed, but vision Free: (3) Chaining and Vision both obstructed:

23. Measurement of area by Planimeter The P lanimeter is most useful in determining the areas of figures plotted to scale, especially when the boundaries are irregular or curved such as river boundaries etc. Area (Δ) : M (F.R.- I. R± 10 N +C) M: The multiplier whose value is marked on the tracing arm next to the scale division F.R.: The final reading. I. R.: The initial reading. N= The number of times the zero mark of the dial passes the fixed index mark C= The constant marked on the top of the tracing arm just above the scale division.

24. Compass Survey-Introduction-types of traversing In traverse surveying the directions of survey lines are fixed by angular measurements and not by farming a network of triangles as is done in chain surveying. A traverse survey is one in which the framework consists of a series of connected lines, the lengths and directions of which are measured with a chain or tape, and with an angular instrument respectively. A traverse may be classed as (a) closed (b) unclosed or open Closed Traverse : A traverse is said t o be closed when a complete circuit is made, i.e. when it returns to the starting point forming a closed polygon as in fig. It is particularly suitable for locating the boundaries of lakes, woods etc. and for survey of moderately large areas. Unclosed or Open Traverse : A traverse is said to be open or unclosed when it does not form a closed polygon as shown in fig. It consists of lines extending in the same general direction and not returning to the starting point.

25. Description of prismatic and Surveyor’s compass

26. BEARING OF LINES The bearing of a line is the horizontal angle which the line makes with some reference or meridian. The reference direction employed in surveying may be True meridian Magnetic meridian Arbitrary or assumed meridian Designation of bearings: Whole circle System: Quadrantal system :

27. Plane table survey-basic definitions-setting of plane table-orientation-methods of plane tabling

28. Levelling Levelling may be defined as the art of determining the relative heights or elevations of points or objects on the surface of the earth. Methods of Levelling Simple Levelling Differential Levelling Profile Levelling

29. Common terms of Leveling Level surface Level line Horizontal line Vertical line Vertical plane Vertical angle Datum surface Elevation Bench mark Line of collimation Telescope Back sight(B.S) Foresight(F.S) Intermediate sight (I.S) Change Point(C.P) Height of Instrument (H.I) Focusing Parallax

30. CLASSIFICATION OF LEVELLING 1. Check Levelling 2. Profile Levelling 3. Cross Sectioning 4. Reciprocal Levelling 5. Barometric Levelling 6. Hypsometry Levelling 7. Trigonometrical Levelling

31. Levelling instruments Two instruments are required to determine the reduced levels of points. They are: ( i ) a level and (ii) a levelling staff. The level is used to provide a horizontal line of sight and the levelling staff which is a graduated rod is used to read the vertical height of the line of sight above the selected station.

32. The Level Various types of levels are used for levels viz. (1) Dumpy level (2) The Wye or Y level (3) The coock’s reversible level (4)The crushing's level (5)Tilting level and (6) The automatic level The dumpy level is widely used for levelling works. For small and rough levelling works, The dumpy level is very study, compact and stable equipment. The telescope is rigidly fixed to the frame. Therefore, the telescope cannot be rotated about the longitudinal axis and also cannot be removed from the support.

33. Dumpy Level

34. The Levelling staff 1.Folding type 4-m Levelling Staff 2.Invar precision leveling staff 3.Sop with telescopic staff

35. Levelling Difficulties 1.Ascending or Descending a Hill 2.Levelling across a Hill or Hallow 3.When the staff is too near the level 4.When the staff is too low or too high 5.When the B.M or Staff Station is above the line of sight 6.Ponds and Lakes too wide to be sighted

36. TEMPORARY ADJUSTMENTS : Setting up the level Fixing the instrument on the tripod: Leg adjustment: Levelling up: Focussing the eye piece: Focussing the object glass:

37. BENCH MARKS 1.G.T.S Bench Marks: 2.Permanent Bench Marks: 3. Arbitrary Bench Marks: 4. Temporary Bench Marks:

38. ERRORS IN LEVELLING The following are the principal sources of error in leveling 1. Instrumental Error : Imperfect adjustment : Faulty focusing tube : Defective bubble tube : - Error of Manipulation (a) Careless levelling up of the instrument: the instrument should be accurately levelled . The hand should not rest on the tripod while the readings are being taken. (b) The bubble not being exactly in the centre of its run at the instant of sighting (c) The staff not being held plumb. The staff must be held perfectly vertical. 3.Error in Sighting; - 4. Error due to settlement of the Level and Staff: 5. Error due to Natural Causes: -

39. (6) Common Mistakes in Levelling : Foresight and back sight not being taken on exactly the same point, Reading the staff upwards instead of downwards, Reading the stadia hair instead of the central hair, Reading the wrong number of meters and decimeters, Entering back sights in F.S Column and vice versa Transposing the figures, Adding foresights and subtracting back sights in reduction of levels, Omitting an entry, The staff not being fully extended.

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