Leveling basic surveying third year engineering
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This document discusses different types of levels used in engineering projects. It provides details on dumpy levels, tilting levels, automatic levels, and digital levels. Dumpy levels have a rigidly fixed telescope but are simple and stable. Tilting levels allow the telescope to tilt for precise work. Automatic levels have a compensator to keep the line of sight horizontal. Digital levels use electronic image processing to determine heights and distances from a barcoded staff, reducing human error and allowing data transfer. Accurate elevation determination is important for engineering projects.
Leveling basic surveying third year engineering
- 2. It deals with angular and linear measurement in a vertical plane. NEED: For execution of Engineering Projects it is very necessary to determine elevations of different points along the alignment of proposed project. Levelling : The art of determining relative altitudes of points on the surface of the earth or beneath the surface of earth is called levelling.
- 3. APPLICATIONS: i) Taking rail levels . ii)Initial ground levels for earthwork calculations. iii)Levels for measurement of earthwork etc.
- 5. BASIC COMPONENTS OF LEVEL: Telescope– to providealineofsight Level Tube – to make line of sight horizontal Levelling head – to bring the bubble of tube level at the centreofitsrun. Tripod– to supporttheabovethreeparts ofthelevel. TELESC O PE : Telescope is an optical instrument used for magnifyingand viewing the images ofdistantobjects. It consists oftwo lenses. The lens fitted near the eye is called the eye piece and the other fittedattheend near to the objectis calledthe objective lens.
- 6. The objective provides areal inverted image infront ofthe eye piece at adistance lesser than its focal distance. Two essential conditions are involved. : i) The real image ofthe obj ect,must be formed. Ii) the plane ofimage must coincide with that ofcross hairs. Focusing of Telescope : The operation of obtaining aclear image ofthe obj ect in the plane ofcross hairs is known as focusing.
- 7. 2. LevelTube : Also known as BubbleTube consists of aglass tube placed in abrass tube which is sealed with plaster of paris. Level tube is filled with either or alcohol, the remaining space is occupied by an air bubble. The centre of air bubble always rest at the highest point of the tube. Outer surface of the bubble tube is graduated in both the directions from the centre. The line tangential to the circular are at its highest point i.e. the middle of tube is called the axis of bubble tube. When the bubble is central the axis of bubble becomes Horizontal. The level tube is attached on the top of telescope by means of capstan headed nuts.
- 8. 3)Levelling head : Levelling head generally consists oftwo parallel plates with 3 foot screws.Upper plate is known as Tribrach and lower plate is trivet which can be screwed on to the tripod.Levelling head has to perform 3 distant functions : i) to support the telescope ii) to attach the level to the tripod iii) to provide ameans for level (foot screws)
- 9. IMPORTANT TERMS: a)DATUM – or Datum plane is an arbitrarily assumed level surface or line with reference to which level of other line or surface are calculated. b)LINE OF COLLIMATION- - the line which passes through the Intersection of the cross hairs of the eye piece and optical centre of the objective and its continuation is called as line of collimation. This is also known as line of sight. c)REDUCED LEVEL (RL) – Height or depth of a point above or below the assumed datum is called Reduced level.
- 10. d) BENCH MARK – (BM) – B.M.is a fixed reference point of known elevation. It may be of the following types. i) 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).
- 11. ii) Permanent Bench Mark : They are fixed points of reference establishwith reference to GTS Bench mark (10 km.interval). iii) 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).
- 12. e)Mean Sea Level (M.S.L.) :M.S.L.is obtained by making hourly observations of the tides at any place over a period of 19 years. MSL adopted by Survey of India is now Bombay which was Karachi earlier. f)Level Surface : The surface which is parallel to the mean sphereoidal surface of the earth is known as level surface. g)Line of Collimation : It is the line joining the intersection of the cross hair and the optical center of the objective and its extensions,it is also called line of sight or collimation.
- 13. h) Height of Instrument (HI) : The elevation of the line of sight with respect to assumed datum is known as HI. i) Back sight : (B.S.) - The first sight taken on a levelling staff held at a point of known elevation. B.S. enables the surveyor to obtain HI +sight i.e. Height of Instrument or line of sight. j) Fore Sight : (F .S.) – It is the last staff reading taken from a setting of the level. It is also termed as minus sight. Fore sight is the sight taken on a levelling staff held at a point of unknown elevation to ascertain the amount by which the point is above or below the line of sight. This is also called minus sight as the foresight reading is always subtracted from height of Instrument.
- 14. k) Change Point (CP) : The point on which both the foresight and back sight are taken during the operation of levelling is called change point. l) Intermediate Sight (IS) : The foresight taken on a levelling staff held at a point between two turning points, to determine the elevation of that point, is known as intermediate sight.
- 15. TYPES OF LEVELS: i) Dumpy level ii)Tilting level iii)Automatic level iv)DigitalAuto level
- 16. DUMPY LEVEL This are the basic levels used in construction work. The telescope is attached to a single bubble and the assembly is adjusted either by means of ascrewed ball-joint or by footscrews which are adjusted first in one direction then at 90 degrees.
- 17. DUMPY LEVEL
- 19. ADVANTAGES: ● It is simple compact and stable. ● Fewer adjustments to be made. ● Simple construction with fewer movable parts. ●Longer life of the adjustments. DISADVANTAGE: ● The telescope is rigidly fixed to its support therefore cannot be rotated about its longitudinal axis
- 20. TILTING LEVEL It consists of a telescope attached with a level tube which can be tilted within few degrees in vertical plane by a tilting screw. The main peculiarity of this level is that the vertical axis need not be truly vertical, since the line of collimation is not perpendicular to it. The line of collimation,is,however,made horizontal for each pointing of telescope by means of tilting screw. It is mainly designed for precise levelling work.
- 23. ADVANTAGES : ● Helpful in quick levelling. ● Ball and socket arrangement permits the head to be tilted and quickly locked nearly level.
- 24. AUTO LEVEL
- 26. The Automatic level : Also termed as self aligning level. It has an compensator which consists of an arrangement of three prisms.The two outer ones are attached to the barrel of the telescope.The middle prism is suspended by fine wiring and reacts to gravity .The instrument is first levelled appproximately by the circular bubble ,the compensator then deviate the line of sight by the amount that the telescope is out of sight.
- 27. ADVANTAGES: i) Much simpler to use ii)High precision – Mean elevation error on staff graduated to 5mm division varies between +0.5 to 0.8 mm per km of forward and backward levelling. iii)High speed :The speed of Dumpy level is about 25% lower than tilting level. iv)Freedom from errors – Accuracy is increased by an errect telescope image. v) Range of application – level can be used on medium and large sized projects and setting bench marks.
- 28. DIGITAL LEVEL: It uses digital-electronic image processor using a charged-coupled device(CCD) for determining heights and distances. Its accuracy in rod reading is 0.5mm and the maximum range is 100m.
- 30. ADVANTAGES : ● Data can be transferred to computer directly. ● Error in writing of data and calculations can be minimised. DISADVANTAGE: ● It needs clear and better illuminated area for levelling hence not useful in cloudy area.
- 31. • Digital leveling systems for surveying rely on an electronic laser to scan a level staff with bar code markings. • This type of level reduces the chance of human error when interpreting graduation marks, and a digital display ensures accurate readings. • When job sites need fast and accurate height determinations, precision digital leveling equipment serves as valuable timesaving technology. • An upside to digital levels is the potential for data integration. A surveyor can store readings in the internal memory and refer to them later, or transfer data to computers using external memory ports. • Contractors should be aware that digital levels require a battery, which is often rechargeable, to operate. • Digital levels use electronic image processing to evaluate the special bar-coded staff reading, This bar-coded pattern is converted into elevation and distance values using a digital image matching procedure within the instrument.
- 32. ADVANTAGES OF DIGITAL LEVEL Correction of collimation error: Can be reliably determined and saved using the four integrated Check and Adjust procedures or it can be entered manually Minimize human error: Fatigue-free observation as visual staff reading by the observer is not required. User friendly menus with easy to read, digital display of results. Earth curvature correction: The measurements made are automatically free of the influence of the earth’s curvature. Measurement of consistent precision and reliability due to automation. Automatic data storage eliminates booking and its associated errors. We can operate in low light conditions. Fast, economic surveys resulting in saving in time (up to 50% less effort has been claimed by manufacturers). Data on the storage medium of the level can be downloaded to a computer enabling quick data reduction for various purposes.
- 33. COMPONENTS OF DIGITAL LEVEL Main components of digital level consist of two parts: Hardware (Digital level and levelling staff) and Software. 1. Both digital level and associated staff are manufactured so that they can be used for both conventional and digital operations. 2. Typically digital level has the same optical and mechanical components as a normal automatic level. 3. However, for the purpose of electronic staff reading a beam splitter is incorporated which transfers the bar code image to a detector diode array. 4. The light, reflected from the white elements only of the bar code, is divided into infrared and visible light components by the beam splitter. 5. The visible light passes on to the observer, the infrared to diode array. 6. The acquired bar code image is converted into an analogous video signal, which is then compared with a stored reference code within the instrument.