30838893 chain-survey


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30838893 chain-survey

  1. 1. Surveying Primary divisions of surveying: 1. Plane Surveying 2. Geodetic SurveyingPlane surveying does not take into account the curvature ofthe earth’s surface, and the surface of the earth is treated as aplane surface.If the area to be surveyed is more than 1000 km2, the anglesmeasured on the surface of the earth can not be in a planesurface, but are in a curved surface.Therefore, Geodetic surveying (which consider curvature ofearth) is used for achieving high precision for large areas.
  2. 2. Classification of Surveying Classification of surveying broadly based on: 1. The function of survey 2. Instruments employedClassification based on Classification based onfunction of survey: Instruments Employed:Land surveying Chain surveyCity surveys Compass surveyRoute surveys Plane-table surveyMine surveys Levelling surveyGeological surveys Photogrammetric surveyMilitary surveys etc. EDM survey
  3. 3. Principles of surveying1. Fixing a point in relation to points already fixed3. Working from the whole to the part
  4. 4. Definitions of some basic termsLevel surface: is the equipotential surface of the earth’s gravity field.- A body of still water provides the best example of a level surface.Horizontal line: A line tangent to a level surface is a horizontal line.Horizontal plane: is a plane which is tangential to a level surface at aparticular point.Horizontal angle: An angle measured between two intersecting linesin a horizontal plane.Vertical Line: is a line perpendicular to the horizontal planeVertical Plane: A plane containing a vertical lineVertical Angle: Angle between two intersecting lines in a verticalplaneElevation: The vertical distance of a point from an assumed datum ormean sea level.
  5. 5. Difference between a PLAN and a MAPThe distinction between plan and map is arbitrary. It is difficultto say exactly when a plan becomes map.In general a PLAN is ORTHOGRAPHIC REPRESENTATION offeatures on or near earth on a horizontal plane. The earth’scurvature is not taken into account. Therefore preferable forsmaller areas to avoid distortions due to curvature of the earth.A MAP is also a graphical representation of features but differsfrom a PLAN when the scale is small and is constructed usingaprojection system other than ORTHOGRAPHIC. In general MAPSwill give some additional information such as about thetopography with the help of contours.
  6. 6. Land SurveyingNeed:- To secure necessary data of a part of land for the purpose of demarcating its boundaries, determining its area, preparing its plan or map, execution of engineering project etc.Collection of Data:-Collection of data can be done by any one or combination of surveying methods.Ex;- Chain surveying, compass surveying, theodolite surveying, remote sensing etc.Factors controlling the type of surveying:-7. Depending on accuracy required8. Extent and type of the area to be surveyed9. Time available for the survey work10.Economic aspects
  7. 7. Execution of surveyingSurveyor has to choose the best approach sothat work can be completed within given time-frameand available funds.
  8. 8. Measurement of Horizontal DistancesThe commonly used techniques in the basicengineering are: Pacing Measuring Wheel Taping and/or Chaining Electronic distance measuring devices Optical devices
  9. 9. Pacing A pace is defined as ONE STEP A stride is consider TWO steps The ability to pace distance is very useful A person can determine their pace by counting the number of paces necessary to walk a distance that has been previously measured.
  10. 10. Measuring Wheels
  11. 11. Tape and Chain
  12. 12. Electronic Distance Measurement (EDM) SystemsEDMs are very useful in measuring distances that are difficult to access or long distances
  13. 13. Chain SurveyingChain surveying the simplest method of surveying in which only linearmeasurements are made and no angular measurements are taken.The area to be surveyed is divided into a number of triangles and the sidesof the triangles are directly measured in the field.Since the triangle is a simple plane geometrical figure, it can be plottedfrom the measured length of its sides alone.In chain surveying, a NETWORK of TRIANGLES is preferred.Preferably all the sides of a triangle should be nearly equal having eachangle nearly 60o to ensure minimum distortion due to errors inmeasurement of sides and plotting.Generally such an ideal condition is not practical always.Usually attempt should be made to have WELL CONDITIONED TRIANGLESin which no angle is smaller than 30 o and no angle is greater than 120o.
  14. 14. Chain SurveyingThe arrangement of triangles to be adopted in the field dependson the shape, topography and the natural or artificialOBSTACLES met with.Chain surveying is suitable for the following cases:2. Ground fairly level and open with simple details3. Large scale plans (1 cm = 10 m)4. Extent of the area comparatively smallChain surveying is unsuitable for the following cases:7. Area crowded with many details8. Wooded countries9. Undulating areas10. Extent of large area
  15. 15. Chain SurveyingDefinitions:Main survey stations-Is a point where TWO SIDES OF A TRIANGLE MEET.- THESE ARE THE POINTS AT THE BEGINNING AND AT THE END OFTHE CHAIN LINE.Tie stations (or) subsidiary stations:-These are the points selected on the main survey lines for runningauxiliary lines.Main survey lines:- These are chain lines joining the main survey stationsTie or subsidiary lines-The chain lines joining the tie stations or subsidiary stations arecalled as tie or subsidiary lines.-These lines help in locating the interior details which are far awayfrom the main survey lines.
  16. 16. Chain SurveyingDefinitions:Base Line- the longest of the main survey line- various survey stations are plotted w.r.t. this line.Check Lines:-Those lines which are run to check the accuracy of the field work are calledas check lines or proof lines.-The length of the check line in the plan must agree with its measured lengthin the field.- each triangle must be provided with a check line.Offsets:- Offsets are lateral distances measured from survey lines-Offsets are taken from survey lines to determine the locations of details.-Perpendicular offsets are called as simply “OFFSETS”-Oblique offsets are called as oblique offsets.
  17. 17. Chain Surveying Tape and Chain
  18. 18. Chain SurveyingMetric surveying chains:Length of chain: 20 m or 30 mNumber of links per meter length : 5Length of each link : 20 cmTallies are provided at every 5 mSmall brass rings are provided at every meter except wheretallies are provided.Metallic tape:Length of tape: 20 m or 30 mThe linen tape is reinforced with fine brass or copper wiresto prevent stretching or twisting of fibres and is then calledas a metallic tape.
  19. 19. Chain SurveyingArrows:These are also called as marking or chaining pins10 arrows are provided along with each chain.Used to mark end of the chain during the process ofchaining.Cross Staff: - used to make perpendicular lines
  20. 20. Basic Trignometry C a A2 + B2 = C2 Bb c a+ b+ c = 180o A sin b = B / C cos b = A / C tan b = B / A