mod 6

• Two types of leveling

  • Direct Leveling
  • Indirect Leveling
• Conventional and traditional leveling methods

  • Direct or spirit leveling
  • Differential leveling
  • Double-rodded leveling
  • Three wire leveling
  • Reciprocal leveling
  • Trigonometric leveling
  • Profile leveling
  • Stadia leveling
  • Barometric leveling
  • Cross-section leveling
  • Borrow-pit leveling
• Newer and more precise leveling methods

  • Total geodetic stations
  • Airborne profile recorder
  • Satellite doppler systems
  • Inertial surveying systems

  
• Differential leveling


  The process used in the establishment of differences in elevation between two or more points with respect to a datum or mean sea level
• Principle of differential leveling


  1. The level, an instrument with telescope, provides a horizontal line of sight (collimation axis) that can be trained in any direction

  2. Read the graduated rod held vertical on a point of known elevation (BM) to measure the difference in elevation (DE)

  
• Procedure for differential leveling

  1. BM 1

  2. TP 1

  3. BM 2

  4. TP 2
• Error of closure (EC) = Computed Elevation - Known Elevation
• Allowable error of closure (AEC) = c √ k, where c is a constant and k is the total loop distance along the line of sight in km
• Double-rodded leveling


  The process used in the establishment of differences in elevation between two or more points by employing two level routes simultaneously
• Three-wire leveling


  • The process used in the establishment of differences in elevation between two or more points using equipment with stadia hairs
  • All three horizontal hairs are read and the average is taken as the correct value
• Profile leveling


  Method of determining the elevations of series of points (or difference in elevation between points) at measured intervals along a line such as the centerline of a proposed ditch or road or the centerline of a natural feature such as a stream bed

  
• Profile


  A curved line which graphically portrays the intersection of the imaginary vertical plane with the ground surface
• Stationing


  A numerical designation indicating the horizontal distance from the starting point of any point along a profile line

  
• Full station


  Points established along the profile level route at uniformly measured distances
• Plus station


  Any intermediate points between full stations, taken at breaks in the ground surface and critical points
• Intermediate points (IFS)


  Rod readings taken along the centerline of the proposed projects to provide an accurate representation of the ground surface

  
• Vertical exaggeration


  A process of drawing the vertical scale for a profile much larger than the horizontal scale in order to accentuate the differences in elevation
• Profile paper


  A special heavy grade graphing paper used for plotting profiles
• Reciprocal leveling


  The procedure to determine the difference in elevation between two points when it is difficult or impossible to keep backsights and foresights short and equal
• Reciprocal leveling procedure


  Reading, throwing out of level, releveling and reading again (minimum of two repetitions)
• If the value of TDE is negative, it only tells us that the point is higher than the other point
• Reciprocal leveling between two points A and B


  1. Set up instrument near A

  2. Calculate mean rod readings and difference in elevation (DE1)

  3. Set up instrument near B

  4. Calculate mean rod readings and difference in elevation (DE2)

  5. Calculate true difference in elevation between A and B (TDE)

  6. Calculate elevation of B

  
• Trigonometric leveling


  Procedure that involves observing vertical (or zenith) angle and slope distance between two points

  
• Determining difference in elevation using trigonometric leveling


  1. Calculate vertical distance V

  2. Calculate difference in elevation DEab

  
• Trigonometric leveling should be limited to horizontal distances not exceeding 300 m

  
• Determining difference in elevation using reciprocal vertical angle observations

  Calculate DEab using reciprocal vertical angles
• Determining difference in elevation and elevation of B considering curvature and refraction (Sample Problem 1)

  1. Calculate vertical component of inclined distance (v)

  2. Calculate combined effects of curvature and refraction (hcr)

  3. Calculate difference in elevation between A and B (DEab)

  4. Calculate elevation of B

  
• Determining elevation of water tank's base considering curvature and refraction (Sample Problem 2)


  1. Calculate vertical distance from horizontal line of sight to top of water tank (v)

  2. Calculate combined effects of curvature and refraction (hcr)

  3. Calculate difference in elevation between P and B (DEpb)

  4. Calculate elevation of water tank's base
• Cross-section leveling


  Short profile taken perpendicular to the centerline of projects
• Borrow pit leveling


  Method of determining relative elevation of points in borrow pit excavations to calculate earthwork volumes
• borrow pit leveling

  1. Divide area into regular geometric grids

  2. Take elevations at grid corners

  3. Label grids with numbers and letters