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Chapter 8 – Leveling, Cont.

Chapter 8 – Leveling, Cont. Adjustment of Circuits Precise Leveling Profile Leveling Cross-sectioning. Adjustment of Circuits. Misclosure Difference between determined and known elevation Error adjusted by proportioning misclosure Proportion based on sources of errors

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Chapter 8 – Leveling, Cont.

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  1. Chapter 8 – Leveling, Cont. • Adjustment of Circuits • Precise Leveling • Profile Leveling • Cross-sectioning

  2. Adjustment of Circuits • Misclosure Difference between determined and known elevation • Error adjusted by proportioning misclosure • Proportion based on sources of errors • Distance from start – better • Number of set-ups

  3. Adjustments are Cumulative • Given: Misclosure = 0.05’ over 5 set-ups • Assume: each set-up contributed equally • Adjustment for each set-up = -Misclosure/No. of Setups = -0.05/5 = -0.01’ • Adjustment to the 4th point = -0.01*4 = 0.04’

  4. Precise Leveling • Shade the level • Three-wire leveling • Precise Level Rods • Double-rodded Lines

  5. Profile Leveling • Used in route surveys • Route: definite beginning and end points • Follows a baseline or center line • Determine terrain along a center-line • Tells you nothing about cross-section • Location reference – Stationing • Assign an arbitrary starting point • Every 100’ is one station • Sta 6+53.25 is 653.25’ from the assigned start • Don’t assign start point to 0+00

  6. Profile Leveling • Elevations needed every 100’, 50’ or 25’ • Rough elevations – nearest 1/10th • Too many set-ups if each point is a BM • Take intermediate shots – IFS • Find TP at acceptable limits of sight

  7. Profile Leveling

  8. Profile Drawing • Scales not the same: V & H • Fit a smooth curve • Assume: no intermediate shots means straight grade between

  9. Cross-sectioning • Determines elevations along a line perpendicular to centerline • Prism glass • Wing-ding • Shots at pre-determined distances • Rod-person chooses additional points

  10. Cross-sectioning Notes • Often laid out bottom to top • Centerline appears as IFS • All other shots shown on grid • Reading/Distance, e.g. 3.2/16 • Rod Reading = 3.2 • Rod located 16’ right or left • Elevations calculated from last HI

  11. Cross-sectioning Notes

  12. Borrow-Pit Cross Sections • Lay out a grid • Every 25’, 50’, etc. • Use lath to find grid points • Label A1, B3, etc. • Shots at grid points are IFS

  13. Borrow Pit Cross Sections

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