Chapter 8 – Leveling, Cont.
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Adjustment of Circuits
Precise Leveling
Profile Leveling
Cross-sectioning
Adjustment of Circuits
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Misclosure
Difference between determined and known elevation
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Error adjusted by proportioning misclosure
Proportion based on sources of errors
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Distance from start – better
Number of set-ups
Adjustments are Cumulative
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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’
Precise Leveling
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Shade the level
Three-wire leveling
Precise Level Rods
Double-rodded Lines
Profile Leveling
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Used in route surveys
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Determine terrain along a center-line
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Route: definite beginning and end points
Follows a baseline or center line
Tells you nothing about cross-section
Location reference – Stationing
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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
Profile Leveling
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Elevations needed every 100’, 50’ or 25’
Rough elevations – nearest 1/10th
Too many set-ups if each point is a BM
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Take intermediate shots – IFS
Find TP at acceptable limits of sight
Profile Leveling
Profile Drawing
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Scales not the same: V & H
Fit a smooth curve
Assume: no intermediate shots means
straight grade between
Cross-sectioning
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Determines elevations along a line
perpendicular to centerline
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Prism glass
Wing-ding
Shots at pre-determined distances
Rod-person chooses additional points
Cross-sectioning Notes
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Often laid out bottom to top
Centerline appears as IFS
All other shots shown on grid
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Reading/Distance, e.g. 3.2/16
Rod Reading = 3.2
Rod located 16’ right or left
Elevations calculated from last HI
Cross-sectioning Notes
Borrow-Pit Cross Sections
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Lay out a grid
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Every 25’, 50’, etc.
Use lath to find grid points
Label A1, B3, etc.
Shots at grid points are IFS
Borrow Pit Cross Sections