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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 - PowerPoint PPT Presentation
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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 Distance from start – better Number of set-ups
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’
Precise Leveling
Shade the level Three-wire leveling Precise Level Rods Double-rodded Lines
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
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
Profile Leveling
Profile Drawing Scales not the same: V & H Fit a smooth curve Assume: no intermediate shots means
straight grade between
Cross-sectioning Determines elevations along a line
perpendicular to centerline Prism glass Wing-ding
Shots at pre-determined distances Rod-person chooses additional
points
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
Cross-sectioning Notes
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
Borrow Pit Cross Sections
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