Chapter 8 Leveling Cont n n Adjustment of

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

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

Adjustments are Cumulative n n 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 4 th point = -0. 01*4 = 0. 04’

Precise Leveling n n Shade the level Three-wire leveling Precise Level Rods Double-rodded Lines

Profile Leveling n Used in route surveys n n n Determine terrain along a center-line n n Route: definite beginning and end points Follows a baseline or center line Tells you nothing about cross-section Location reference – Stationing n n 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 n n n Elevations needed every 100’, 50’ or 25’ Rough elevations – nearest 1/10 th Too many set-ups if each point is a BM n n Take intermediate shots – IFS Find TP at acceptable limits of sight

Profile Leveling

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

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

Cross-sectioning Notes n n n Often laid out bottom to top Centerline appears as IFS All other shots shown on grid n n 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 n Lay out a grid n n Every 25’, 50’, etc. Use lath to find grid points Label A 1, B 3, etc. Shots at grid points are IFS

Borrow Pit Cross Sections