Project No. 2
(Field)
Reconnaissance
Gradeline Location
Low-Volume Road Design
Forest Operations
ESRM 468
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Project No. 2 (Field) Reconnaissance Gradeline Location |
Low-Volume Road Design Forest Operations ESRM 468 |
Phase Two: Reconnaissance and Gradeline Location
Purpose: To establish a gradeline between two control points.
Equipment Required:
Procedure (Two-man Crew)
1. Select the grade to be run from a topog map as the trial gradeline value.
2. Starting at a given control point, set a double band of flagging on a tree at eye-level (Height of-Instrument H.I.) of abney man.
Notekeeper records station number, side slopes left and right, grade, and possibly compass bearing. Also notes soil condition (rock, soil depth, timber stand, etc)
3. From the double band, move ahead (Abney-man) at a paced distance of no more than 50 feet, moving up and down -hill until you are
"on-grade".
Tie flagging on a tree branch at eye elevation. (HI) and mark information on ribbon.
Information marked on ribbon
4. Move to next point, again pacing the distance and repeat procedure. In heavy brush use 25 foot stations.
As soon as the Abney man ties the ribbon, the notekeeper moves up, brushing the sight-line if needed. When arriving at new station, record station number, side slopes etc.
5. Continue this procedure until the 2nd control point is reached. Make proper adjustments of grade when running through creeks or sharp hollows or around ridges by shooting level (zero percent grade) or lowering grade e.g. 5 percent)
6. If intermediate control points appear, step up or down the hill as necessary and adjust trial grade and continue towards
Control Point #2.
Adjusting the Gradeline
If you run into lntermediate control points, step up or down in elevation to place the gradeline where you think the road CL should be, and contlnue runnlng the trlal gradellne. Later, go back and re-run the abandoned gradeline, as shown below:
a. From Control Point #l to the Intermediate Control Point (Rock Cliff) gradeline was run at -10% for 1500' , thus, loss in elevation was 150' (15 stations @ -10 %).
b. But to get above the cliff an adjustment of + 15' was required - so only 135' of elevational loss was needed.
To calculate the new grade needed, divlde 135' by 1500' which is 9% gradient (135'/1500' = 0.09), and run a new gradeline from the intermediate control point at +9% back to Control Point #1. Remove the original 10% line as you go.
By keeping track of the distances flagged, you can make these adjustments. Otherwise you are flying blind.
Avoiding or Reaching Intermediate Control Points
If in order to tie into the saddle or the county road you must exceed the allowable grade, or if in order to properly hit the saddle or road, the trial grade has to be decreased or increased make the necessary adjustments as set out below:
a. Problem
Trial gradeline requires exceeding the allowable grade limit.
Solution:
Increase length of gradeline with switchback or additional line.
b. Problem
Trial gradeline climbs too fast or drops too fast.
Solution:
Lower or raise the grade on a portion of the line, or measure the total difference in elevation for the total distance between Control Point #l and 2 and calculate the constant grade required to join them. Start at either end and run a new gradeline at this percent of grade.
Carrying grade over (through) ridge
Miscellaneous Comments
Start your gradeline from the most difficult (most restricted) point and work towards areas or points that are less critical
When running gradelines near the maximum limit in the field, always use a grade of 1 percent less than used for paper location. For example, if paper grade is 12 percent, use 11 percent in the field to run gradeline.
Altimeters are extremely useful during field reconnaissance. If you have one, record elevation any time you cross a signifcant topographic feature you can clearly identify on the map. For example, when crossing a creek, take the elevation. You can then use those points as fixpoints to plot out your gradeline on the map.
Checking abneys or clinometers
Those instruments can be out-of-adjustments. Every time you start a project you have to check them. Either sight on each other and see if you get the same reading or use the method below
They can be verified by the 2-peg method described below. Clinometers can not be adjusted in the field. They need to be sent in to the manufacturer for adjustments.