ARMY TM 5-5420-212-10-1
MARINE CORPS TM 08676A-10/1-1
I.
Shift bearing
(1)
Determine the amount of excess near bank bearing by subtracting the maximum bearing allowed from
the amount calculated using g.(1) or g.(2) above. At this point decide how to use the excess bearing as follows:
either
(a)
Add the excess bearing to the initial far bank bearing (0.4 m)
or
(b)
Add the initial far bank bearing and near bank bearings together, then divide by 2, resulting in an
equal amount of bearing on both banks
or
(c)
Add the initial far bank and near bank bearings together, then divide the total bearing as necessary,
as long as minimums are met and maximums are not exceeded.
(2)
Regardless of what is done, the locations of the F, F’, RB, and O pegs will change or shift on the site.
The location of the A and A’ pegs do not change, nor does the width of the AR Gap.
(3)
There are situations that will result in the maximum bearings being exceeded on both banks, due to
overlaps of gaps and bridge lengths or by making an error in the design process. When this occurs the options are as
follows:
either
(a)
Dig out the soil from the bank until the bearing area will be less than maximum.
or
(b)
Pack up (place timbers) under the end of bridge upon completion. This packing must provide
enough bearing surface to equal the minimum bearing for the bridge.
j.
Key construction points
Locate the key construction points on the site and take elevations as follows:
(1)
Estimate or measure the elevations of the F, RB, and O pegs. Convert the elevation of the RB to datum,
0.0 elevation. The elevations will be used to assist in determining the value of H (height of the far bank), which will be
compared to the value of N (amount of nose lift).
(2)
Convert the elevations of the F and O pegs, using the RB as Datum. Elevations above the Datum line
are positive, elevations below the Datum are negative.
(3)
Determine X.
For push launch X = (L + 0.23 m) - (AR Gap + 0.4 m)
For jack launch X = (L - 0.23m) - (AR Gap + 0.4m)
(4)
Place the elevations on the pro-forma as shown in Figure 3-7 or 3-8.
3-21
