ARMY TM 5-5420-212-10-1
MARINE CORPS TM 08676A-10/1-1
2
If the actual slope of the bank does exceed 45 degrees from the horizontal, place A and A’
pegs a distance H from the toe of slope which is equal to the height of the bank measured from the toe of
slope to the top of the gap, as shown in Figure 3-6.
FIGURE 3-6 Angle of Repose with Slope of Bank More than 45 degrees
NOTE
Use a bit of “common sense ” when applying 1 and 2 to an actual gap.
3
Measure the distance from the edge of firm ground on the near bank (A peg) to the edge
of firm ground on the far bank (A peg) using one of the methods described below. This distance is known
as the AR Gap.
Triangulation method
A string line with a weight attached thrown across the gap and measured while being
retrieved.
If in a relatively secure area and site conditions allow, a tape measure should be used.
b. Select Bridge
Select the type of bridge to be built, based on AR Gap, MLC required, and resources available. This step
is common to all lengths and configurations.
(1)
Apply the AR Gap determined to the AR Gap Range columns of Table 3-6 starting with section A,
then 8, C, and finally D.
(2)
Read down the columns until an AR Gap Range is found that brackets the AR Gap measured.
(a) Read across to check the MLC given against the MLC required by the testing authority. The
MLC given must meet or exceed the MLC required.
(b) Consideration must be given at this time to the soil bearing capacity and the bearing require-
ments of the bridge.
1
If the AR Gap measured is closer to the lower part of the range, then the bridge will be
approaching maximum bearing on the ground.
2
If the AR Gap measured is closer to the higher part of the range, then the bridge will be
approaching the minimum bearing on the ground.
(c) It is also necessary to consider the amount and type of traffic and weather, eg, will the
bridge take large numbers of heavy tracked vehicles during 24 hours of rain.
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