ARMY TM 5-5420-212-10-1MARINE CORPS TM 08676A-10/1-1b.The time for construction can be decreased through drill training and thorough planning of the mission.c.Poor site conditions, inclement weather, and unskilled personnel will increase construction time.3-9WORK PARTY REQUIREDThe work parties required for all MGB’s are given in Table 1-5. Decreasing the size of the work party willconsiderably increase building times. Increasing the number of personnel will not necessarily decrease the building times.Section IV. DesignMGB design is a two phase operation to determine the length of the bridge, type of construction, correct setting ofroller beams, setting of the launching nose cross girder, and determining the time, personnel, and bridge loads required.3-10DESIGN PHASE 1In this phase, the preliminary studies, site selection and reconnaissance are performed to determine the bridgelength, type of construction, and the location and elevations of the key construction points on the site. This is the onsitephase. Two parts of this phase are common to all bridge lengths (measuring the AR Gap and selecting the bridge).a.Measure the angle of repose (AR) Gap(1)Select a bridge centerline. The length of the centerline (on each bank) will be determined by the Rdistance (construction space) required for the bridge that will be built. R Distances range from 5.8m to 40.5m (does notinclude the length of the launch vehicle or the push bar). Initially a centerline should extend approximately 5.0m on eachbank. Once the AR Gap and the bridge length has been determined, the centerline will be extended to the correct RDistance plus the length of the launch vehicle and the push bar. This will ensure that there is sufficient space on bothbanks for vehicle access or egress, and space on the near bank for construction of the bridge. There should be sufficientclear area extending out 3.0m on both sides of the centerline for its full length to allow for bridge construction. Additionalclearance on each side is required for pallet placement and off-loading.(2)Determine the location of firm ground on both the near and far banks.(a)For the field method of determining firm ground, assume the AR of the soil to be at 45 degrees.The soil bearing capacity should be at least 2 tons per square foot. Capacities less than 2 tons will require placement oftimber packing under the bridge.(b)At the edge of firm ground on the near bank, place the A’ peg. At the edge of firm ground on the farbank, place the A peg. The distance between the two pegs is known as the AR Gap. Keep in mind that the MGB must notbear on the ground for more than 2.1m (for SS) or 2.3 m (for DS), regardless of its length.1If the actual slope of the bank does not exceed 45 degrees from the horizontal, place A and A’pegs as shown in Figure 3-5Figure 3-5. Angle of Repose with Slope of Bank Less than 45 degrees.3-16
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