propelled. This concentric force tends to move thematerial under the wheel, rather than to push it away.These forces result in a more direct vertical force thanthose of the forces under the tiller wheel.ROLLING TECHNIQUESRoller techniques arc basically the same with anytype of roller. Some things you must consider aresteering, changing direction and speed, and rollingsequence.SteeringSteering sharply causes scuffing and damage to thesurface; therefore, turns should be made slowly andgradually. You may have to back up several times tocomplete a turn.Changing Direction and SpeedStarting and stopping should be done gradually toavoid scuffing the surface. Start stopping well ahead ofthe point where you want to stop. Engage the directioncontrol slowly to avoid any wheel spin.Rolling speed is 1 1/2 to 3 miles an hour. You mustdevelop a rolling sequence to ensure the compaction isuniform throughout the fill.Rolling SequenceOverlapping is part of the rolling sequence. Whenrolling deep, loose fills, you should overlap at least halfthe drum width. Gradual extension of the rolled materialinto the unrolled area makes possible greater con-centration of weight on local ridges and high spots.In rolling a graded area with a side slope, as acrowned or banked road, you should work from thebottom to the top. The lower edges of the rolls have atendency to push downhill, which can be best resistedby compacted material. In working uphill, the creep ofsoil away from the upper edge helps to preserve theslope.A crowned road is rolled according to the patternshown in figure 11-46, starting at one edge and workingto the center line. Then move diagonally to the oppositeside and work to the center line from that side. Eachrerolling is done in the same manner.It is efficient to roll in sections as long as you canoverlap the sections, as shown in figure 11-47.Banked or sloped elevated curves are rolled in thedirection of travel, from the bottom (low side) to the top,as shown in figure 11-48. The rolling transition from theroad crown to the bank curve is made by a diagonal fromthe center of the crown to the low side of the bank. Therolling transition from bank to crown is made straight tothe adjoining low side of the road crown.Rolling should be continued until no compactionadvantage is noted on the fill from successive passes.Too much water in the fill material may makecompaction impossible. This may require scarifying andwindrowing the fill to aerate the material. A rubbery, orspongy, rolling action of the fill that springs back intonearly its original condition when the rollers havepassed may indicate trapped water below the surface.The robbery, or spongy, area may require stabilizationby other means, such as excavating the area andFigure 11-46.-Crowned road rolling sequence.11-24
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