propelled. This concentric force tends to move the
material under the wheel, rather than to push it away.
These forces result in a more direct vertical force than
those of the forces under the tiller wheel.
Roller techniques arc basically the same with any
type of roller. Some things you must consider are
steering, changing direction and speed, and rolling
Steering sharply causes scuffing and damage to the
surface; therefore, turns should be made slowly and
gradually. You may have to back up several times to
complete a turn.
Changing Direction and Speed
Starting and stopping should be done gradually to
avoid scuffing the surface. Start stopping well ahead of
the point where you want to stop. Engage the direction
control slowly to avoid any wheel spin.
Rolling speed is 1 1/2 to 3 miles an hour. You must
develop a rolling sequence to ensure the compaction is
uniform throughout the fill.
Overlapping is part of the rolling sequence. When
rolling deep, loose fills, you should overlap at least half
the drum width. Gradual extension of the rolled material
into 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 a
crowned or banked road, you should work from the
bottom to the top. The lower edges of the rolls have a
tendency to push downhill, which can be best resisted
by compacted material. In working uphill, the creep of
soil away from the upper edge helps to preserve the
A crowned road is rolled according to the pattern
shown in figure 11-46, starting at one edge and working
to the center line. Then move diagonally to the opposite
side and work to the center line from that side. Each
rerolling is done in the same manner.
It is efficient to roll in sections as long as you can
overlap the sections, as shown in figure 11-47.
Banked or sloped elevated curves are rolled in the
direction of travel, from the bottom (low side) to the top,
as shown in figure 11-48. The rolling transition from the
road crown to the bank curve is made by a diagonal from
the center of the crown to the low side of the bank. The
rolling transition from bank to crown is made straight to
the adjoining low side of the road crown.
Rolling should be continued until no compaction
advantage is noted on the fill from successive passes.
Too much water in the fill material may make
compaction impossible. This may require scarifying and
windrowing the fill to aerate the material. A rubbery, or
spongy, rolling action of the fill that springs back into
nearly its original condition when the rollers have
passed may indicate trapped water below the surface.
The robbery, or spongy, area may require stabilization
by other means, such as excavating the area and
Figure 11-46.-Crowned road rolling sequence.