Page 127 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

ROCK, SOIL, AND MUD 3.21

FIGURE 3.13 Corduroy road cross sections.

Fill for mud coverage should be as dry as possible and possess good packing qualities. It
should be put on in sufficient thickness that the truck tires will not reach through to mix it with
the mud. It is strengthened by compacting with a roller, jeep, or empty truck before carrying
loaded trucks. A layer of fine-textured, hard-packing soil topped with gravel is often satisfactory,
but clean broken rock in coarse sizes up to one-half the fill thickness is longest-lasting.
Flat stones should be placed on edge, whenever possible, so that they will not shift under load.
Natural drainage must not be blocked. Iron or steel culvert pipe is most satisfactory on soft bottoms,
as it will keep its position and resist separation and breakage.
Swamp Surfaces. Most swamps are covered with vegetation that gives them some surface stability.
Wet swamp sod, in which a person’s feet will sink slightly, ordinarily will support a light crawler
machine moving steadily across it in a straight line or gradual curves. Crossing should be tried
with caution, particularly if the unit has narrow tracks, or high grousers which tend to cut the sod.
Sharp turns, if necessary, should be made in the firmest or best-matted sections, or extra support
should be provided. Bushes and close-growing saplings which can be walked down by the machine,
without cutting, provide excellent natural support.
Although a shovel can be safely walked on quite soft ground, it cannot stand or work on it. If
standing, its weight slowly displaces mud beneath it, and as that creeps away, the sod or crust left
without support shears and breaks. This process is greatly accelerated by working, as the vibration,