Page 362 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.24 THE WORK

to allow excessive surface water to enter the tile. Underdrainage may be required in the gutter at
the foot of the slope, and in or behind wet spots in the slope to catch the seepage.
In areas of rapid runoff, a roadway may be protected along its entire uphill side by a system of
diversion ditches that channel all drainage into culverts or access dips. For economic reasons this
type of work is limited to diggable soils on slopes that are accessible to machinery.
Fills usually have less drainage across them, but because they are not as well bonded together,
they are more subject to surface erosion than cuts. Water may flow onto them from the road and from
slopes above the road. They can be protected by berms along the outer edge of the road shoulders,
which will prevent water from going down the side of the fill, except at points protected by pipes,
flumes, or pavement.
Fills which are built on sidehills have a tendency to slide along the old surface, unless it is well
roughened. Leaving of stumps and boulders, roughening by plowing, and placing of subdrains to
stop seepage of water along the joint are common methods of reducing this danger.
Any soil, whether original bank or fill, which rests on smooth, steep rock slopes is liable to
slide. The most important step in preventing slippage is to divert groundwater moving down the
surface of the rock.

Grading. Steep side slopes should be finish-graded as they are made, as it may be difficult and
dangerous to work them afterward. But if it becomes necessary, a wide-track dozer may work a
long slope in strips, from the top down or diagonally.
Horizontal trimming by use of graders or dozers on steep side slopes may be made safer by cabling
to another machine moving parallel to it on the top of the bank. Two cables are used, attached to
the front and rear of the lower machine.
It is not safe to operate unsupported heavy equipment along slopes that contain rocks, soft
spots, or frozen ground.
Topsoiling. The best protection for a dirt slope is a good cover of vegetation. Grass, weeds,
bushes, and trees are all effective controllers of erosion. See Fig. 8.16. The type selected will
depend on the locality, soil, and season.
On most jobs, it is necessary to place a layer of topsoil over the fill or exposed earth in order
to get a good growth. Occasionally plants will grow well enough on raw earth, or with the aid of
some lime or fertilizer.
Deep topsoil is favorable to growth, but it may discourage plants from rooting into the subsoil,
and absorb too much water so that it will slide off during rains. For this reason, and for economy,
topsoiling of steep slopes is usually limited to a depth of 2 to 4 inches.
The fill surface should be roughened so as to bond with the topsoil. A sheepsfoot or tamping
roller is one of the best tools for accomplishing this. If the slope cannot be worked, the roller may
be operated by a dragline at the top. The drag cable is used to pull the roller up and to let it down,
and the walking of the shovel moves it along the slope.
Topsoil may be pushed up a slope from stockpiles at the bottom, pushed down it from piles
trucked to the top, or distributed over the surface by a clamshell working from either top or bot-
tom, and the resulting piles shoveled or raked out by hand.
The Gradall is an excellent tool for final shaping of the subsoil and spreading topsoil on any
area it can reach.
Freshly spread topsoil gullies readily and needs protection on slopes. A thin coat of sprayed
asphalt emulsion will carry off rain, and still allow grass to grow through it.
A layer of hay or straw may be mixed into topsoil by a tamping roller to hold it. The hay should
be well cured, as rapid decay would make its useful life too short. It is apt to absorb so much nitro-
gen from the soil as to interfere with growth of seedlings. Use of barn straw that contains some
manure, or adding nitrogen fertilizer, cures this difficulty.
Some hay and straw contain enough grass and weed seeds to establish a good cover. Other
types are deficient and require that the ground be seeded. Seed can be mixed with water and
sprayed onto slopes.