Page 378 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.40 THE WORK

If the cut floor is soft, it is the best practice to use a dragline working from the top. However,
if none is available, or the digging is too hard for it, the front shovel may work from supporting
platforms and have a gravel, stone, or other road built behind it for the trucks. If it is working on
the bottom level, the road can be left to facilitate surfacing work.
A busy shovel should have at least occasional help from a dozer, which can level the pit floor,
clean up spilled dirt, get boulders out of the way, and assist stalled trucks. Even if the shovel can
handle the operation without assistance, it will produce more if it needs only to dig.
A shovel cut should be started on the low side of the grade, and worked uphill so that it will
drain. The floor should be shaped carefully to avoid excessive working over.

LOADER CUTS

Cuts made with front-end loaders, of either the crawler or wheel-mounted type, are similar to
shovel cuts in many basic features. They are moderately deep, usually between the height of the
push arm hinges and the maximum lift of the bucket edge. They should be sloped to drain, to avoid
difficulties with rain or groundwater.
The loader is not as efficient as the shovel if the ground is muddy, soft, or loose; or if the bank
is extremely hard. While it can work in narrow places, production may be greatly reduced by lack
of generous space in which to turn.
The loader can keep its working area smooth and free of rocks. However, if there are enough
trucks to keep it busy, it is often better to send in another machine for cleanup.
If the distance is 1,200 feet or less, large rubber-tire loaders may carry their loads to the fill
more economically than trucks can haul them. See Chap. 16.
Belt and wheel loader cuts will be discussed in Chap. 14.

FILLS

Fills are made to bring a road or area up to a desired grade, to elevate it above water or drifting
snow, to bury stumps or rocks, or to add strength to ground too unstable to support road surface
or traffic.
Fill may be obtained by the removal of high spots or banks along the same road or project, by
digging gutters or ditches alongside or near the fill, or by hauling from necessary excavation on
other jobs, from commercial pits, or borrow pits opened just to obtain the fill.
Nearby cuts on the same project are usually the cheapest source, as the digging costs and part
of the hauling can be charged against the excavation. Also, excavation in adjacent hills will lower
the grade, and thereby decrease the volume of fill needed to carry the road across hollows.
Roads in hilly country are often engineered to balance the cuts and fills, so that all the material
cut out of high spots is just enough to build up all the low spots. However, where the road crosses
ridges of hard rock close to the surface, good borrow is available nearer fills, or snow removal prob-
lems are severe, it may be advisable to keep cuts to a minimum and haul in dirt.
Where very heavy hill cuts must be made without a corresponding need for fill, the surplus may be
wasted in dumps off the road. This may be preferred to raising road levels to absorb the fill, because
of the economy of a waste dump compared with a compacted highway fill. Also, high fills may require
purchase of extra land width to avoid the need for steep and dangerous side slopes.
Cuts and fills on a road are sometimes so far apart that combining them would cost more than
wasting spoil from the cut nearby and getting the fill from borrow pits.
Types of Fill. Any type of mineral earth or rock can be used as road fill, but clay and silt are
generally undesirable. They soften when wet, frequently with changes in volume, and may act as
a wick to bring groundwater to the surface. Humus is avoided, particularly in its pure state,
because of lack of bearing strength and excessive water absorption. Topsoil, a mixture of mineral
soil and humus, may or may not be permissible, depending on its qualities and its location in the fill.