Page 340 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.2 THE WORK

build and will serve the same purpose. A vehicle may turn into one, and back out on the road again
when opposing traffic has passed.
Small streams are best bridged with corrugated metal culvert pipe and fill. Occasionally, bottoms
may be hard enough to permit easy fording.
Fords are the most economical means of crossing larger streams. A soft bottom can sometimes
be made safe by a rock fill. Its downstream edge should contain heavy boulders. Its surface can be
crushed rock or clean gravel. It may be placed over a culvert pipe that will handle normal stream
flow but not high water.
If a ford is not practical, multiple-culvert pipe, log or timber bridges or trestles, or prefabricated
steel bridges may be used.
Roads built for use in a dry season may be so constructed that they will be washed out when
the rains come, if the contractor believes they will have served their purpose by then.
The bulldozer, or angle dozer, is usually the primary tool for cutting a pioneer road. Methods
are described in a later section.
In sidehill cuts, the road surface should slope down to the bank or inner side, and may have a
berm (ridge) along the outer edge. This shape allows for fill settlement, reduces washing of the
fill slope, and decreases danger of sliding off the road.
Drainage from the road surface and the hill slope is carried along the inside bank to culverts,
or to outward-dipping sections of road reinforced with rock or blacktop. Overhangs or sluices
must be provided to carry the water across the fill.
One of the constructions used by the U.S. Forest Service is shown in Fig. 8.1.

Access and Farm Roads. A pioneer road is an access road for each otherwise isolated piece of
the job it services. However, the term access road usually means a road by which a whole job is
connected to a highway system, and is generally used in connection with pits and dams.
The quality of construction is variable. If the project is small, or to be quickly finished, and no
substantial amount of raw material is to be trucked in or products taken out, rough pioneer construc-
tion may suffice. More often, it must be built as a haul road. Occasionally, a first-class highway
will be required.
Farm roads are usually graded native soil, two lanes wide, with gravel, dirt, or other low-cost
surfacing.
Haul and Logging Roads. There is no sharp distinction between these two types. Both must carry
heavily loaded trucks at a good speed, and are ordinarily located according to a favorable terrain,
rather than property lines. The logging road is likely to be longer, to climb to much greater ele-
vations, and, under modern lumbering practice, to be permanent. The haul road will carry a much
greater traffic for a limited time, and then often will be abandoned.
As compared with the pioneer and access types, these roads differ in that grades are limited.
Ten percent is the usual maximum for the logging road, and in haul roads grade is sometimes kept
as low as 3 percent of climb in the direction of load movement. Culverts and bridge capacities are
designed according to the period of use, and the comparative expense of large openings, or repair-
ing washouts over smaller ones.
The long climbs needed on log roads in mountainous country are best ascended at even grades,
which can only be attained by careful survey of possible routes. Where the direct distance along
a valley wall is too short to provide the ascent at the required grade, the road may be run back into
spur valleys instead of crossing them on trestles, or may ascend the slope in a series of switch-
backs, or hairpin turns. The turns require a wide space, which, for economy, should be placed
where the grade is flatter than ordinary, or where excavation will require minimum blasting.
These factors limit the route rather closely to that originally surveyed, although occasionally, if
the contractor runs into unexpected difficulties, he or she can have the road shifted to avoid them.
The haul road seldom has long ascents and descents, but switchbacks and side wanders must
often be used to get them out of a deep pit or over a massive ridge.
Logging roads are surfaced with local material where possible, from cuts or borrow pits along
the road. Any fairly hard and porous material, such as gravel, disintegrated granite, or broken