Page 342 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.4 THE WORK

Subdivision roads may be financed partly by sale of topsoil, gravel, fill, and other surplus
material. Construction costs may be reduced and swampland “reclaimed,” except where area must
be kept as a wetland, by using such areas as dumps for quarry waste or other clean, solid fill.
Fills made over swamps are subject to severe settlement. For a good-quality road, mud should
be removed for use in landscaping lots, so that road fill may rest on a firm bottom. Or geotextile
blankets can be used as described in Chap. 3 and depicted in Fig. 3.12.
City Streets. City streets are built to exact specifications, often under circumstances which do
not allow maximum output from either machines or workers.
All operations are likely to be impeded by traffic, which will probably require working the job
in sections limited to a few blocks, and frequently to half the street width. Provisions must often be
made to pass traffic on intersecting streets through the work. In addition to direct interference with
work schedules, congestion will probably delay trucks and machines entering and leaving the job.
Removal of old pavement is usually the first construction step. Asphalt paving, on a gravel or
crushed-rock base, can be dug by most front loaders, or backhoes. Occasionally it is hard enough
to require preliminary breaking with a ripper or scarifier, or direct loading with a large excavator.
A backhoe can dig close to manholes, but care should be taken not to hook into them, or into
a widened masonry base, as these are easily broken or crushed. Pavement chunks sliding up on
the manhole cover may be thrown into the bucket by hand.
Concrete pavements and bases are tough, particularly if reinforced. They may be bonded to the
manholes or their bases so as to require breaking away by air hammers, ahead of backhoe digging.
They break out in big slabs which are difficult to pick up in the bucket, and to dump out of a small or
medium truck.
Soil beneath the pavement is removed with it to required depth. It may be native soil, or rock,
dirt, or even garbage fill. It may be honeycombed with pipes and conduits that may belong to the
city, or to various utility companies.
If the grade is to be lowered, some of the pipes may have to be dug in more deeply. In any case,
extensive repairs, enlargements, or relocations of piping are liable to be done between the removal
of the old pavement and the laying of the new. This will involve a lot of ditching and probably
considerable delay.
The subgrade is graded and compacted according to specifications. Because of interference with
manholes, and the need for working in short sections, a large amount of handwork will probably be
required.
Highways. Highways make up the bulk of the excavating contractors’ road work. Modern standards
of width, grade, and alignment require heavy cuts and fills in rough or rolling land, and grading
and compaction of subgrades involve heavy work on any terrain.
Contracts may be let on a basis of a fixed price for a job; a fixed price plus specified extras, such
as allowance for overhaul, rock blasting, slides, or other difficulties whose extent cannot be con-
veniently estimated in advance; or on a price-per-yard basis. Less frequently, they are constructed
on a cost-plus or equipment rental arrangement.
Highway earthwork jobs may involve widening and straightening of roads, building a new
road in the approximate location of the present one, building a new road which will run along or
cross the old one only occasionally, or building a totally new road crossing undeveloped country.
There are of course no definite lines of distinction among these types.
A requirement of most highway construction is to provide for continuance of traffic along any
roads running along or crossing the job. This may be a controlling factor in job sequence.

Airports. An airport runway is essentially a very wide, short, straight road. It is usually located
on the flattest land available, but deep fills are often required.
Banks of cuts must be graded back to very gentle slopes to avoid choppy air currents. Borrow
is frequently obtained from the glide areas at the ends of the runway. It is standard practice to cut
away any ridges which might be hit by a plane climbing slowly off either end of the runway.