Page 350 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

8.12 THE WORK

A grader equipped with automatic blade control can grade widths up to 40 feet from a single
line of blue tops, resulting in substantial savings in grading and staking time.

Care. Operators should be very careful when working around stakes as they are valuable, both
as guides to correct work and in relation to replacement cost. In general, an occasional stake can be
replaced readily, sometimes without instruments, but a group of them may involve considerable
work for surveyors.
Errors. A new set of stakes may not agree in grade or location with the missing ones. This diffi-
culty could arise from an error in the original settings or in replacing them. A satisfactory road can
often be built according to an error, but seldom when right and wrong markings are mixed together.
Stakes are accepted as correct until discrepancies are noted. If any stake appears to be out of
line, or badly off grade, it may have been moved or disturbed; it may be a baseline or other mark-
er; or a mistake may have been made in placing or marking it.
When possible, the surveying crew should be recalled to check it. If this is not practical, the
supervisor may be called upon to use his or her judgment as to whether it should be remeasured.
It should not be disturbed, however, unless absolutely necessary, as the suspected stake may be
right and others wrong.

GRAVEL ROADS

Surfaces of bank gravel and other low-cost materials are so frequently required for haul, access,
and other work roads that a brief discussion of them is in order.

Bank Gravel. Bank gravel is a natural mixture of pebbles and sand. For road-building purposes,
it should contain some fines that will act as a binder. Most deposits contain cobblestones and boulders.
Specifications for road gravel vary greatly. The following spread includes most of them:

Sieve % passing each sieve
2 inch 80–100
1 inch 60–100
1
⁄ 4 inch 40–85
10 mesh 15–70
200 mesh (fines) 5–25

In general, gravels with over 10 percent fines are not suitable for roads that will be subjected to freez-
ing. Less than 5 percent may lead to loosening up in hot, dry weather. However, an increase in the
percentage of coarse particles will lessen the softness caused by too much binder. Variations in particle
shape and material will also affect results considerably. Increase of depth may make up for weakness.
There is no consistent difference between the parts of gravel banks which are above and below
the water table. Water levels usually are different at the times when the material is deposited.
However, there is very often a difference in color due to above-water oxidation of certain pigments.
Engineers frequently write ideal specifications for gravel that is not obtainable, and contracts
are let to use practical grades on a price or availability basis.

Screened Gravel. Specifications may call for screening gravel to be used in the top course or in
the full road depth. Maximum size stones may be limited to 1-, 2-, or 4-inch diameters.
Screening is desirable to obtain a smooth, easily worked surface, but it often involves wasting
of an excessive amount of stone which could be worked into the road. The resulting loss of
strength may affect the road stability, particularly in crossing soft or wet ground.