Part 6 (2/2)

=Use of Blade Grader=--Heavy blade graders designed to be drawn by a tractor are suitable for shaping the earth road So and excellent control for regulating the depth of cutting Often two such graders are operated tandem These machines have a device which perrader independently of the tractor Thus the grader can be steered off to the side to cut out the ditches, while the tractor continues to travel on the firrader is usually fairly free froe lumps and can readily be smoothed to a satisfactory surface for the use of traffic The sods and weeds will be drawn into the road along with the earth just as they are when the elevating grader is employed Precaution etable matter decays, and to smooth the surface for the use of traffic

=Costs=--The cost of shaping an earth road in the h rather wide limits because the nature and areatly Soraded satisfactorily for 30000 per mile, while others will cost 70000

But 42500 per rader work plus a ht knolls For the a country, followed by grader shaping, 100000 to 180000 percountry where the roads are undulating and require sorade reduction on every hill For hilly roads one of the rade reduction will be required and the cost will obviously depend upon the a in such cases as the cost may reach 10,00000 per mile, or ardless of the care hich an earth road has been graded, it will be yielding and will readily absorb water for a long time after the completion of the work The condition of the surface will naturally deteriorate rapidly during the first season it is used unless the road receives the constant maintenance that is a prerequisite to satisfactory serviceability The road drag is generally reco is properly used it will serve to restore the shape of the surface as fast as it is destroyed by traffic

Good results with the drag depend upon choosing the proper ti the drag The best ti is as soon after a rain as the road has dried out enough to pack under traffic If the work is done while the road is too wet, the first vehicles traveling the road after it has been dragged will ood done by the drag If the road is too dry, the drag will not sularities A little observation will be required to deter on any particular soil, but usually after a rain or thaw there is a period lasting a day or then conditions are about right

[Illustration: Fig 13--Road Drag]

The drag is used merely to restore the shape of the surface and to do so a small amount of material is draard the e of loose material left in the middle after the work is coradually work across the road on successive trips, finally finishi+ng up at the side opposite that at which the start wasshould start on the opposite side fro his weight on the drag, the operator can adjust the cutting edge so that very little loose material is moved crosswise of the road and that is the proper e will reht one is left it should be re

In addition to the dragging, weedsthe road about twice a year, the ditches must be kept cleaned out and culverts open

All of the maintenance for 10his entire time to the work, and that is the only method that has proven adequate to the problem

EARTH ROADS IN ARID REGIONS

In areas where the rainfall is less than 18 inches per year, and especially where it is 10 inches or less, an entirely different road problenificance prin of cross section and ditches and the culvert provisions are entirely different froions

Frequently the rainfall in seions will be seasonal and provisionthe rainy season, but, in general, road design is adapted to prevention of erosion rather than to eli effects of surface water Generally the rainy period does not last long enough to warrant expensive construction to elieneral effects In fact, the saturation of the soil is more likely to be a benefit than otherwise

Earth roads are likely to be satisfactory except where the traffic is sufficient to grind the surface into dust to such an extent that an excessive dust layer is produced In such locations the proble continued dry weather

Grade reduction will have the same importance as in humid areas and will be carried out in the sae fro accu sand or dust Crude petroleum oils have been satisfactory for maintenance in such locations when used on stable soils

=Value of Earth Roads=--The serviceability of the earth road depends to a large extent upon the care exercised in its maintenance The only part of earth road construction that is perrade reduction The cross section that is so carefully shaped at considerable cost oes through unusually wet periods Traffic will continually seek a new track during the period when the road is muddy and is as likely to cross the ditch to the sod near the fence as to use any other part of the road Continual and persistent maintenance is therefore essential to even reasonable serviceability At best the earth road will be a poor facility for a considerable period each year in the regions of year-around rainfall In most localities, roads of distinctly minor importance are of necessity only earth roads and for the comparatively small territory they serve and the small amount of traffic, they probably serve the purpose For roads of any importance in the humid areas of the United States, the earth road cannot carry satisfactorily the traffic of a prosperous and busy community

CHAPTER VI

SAND-CLAY AND GRAVEL ROADS

In Chapter IV, mention was made of the variation in serviceability of road surfaces coht-of-way of the road It has been found that soils of a clayey nature in which there is a considerable percentage of sand usually afford a serviceable road surface for light or moderate traffic, especially in areas where cliether with the construction of experimental roads of various mixtures of sand and clay, has led to a fairly co of the principles of construction and range of capacity of this type of road surface, which is known as the sand-clay road

The sand-clay road surface consists of a natural or artificial mixture of sand and clay, in which the areater than sufficient to fill the voids in the dry sand It may be assumed that the sand contains 40 per cent of voids and that at least 45 per cent of clay is required to fill the voids and bind the sand grains together, because the clay spreads the sand grains apart during thethe voids As a matter of experiment, it is found to be impractical to secure by available construction methods mixtures of sufficient uniforreat exactness in proportioning the co the materials is desirable

Successful utilization of this type of surface requires considerable study of available ations of their behavior when combined Extensive and exhaustive experiments have been conducted with sand-clay mixtures in various places where they are widely used for road surfaces and the following general principles have been deduced

=The Binder=--In the sand-clay road, stability is obtained by utilizing the bonding properties possessed to soree by all soils Naturally this characteristic may be expected to vary widely with the several types of soil It is generally considered to be a coeneral one that is often applied to soils differing greatly in physical characteristics and the ternificance in this connection

Those soils that are properly and technically called clay are decidedly sticky et and are the best materials for sand-clay construction Of the clays, those that produce a tough stickya s it into a ball and i in water If the ball retains its shape for some little time, it is likely to prove a very satisfactory binder, but, if it becomes plastic and loses its shape, it will be an inferior binder, as a general rule The ball clay, as the former is called, may be of any color common to soils, not necessarily yellow or reddish as is so varying percentages of sand and the binder to be used may be made up and iest is of course the best combination of the materials and indicates the mixture to use in the construction