Part 6 (1/2)
=Variations in Soils=--The nature of the existing soil will obviously determine the serviceability and physical characteristics of the road surface it affords That is to say that even under the most favorable conditions some earth roads will be much more serviceable than others, due to the better stability of the natural soil Soh when dry and therefore resist to a degree the tendency of vehicles to grind away the particles and dissipate them in the form of dust Such soils retain a reasonably smooth trackway in dry weather even when subjected to considerable traffic Other soils do not possess the inherent tenacity and stability to enable therind away rapidly Roads on such soils become very dusty These are the extremes and between the varying degrees of stability, and, in consequence, differing rates of wear
Sirees of stability et
It is to be expected that soils will differ with the geographical location, for it is well known that there is a great variation in soils in the various parts of the world But wide differences are also encountered in the soil on roads very near each other and even on successive stretches of the same road It is for this reason that earth roads often exhibit great differences in serviceability even in a restricted area
=Variation in Rainfall=--The stability of a soil and its ability to support the weight of vehicles varies greatly with the amount of water in the soil A certain small amount of moisture in the soil is beneficial in that practically every soil compacts more readily when ether the particles But most soils also become unstable when the amount of water present is in excess of that small amount referred to above and the stability decreases very rapidly as the amount of water in the soil increases
The serviceability of an earth road will change continually as the eneral utility of the earth road system in any locality is dependent to a considerable extent upon the amount and seasonal distribution of precipitation Theearth roads appropriate to any locality must of necessity be adapted to the cliive the highest possible degree of serviceability will be exceedingly variable froreat hue of serviceability, while in arid regions they may possess sufficient durability for a considerable volun adopted for earth roads and the methods of maintenance followed should therefore be carefully evolved to meet the soil and climate conditions where the roads are located These will differ greatly throughout a state or even a county
=Cross Sections=--The general principles of road design were set forth in Chapter IV In Fig 11 are shown typical cross sections for earth roads adapted to various conditions as indicated It is not apparent that one form of ditch is particularly preferable to the other and since soineers prefer the V section and others the trapezoidal section both are shown It would appear that the V shaped ditch is sorader while the trapezoidal is readily excavated with the slip or fresno scraper
The ditch capacity required and consequently the die requirements, as was pointed out in Chapter III
[Illustration: Fig 11 Cross Section for Earth Roads]
EARTH ROADS IN REGIONS OF CONSIDERABLE RAINFALL
In the zones where the annual precipitation exceeds 30 inches distributed over several months, earth roads will be unserviceable for a considerable period each year unless they are constructed so as tofor the best possible drainage and by adopting a method of maintenance that will restore the surface to a smooth condition as quickly as possible after a period of rainy weather or after the ”frost co
Before the construction of the desired cross section is undertaken, all of the grade reduction should be completed, except for rader in the manner that will be described presently
Where any considerable change in grade is to be effected, the earth can be moved in several ways and of these the most economical cannot be readily determined Ordinarily a contractor or a county will use the equipht be raphy is such as to perrade reduction to load the earth into duons in which it is hauled to the fill or waste bank The elevating grader consists essentially of a heavy shear plow or disc plohich loosens the earth and deposits it on acanvas apron The apron carries the on which is driven along under the end of the apron When the wagon is loaded, the grader is stopped while the loaded wagon is hauled out and an empty one drawn into position The rader is either a tractor or five or six teams of mules Foris necessary or where the ground is yielding, mules are preferable to a tractor The apron is operated by gearing frorader Generally four rader and six or eight in the lead This eous when the material on hauling in such cases is the most economicalgrader and one having a co of 30 to 45 horsepower is required
=Maney Grader=--If the haul is long and the nature of the cut will not perrades or lack of roorader of the Maney type may be used
This consists of a scoop of about one cubic yard capacity, suspended fro, the scoop is let down and filled in the same manner as a theeled scraper or ”wheeler” The pull required to fill a Maney grader is so great that a tractor is ordinarily employed in place of a ”snap” teaue, without interfering with the tearader after it is loaded
For this service a tractor having a co of 25 to 30 horsepower is required
=Wheel Scraper=--Forearth for distances between 150 and 500 yards, the wheel scraper of a capacity of about 1-1/2 yards is quite generally employed The soil must be loosened with a plow before it can conveniently be loaded into the wheeler and a heavy plow is ordinarily employed for that purpose Two furroith the ploill loosen a strip of earth about as wide as the scoop of the scraper and if more is loosened it will be packed down by the scrapers wheeling in place to load A helper or ”snap” tea, after which the wheel scraper is handled by one team
=Slip Scraper=--The slip scraper differs from the wheel scraper in that the scoop is not suspended froround It is drawn by one team and the capacity is two to five cubic feet, but the ed along and theabout the economical limit
=Fresno Scraper=--The Fresno scraper is one for four horses or mules for efficient work It differs somewhat froer capacity, but is a drag type of scraper much favored in the western states
SHAPING TO PROPER CROSS SECTION
If a road has been graded so that the profile is satisfactory or if the existing profile of the location is satisfactory, and the surface is to be shaped to a prescribed cross section, either the elevating grader or the blade graderGrader Work=--If the elevating grader is used in shaping the earth road, the apron will be lowered and the material will be excavated at the sides of the road and deposited on the ons will accoh places and haul the material to the low places After the earth has been deposited it must be worked over to secure the correct cross section and be made passable for vehicles This requires that clods be broken, weeds and grass that areand that the surface be carefully srader This latter operation will have to be repeated several times before a satisfactory surface is secured But this hly ilected
Nothing so detracts from an otherwise creditable piece of work as failure to provide a smooth surface for the use of vehicles It is especially uncohway if sods and weeds in quantity are left in the road after it has been graded The huetable matter decays increases the porosity of the road surfaceit more absorbent than soil without hu froeously be used to draw the elevating grader on this class of work, but will be greatly handicapped if there are wet sections along the road, through which the tractor must be driven In many cases its use is prohibited by such conditions and for all-round service of this character, mules are preferred for rader Outfit]