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Show GflELJAO WORK Construction Is Usually Divided Into Two Entire Distinct Classes. SUBHRABE FGRTHE SOKFAOE Some of Most Important Details Requiring Re-quiring Careful Attention Are Frequently Fre-quently Overlooked Some Precautions to Observe. Figure 1 shows a typical cross section sec-tion for a gravel-road surface and indicates in-dicates the customary steps involved in the construction of such a surface. The limiting thicknesses shown on this cross section are by no means followed universally, hut are believed to represent repre-sent the best currentr practice. The minimum thickness shown is supposed to be employed where the traffic is light and the subgrade is uniformly stable, while the maximum thickness Is adapted for opposite conditions. Perhaps the most usual compacted thickness of surface is eight Inches at the center and six inches at the edges. The difference in thickness between the edges and center is effected by making the crown of the subgrade flutter flut-ter than that of the surface. The construction of a gravel road usually is divided into two entirely distinct dis-tinct classes of work. The work of grading and preparing the subgrade exclusion of vegetable matter from fills, (3) provision for draining wet-weather wet-weather springs which occur In the subgrade, and (4) the matter of thoroughly thor-oughly loosening and distributing the materials contained in old road crusts. After the roadbed has been graded and drained properly, and the details mentioned above have received proper attention, the work of preparing the subgrade consists simply in forming a trench, us shown in figure 1. to receive the gravel surface. The trench may be formed largely with a grading machine, ma-chine, but the final shaping should be effected by means of picks and shovels and rolling. It is customary to provide grade stakes at intervals of about 50 feet, to serve as a guide for the pick and shovel work, and where extreme accuracy is desired cords may be stretched between the stakes to insure that the subgrade conforms to the required grade throughout. The rolling roll-ing is done ordinarily with a power roller weighing about ten tons. In order that the subgrade may be well drained during the process of spreading and compacting the gravel it Is frequently necessary to provide shoulder drains at comparatively short intervals. Such drains are constructed by opening small ditches through the shoulders and partially filling them with gravel. rs r w : I"5 1 "sgjsT3 .Cross section ready to nu'nt the surfacing msleraL "xtf I S f w f S "I SsjjsS Cross :--ctioo showing the first course of eravtl spread and rolld s$jj1'' Broken line shows the finished road section. I S 1 W f $ 1, J ) .,, to It inches 1 10 u jmfoj v05t r?Izs waon-of completed rodA. z' TYPICAL CROSS SECTIONS SHOWING METHOD OF CONSTRUCTING GRAVEL BOW) "W" should be at least 10 feet for single track roadway and "5"eneraJly not less than 5 feet., for double track.'Wshould oe not less than W feet and 'S' not less than 3 feet. "H" crown, varies from j inch per foot tor level grade, to I inch per foot for a grade of 5 . Via. 1 falls into one class, and that of hauling, haul-ing, spreading and compacting the gravel into the other. The first class of work has been discussed at considerable consid-erable length In connection with earth and sand-clay roads, but since it is desired to emphasize certain features of subgrade preparation that are of increased importance in connection with gravel-road construction, both classes of work will be considered In the following discussion : Preparation of the Subgrade. In grading the roadbed and preparing prepar-ing the subgrade for a gravel surface, it should be borne In mind also that the more expensive a road surface, the greater should be the care exercised to prevent H from being damaged through settlement or upheaval of the subgrade, and the greater should be the accuracy with which the subgrade is constructed, so that no unnecessary surfacing material may be required to correct irregularities in grade and cross section. No matter what the soil conditions may be, the subgrade for a gravel road surface, when completed, should conform closely In grade and cross section with the requirements of the plans and should present an even, uniform appearance. Also, it should be as firm and unyielding as the conditions will permit. Some of the most Important details requiring careful attention in preparing prepar-ing the subgrade, and which are perhaps per-haps most frequently overlooked, are (1) backfilling culvert trenches so as to prevent subsequent settlement, (2) |