56 BULLETIN 724, U. S, DEPAETMENT OF AGRICULTURE. 



data are intended to serve only as an aid in making the necessary 

 ■stud}^ : 



A. A cubic yaivl of loose gravel ordinarily weighs between 2,700 and 3,300 

 pounds, the average weight being about 3,000 pounds. 



B. Loose gravel will shrink from 12 to 15 per cent in volume when compacted 

 in a road foundation. In determining the loose volume of gravel required for a 

 given project it is customary to compute the compacted volume and add from 

 20 to 30 per cent to cover waste, shrinkage, and loss in handling. 



C. The average cost of loading pit gravel by hand into wagons is about 20 

 cents per cubic yard. Where the amount of 'work to be done is sufficient to war- 

 rant the installation of a steam shovel or the construction of a special scaffold 

 so that wheeled scrapers may be used for loading, the cost of this work usually 

 may be reduced, the reduction sometimes amounting to 50 per cent or more. 



D. The co.st of screening gravel varies greatly according to the character of 

 the pit-run material and the kind of screening equipment employed. Hand 

 screening costs from 25 to 40 cents per -cubic yard, while with a properly ar- 

 ranged mechanical screen the cost should not often exceed 15 or 20 cents per 

 cubic yard. 



E. The cost of hauling depends on the equipment used and the condition of 

 the road over which the hauling is done. With teams at $5 per day and the 

 roads such that two tons may be hauled at a load, the average cost is about 25 

 cents per ton mile, or 37J per cubic-yard mile. 



F. The cost of spreading gravel, on five road projects recently supervised by 

 the Office of Public Roads and Rural Engineering, ranged from about 3 cents 

 to about 8 cents per cubic yard. The average cost was about 6^ cents per 

 cubic yard and the average cost of labor was about 20 cents per hour. The 

 wagons used in all cases were built so that they dumped directly upon the 

 subgrade and were designed to spread the material to a considerable extent 

 while it was being dumped. 



G. The cost of rolling the gravel on the above five projects ranged from 

 slightly less than one-half cent to about 1 cent per square yard. The average 

 cost was about 0.6 of a cent per square yard. This included only the labor cost 

 and if fuel for the roller and depreciation were considered the average cost 

 probably would approximate lA or 2 cents per square yard. 



CRUSHED-STONE FOUNDATIONS. 



Crushed-stone foundations have been made from practically all 

 kinds of stone ordinarily available for such a purpose ; and provided 

 the stone be sound and du.rable, there is, in general, no occasion for 

 limiting the varieties that may be so used. A moderately soft or 

 brittle stone should prove equally as satisfactory for a foundation 

 as one that is extremely hard and tough and usually would be much 

 easier to crush, as well as to compact, than the hard, tough stone. The 

 only requirements really essential are (1) that the sto.ne shall possess 

 sufficient resistance against crushing to withstand any load likely to 

 come upon it, (2) that it will not be affected by the action of ground 

 Avater, and (3) that it Avill bond together under the roller to form a 

 dense, well compacted foundation. These requirements are based on 

 the assumption that the foundation always will be protected from the 



