56 BULLETIN 724, IT. S. DEPARTMENT OP AGRICULTURE. 
data are intended to serve only as an aid in making the necessary 
study : 
A. A cubic yard 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 cost 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 37^ 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 tlie labor cost 
and if fuel for the roller and depreciation were considered the average cost 
probably would approximate 1| 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 durable, 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 stone 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 
water, and (3) that it will 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 
