84 BULLETIN 724, U. S. DEPARTMENT OF AGRICULTURE. 



rected with No. 1 stone, and the rolling shall continue until the stone is well 

 compacted and the surface is uniform in grade and cross section. 



The second course of stone shall consist of a single la;j'er of No. 2 stone 

 spread uniformly to a depth not exceeding 4 inches. The stone shall be spread 

 and rolled in the manner prescribed for the first course. When completed the 

 surface of the second course of crushed stone shall be smooth, firm, well com- 

 pacted, and continuous, and shall have the cross section and grade indicated 

 by the drawings. 



After the second course of stone has been spread, rolled, and completed as 

 above specified, screenings shall be spread uniformly over the surface to a 

 depth of approximately one-half inch. The spreading shall be done with 

 shovels from piles along the road, from dumping boards, or from carts. In no 

 case shall an entire load of screenings be dumped directly upon the second 

 course. 



After the screenings are spread they shall be dry rolled until the voids of 

 the second course are filled. The foundation shall then be sprinkled with 

 water from properly constructed sprinkling wagons and rolled with a power 

 roller of the type and weight specified for the first course. The amount of 

 water used shall be sufficient to wet the stone thoroughly, but shall be put on 

 in such quantity and manner as not to wet and soften the subgrade. Screen- 

 ings shall be added and the sprinkling and rolling continued until the surface 

 ceases to show the marks of the roller and a grout of water and rock dust 

 flushes ahead of the roller. 



After the foundation is completed, as above specified, no materials or traffic 

 shall be placed or allowed upon it for at least 24 hours. 



TELFORD FOUNDATION. 



The Telford foundation shall conform to the cross-section drawings shown 

 on the plans and when completed shall be true in all respects to the line and 

 grade as staked out by the engineer. 



TELFORD STONES. 



The stone used shall be sound and durable and, in the judgment of the 



engineer, equal in quality to that obtained from the quarry located 



at . The individual blocks shall be approximately rectangular in shape 



and shall conform to the following limiting dimensions : 



Depth — Equal to the depth of the foundation as shown on the pdans. 



Length — Not less than the depth and not greater than one and one-half 

 times the depth. 



Width — ^Not less than one-half the depth and not more than the full depth. 



SETTING THE TELFOBD. 



The stones shall be set by hand with their long dimensions at right angles 

 to the direction of the road and in approximately straight courses. They shall 

 break joints roughly in the courses and shall fit in snug contact, one against 

 the other. Each stone shall rest on its broadest edge and shall be rammed 

 to a firm uniform bearing on the subgrade. 



After the stones are set as above provided all interstices that appear in the 

 surface of the foundation shall be filled with spalls which shall be firmly 

 wedged into place by means of a hand hammer. All projecting stones which 

 extend more than 1 inch above the established .surface of the foundation shall 



