64 BULLETIN 724^ U. S. DEPARTMElSrT OF AGEICULTUEE. 



CONSTRUCTION. 



In constructing a Telford foundation the stones are set by hand on 

 the prepared subgrade so as to break joints roughly in the courses, 

 which should be approximately straight across the road. Each stone 

 should be placed with its long dimension in the direction of the 

 courses and should be bedded evenlj^ on the subgrade. The stones 

 should be set together as closely as practicable and should be wedged 

 firml}' in place by means of spalls as the setting proceeds. 



Ordinarily, the Telford stone is hauled out and distributed on the 

 subgrade ahead of the men who do the setting, the individual pieces 

 being of such size that they may be handled readily by one man. 

 Then, as the stone is needed for use, it is broken to the required size 

 with sledge hammers and placed in the foundation as above described. 

 Under average conditions two laborers to each stone setter are re- 

 quired to select and carry the stone to where it is needed, and to assist 

 in wedging up the foundation with spalls. 



As the wedging proceeds all projections of more than about 1 inch 

 above the intended surface of the foundation should be broken off 

 with hammers and the spalls thus obtained used as wedges. When 

 the laying and wedging are complete, the surface of the foundation 

 should present a fairly uniform appearance and should be free from 

 open or loose joints. 



As soon as practicable after the stone is placed the foundation 

 should be rolled with a power roller weighing about 10 tons. If de- 

 pressions develop under the roller that indicate failure of stone or soft 

 subgrade, they should be corrected by taking up and relaying the 

 affected portions, and the rolling and relajdng should continue until 

 no such depressions occur. If the road crust is such as to require a 

 smooth foundation, the irregularities of the Telford may be over- 

 come by spreading a layer of coarse sand or stone screening over the 

 surface while the rolling is in progress. In the past, however, Tel- 

 ford foundations usually have not been employed except in connection 

 with macadam or gravel road crusts, and with these the small irregu- 

 larities of the Telford surface are not ol^jectionable. 



COST OF TELFOED FOUNDATIONS. 



The cost of setting Telford varies with the character of stone used. 

 Where the stone is laminated, for example, the individual pieces 

 usually will be such as to fit snugly together and comparatively little 

 wedging with spalls will be necessary. Thin-bedded limestone lays 

 especially well in Telford construction. But if the stone is unstrati- 

 fied, it will break into irregular pieces, and the work of breaking off 

 projections and wedging up the foundation will be increased corre- 

 spondingly. A study of available data shows that where the stone is 



