RAILROAD LOCATION AND CONSTRUCTION — MACKENZIE. 119 



The ground in front of the wall slionld not he counted upon 

 to assist in the support of the wall, and a factor of safety of not 

 less than 3 should l;)e used. 



Safe 'pre fisures on foundations under ivalls. — 



Safe pressure on Gravel 2 to 3 tons per sq. ft. 



Sand " 



" " Loam Ih " " 



Silt and Alluvium 1 ton 



Cky 1 to 2| tons 



Brldfje -Piers and their foundations. — Masonry piers for 

 bridges will cost from .S8 to 815 per cubic yard, exclusive of the 

 foundations on which they rest. 



For 50 ft. span, make piers 4 ft. thick under coping. 



" 150 " • '. 6 



" 200 " " 7 ■' " 



" 250 " " 7 1 to 8 for piers 80 ft. high. 



Sides and ends of piers Imtter half inch or three-quarter inch 

 per ft. Aljutments batter one inch per ft. 



Where sloping ice-breakers are not required, a round-ended 

 pier is the best shape. 



Grouting should not be used in first-class work, but flush up 

 fully with cement mortar as built. 



Foundation piles driven and cut ofl* with a saw, under 12 to 

 14 ft. of water, will cost 35 cents per lineal ft. of part remaining 

 in the work (say 17 ft.) 



The best formula for pile driving is — 



2 WH 



S+ 1 

 in \^diich 



L = safe load in His. 



W = weight of hammer in 11)S. 



H = fall of hammer in feet. 



S = penetration in inches under last lilow. 



