PREPARING THE FOUNDATIONS. 



Soft Ground. The materials should be excavated to a solid stratum or piles spaced about 

 zj to 3 ft. ivnters should be driven over the foundation to a good refusal. The piles should be 

 nit oil Ix low low water level to carry a timber grillage, or concrete may be deposited around the 

 lu .ids of the piles. Where water cannot be excluded it will be necessary to use one of the following 

 mi -tluxls: open caisson, crib, coffer dam, or pneumatic caisson. 



In using an open caisson the masonry is built up or the concrete is deposited in a water tight 

 box built of heavy timbers or of reinforced concrete, the caisson being sunk as the pier is built up. 



si?. 



To suit superstructure, but not less 

 than y-u 'for girders and trusses 

 or 2-6 'for solid floor. 



nt For high back walls. 

 Ifbackwallisleu than 5'0' 

 hiqh to be Class A Concrete, 



to be used -.vhere soft 



maler'at is found Where 



of rails to be 6 from 

 bottom. 



-Number ofpiks, if required, 

 to be determined by character of underlying 

 material. 



Foundation to suit local conditions, but not to 

 be/ess than4'-0 "deep unless good rock /: 



nil exposed corners % edges to be rounded to 

 I inch radius. 



TYPE A. \^' v ;jL..j 4~...|....J ' j! TYPE B. other porous material. 



Flaring Wings. JL~ -j -^ j^ r-"^ !| Straight Wings. 



To be used at crossings of Streams U-^j -4- ft; -4*- Tobe used at Street and 



and at other places where this &!... J..- .^15 Highway crossings where 



type is desirable. igj :(| flaring wings are not desir- 



RngltflisysualfyJO butmaybe -%j PLAN. \ able, fit Streets arnf Highways M of bat- 

 -varied to yuit locdi conditions. ^ >w ten's usually placed on building line 



ten's usually pkced on building li 



FIG. 4. MASONRY ABUTMENTS, N. Y. C. & H. R. R. R. 



The caisson is commonly floated into place and then is sunk on piles which have been sawed off 

 to receive it, or on a solid rock foundation. The sides of timber caissons are usually removed 

 after the pier is completed. 



Timber cribs are made of squared timbers placed transversely and longitudinally, and bolted 

 together so as to form a solid structure with open pockets. The crib is sunk by loading the 

 pockets with stone. No timber should be left above the low water mark in open caissons or cribs. 



A coffer dam is usually made by driving two rows of sheet .piling around the pier, the space 

 between the rows of piling being filled with clay puddle. For small depths a single row of sheet 

 piling is often sufficient. Where the depth is too great for one length of sheet piling, additional 

 rows are driven inside the first. Steel sheet piling is now much used for difficult foundations. 

 Steel sheet piling can be driven through ordinary drift and similar material, is not limited in 

 depth, and is practically water tight when used in a single row. It can be drawn and used again. 

 It is almost impossible to shut off all the water with a coffer dam, and pumps should be provided. 



Pneumatic caissons should only be used under the direction of experienced engineers and 

 will not be considered here. 



For details of sinking piers see Jacoby & Davis' " Foundations of Bridges and Buildings ", 

 McGraw-Hill Book Company. 



