58 



BULLETIN 126, U. S. DEPARTMENT OF AGRICULTURE. 



KINDS OF JOINTS. 



Various kinds of joints are used to prevent cracks in concrete 

 linings : 



(1 ) One of the most common is the plain abutting joint. This 

 joint is simple, cheap, and easily made. Expansion, likewise, is pro- 

 vided for in the frequency of the joints. It has, however, several 

 weak features which render its use questionable. One of these is the 

 lack of any bond between the sections. Were it not for the con- 

 nection with the bottom ut the toe each side section might be 



Tar Pa per 



Wooden Strip to be replaced by Asphalt 

 jt Tar Paper. 



5Z1 



[J; A J j [ i> V 



-^'■~ ; y 



J^jfczhzf 



■■4r\y&> : &> 



Steel Dowel- pins , ^ 



Pipe and DoWel-pin. 



g FC ' Scobey. 





Asphalt. 



Fig. 3. — Typical joints for concrete-lined canals. 



regarded as a separate slab, liable to be thrust upward by pressure 

 from behind or to fall backward when the earthen support is removed. 

 Both of these effects are quite probable, and may be seen in the lining 

 of the New York Canal of the Payette-Boise project (fig. 4). An- 

 other defect is the difficulty experienced in filling the seam with any 

 material which will render the joint water-tight, it being too narrow 

 to calk. 



(2) The abutting joint is frequently modified by introducing one or 

 more plies of tar paper (fig. 3, h). While the paper provides for 



