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 at the toe each side section might be 
^-Tar Paper 
Asphalt Coating ) •* ■> ->^W vaV--v-':.>?f2 ^ 
or Tar Paper -Strip Corrugated Iron. 
d 
S 
Sheet Metal. 
9 
Asphalt Coat'or Tar Paper. 
'^^A-'^^-.^y^-L 
Tar Paper 
Wooden Strip to be replaced by Asphalt, 
f Tar Paper. 
ppagj 
Steel Dowel -pins (l */ 
y Au aM#^ 
-3 \v" J 
Wood 
Pipe and Dowel- pin. Core^ 
■2'/2 Stakes 
Asphalt. 
re Scobe 
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, b). While the paper provides for 
