USE OF CONCRETE PIPE IN IRRIGATION. 19 
but it is desirable that all irrigation systems in such localities be 
installed in the fall or winter. In any case it is best to allow the pipe 
to assume its permanent length in the trench before the mortar in 
the joints has thoroughly hardened, and to fill the pipe soon and keep 
it full of water continually thereafter. 
There is one 8-inch stock, unreinforced concrete pipe laid in the 
desert soil of Antelope Valley, Calif., that is under a continual pres- 
sure of about 80-foot head. No leaks have been observed in this pipe 
since the water was turned in over two years ago. This pipe is always 
full, the water which it conveys being used for domestic purposes as 
well as irrigation. Other pipes in the same locality are continually 
giving trouble, and in most cases such trouble can be traced to the 
alternate wetting and drying out of the pipe. 
There is little doubt that the best engineering practice to be fol- 
lowed in laying concrete pipe is to provide expansion joints at fre- 
quent intervals. Effective expansion joints will allow the pipe to be 
in longitudinal equilibrium at all times, and thus protect the pipe 
from stresses which may cause failure. Practically all engineers have 
provided expansion joints in buildings, retaining walls, concrete 
bridges, and other important structures, yet such joints in concrete 
pipe lines are comparatively unknown. Of course, temperature 
changes are less in buried concrete pipe than in many structures, but 
as has been stated, expansion due to a saturated or even moist condi- 
tion may be considerable. 
It is not difficult to provide expansion joints for pipe that does not 
carry water under pressure. One contractor has telescoped an 8-inch 
pipe in a 12-inch, calking part of the space between the pipe with 
burlap and then filling with tar or asphalt, finishing off the joint by 
calking with burlap. This joint will answer for low heads. Tar 
or roofing paper has also been used for pipes under very low heads 
or running less than full. The tar paper is wired to the outside of 
the adjoining pipes over the joint, the pipe is not butted close together, 
and the space filled with an asphalt mixture. A strip of galvanized 
sheet metal is placed under the joint inside the pipe to hold the asphalt 
in place. Clay pipe or concrete pipe made with a bell end is some- 
times laid by pouring hot asphalt into every joint. There should be 
no expansion troubles with this installation if the pressure is not 
sufficient to force the asphalt mixture from the joints. Expansion 
joints have been made by painting heavy oil over one end of the abut- 
ting joints and then cementing a band of mortar over the joint, but 
it is doubtful if this joint will slip except under the most favorable 
conditions. Expansion joints have also been formed by placing an 
oiled thimble of galvanized sheet iron in the center of the shell of a 
joint of pipe after one-half of the pipe has been made and while the 
concrete is still in the molds, pouring asphalt over the ends of the 
