CONCRETE LINING FOE IRRIGATION CANALS. 71 



TUCSON FARMS CO., TUCSON, ARIZ. 



The water for this project is obtained by pumping from numerous 

 wells. During the winter and spring of 1912-13 a reinforced 

 concrete lining was placed in about 2\ miles of the new main canal 

 for the prevention of seepage losses through a sandy and gravelly soil. 



The canal has a trapezoidal cross section entirely in excavation and 

 as lined is capable of carrying a 2.9-foot depth of water. The bottom 

 width ranges from 2 to 4f feet and the side slopes are 1 to 1. The 

 greater part of the concrete used in this construction is a 1 : 4 : 4 mix- 

 ture and the lining is 3 inches thick throughout. 



In grading the channel for lining, a framed template was used to 

 get a true section. The reinforcement is made of round steel bars 

 intersecting at right angles and wired together. Four longitudinal 

 bars, ^-inch diameter, were placed one on each side of the bottom 

 for the lining floor and one on each side near the top of the side walls. 

 Then at right angles to these, as stated, |-inch crossbars were spaced 

 12 inches apart. Each crossbar was continuous and extended from 

 the top of the lining on one side through the lining to the top of it on 

 the opposite side of the canal. When it was not possible to obtain 

 the |-inch bars, ^-inch bars were substituted and spaced 18 inches 

 apart. 



Wooden-framed forms built in 12-foot sections were then set in 

 position over the steel reinforcement, blocked to place, and the ad- 

 joining ends bolted together. Then J-inch steel backing plates, 2 

 feet wide and long enough to reach to the bottom of the earth section, 

 were slipped behind the forms and under the reinforcement. Before 

 placing the concrete, wooden spreader-strips 2 by 3 inches were set 

 between the wooden forms and the backing plates. Each spreader 

 contained a staple driven almost full length into its side near the 

 bottom, and in setting the spreader the staple loop was slipped over 

 the end of the crossbar and the spreader was then slid into position. 

 In this way the bar was carefully held in position while the concrete 

 was being placed in the forms. A spreader was set beside each cross- 

 bar, and as the concrete for the side lining was tamped and puddled 

 into place the spreaders were gradually removed, leaving the cross- 

 bars firmly embedded in the concrete. The steel plates likewise were 

 withdrawn as the walls were built up. When the side forms were 

 filled with concrete to within 3 inches of the top, the longitudinal bars 

 were placed and wired to the crossbars. The remaining concrete was 

 then placed and smoothed with an edging trowel. 



Expansion joints were provided by setting 1 by 3 inch wooden 

 strips in the middle of each form in the same manner as the spreaders, 

 except that no staples were used and the joint strips were not removed 



