72 BULLETIN" 126, TJ. S. DEPARTMENT OP AGRICULTURE. 



afterwards. To keep them in position while concrete was being de- 

 posited, each one was lightly nailed to the side of the form, and 

 before the latter was removed the nails were withdrawn. 



The forms were left intact for a period of 8 hours at least, and they 

 usually remained undisturbed over night during a period of 14 to 20 

 hours. After their removal any defects in the wall surface were 

 "picked" out and the cavities smoothly plastered with a 1:1 J or 2 

 cement mortar. 



The canal bottom was then carefully cleared of litter, its surface 

 smoothed, and solidly tamped. All reinforcement bars that may 

 have become bent were straightened. The bottom piece of the 

 expansion joint was fitted to the two side pieces and its top care- 

 fully laid to grade. (PI. X, fig. 1.) The concrete for the floor lining 

 was then tamped and puddled into place, and when it had reached 

 the required thickness the surface was easily brought to grade and 

 smoothed by the use of a straightedge resting on the bottom joint 

 strips as guides. 



The entire lining was kept wet by continual sprinkling during a 

 period of three to five days. After this was discontinued a wash coat 

 of neat cement mortar was applied to the surface with a brush. (PL 

 X, fig. 2.) 



A 1:4:4 mixture of concrete was used on all the work except for 

 about 1,000 feet of bottom where there was excessive external water 

 pressure. In this portion of the canal a 1:3.2:3.2 mixture was used. 

 As a further protection in one very wet and miry place, additional 

 reinforcement was used in the bottom. Extending over a length of 

 about 5,000 feet of the largest canal section near the Santa Cruz Kiver 

 bed, "weep holes " were formed in the bottom to relieve external water 

 pressure. Two-inch tapering plugs extending entirely through the 

 lining floor were set in the freshly laid concrete and these plugs were 

 later removed as soon as the concrete had set sufficiently to retain its 

 shape. Two rows of these holes were made 2 J feet apart and spaced 

 4 feet longitudinally. During construction a considerable portion of 

 the canal was drained. A line of 8-inch tiling was laid in the bottom 

 and pumps attached thereto were installed at intervals of about 

 1,000 feet to withdraw the accumulated water. 



The contractor received $12.50 per cubic yard for the finished 

 concrete lining, using slab measurement. This included all costs 

 except the original purchase price of the steel reinforcement. How- 

 ever, no excavation was included and the company paid extra for 

 the wash coat. The contractor rented a rock crusher and delivered 

 the rock. Sand was obtained from the river bed. 



