78 BULLETIN 126, U. S. DEPARTMENT OF AGRICULTURE. 



to provide considerable slab strength, the floor lining is from 4 to 6 

 inches thick. The linings for hydraulic fills recently completed are 

 6 inches thick and reinforced with No. 6 wire fabric 6 by 6 inches. 



Linings of 2 § to 2^ inches thickness have been used on four stretches 

 of lined canal having lengths of 250, 250, 575, and 1,000 feet, respec- 

 tively. The bottom width is 44 feet and water depth of 5.5 for the 

 first three and 34 feet and 7 feet, respectively, for the fourth. All 

 slopes are 2 to 1. In preparation for the linings the canal sections 

 were carefully graded and aligned by chalk line and straightedge. 

 Fills were made a little high, with loose sand where possible, and 

 after saturating with water were graded. Fills as high as 10 feet 

 were graded and aligned within two or three clays after the material 

 was placed with a scraper, but they were made of clean sand thor- 

 oughly saturated with water. No settlement has been noticed. 

 The lining was laid in cross strips 3 feet long longitudinally, and these 

 were imperfectly bonded to permit cracking at the joints. The 

 latter, being numerous, permitted only narrow cracks, which are 

 unimportant. It is said that in part of this lining the water reaches 

 a velocity as high as 20 feet per second at times and that no appreci- 

 able injury to the concrete has occurred after five or six years of use. 



SOUTH SAN JOAQUIN IRRIGATION DISTRICT, MANTECA, CAL. 



Concrete lining has been placed on 7 miles of the main canal, 3 

 miles of which is owned jointly with the Oakdale irrigation district. 

 A typical lined channel has a bottom width of 1 1 .36 feet, side slopes 

 \ to 1, and is planned to carry a 9-foot depth of water and allow 2 

 feet additional for splash. This design, having a grade of 0.0775 per 

 100 feet, is intended to have a capacity of 850 second-feet. An excess 

 grade for curves was computed from the following formula: 



TT 100 v 3 

 2gr- 



where He is the excess grade in feet per 100 feet; v is the uniform 

 velocity of water in feet per second; r is the radius of the curve in 

 feet. The value of n for Kutter's formula was taken as 0.015. The 

 lining thickness averages 4 inches for the bottom and 4 to 6 inches 

 for the sides of the canal. A mixture of 1 : 3 : 6 concrete, placed behind 

 forms and in alternate sections 12 to 16 feet long, was used without 

 allowing expansion joints. In many places where the channel is in 

 rock cut no back forms were used, and in such case the alignment is 

 irregular and follows the contour of the side walls. 



The cost of the concrete in the completed work was about $14.50 

 per cubic yard. 



