USE OF CONCRETE PIPE IN IRRIGATION". 13 



pressure pipe. Pipes of 8 to 12 inches in diameter are made in stock 

 of double thickness, which will stand heads of 150 feet and over, but 

 the prices are about three times as high as stock pipe. Stock pipe 

 should be safe under pressures of from 20 to 35 feet. 



In connection with the above-quoted prices, it may be stated that 

 many pipe manufacturers who operate small plants sell pipe much 

 cheaper than the figures given. 



LAYING CONCRETE PIPE. 



Concrete pipe should be laid deep enough in the trench so as to 

 reduce the range of temperature and to be safe from injury against 

 plows, subsoilers or other farm implements. There should be at least 

 12 inches of earth over the top of all kinds of pipe, and high 

 pressure pipe should have a top covering of at least 18 inches. Tem- 

 perature changes in the shell of the pipe are greatly reduced when the 

 pipe is buried deeply, and less trouble is experienced from expansion 

 and contraction. The moisture content within the shell of the pipe 

 is likewise kept more uniform than where the upper half is laid near 

 the surface of the ground. 



The trench should be wide enough to allow room for a man's feet 

 when he is straddling the pipe in the act of laying the pipe. It 

 is a mistake to make the trench too narrow, especially when large- 

 sized pipe is laid, as there must be room to finish off the joints. 

 Excavation in soil that is not too hard or rocky may be done with a 

 plow and V scraper. Road scrapers and ditchers are sometimes used 

 to start large excavations, but trenches so made are too wide as a rule. 

 There are several makes of tile trenching machines that are used for 

 large installations, and where there are no obstructions to interfere 

 with the machine it may pay to use one. These may be operated over 

 the same trench twice, thus making it of nearly double width. For 

 the most part trenching is done with pick and shovel — handwork 

 being necessary where pipe is laid among full-grown trees in an 

 orchard. 



Some contractors lay pipe by force account, charging a commission 

 of 10 to 15 per cent for tools and supervision, for the reason that it 

 is difficult to make an estimate of the cost of excavation, as trenching 

 in hardpan, adobe, or soil full of boulders may cost several times as 

 much as a trench in loose loam or sand. Some trenching in favorable 

 soil has been done for 3 to 7 cents per foot for 12-inch pipe, while 

 the actual cost of a trench for 24-inch pipe near Azusa, Calif., where 

 bowlders were encountered, was about 35 cents per foot. Trenching 

 for 12-inch pipe in adobe soil near Santa Ana, Calif., with a trench- 

 ing machine was done for 5 cents per foot. Handwork for heavy soil 

 often costs 15 to 20 cents per foot for 12-inch pipe. 



