Summary 169 



tamped pipe, made of rich well-proportioned mortar, under a roof, 

 and thoroughly cured. 



9. Tamping alone does not produce a smooth interior, and the 

 pipe should be washed inside with neat cement. 



10. Greater strength can be secured by increasing the thickness 

 of the pipe wall and by using a wet consistency of the mortar. 



WET-POURED PIPE 



11. Wet-cast pipe is usually of large diameter, and is rein- 

 forced. When properly made, it attains great strength, and is 

 adapted for use under high heads, as in water-supply mains and in 

 important siphons. On account of the great number of forms re- 

 quired, its cost is relatively high. 



PIPE L.WING 



12. The bell and spigot joint is used largely in the East and 

 the tongue and groove joint in the West. While the former is the 

 logical joint for cast-iron pipe, the latter has important advantages 

 for cement pipe and can be recommended for sewer pipe as well as 

 for irrigation pipe. 



13. Pipe should not be laid in hot weather, except in the early 

 part of the day before the pipe becomes heated, as otherwise con- 

 traction cracks may occur. All concrete work of similar nature 

 should be done in cool weather if possible. 



14. Pipe should be laid with straight alignment and even 

 grades. The cover of earth should be at least 12 inches. Mortar 

 of one to two proportions with 8 percent hydrated lime is best for 

 the joints. 



FAILURES OF CEMENT PIPE 



15. The ordinary causes of failure are excessive internal press- 

 ure (in irrigation pipe), great depth of backfill (in sewer pipe and 

 drain tile), contraction while curing, unequal settlement, and water 

 hammer in pipe lines in which air is trapped. 



16. In hot, dry climates there are special dangers in the use of 

 pipe that is allowed to become dry after it is cured. When such 

 pipe absorbs water again, it may destroy pipe-line structures, may 

 buckle on curves, and may fail by distortion of the pipe section or 

 by differential expansion of the pipe wall. The best remedy is pre- 

 vention ; dry pipe should not be laid. 



17. The nature of the soil and the character of the bedding are 



