1.6 BULLETIN 906, U. S. DEPARTMENT OF AGRICULTURE. 



lean mixture, it is apt to split even under low pressures. A poor 

 grade of pipe may appear to be in good shape when first installed, 

 but may fail after a year or more due to softening of the concrete. 

 It is common, however, to detect causes of failure as soon as the pipe 

 is filled with water. 



More or less seepage is common to most grades of hand-tamped 

 pipe, but if it is not too pronounced it usually disappears in time. 

 Such materials as silt, clay, or fine sand are often used to fill up the 

 pores and prevent seepage. x\s mentioned above, pipe made of a dry 

 mixture is more subject to seepage than wet-mixed pipe, and the 

 joints are more difficult to make in a dry, porous pipe. 



If the pipe is of good quality any leaks that occur are usually at 

 the joints. When pipe is laid by inexperienced men leaks at the 

 joints are common, caused by poor mortar connection or by the 

 mortar falling from the joints when the pipe is being laid. Care 

 should be taken to see that the joints are butted against each other, 

 and that the mortar is squeezed firmly into place. Mortar will often 

 fall out of the joints at the top of the pipe, and the fault may be 

 difficult to detect, particularly in the smaller sizes. When pipe is 

 banded and under pressure it is common for water to seep out be- 

 tween the band and the outside shell of the pipe. Water will some- 

 times seep quite a distance in this manner. This may be caused by 

 a poor union between the abutting ends, or it may be due to dry, 

 porous pipe. Bands or joints will crack if the pipe is not properlv 

 covered with earth, and for this safeguard moist earth is preferable. 



Concrete pipe should not be injured by the roots of orchard trees 

 unless cracks appear. Large roots of shade trees may heave the pipe 

 and cause failure, or small, fibrous roots may enter the pipe and com- 

 pletely clog it. Tree roots sometimes enter the pipe at the connec- 

 tion of orchard risers, the risers being often loosened from the pipe 

 by being hit with plow or cultivator. 



Pipe lines sometimes fill with sand or trash, where the inlet is not 

 properly screened or settling basins provided. If velocities are high 

 enough the pipe will be flushed out without resorting to any special 

 means. Otherwise blowoff valves should be installed. 



Adobe soil will heave and crack and rupture pipe lines very much 

 in the same manner as it affects lined ditches. Most pipe layers 

 are skeptical of the success of concrete pipe laid in adobe soil, and 

 some will not guarantee work under such conditions. In some cases 

 the trouble has been overcome by covering the bottom of the trench 

 with 2 to 3 inches of sand. A good practice seems to be to dig the 

 trench deeper than in sandy loam or sandy soil, and to take extra 

 precautions in forming the joints. A minimum covering of 2 feet 

 over the top of the pipe is sometimes specified in adobe soil. 



