16 BULLETIN 906, IT. S. DEPARTMENT OE 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. As 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 
property 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. 
