CONCLUSIONS. 1 
From the facts developed in this investigation the following con- 
clusions appear to be warranted. 
In considering the design of a concrete pipe or conduit, from a ca- 
pacity standpoint, the fundamentals to be kept in mind are: 
(1) Original interior surf ace. 
(2) Engineering; inspection and supervision of construction. 
(3) The water. 
(4) Acquired interior surface. 
In a jointed pipe, the original. interior surface depends upon that of 
the individual units and of the assembled whole. The smoothest units 
are cast of a wet mixture and allowed to set in rigid, smooth, oiled 
forms. These units are true to shape and assemble into a nearly per- 
fect pipe. As the joints are practically as smooth as the cast surface, 
the number of joints is almost immaterial. 
Most processes that permit immediate removal of the forms do not 
protect the plastic concrete against distortion. Distortion in the 
units means offsets in the pipe that may easily decrease the capacity 
from 10 to 20 per cent. This percentage may be reduced after 
assembling the units by tapering down the offsets with mortar applied 
with a trowel. 
Supervision of the finished joints will usually improve the capacity 
materially. The good results obtained with the band method (see 
p. 85) appear perfectly feasible. 
A brush coat applied to a rough original interior will increase the 
capacity and decrease the percolation. The same coat applied to a 
smooth interior will decrease its capacity and is not needed, under 
ordinary pressures, to prevent percolation, if the pipe is properly 
made. This is true for the reason that methods used in making pipe 
with a smooth interior are also conducive to a dense concrete. Note 
the suggestion that coating may scale off if radically different mix- 
tures are employed for pipe and coat. (See p. 99.) 
Pipe units made with the molds now on the market usually run 
undersize by as much as 3 or 4 per cent (in area) for diameters under 20 
inches. Above that size, the nominal and actual areas are more 
nearly equal. Most pipes made with a wet mixture in short units, 
from which the molds are immediately stripped, " slump" to a slight 
extent, making a section somewhat undersize in area with a slight 
excess in shell thickness. 
From a capacity standpoint monolithic pipes and conduits are 
built under two general conditions: (1) In the open or in the com- 
parative freedom of a trench; (2) in a tunneL Under the first con- 
dition the form adjustment, bracing, supervision, concreting, spading, 
and final inspection can be conducted from both inside and outside, 
with the added advantage of working in the daylight. Naturally 
this tends to result in better workmanship and higher carrying 
capacity than is feasible in a tunnel where all of the above operations 
1 These conclusions were written since receipt of the discussions beginning on p. 92, and axe, therefore, 
based on all the data in the paper. 
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