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 surface. 



(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 jqints 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 writ ton since receipt oi the discussions beginning on p. 92, and are, therefore, 

 based on all the data in the paper. 



74 



