42 



HIGHWAY CONSTRUCTION 



Earthenware Pipe Culverts. Construction. In laying the 

 pipe the bottom of the trench should be rounded out to fit the lower 

 half of the body of the pipe with proper depressions for the sockets. 

 If the ground is soft or sandy, the earth should be rammed carefully, 

 but solidly in and around the lower part of the pipe. The top surface 

 of the pipe should, as a rule, never be less than 18 inches below the 

 surface of the roadway, but there are many cases where pipes have 

 stood for several years under heavy loads with only 8 to 12 inches of 

 earth over them. No danger from frost need be apprehended, pro- 

 vided the culverts are so constructed that the water is carried away 

 from the level end. Ordinary soft drain tiles are not in the least 

 affected by the expansion of frost in the earth around them. - 



The freezing of water in the pipe, particularly if more than half 

 full, is liable to burst it; consequently the pipe should have a suffi- 

 cient fall to drain itself, and the outside should be so low that there 

 is no danger of back waters reaching the pipe. If properly drained, 

 there is no danger from frost. 



Jointing. In many cases, perhaps in most, the joints are 

 not calked. If this is not done, there is liability of the water being 

 forced out of the joints and washing away the soil from around the 

 pipe. Even if the danger is not very imminent, the joints of the 

 larger pipes, at least, should be calked with hydraulic cement, since 

 the cost is very small compared with the insurance against damage 



I II II HI I.I I I I II II II i I 



_-i 1 i l j_. 



!-!_ . -j __ -1-, 



- Fig. 18. 



thereby secured. Sometimes the joints are calked with clay. Every 

 culvert should be built so that it can discharge water under a head 

 without damage to itself. 



