142 LAND DRAINAGE 



the ditch. Because of these three facts it will be found 

 that if a lot of tile is laid promiscuously, end to end 

 in the hollow at the bottom of the ditch, many of the 

 joints will be so open that sand will very readily drop 

 through into the tile drain; consequently if the tile are 

 left in this position, and the ditch , filled, the drain will be 

 clogged in a very short time. There should be no open 

 joints. 



" The tile is sometimes clogged by the development of 

 roots that gain entrance through the joints of the tile. 

 The depth at which the tile are laid has very little to do 

 with this difficulty. It is determined by the presence of 

 a perpetual flow of -water in the tile from some spring. In 

 dry periods this water seeps from the joints and moistens 

 the soil, which condition attracts the roots. Protection 

 of the upper half of the joint against the admission of 

 silt is some aid in preventing the entrance of roots into 

 the tile." FIPPIN. 



186. Fitting the joints. If, when a section of tile 

 is laid in place, it does not fit tightly against that al- 

 ready laid, it is usually found that by rolling it to the 

 right or left, it can be made to fit so tightly as practically 

 to prevent the passage of soil particles except quicksand 

 or fine silt. Sometimes this cannot be done, in which 

 case a new piece of tile must be substituted. A piece 

 that cannot be made to fit in one place will frequently 

 readily fit in another place in the same line of tile. 



187. Blinding. As the work of laying the tile pro- 

 gresses, the workman should shovel in a sufficient amount 

 of loose soil to settle down about the sides and partly, or 

 wholly, cover the tile. This holds the tile in place until 

 the filling can begin. Sometimes, instead of shoveling 

 in the soil from the surface, some earth is loosened from 



