494 



REPORT OF OFFICE OF EXPERIMENT STATIONS. 



The difficulties of construction are often serious and perplexing 

 (PI. XXIV, fig. 2). The sides of the trench must often be sheathed 

 closely to prevent the earth from caving and filling the trench before 

 the tiles or wooden boxes, which are also used, can be placed in po- 

 sition. 



COLLECTING PITS AND SAND TRAPS. 



Sometimes it is not practicable to place the tile deep enough to 

 collect the water which presses up from below, in which case pits 

 are excavated 4 feet or more deep directly beneath the drain and 

 are filled with gravel before the tiles are laid (fig. 6). These collect 

 the water which rises and passes off through the drain and are 

 found to be a valuable supplement to the ordinary tile or box drain. 



"VVliere a steam-trenching machine is used some device for sustain- 

 ing the unstable earth until the tile can be laid must be employed 

 (PI. XXV, fig. 1). An outfit of broad-faced wheels, or in some 

 cases a caterpillar tj'pe of truck, must be used to sustain the ma- 



1*^^ V*. • • •"' • ."/' 



End Section 



Fig. 6. — Collecting pits in connection with tile drains as used in Montrose County, Colo. 



chine as it passes over the soft ground. It has also been found 

 necessary in some localities to attach shields to the excavating wheel 

 and a shield for the shoe to hold the trench open until the tile can be 

 placed in position. This improvement is used at Montrose, Colo., 

 and at Roswell, X. Mex. It is needless to say that draining under 

 such difficulties is at best expensive, yet when we remember that 

 one or two well-located and constructed drains will often dry an 

 entire field of considerable size, the cost per acre is quite reasonable. 

 Sand traps or silt wells are a necessary adjunct to nearly all lines 

 of tile drains, and should be placed at junctions with other lines and 

 at convenient points along each drain. Their office is to cause the 

 sand which is carried by the drain to deposit itself in the well, from 

 which it can be removed when necessary. They are box wells, 3 by 3 

 feet in section, extending from a point 2 feet below the drains to the 

 surface of the ground. The drains discharge into the well, dropping 

 the sand which was held in suspension, the water passing out through 

 the drain on the opposite side. 



