DRAINAGE OF IREIGATED SHALE LAND. 



21 



vertical lumber sheeting. The boards should fit tightly ; they may 

 be driven with a heavy maul and removed with a light derrick or 

 grabhook. Where the sheeting is driven and pulled by hand, planed 

 2 by 6 inch planks have been found the most satisfactory. Sizes 

 larger than this are driven and pulled with difficulty. The bottom 

 end of each of these planks should have a long bevel on one side, so 

 that it will drive readily and straight. The tops of the planks should 

 be beveled slightly, or a cap used to prevent "brooming" while 

 being driven, and the planks should be long enough to extend below 

 the grade line. As the material is excavated, two mofe heavy planks 

 should be placed near the bottom and held apart by trench jacks 

 to prevent the weight of the material from displacing the bottom of 

 the sheeting. These can be used also for the workmen to stand on 

 when the bottom of the trench becomes too soft. In the latter event 

 it becomes necessary to place boards under the tile in order to hold 

 them on the grade and prevent them from sinking. When large-sized 

 tile are used a cradle must be placed under them. This cradle re- 

 sembles a ladder, the strips running lengthwise being of 2-inch mate- 

 rial and spaced so that the sides of the tile will rest against them 

 as well as on the crosspieces of broad 1-inch lumber. The tile should 

 be covered by some material such as cinders, gravel, or broken shale. 

 Hay and straw have been used with success. The tile should be well 

 blinded and weighted down before removing the sheeting, which 

 should be pulled slowly and carefully to prevent the soft material 

 that sloughs in from the sides from pushing the tile off grade. 

 Trenching machines especially built with shields for soft material 

 would handle some of these soils satisfactorily. 



The excavation of ditches should begin at their outlets or at their 

 junctions with other drains and proceed toward the upper end. 

 Trenching should be done as neatly as possible and should follow 

 closely the line of stakes ; where the drain changes direction the turn 

 should be made by a neat curve. If possible, the top soil should be 

 thrown out on one side of the ditch and the shale on the other, and 

 in back-filling the shale should be put in first. 



No attempt should be made to grade the tile by the water in the 

 ditch. Grades for the drains always should be established by sur- 

 veys, and the ditch should be dug accurately to the depths specified ; 

 these depths should be measured from the grade stakes set for that 

 purpose, and the ditch graded evenly on the bottom by means of the 

 " line and gage " method or by any other equally accurate device for 

 obtaining an even and true bottom upon which to lay the tile. 



The tile should be laid as close as possible, beginning at the lower 

 end and proceeding upstream. They should be turned about until 

 their upper edges close. If there is silt or other fine material that is 

 likely to run into the tile, the lower edges must be laid close and the 



