26 



BULLETIN 190^ U. S. DEPARTMENT OF AGEICULTURE. 



driven by means of a heavy maul and may be removed by a three- 

 legged derrick and a special grabhook,as shown in the figure. 



If the soil in the bottom of the completed trench be so soft that it 

 will not support a man's weight, boards should be laid under the tile 

 to keep them in line and on grade. For large-sized tile the planks 

 should be built into a triangular trough ; or, if conditions are exceed- 

 ingly bad, piles should be driven and planks secured to them in the 

 form of a cradle. Under such conditions it is often advisable to 

 employ sewer pipe in place of drain tile, as the bells aid in keeping 

 the Ime intact. Second-quality pipe is suitable and may generally 



be purchased at about 

 coffa^^ooaA/^u/ ^ '^"/^"'l^^ ■-. - thesame cost as drain 



ifVith iron bands Sy /^. ...i <(mn\ W\ ^ i-. ^^ " j."1 TTi i- 



tiLe. Under ordmary 

 conditions, howerer, 

 the use of sewer sec- 

 onds is not recom- 

 mended, as the cost 

 of freight and haul- 

 ing is higher than for 

 drain tile and the 

 former are heavier 

 and more difficult to 

 handle. Also in sta- 

 ble groimd it is nec- 

 essary to dig out 

 places for the bells, 

 which cons iderably 

 increases the cost of 

 trenching. 



The tile should be 

 hauled and distribut- 

 ed in one operation 

 and should be strung 

 out end to end in a 

 line about 10 feet to one side of the proposed trench, with an occa- 

 sional length laid down to allow for breakage. 



Lines and grades for drainage work should be carefully established 

 by surveys. To obtain a guide for hand trenching, a cord or wire 

 should be stretched along the ground at one edge of the proposed 

 trench, and to afford a convenient method of determming the proper 

 depth at all points grade planks should be set up at each 50-foot sta- 

 tion, as shown in figure 21. These planks should all be of the same 

 height above the proposed grade of the trench, so that a cord stretched 

 over the center of the trench will be at a uniform height above grade. 



Fig. 20. — Method of sheeting trenches of moderate depth (Miller 

 system) . 



