THE FULL SECTION METHOD 157 



il lately widened by digging away the earth at each side, and by 

 strutting the opening by temporary posts resting on blocking, 

 and carrying longitudinal bars supporting pol ing-boards. This 

 process of widening is continued in this manner until the full 

 roof section, No. 1, Fig. 81, is opened, when a heavy transverse 

 sill is laid, and permanent struts are 

 erected from it to the longitudinal bars, 

 the temporary posts and blocking being 

 removed. The excavation of part No. 2 

 then begins by opening a center trench 

 and widening it on each side, temporary 

 posts being erected to support the sill 

 above. As soon as part No. 2 is fully ex- 

 cavated, a second transverse sill is placed Fl ,- --i>ugr*m snow- 



ing Sequence of Ezcava- 



below the first, and struts are placed tu.n in English Method 



rri . of Tunneling. 



between them. The excavation of part 

 N - >. :J is carried out in exactly the same manner as was part 

 N>. '2. The lengths of the various sections, Nos. 1, 2, and 3, 

 generally run from 12 ft. to 20 ft., depending upon the 

 character of the soil. 



Strutting The strutting in the English method of tunnel- 

 ing consists of a transverse framework set close to the face of 

 the excavation, which supports one end of the longitudinal 

 en >uii lars, the other ends of which rest on the completed 

 lining. The transverse framework is composed of three hori- 

 zontal sills arranged and supported as shown ly Fig. 82. The 

 bottom sill .1 is carried by vertical posts resting on blocking on 

 the floor of the excavation. From the bottom sill vertical 

 struts rise to support the middle sill B. The top sill, or miners* 

 sill (7, is carried by vertical posts or struts rising from the 

 middle sill H. The vertical struts are usually round timbers 

 from <; ins. to 8 ins. in diameter; and the sills are square tim- 

 bers of sufficient section to carry the vertical loads, and gener- 

 ally made up of two posts scarf -jointed and hutted to permit 

 tin -i 11 to be more easily handled. la firm soils the struts be- 



