THK FULL SECTION METHOD 



is loose some of the members of the framework are doubled 

 and additional bracing is introduced as shown by Fig. 90. 



The frames just described are placed at intervals of about 

 4 ft. along the excavation, and are braced apart by horizontal 

 struts. Some of the longitudinal bearing beams, as at 6, Fig. 

 90, also extend through two or three frames, and help to tie 

 them together. Finally, the longitudinal poling-boards extend- 

 ing from one frame to the next along the walls of the excava- 

 tion serve to connect them together. The short transverse 

 beam e, Fig. 90, located just above the floor of the invert, 

 serves to carry the planking upon which the train car tracks 

 are laid. Besides the timber strutting peculiar to the Austrian 

 method, the Rziha iron strutting described in a previous chapter 

 is frequently used in tunneling by the Austrian process. 



Centers. The two forms of centers used in the English 

 method of tunneling are also 

 used in the Austrian method. 

 One of the methods of support- 

 ing these centers is shown by 

 Fig. 91. The tie-beam. of the 

 center rests on longitudinal tim- 

 bers carried by the strutting 

 frames and intermediate props. 

 In single-track tunnels it is the 

 frequent practice also to curry 

 the ends of the tie-beams in re- 

 cesses left in the side wall ma- 

 sonry, with intermediate props 

 inserted to prevent flexure at 

 the center. \Vlnn the Rziha 

 iron strutting is employed, it also 

 serves for the centering upon which the arch masonry is built 



Masonry. In the Austrian system of tunneling, the lining 

 is built from the foundations of the side walls upward to the 

 crown of the roof arch in lengths in consecutive rings equal to 



Fm. 91. Sketch Showing Manner of 

 Constructing the Lining Muonry, 



Austrian Mctli<~l. 



