t, HUMAN M1MHOD 



147 



boards extending from one frame to the next The cap-pieces 

 of the strutting for the bottom drifts serve as sills for the 

 exactly similar strutting of the heading next above. To sup* 

 port tin- additional \veight, aiid to allow the construction of the 

 side walls, the strutting of the bottom drifts is strengthened by 

 inserting an intermediate post lietween the original side JMISUS 

 of each frame. These intermediate posts are not inserted at 

 the center of the frames or bents, but close to the wall masonry 

 line as shown by Fig. 75. This eccentric position of the po.st 



. Sk.-t.-h Slioulng Work <f Kx- Fl<;. 76. Sketch Showing Meth<xt f 



caratlntf mi'l TimbvriiiK I'riftx Mini K.M.f Strutting. 



Heading*. 



avoids any interference witli the hauling, and also allows the 

 removal of the adjacent side p"-t \\lien the masonry is 

 constructed. 



Two methods of strutting the soffit of the excavation are 

 employed, one being a modification of the longitudinal system 

 employed in the Knglish method of tunneling described in a 

 succeeding luipter, and the other a modification of the Belgian 

 syst "in previously described. Fig. 76 shows the method of 

 employing the radial strutting of the Belgian system. At the 

 Iteginning the center top heading is strutted with rectangular 

 -"itx such as are employed for strutting the drifts. As this 

 heading is enlarged by taking out the haunch sections, radial 

 posts are inserted, as shown by Fig. 76, which also indicates 



