sTi:i TiiN<, 11 \ 



45 



stone in case the roof of the excavation is very unstable. 

 Planks used in this manner are usually called p< ding-boards. 

 Where the side walls as well as the roof require support, 



20. Ceiling Strutting for 

 Tumifl Hoofs. 



Fi-.. '.'1. ' . 



vertical side posts are employed to carry the roof beams, as 

 shown by Fig. 21; and, when necessary, poling-lxiarda are 

 inserted between these posts and the walls of the excavation. 



Frame Mnittimj. In very loose soils not only the roof and 

 side walls, but also the floor of the heading require strutting. 



Flo. 22. Sill. SMo Podt and Cap 



Knmr Strtittlnu. 



Fro. 23. Rflnforcwl rnnw Fnun* 

 Strnttlnu (r Trrm-hrri.iw MitlrrlnU. 



In these cases frame strutting is ciii||oyod, as shnwn 1y Fig. 

 22. It consists simply of a rretaiitfiilar frame ; at tlio top 

 there is a crown bar supported by two vertical side posts 



