+---------------------------------+-----------+----------------------+ | | ROCK. | SOFT SOILS. | | +-----+-----+--------+------+------+ | |Hard.|Soft.|Compact.|Loose.| Very | | | | | | |loose.| | +-----+-----+--------+------+------+ | | ins.| ins.| ins. | ins. | ins. | |Headings: | | | | | | | Cap-pieces and vertical struts | 6 | 8 | 10 | 12 | 14 | | Sills | | | 8 | 10 | 12 | | Struts | 5 | 5 | 6 | 7 | 8 | | Distance apart of the frames in | | | | | | | feet | 6 | 4.5| 3 | 2.6 | 2.6 | | | | | | | | |Strutting of the tunnel, | | | | | | |longitudinal strutting: | | | | | | | Crown bars | 12 | 14 | 14 | | | | Props vertical or inclined | | | | | | | supporting the crown bars | 10 | 12 | 14 | | | | Sills | 8 | 8 | 10 | | | | Cap-pieces or saddles | 10 | 12 | 14 | | | | Struts to stiffen the structure | 6 | 8 | 10 | | | | Distance apart of the frames (in| | | | | | | feet) | 4.5 | 4 | 3 | | | | | | | | | | |Polygonal strutting: | | | | | | | Cap-pieces and contour pieces | 8 | 10 | 12 | 14 | 16 | | Vertical struts on top | 10 | 12 | 14 | 16 | 18 | | Vertical struts below | 12 | 14 | 16 | 20 | 24 | | Intermediate sills | 12 | 14 | 16 | 20 | 24 | | Lower sills | | | 12 | 16 | 18 | | Raking props | 10 | 10 | 10 | 12 | 12 | | Distance apart of the frames (in| | | | | | | feet) | 6 | 4.5 | 4 | 3 | 3 | | | | | | | | |Shafts: | | | | | | | Horizontal beams forming the | | | | | | | frame | 8 | 8 | 10 | 12 | 14 | | Transverse beams | 8 | 8 | 8 | 10 | 12 | | Vertical struts between the | | | | | | | frames | 8 | 8 | 10 | 12 | 12 |