Page 55 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

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TABLE 5.4 Guidelines for Selection of Steel Sets for 6- to 12-m-Dia

Steel sets R

Rock quality Construction Weight Spacing Spacing of
Excellent method of steel pattern bolt
RQD >90 sets None to None to
Tunnel boring Light occasional occasional
Good machine None to None to
RQD 75 to 90 Light occasional occasional
Drilling and Occasional Occasional or
Fair blasting Light or 1.5 to 1.8 m 1.5 to 1.8 m
RQD 50 to 75 1.5 to 1.8 m 1.5 to 1.8 m
Boring Light
machine 1.2 to 1.8 m
Light to 1.5 to 1.8 m
Drilling and medium 1.2 to 1.5 m 0.9 to 1.5 m
blasting
Light to
Boring medium
machine

Drilling and
blasting