With reference to Problems 8.5 and 8.6, 9 ft wide by 12 ft high grizzly drifts below the undercut level are first supported with 3/4 in diameter, grade 55 resin bolts 6 ft long (grouted full length) and wire mesh. A continuous concrete liner may be added later. Compressive strength of concrete is 5,500 psi. Unit weight of adjacent rock is 180 pcf, angle of internal friction is 42◦ and cohesion is 3,450 psi. Three sets of nearly orthogonal joints transect the rock mass. Joint friction angles vary between 27◦ and 38◦, while joint cohesion varies from 7 to 70 psi. Fracture persistence determined from trace length scans is 87%, so only 13% is in intact rock. What thickness of liner should be used if a rock mass safety factor of 1.5 and a concrete liner safety factor of 1.4 are specified when the abutment load factor is 185%?