With reference to Problems 8.5 and 8.6, 2.7 m wide by 3.7 m high grizzly drifts below the undercut level are first supported with 3/4 in diameter, grade 55 (379 MPa yield strength) resin bolts 1.8 m long (grouted full length), and wire mesh. A continuous concrete liner may be added later. Compressive strength of concrete is 37.9 MPa. Unit weight of adjacent rock is 28.5kN/m3, angle of internal friction is 42◦ and cohesion is 23.8 MPa. Three sets of nearly orthogonal joints transect the rock mass. Joint friction angles vary between 27◦ and 38◦, while joint cohesion varies from 48 to 480 kPa. 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%?