Geomechanics and Ground Control · Ground Control · 2 marks · Multiple choice
An 8 m diameter tunnel has rock-mass quality Q = 1.0 and excavation support ratio ESR = 1.0. Using the supplied Grimstad–Barton (1993) chart, choose the tunnel-wall fibre-reinforced shotcrete and bolt requirement.
Correct answer: (C) Shotcrete 5–9 cm; bolts 2.7–2.8 m
Explanation
Equivalent dimension is diameter/ESR = 8. For wall support in the intermediate Q range, use the wall-adjusted rock quality, 2.5Q = 2.5. Plot this against equivalent dimension 8 on the supplied chart: the fibre-reinforced shotcrete band is 5–9 cm, and the right-hand bolt-length scale reads about 2.7–2.8 m. Hence C. Treating this as an unadjusted roof-support point selects an unnecessarily heavier band.
More Ground Control questions
GATE 2023 MN Q48– Pillar strength is S p=S 1(0.64+0.54w/h-0.18w2/(lh)), with l≥w. A 30 m square pillar of…
GATE 2023 MN Q62– The 20 m high rock slope shown has a 45° face and a potential sliding joint at 30°. Rock…
GATE 2022 MN Q21– Which vertical-stress profile shown corresponds to the tributary-area method of pillar…
GATE 2022 MN Q33– A metal-mine drive has roof span 4 m. Using the modified Lauffer chart, find the factor…
GATE 2022 MN Q38– A three-point borehole extensometer has anchors 1, 2, 3 from deepest to shallowest, as…
GATE 2022 MN Q49– A circular tunnel of radius 3 m is in a hydrostatic field of 15 MPa. Rock E=5 GPa and…
