Research Article
Alteration in Material Properties of an Intact Rock due to Drilling and Bolting Operations
Table 3
(a) Properties of virgin rock mass and weaker zone around bolts. (b) Properties of rock bolts.
| (a) |
| | Property | Virgin rock mass | Zone around bolts |
| | Unit weight (, kN/m3) | 27 | 27 | | Intact UCS (, MPa) | 80 | 59 | | Intact modulus (, MPa) | 12800 | 7000 | | GSI | 45 | 45 | | 12 | 12 | | near tunnel periphery | 0.3 | 0.0 | | away from tunnel periphery | 0.0 | — | | near tunnel periphery | 1.683 | 1.683 | | away from tunnel periphery | 1.190 | — | | near tunnel periphery | 0.022 | 0.022 | | away from tunnel periphery | 0.011 | — | | | 0.51 |
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| (b) |
| | Property | Value |
| | Bolt type | Plain strand cable | | Borehole diameter, mm | 40 | | Cable diameter, mm | 25 | | Bolt modulus, MPa | 200000 | | Cable peak, MN | 0.6 | | Water : cement ratio | 0.5 | | Bolt length, m | 6 | | Spacing, m | 1.5 m c/c in roof | | 2.5 m c/c in wall and floor |
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