Question

A circular tunnel is being excavated in a blocky rock mass by drilling and blasting. An excavation disturbed zone (EDZ) around the tunnel extends 0.70 m into the rock from the excavation surface. Considering the unit weight of the rock as 25 kN/m³, the support pressure required at the crown of the tunnel to stabilize the loose blocks of the EDZ is \(\underline{\hspace{1cm}}\) kPa. (round off to one decimal place)

Hint:

To calculate the support pressure required for tunnel stabilization, multiply the unit weight of the rock by the depth of the excavation disturbed zone.

Answer 1

Correct Answer: 17.5

The support pressure \( P \) required to stabilize the loose blocks in the excavation disturbed zone can be calculated using the formula: \[ P = \gamma h, \] where:
- \( \gamma \) is the unit weight of the rock (25 kN/m³),
- \( h \) is the depth of the EDZ (0.70 m).
Thus, \[ P = 25 \times 0.70 = 17.5 \, \text{kPa}. \] Thus, the support pressure required is \( \boxed{17.5} \, \text{kPa} \).