Regarding drilling for tunnelling works, identify the correct combined statement about equipment, drill allocation per face area, and borehole diameter tolerance for cartridges.

Introduction / Context:Efficient drill-and-blast tunnelling depends on appropriate equipment, adequate resource allocation, and correct hole geometry. Pneumatic drills (and modern hydraulic/electric variants) provide the energy for fast drilling. Matching the number of drills to the face area and ensuring proper hole diameter tolerance for cartridges are standard planning considerations.

Given Data / Assumptions:

• Pneumatically operated rock drills are commonly used (especially in conventional setups).
• A practical allocation is about one drill per 4–5 m^2 of face.
• The borehole diameter should slightly exceed the explosive cartridge diameter, typically by a few millimetres.

Concept / Approach:

Hole diameter tolerance prevents cartridge jamming and facilitates proper coupling with stemming. Adequate drill count allows parallel drilling of cut, stoping, and lifter holes, maintaining cycle time. Pneumatic rigs remain prevalent, with modern upgrades improving penetration and reliability.

Step-by-Step Solution:

Verification / Alternative check:

Contractor method statements and blasting guidelines specify small clearances between charge and hole diameter, validating the 6 mm order of magnitude, and optimize drill allocation to meet cycle times.

Why Other Options Are Wrong:

• Only (a) and (b): Omits the necessary hole-cartridge clearance guidance.
• Any single item alone is incomplete; drilling success requires all aspects.

Common Pitfalls:

• Too tight holes causing misfires or incomplete loading.
• Under-resourced drilling leading to long cycle times and poor fragmentation.

Final Answer:

All of the above.