In the full-face method of tunnel excavation, into how many working sections is the face generally divided for efficient drilling, blasting, and mucking?

Introduction / Context:
The full-face method advances the entire perimeter of the tunnel, but for practical drilling and blasting the face is commonly organized into zones. Subdivision helps with sequencing (cut, stoping, lifters), improves fragmentation control, and facilitates mucking while maintaining face stability and access for support installation.

Given Data / Assumptions:

• Method: full-face excavation of the entire outline.
• Objective: determine the typical number of working sections used in practice.
• Assume conventional drill-and-blast in rock with standard patterns.

Concept / Approach:

In many method statements, the face is divided into three practical zones that align with blasting patterns: a central cut (to create relief), the surrounding stoping holes, and the bottom (lifter) holes near the invert. This three-part organization synchronizes drilling, charging, and mucking cycles and yields a stable advance profile.

Step-by-Step Solution:

Verification / Alternative check:

While variations exist (e.g., additional wedges or pre-splitting), the tripartite division remains a textbook convention for organizing the blast round and mucking sequence.

Why Other Options Are Wrong:

• Two sections: Over-simplifies and can hinder controlled breakout.
• Four or five: Possible in special cases but not the general baseline.
• One undivided section: Impractical for controlled blasting and mucking logistics.

Common Pitfalls:

• Assuming 'full-face' means no internal sequencing.
• Neglecting to provide proper cut relief, causing poor fragmentation and overbreak.

Final Answer:

three sections