For tunnelling in firm ground, which excavation approach is generally adopted to balance speed, stability, and control of overbreak?

Introduction / Context:
The choice of tunnelling method depends largely on ground conditions. In firm ground with reasonable stand-up time, the heading can be advanced across the full section. This reduces cycle interfaces and can shorten construction time compared with multi-stage or pre-support-intensive methods.

Given Data / Assumptions:

• Ground: firm (neither running nor very weak).
• Goal: select the generally adopted method.
• Consider drill-and-blast or mechanical excavation without heavy pre-support.

Concept / Approach:

The full face method advances the entire perimeter in one operation, relying on the ground’s ability to remain stable during drilling, blasting, and support installation. In firm ground, this is typically the most efficient approach, limiting construction joints and simplifying ventilation and mucking logistics.

Step-by-Step Solution:

Verification / Alternative check:

Textbook method-selection charts place full-face at the firm–competent end of the spectrum, with benching and drift reserved for reduced stability or large spans needing staged excavation.

Why Other Options Are Wrong:

• Top heading and benching/drift: Useful but not the general first choice in firm ground.
• Forepoling: Intended for running ground, not firm formations.

Common Pitfalls:

• Choosing staged methods without need, increasing time and cost.
• Failing to provide timely support even in firm ground after full-face blasts.

Final Answer:

Full face method