Introduction / Context:
Cut holes form the heart of a tunnel blast round. They create the initial void (free face) that allows the remaining holes to break into the opening. Several cut patterns exist, including wedge, pyramid, fan, burn/parallel, and the widely taught V-cut. Knowing the commonly adopted pattern helps plan efficient rounds and minimize overbreak.
Given Data / Assumptions:
- Tunnel face blasting with drill-and-blast methods.
- Objective: select the most commonly adopted cut-hole pattern in general practice.
- Rock quality and equipment may influence the exact choice, but one pattern is standard in many textbooks and exams.
Concept / Approach:
The V-cut uses pairs of holes angled to form a V-shaped wedge. Upon detonation, the central wedge ejects, creating a free face that allows adjacent easers and trimmers to break effectively. The V-cut accommodates varying tunnel sizes and drilling rigs, is simple to lay out, and is especially popular in educational and field practice contexts where reliability and familiarity are valued.
Step-by-Step Solution:
List cut options: wedge, pyramid, fan, V-cut, burn/parallel.Identify the widely used, easy-to-implement pattern across broad conditions: V-cut.Confirm that the V-cut effectively creates a central wedge removal to start the round.
Verification / Alternative check:
Compare with burn cuts (common in very hard rock with parallel holes) and fan/pyramid cuts (used for specific conditions). Training manuals frequently present V-cut as the go-to baseline pattern.
Why Other Options Are Wrong:
Horizontal wedge/pyramid/fan cuts are valid but less universally adopted than the V-cut in general-purpose tunnelling instruction.“All the above” exaggerates adoption equivalence; one pattern dominates as the common baseline.
Common Pitfalls:
Assuming “burn cut” or “fan” is always superior—choice is context-dependent, but the most commonly adopted teaching standard remains the V-cut.
Final Answer:
V-cut
Discussion & Comments