With respect to the heading-and-benching method of tunnelling, identify the statement that is NOT correct about drilling and blasting practice for the head and the bench.

Question

Accepted Answer

Introduction / Context:In heading-and-benching, the upper part (heading) is advanced first, followed by the lower bench. Drilling and blasting are staged to control overbreak, manage ventilation after shots, and sequence mucking efficiently. Understanding which operations are sequenced versus simultaneous is crucial for safe and efficient progress. Given Data / Assumptions: The method divides the face into head and bench portions. Typical drill lengths are about 3.0 m to 3.5 m per round. Blasting is performed in a controlled sequence, not as a single combined detonation. Concept / Approach: Correct practice loads and fires the head first to create relief and ensure controlled breakage at the crown. Only after ventilating and clearing as required is the bench drilled/loaded/fired (or at least fired in a delayed sequence) to avoid excessive vibration and hazards. Therefore, the statement that the head and bench holes are “loaded together” for one joint blast is not correct in standard sequencing. Step-by-Step Solution: Confirm two-portion advance: head then bench → true.Typical hole lengths: 3–3.5 m → true.Assess loading and firing: staged sequencing, not combined loading for simultaneous blasting → the incorrect statement is “loaded together”. Verification / Alternative check: Method statements commonly specify firing the heading cut and stoping first, then bench lifters, often with delays and separate rounds, validating the staged approach. Why Other Options Are Wrong: (a), (b), (c), and (e) describe standard staged practice. Common Pitfalls: Trying to blast both portions together, leading to uncontrolled damage and ventilation overload. Insufficient delay timing between head and bench rounds. Final Answer: The holes in head and bench are loaded together with explosive for blasting

Tunnelling Questions

Questions

Practice smarter