JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year ADVANCED SURFACE MINING Previous Question Paper (January/February - 2023 - R18)

The stripping ratio is defined as the ratio of the volume of overburden material that must be removed to the quantity of mineral or ore recovered from a surface mine. It is typically expressed as cubic meters of overburden per tonne of ore (m³/t) or cubic meters of overburden per cubic meter of ore (m³/m³).

An echelon blast pattern with staggered holes is designed to create a V-shaped or angled initiation sequence, which improves fragmentation and directs rock movement toward the free face. In this configuration, the holes are arranged in three rows of 10, with each row offset from the previous one.

The initiation sequence is controlled by the timing of the surface connectors and the down-the-hole (DTH) delays:

1. Surface Connection: The 17 ms NONEL surface delays are connected between adjacent holes in a row or between rows to create the echelon timing. This creates a short delay interval (17 ms) between consecutive holes in the firing sequence.
2. Down-the-Hole (DTH) Delay: The 400 ms DTH delay acts as the primary initiation delay for each individual hole, ensuring that the surface timing sequence is completed before the explosive charge detonates at the bottom of the hole.
3. Pattern Layout: The holes are arranged in a staggered grid where the distance between rows (burden) and the distance between holes in a row (spacing) are adjusted to ensure the 17 ms delay creates the desired echelon wave front.

This combination ensures that each hole fires sequentially along the echelon line, providing a relief of burden for subsequent holes and minimizing ground vibration by limiting the maximum instantaneous charge weight.