Question 12 of 27

Question 3.1 open cast dragline operations (6 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

3.1.1 Range diagram is a scaled plot of the dragline’s digging and dumping envelope (a circle of radius = operating radius, offset by boom length/height) overlaid on the pit cross-section, used to check that a given overburden depth, pit width and spoil placement all lie within the machine’s physical reach before committing to a mine plan — the same reach circle used numerically in Question 3.4.

3.1.2 Side casting is the basic single-pass dragline method: standing on the ORIGINAL ground surface (or the previous cut’s spoil), the dragline digs overburden from the current cut and swings it directly to the SIDE, dumping it into the void left by the previous cut — simple, low-cost, but limited to overburden depths within the machine’s single-pass reach and stacking-height capability (worked numerically in Questions 3.7–3.9).

3.1.3 Advanced bench uses an auxiliary stripping unit (dozer, scraper, or a smaller dragline) to pre-strip a shallow bench of overburden ahead of the main dragline and cast it forward toward the pit, effectively pre-positioning material closer to the main machine so its own single-pass reach can then handle a total overburden thickness beyond its normal unaided capability.

3.1.4 Pullback is a two-pass technique: the dragline first casts overburden side-ways as far as it can reach (as in 3.1.2), leaving some spoil close to the pit edge that could otherwise encroach on the next cut; the machine then re-handles (“pulls back”) that near spoil a second time, moving it further from the crest to make room for the advancing pit and to keep the spoil pile’s toe clear of the highwall.

3.1.5 Extended bench splits the overburden vertically: the dragline casts the LOWER portion of overburden (nearest the coal) by normal side-casting, while the UPPER portion is bulldozed or pre-stripped separately and cast into a widened, extended spoil area, effectively increasing the total overburden depth the operation can handle beyond the dragline’s single-pass digging-depth/stacking-height limit — directly relevant if the dragline in Question 3.9 were found to fall short.

3.1.6 Multiple pass operations use two or more successive dragline passes over the SAME overburden column: the first pass casts what it can reach into the void, then the dragline (or a second unit) re-handles part of that spoil a further pass to move it clear, splitting one deep cut into several shallower re-handling stages — the general case pullback and extended bench are both special instances of.