A sliding time window heuristic for open pit mine block sequencing
Wood, R. Kevin
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The open pit mine block sequencing problem (OPBS) seeks a discrete-time production schedule that maximizes the net present value of the orebody extracted from an open pit mine. This integer program (IP) discretizes the mine's volume into blocks, imposes precedence constraints between blocks, and limits resource consumption in each time period. We develop a "sliding time window heuristic" to solve this IP appropximately. The heuristic recursively defines, solves and partially fixes an approximating models having: (i) fixed variables in early time periods, (ii) an exact submodel defined over a "window" of middle time periods, and (iii) a relaxed submodel in later time periods. The heuristic produces near optimal solutions (typically within 2% of optimality) for model instances that standard optimation software fails to solve. Furthermore, it produces these solutions quickly, even though our OPBS model enforces standard upper-bounding constraints on resource consumption along with less standard, but important, lower-bounding constraints.
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