Abstract
This paper presents a phase planning method specially designed for coal deposits with nearly horizontal, bedded coal seams. The geology of this type of deposit is modeled into a column model, instead of a block model, to avoid coal-rock mixing in blocks. A nested pit generation algorithm is developed for producing a series of nested, least-strip ratio pits with a column model as its input. The algorithm completely overcomes the troublesome gap problem. Taking the least-strip ratio pits as possible phase states, a dynamic programming formulation is proposed to simultaneously optimize the number of phases, the phase-pits, and the ultimate pit, with an objective of maximizing the net present value. The merits and capability of the proposed method are demonstrated through a case study on a large coal deposit.
Highlights
Large open pit mines are often mined in a number of phases, with intermediate pits for the phases referred to as phase-pits or pushbacks. e phases must be carefully planned since they provide a long-term strategic guide for the sequential development of a mine and for detailed production scheduling
Technical parameterization of reserves is another method for nested pit generation, with an objective of finding the family of “technically optimal pits.”
To facilitate the solution process and to overcome the gap problem, they solved the linear programming relaxation version of the integer programming (IP) model first and, applied a method known as “pipage rounding” to Mathematical Problems in Engineering convert a fractional solution into an integral solution. e authors claimed that their approach completely overcomes the gap problem
Summary
Large open pit mines are often mined in a number of phases, with intermediate pits for the phases referred to as phase-pits or pushbacks. e phases must be carefully planned since they provide a long-term strategic guide for the sequential development of a mine and for detailed production scheduling. Dagdelen and Johnson formulated the pushback optimization problem into an integer programming (IP) model and used Lagrangian relaxation for solution [8] All these methods have an inherent gap problem; that is, the size increment between two consecutive pits can be very large. Gu et al proposed a method capable of providing simultaneous solutions to the three elements [19] It consists of a heuristic algorithm for generating a series of geologically optimal pits and a dynamic programming (DP) formulation for sequencing the pits, but the method is for metal mines. Based on the basic framework from a previous research for metal mines [19], we have developed a phase planning method for open pit coal mines with nearly horizontal and bedded coal seams, with the objective of simultaneously optimizing the number of phases, the phasepits, and the ultimate pit
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