Nelson Morales

Aggregation heuristic for the open-pit block scheduling problem

In order to establish a production plan, an open-pit mine is partitioned into a three-dimensional array of blocks. The order in which blocks are extracted and processed has a dramatic impact on the economic value of the exploitation. Since realistic models have millions of blocks and constraints, the combinatorial optimization problem of finding the extraction sequence that maximizes the profit is computationally intractable. In this work, we present a procedure, based on innovative aggregation and disaggregation heuristics, that allows us to get feasible and nearly optimal solutions. The method was tested on the public reference library MineLib and improved the best known results in the literature in 9 of the 11 instances of the library. Moreover, the overall procedure is very scalable, which makes it a promising tool for large size problems.

Gathering radio messages in the path

In this paper, we address the problem of gathering information in one node (sink) of a radio network where interference constraints are present: when a node transmits, it produces interference in an area bigger than the area in which its message can actually be received. The network is modeled by a graph; a node is able to transmit one unit of information to the set of vertices at distance at most dT in the graph, but when doing so it generates interferences that do not allow nodes at distance up to dI(dI ≥ dT) to listen to other transmissions. We are interested in finding a gathering protocol, that is an ordered sequence of rounds (each round consists of noninterfering simultaneous transmissions) such that w(u) messages are transmitted from any node u to a fixed node called the sink. Our aim is to find a gathering protocol with the minimum number of rounds (called gathering time). In this article, we focus on the specific case where the network is a path with the sink at an end vertex of the path and where the traffic is unitary (w(u) = 1 for all u); indeed this simple case appears to be already very difficult. We first give a new lower bound and a protocol with a gathering time that differ only by a constant independent of the length of the path. Then we present a method to construct incremental protocols. An incremental protocol for the path on n + 1 vertices is obtained from a protocol for n vertices by adding new rounds and new calls to some rounds but without changing the calls of the original rounds. We show that some of these incremental protocols are optimal for many values of dT and dI (in particular when dT is prime). We conjecture that this incremental construction always gives optimal protocols. Finally, we derive an approximation algorithm when the sink is placed in an arbitrary vertex in the path.

On the asymptotic behavior of nearest neighbor search using pivot-based indexes

This paper presents an asymptotic analysis for the nearest neighbor search with pivot-based indexes. We extend a previous analysis based on range queries with fixed tolerance radius, because there is a probability that the nearest neighbor is missed. We introduce a probabilistic analysis and then we show the expected search cost for range-optimal algorithms. Finally, we also show the analysis of the proposed search algorithm taking into account the extra CPU time, which leads to further insights on the efficiency of different implementations of this algorithm.

Comparison between the application of the conventional mine planning and of the direct block scheduling on an open pit mine Project

Historically, since the 60s, traditional mine planning consists of several distinct stages: 1) Definition of the ultimate pit the portion of the blocks that results in the greatest total value; 2) Pushback selection based on the generation of nested pits, obtained with the change in the value of the ore price; 3) Long-term production scheduling. Although considered quite satisfactory, this methodology presents some flaws: The stages, even if considered individually optimal, may not be when put together. The opportunity cost is not considered and the cut-off is fixed. Due to the recent computational advances, a new technique has been growing and is more reliable: the direct block sequencing. In this methodology, the steps are consolidated into only one process, improving the economic results, reducing the total execution time and obtaining, in fact, an optimal planning. The aim of this work is to compare the results of the two planning methods applied in a database of a Brazilian iron ore mine and to show the real advantages and disadvantages of each one. To solve the direct block sequencing technique, Doppler was used, a tool developed by Delphos Mine Planning Laboratory, located at the University of Chile. The traditional methodology was executed through Whittle software. Lastly, a medium-term scheduling was performed using Deswik software.

Open pit mine planning considering geomechanical fundamentals

Abstract The objective of this study is to integrate the admissible factor of safety (FoS) into the mine planning. The analysis showed, as expected, that a lower net present value (NPV) is obtained with the increase in the admissible FoS. Most importantly, it demonstrated that the FoS of the slopes of the adjacent phases, which are not part of the final pit, are considerably greater than the admissible FoS. Therefore, the NPV of an open pit mine project can be increased by steepening the slopes of adjacent phases that are not part of the final pit walls.

Discrete event simulation to design open-pit mine production policy in the event of snowfall

ABSTRACT Snowfall can lead to the cessation of production in a truck-shovel mining system. A snow road removal procedure that is performed simultaneously with the production operation is introduced to avoid this situation. A discrete-event simulation model is built to evaluate both operations under different configurations. An operation policy is designed based on the simulations results. This policy defines the manner in which production and snow removal operations are conducted depending on the intensity of the snowfall. The operational policy demonstrates that production can be maintained at high snowfall intensities.