Equipment Selection for Surface Mining: A Review
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paper_title: Technology Development Decision Economics for Real-Time Rolling Resistance Monitoring of Haul Roads

paper_content:

Proponents of advanced technologies for the delivery of constructed facilities assert that information and automation technologies can significantly reduce construction costs. However, technology transfer has been greatly limited as practitioners are reluctant to adopt new technologies for myriad reasons including concerns over expertise requirements, value versus traditional approaches, implementation practicality, and risk. All of these concerns ultimately relate to cost versus benefit. While considerable automation research has been documented, thorough economic justifications in the literature have been rare in comparison. In this paper, the writers present and illustrate a model to assess the economics of construction equipment automation using a case illustration focused on the allowable cost of sensor technologies for real-time, in-field rolling resistance monitoring. Rolling resistance is vital in determining power train requirements, fuel consumption, and travel time associated with hauling operations. The absence of a true understanding of field changes in rolling resistance may result in a lack of insight regarding the interaction of jobsite characteristics and the performance potential of hauling operations.
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paper_title: Equipment size effects on open pit mining performance

paper_content:

This paper discusses the exploitation of economies of scale in open pit mining through the use of increasingly larger equipment. It presents a method adopted to evaluate the impact of increased scale on operational performance factors. The work identifies equipment size sensitive variables (ESSVs) in the mine design process that affect the performance of the production process. Data from a set of case studies show that the ESSV influence extends beyond mine production to encompass milling performance, environmental footprint and community impacts. Some ESSVs (such as reliability, tyre costs and productivity) are shown to be related to the current state of equipment technology and their effects are therefore comparable for different mines. Other ESSVs relate to the mine and deposit characteristics; their effects therefore vary from mine to mine. A detailed analytical approach, developed to model the impact of ESSVs, suggests that for truck/shovel operations, the industry may be approaching a situation of d...
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paper_title: On a number of spare haulage units for the shovel-truck system in open pit mines

paper_content:

Abstract Shovel-truck systems are widely applied in open-pit mining. In these systems spare haulage units are employed as a rule. Recommendations and rules which are used to determine the reserve truck fleet size can give significant difference in estimation of a number of units needed for a given system. The paper consider the problem of proper selection of a spare haulage unit fleet size taking into account economical and technical parameters of trucks, their exploitation process as well as the reliability indices.
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paper_title: A new MIP model for mine equipment scheduling by minimizing maintenance cost

paper_content:

Mining investment has been recognized as capital intensive due mainly to the cost of large equipment. Equipment capital costs for a given operation are usually within the order of hundreds of million dollars but may reach to billion dollars for large companies operating multiple mines. Such large investments require the optimum usage of equipment in a manner that the operating costs are minimized and the utilization of equipment is maximized through optimal scheduling. This optimum usage is required to ensure that the business remains sustainable and financially stable. Most mining operations utilize trucks to haul the mined material. Maintenance is one of the major operating cost items for these fleets as it can reach approximately one hundred million dollars yearly. There is no method or application in the literature that optimizes the utilization for truck fleet over the life of mine. A new approach based on mixed integer programming (MIP) techniques is used for annually scheduling a fixed fleet of mining trucks in a given operation, over a multi-year time horizon to minimize maintenance cost. The model uses the truck age (total hours of usage), maintenance cost and required operating hours to achieve annual production targets to produce an optimum truck schedule. While this paper focuses on scheduling trucks for mining operation, concept can be used in most businesses using equipment with significant maintenance costs. A case study for a large scale gold mine showed an annual discounted (10% rate) maintenance cost saving of over $2M and more than 16% ($21M) of overall maintenance cost reduction over 10 years of mine life, compared with the spreadsheet based approach used currently at the operation.
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paper_title: Reliability Modelling of Surface Mining Equipment: Data Gathering and Analysis Methodologies

paper_content:

As the size and complexity of open pit mining equipment continue to increase, the implications of equipment failure become ever more critical. An unplanned failure can result in significantly higher repair costs than a planned maintenance or repair. Of even more importance is the loss of production associated with larger equipment failures. One method to mitigate the impact of failures is to improve the reliability of the equipment. A first step in reliability improvement is collection and analysis of the appropriate data. This paper will summarize relevant techniques for reliability analysis and identify data requirements and information sources.
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paper_title: A stochastic optimization approach to mine truck allocation

paper_content:

Abstract In the mining industry, truck assignment is an important and complex process and an optimal truck allocation can result in significant savings. In this paper, a truck allocation model is formulated using a chance-constrained, stochastic optimization approach that can accommodate uncertain parameters such as truckload and cycle time. A real-time hauling framework, which consists of the chance-constrained optimization model and a model updater, is developed to compensate for changes in the uncertain key operating parameters. The use of the model updater helps the truck allocation system to adapt to random operational changes. The effectiveness of the chance-constrained approach in dealing with uncertain process parameters, when coupled with model updating, is shown to be a viable implementation framework in the dispatching operation.
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paper_title: A Review of Operations Research in Mine Planning

paper_content:

Applications of operations research to mine planning date back to the 1960s. Since that time, optimization and simulation, in particular, have been applied to both surface and underground mine planning problems, including mine design, long-and short-term production scheduling, equipment selection, and dispatching, inter alia. In this paper, we review several decades of such literature with a particular emphasis on more recent work, suggestions for emerging areas, and highlights of successful industry applications.
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paper_title: Modeling the mining supply chain from mine to port: A combined optimization and simulation approach

paper_content:

This paper describes a method for modeling a complex export supply chain using a combination of optimization and Discrete Event Simulation techniques to enable capacity analysis and evaluation of expansion options. A description of the modeling process is presented along with a case study of a successful implementation of the approach to analyze the export supply chain of PT Kaltim Prima Coal in Indonesia.
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paper_title: Overview of Solution Strategies Used in Truck Dispatching Systems for Open Pit Mines

paper_content:

This paper deals with dispatching systems in open-pit mines. It illustrates the different strategies that exist for solving the dispatching problem and analyses the advantages and disadvantages of these strategies. Moreover, the most important elements that should be part of the dispatching system in the future are highlighted.
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paper_title: An optimisation approach to materials handling in surface mines

paper_content:

In the surface mining industry the equipment selection problem involves choosing a fleet of trucks and loaders that have the capacity to move the materials specified in the mine plan. The optimisation problem is to select these fleets such that the overall cost of materials handling is minimised. The scale of operations is such that although a single machine may cost several million dollars to purchase, the cost of operation outweighs this expense over several years. This motivates the need for a purchase and salvage policy, so that the optimal equipment replacement cycle can be achieved. Mining schedules often appear with multiple mining locations and dump-sites, where a dump-site can also represent a stockpile or a mill. Multiple periods must also be considered, which adds to the complexity of determining the optimal replacement policy for equipment. Further, some mines begin with a pre-existing set of equipment, and the subsequent fleet must be both compatible and satisfy the mill constraints. We also need to consider the possibility of a heterogeneous fleet. The equipment selection problem is cursed with a cascade of inter-dependent variables and parameters. For example, the cost of operating a piece of equipment depends on its utilisation; the utilisation depends on the availability of the equipment; and the availability depends on the age of the equipment. We formally define the equipment selection problem in the Introduction (Chapter 1) and further discuss the complexities of the problem. While numerous methods from Operations Research and Artificial Intelligence have been applied to this problem, optimal multiple period solutions remain elusive. Also, pre-existing equipment and heterogeneous fleets have largely been ignored. We present a comprehensive literature review in Chapter 2, outlining the methods applied and candidly discussing the successes and pitfalls of these approaches. We also organise the literature by linking related fields, such as Shovel-Truck Productivity and Mining Method Selection. In Chapter 3 we extend the match factor ratio, an important productivity index for the mining industry. Previously this ratio was restricted to homogeneous fleets and single location/dump. We provide several alternative ratios that incorporate heterogeneous trucks, heterogeneous loaders and multiple locations. These extensions are then
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paper_title: Solving Large-scale Open Pit Mining Production Scheduling Problems by Integer Programming

paper_content:

Since the initial application of mathematical optimisation methods to mine planning in 1965, the Lerchs-Grossmann algorithm for computing the ultimate pit limit, operations researchers have worked on a variety of challenging problems in the area of open pit mining. This thesis focuses on the open pit mining production scheduling problem: Given the discretisation of an orebody as a block model, determine the sequence in which the blocks should be removed from the pit, over the lifespan of the mine, such that the net present value of the mining operation is maximised. In practise, when some material has been removed from the pit, it must be processed further in order to extract the valuable elements contained therein. If the concentration of valuable elements is not sufficiently high, the material is discarded as waste or stockpiled. Realistically-sized block models can contain hundreds of thousands of blocks. A common approach to render these problem instances computationally tractable is the aggregation of blocks to larger scheduling units. The thrust of this thesis is the investigation of a new mixed-integer programming formulation for the open pit mining production scheduling problem, which allows for processing decisions to be made at block level, while the actual mining schedule is still computed at aggregate level. A drawback of this model in its full form is the large number of additional variables needed to model the processing decisions. One main result of this thesis shows how these processing variables can be aggregated efficiently to reduce the problem size significantly, while practically incurring no loss in net present value. The second focus is on the application of lagrangean relaxation to the resource constraints. Using a result of Mohring et al. (2003) for project scheduling, the lagrangean relaxation can be solved efficiently via minimum cut computations in a weighted digraph. Experiments with a bundle algorithm implementation by Helmberg showed how the lagrangean dual can be solved within a small fraction of the time required by standard linear programming algorithms, while yielding practically the same dual bound. Finally, several problem-specific heuristics are presented together with computational results: two greedy sub-MIP start heuristics and a large neighbourhood search heuristic. A combination of a lagrangean-based start heuristic followed by a large neighbourhood search proved to be effective in generating solutions with objective values within a 0.05% gap of the optimum.
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paper_title: Maximizing the net present value of a project under uncertainty

paper_content:

We address the maximization of a project's expected net present value when the activity durations and cash flows are described by a discrete set of alternative scenarios with associated occurrence probabilities. In this setting, the choice of scenario-independent activity start times frequently leads to infeasible schedules or severe losses in revenues. We suggest to determine an optimal target processing time policy for the project activities instead. Such a policy prescribes an activity to be started as early as possible in the realized scenario, but never before its (scenario-independent) target processing time. We formulate the resulting model as a global optimization problem and present a branch-and-bound algorithm for its solution. Extensive numerical results illustrate the suitability of the proposed policy class and the runtime behavior of the algorithm.
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paper_title: Equipment selection with heterogeneous fleets for multiple-period schedules

paper_content:

In a simple surface mining scenario we consider a mine to have one mining location and dumpsite connected by a truck route. We determine a purchase and salvage policy for trucks and loaders, which minimises the cost of materials handling over a multiple period schedule. This problem becomes large scale when we consider large sets of equipment and long schedules. Pre-existing equipment can lead to heterogeneous fleets; non-uniformity in the operating cost function coupled with compatibility issues also adds to the complexity of the problem. We present an integer programme for this problem, where we introduce a specialised linear constraint set to ensure satisfaction of production requirements while accounting for equipment compatibility. Many aspects of the presented model, such as the consideration of multiple periods and pre-existing equipment, are novel for the mining industry and ensure that the model is both a new and advanced equipment selection tool.
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paper_title: Estimation of large open pit haulage truck requirements

paper_content:

This paper examines the concept of a bare bones base case in the economic evaluation of a mineral property. This is the case that the banks like to see, and the paper examines why. The expression bare bones refers to a cash flow evaluation based on constant metal prices, constant dollars, no inflation, no debt, no interest, on a project basis and after tax. The paper looks individually at the impact of the various assumptions that go into an evaluation, and shows how these can be combined to show an exciting result that may not really exist. An example of an embellished case (the kind that one frequently sees when projects are being promoted) is developed and the cumulative impact is analyzed to show the actual project underneath. The paper also points out some areas to watch for overly optimistic assumptions such as prices, margins, and debt.
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paper_title: A new earthworks estimating methodology

paper_content:

Earthworks and earthmoving operations are a major part of many civil engineering construction projects. Because of their labour and plant intensity, the planning and estimating of such operations is crucial to both the cost and duration of the project; earthworks are considered by many practitioners to be indicators to the success or failure of the project as a whole. Traditionally, a mixture of manufacturers' data (through published charts or computer databases) and historical company data are used in the estimating of earthworks. This process has two main drawbacks. First, plant haul velocity is dependent on the rolling resistance at the soil-wheel interface, which is notoriously difficult to determine; second, the stochastic interface between types of plant provides a non-deterministic system, resulting in estimates of output which may be unrealistically high. An alternative system of earthworks estimating is presented based on a combination of work undertaken in both the soil/vehicle and stochastic estimating fields. This system is demonstrated via a case study based on an actual highway project. The main conclusion to be drawn is that the traditional estimating approach results in a scheme costed well below realistic values.
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paper_title: A new MIP model for mine equipment scheduling by minimizing maintenance cost

paper_content:

Mining investment has been recognized as capital intensive due mainly to the cost of large equipment. Equipment capital costs for a given operation are usually within the order of hundreds of million dollars but may reach to billion dollars for large companies operating multiple mines. Such large investments require the optimum usage of equipment in a manner that the operating costs are minimized and the utilization of equipment is maximized through optimal scheduling. This optimum usage is required to ensure that the business remains sustainable and financially stable. Most mining operations utilize trucks to haul the mined material. Maintenance is one of the major operating cost items for these fleets as it can reach approximately one hundred million dollars yearly. There is no method or application in the literature that optimizes the utilization for truck fleet over the life of mine. A new approach based on mixed integer programming (MIP) techniques is used for annually scheduling a fixed fleet of mining trucks in a given operation, over a multi-year time horizon to minimize maintenance cost. The model uses the truck age (total hours of usage), maintenance cost and required operating hours to achieve annual production targets to produce an optimum truck schedule. While this paper focuses on scheduling trucks for mining operation, concept can be used in most businesses using equipment with significant maintenance costs. A case study for a large scale gold mine showed an annual discounted (10% rate) maintenance cost saving of over $2M and more than 16% ($21M) of overall maintenance cost reduction over 10 years of mine life, compared with the spreadsheet based approach used currently at the operation.
---
paper_title: A stochastic optimization approach to mine truck allocation

paper_content:

Abstract In the mining industry, truck assignment is an important and complex process and an optimal truck allocation can result in significant savings. In this paper, a truck allocation model is formulated using a chance-constrained, stochastic optimization approach that can accommodate uncertain parameters such as truckload and cycle time. A real-time hauling framework, which consists of the chance-constrained optimization model and a model updater, is developed to compensate for changes in the uncertain key operating parameters. The use of the model updater helps the truck allocation system to adapt to random operational changes. The effectiveness of the chance-constrained approach in dealing with uncertain process parameters, when coupled with model updating, is shown to be a viable implementation framework in the dispatching operation.
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paper_title: Effect of truck payload weight on production

paper_content:

Most constructors intuitively understand that there is a relationship between payload weight and haul unit performance. At the same time, project managers constantly push the limits of rated truck payload as they seek increased productivity. This is because it is believed that increased productivity translates into reduced project cost. These ideas are quantitatively examined using payload data from seven Caterpillar 785B off-highway haul trucks working on an earth/rockfill dam in California. Caterpillar's Vital Information Management System was used to collect load data from 54,300 truck cycles representing approximately 14,419 operating hours and haulage of more than 7.25 million metric tons (8 million tons) of material. There was a diminished productivity increase when the load weight exceeded the truck's rated gravimetric capacity. Adding sideboards actually caused the average monthly production of the fleet to decrease. The plot of load times versus load weight appears to indicate a human factors rel...
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paper_title: Overview of Solution Strategies Used in Truck Dispatching Systems for Open Pit Mines

paper_content:

This paper deals with dispatching systems in open-pit mines. It illustrates the different strategies that exist for solving the dispatching problem and analyses the advantages and disadvantages of these strategies. Moreover, the most important elements that should be part of the dispatching system in the future are highlighted.
---
paper_title: Estimation of large open pit haulage truck requirements

paper_content:

This paper examines the concept of a bare bones base case in the economic evaluation of a mineral property. This is the case that the banks like to see, and the paper examines why. The expression bare bones refers to a cash flow evaluation based on constant metal prices, constant dollars, no inflation, no debt, no interest, on a project basis and after tax. The paper looks individually at the impact of the various assumptions that go into an evaluation, and shows how these can be combined to show an exciting result that may not really exist. An example of an embellished case (the kind that one frequently sees when projects are being promoted) is developed and the cumulative impact is analyzed to show the actual project underneath. The paper also points out some areas to watch for overly optimistic assumptions such as prices, margins, and debt.
---
paper_title: A Review of Operations Research in Mine Planning

paper_content:

Applications of operations research to mine planning date back to the 1960s. Since that time, optimization and simulation, in particular, have been applied to both surface and underground mine planning problems, including mine design, long-and short-term production scheduling, equipment selection, and dispatching, inter alia. In this paper, we review several decades of such literature with a particular emphasis on more recent work, suggestions for emerging areas, and highlights of successful industry applications.
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paper_title: A heuristic for solving manufacturing process and equipment selection problems

paper_content:

In a dynamic manufacturing environment, machines and machining process selection based on current part mix may need to be revised if part mix has changed or new machine tools have become available and economical. However, the costs of acquiring new machines and revising manufacturing process may exceed the benefits derived from such expansion or revision. The problem of selecting the best machining process and equipment in a dynamic manufacturing environment is studied in this paper. An integer programming model and a heuristic algorithm were developed to solve the problem of multiple time periods. Lagrangian relaxation was used to generate lower bounds of the integer programming model for testing the optimality of the heuristic solution. Numerical examples are presented to illustrate the model and the solution technique.
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paper_title: Capacity Expansion and Equipment Replacement: A Unified Approach

paper_content:

Businesses frequently have to decide which of their existing equipment to replace, taking into account future changes in capacity requirements. The significance of this decision becomes clear when one notes that expenditure on new plant and equipment is a significant proportion of the GDP in the United States. The equipment replacement literature has focused on the replacement issue, usually ignoring aspects such as future demand changes and economies of scale. On the other hand, the capacity expansion literature has focused on the expansion of equipment capacity to meet demand growth, considering economies of scale but ignoring the replacement aspect. This paper attempts to unify the two streams of research by developing a general model that considers replacement of capacity as well as expansion and disposal, together with scale economy effects. Even special cases of the problems discussed here, such as the parallel machine replacement problem, have been considered difficult so far. However, we show that the problem can be solved efficiently by formulating it in a novel, disaggregate manner and using a dual-based solution procedure that exploits the structure of the problem. We also provide computational results to affirm that optimal or near-optimal solutions to large, realistic problems can be determined efficiently. We demonstrate the robustness of this approach by showing how other realistic features such as quantity discounts in purchases, alternative technology types or suppliers, and multiple equipment types can be incorporated.
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paper_title: Preprocessing and cutting for multiple allocation hub location problems

paper_content:

Abstract In this paper we consider formulations and solution approaches for multiple allocation hub location problems. We present a number of results, which enable us to develop preprocessing procedures and tightening constraints for existing mixed integer linear programming formulations. We employ flow cover constraints for capacitated problems to improve computation times. We present the results of our computational experience, which show that all of these steps can effectively reduce the computational effort required to obtain optimal solutions.
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paper_title: The study of a fuzzy set theory for the selection of an optimum coal transportation system from pit to the power plant

paper_content:

ABSTRACT In this paper, we purpose a fuzzy multiple attribute decision making for the selection of an optimal transportation system to a power station to be established in an open pit coal mine located Can, west of Turkey. So far, various types of formulations or solutions methods have been proposed with transportation systems, but most of them exclusively considered linear functions as objective functions. Real world study is decision making under subjective constraints of different importance, after using uncertain data (linguistic variables), where compromises between competing criteria are allowed. The authors have explained in theory and by detailed example a new combination of fuzzy set of transportation systems.
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paper_title: Expert system for equipment selection for earth-moving operations

paper_content:

Proper earth‐moving equipment selection is a major factor when trying to satisfy a project's budget and schedule requirements. The selection of the equipment is best performed by personnel with experience in earth‐moving operations. In this research project, a rule‐based expert system (i.e., VP‐Expert) was used to develop a system for selecting earth‐moving equipment. The system, with 930 rules, interprets information concerning a particular project's soil conditions, operator performance, and required earth‐moving operations. The knowledge for the development of the expert system was obtained from several experts working for two contractors, an equipment rental company, equipment manufacturers' sales representatives (e.g., Caterpillar, Case) and several geotechnical engineers. The system was tested, using the requirements for an actual project, by three contractors. The contractors' selections compared favorably with the developed expert system with regard to the size and type of equipment needed to perf...
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paper_title: An exact algorithm for the vehicle routing problem based on the set partitioning formulation with additional cuts

paper_content:

This paper presents a new exact algorithm for the Capacitated Vehicle Routing Problem (CVRP) based on the set partitioning formulation with additional cuts that correspond to capacity and clique inequalities. The exact algorithm uses a bounding procedure that finds a near optimal dual solution of the LP-relaxation of the resulting mathematical formulation by combining three dual ascent heuristics. The first dual heuristic is based on the q-route relaxation of the set partitioning formulation of the CVRP. The second one combines Lagrangean relaxation, pricing and cut generation. The third attempts to close the duality gap left by the first two procedures using a classical pricing and cut generation technique. The final dual solution is used to generate a reduced problem containing only the routes whose reduced costs are smaller than the gap between an upper bound and the lower bound achieved. The resulting problem is solved by an integer programming solver. Computational results over the main instances from the literature show the effectiveness of the proposed algorithm.
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paper_title: Network Design for Express Shipment Delivery

paper_content:

Service network design problems arise at airlines (passenger and cargo), trucking companies, railroads, etc., wherever there is a need to determine cost minimizing routes and schedules, given constraints on resource availability and level of service. We focus on a particular service network design application, namely, the express shipment delivery problem, and we develop models and a solution technique designed specifically for large-scale express delivery problems with time windows. Using data from an express delivery company, we demonstrate that our approach can produce savings in total operating costs and provide a valuable tool for making decisions at strategic and tactical levels.
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paper_title: Mining method selection by multiple criteria decision making tools

paper_content:

Mining method selection is the first and most important problem in mine design. In this selection some of the parameters such as geological and geotechnical properties, economic parameters and geographical factors are involved. The mining engineer must balance the input parameters and select the method that appears to be the most suitable; mining method selection is both an art and a science. Distinguishing all parameters that have an effect in mining method selection and in the determination of weighting factors of any parameter is a difficult task in an ordinary environment. This paper attempts to determine important parameters that impact on the mining method selection and demonstrates the calculation of the weighting factors for each selected parameter. This study has been directed to the research of a methodology for the selection of an optimal mining method. Different fuzzy methods are presented as an innovative tool for criteria aggregation in mining decision problems. Two methods of fuzzy multiple criteria decision making are used for selecting the optimal method with which to mine anomaly No. 3 of the Gol-Gohar iron mine. This paper finally presents a comparison of the selection methodologies and further discusses the most appropriate method investigated.
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paper_title: Simulation Verifies Queuing Program for Selecting Loader-Truck Fleets

paper_content:

Proper equipment selection can yield substantial savings in time and cost. MicroCYCLONE simulation package is used to verify the FLEET queuing program. FLEET models multiloader‐truck systems using exponential distribution at steady state. A few FLEET assumptions are redefined to closely model real‐world construction processes. Graphical solutions illustrate effects of the cycle‐time modeling and transient state on multiloader‐truck fleet selection. FLEET is shown to be an accurate model of the steady‐state, multiloader‐truck process if exponential distribution did accurately fit load‐ and travel‐time distributions. But, erlang or beta distribution more closely fits actual load and travel times in construction. Modeling load and travel times of loader‐truck fleets with exponential, instead of beta, distribution results in underestimation of production and overestimation of unit cost by 4–7%. Simulation results of a more accurate model that uses beta distribution and considers transient state, in addition t...
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paper_title: Optimization of Earthmoving Operations in Heavy Civil Engineering Projects

paper_content:

Large scale earthmoving operations require the use of heavy and costly construction equipment. Optimum utilization of equipment is a crucial task for the project management team. It can result in substantial savings in both time and cost of earthmoving operations. This paper presents optimization model for earthmoving operations in heavy civil engineering projects. The developed model is designed to assist general contractor in optimizing planning of earthmoving operations. The model utilizes genetic algorithm, linear programming, and geographic information systems to support its management functions. The model assists in planning earthmoving operations; taking into consideration: (1) availability of resources to contractors; (2) project budget and/or time constraints, if any; (3) scope of work; (4) construction site conditions; (5) soil type; (6) project indirect cost; and (7) equipment characteristics. The model also determines the quantities of earth to be moved from different borrow pits and those to be placed at different landfill sites to meet optimization objective set by the user and to meet project constraints. The model has been implemented in prototype software, using object-oriented programming. Two numerical example projects are presented to validate and demonstrate the use of the developed model in optimizing earthmoving operations.
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paper_title: Capacitated Network Design - Polyhedral Structure and Computation

paper_content:

We study a capacity expansion problem that arises in telecommunication network design. Given a capacitated network and a traffic demand matrix, the objective is to add capacity to the edges, in multiples of various modularities, and route traffic, so that the overall cost is minimized. We study the polyhedral structure of a mixed-integer formulation of the problem and develop a cutting-plane algorithm using facet defining inequalities. The algorithm produces an extended formulation providing both a vary good lower bound and a starting point for branch and bound. The overall algorithm appears effective when applied to problem instances using real-life data.
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paper_title: Use of genetic algorithms in a mining problem

paper_content:

ABSTRACT This paper introduces the principles of genetic algorithms and presents their properties and structure. The application of genetic algorithms in the mining problem of ore grade estimation is discussed and the results are compared with previously published data. The outcome of this paper indicates the potential of genetic algorithms in mining applications.
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paper_title: Overview of Solution Strategies Used in Truck Dispatching Systems for Open Pit Mines

paper_content:

This paper deals with dispatching systems in open-pit mines. It illustrates the different strategies that exist for solving the dispatching problem and analyses the advantages and disadvantages of these strategies. Moreover, the most important elements that should be part of the dispatching system in the future are highlighted.
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paper_title: Computational Experience with a Difficult Mixed-Integer Multicommodity Flow Problem

paper_content:

The following problem arises in the study of lightwave networks. Given a demand matrix containing amounts to be routed between corresponding nodes, we wish to design a network with certain topological features, and in this network, route all the demands, so that the maximum load (total flow) on any edge is minimized. As we show, even small instances of this combined design/routing problem are extremely intractable. We describe computational experience with a cutting plane algorithm for this problem.
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paper_title: A Hybrid Tabu Search/Branch-and-Bound Algorithm for the Direct Flight Network Design Problem

paper_content:

This paper introduces a network design problem with a structure that is encountered in many transportation processes. The general organization of these systems is as follows. Freight has to be transported between a large number of origins and destinations. To consolidate the freight, it is first shipped to a terminal. Next, it is transported directly to a terminal where it is re-loaded and shipped to its destination. The task is to decide which terminals have to be used and how the freight is transported among the terminals. We describe an application where the terminals are airports and the freight is letter mail. Here, the transportation between terminals is by air, which is required due to temporal constraints. The economical impact of these decisions is huge because air transportation is costly and the process is repeated every night. We show how the problem can be modeled as a capacitated warehouse location problem with side constraints and propose a hybrid Tabu Search/Branch-and-Bound algorithm, which solves large real-world instances with acceptable computation times.
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paper_title: Truck Capacity Selection for Earthmoving

paper_content:

In a major earthmoving operation involving a loader and trucks, a careful selection of equipment size can result in substantial savings both in time and cost. When planning an earthmoving operation, usually the size of the loading unit is selected based on the production required. The optimal truck capacity is either selected by comparing the production cost of various truck capacities or by using a rule of thumb that recommends truck capacities four to five times the capacity of the selected loader. The objective of this study is to investigate the optimal truck capacity for various loader sizes. To achieve this objective, specifications and costs of a number of loaders and trucks commonly used in earth‐moving are used.
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paper_title: An optimisation approach to materials handling in surface mines

paper_content:

In the surface mining industry the equipment selection problem involves choosing a fleet of trucks and loaders that have the capacity to move the materials specified in the mine plan. The optimisation problem is to select these fleets such that the overall cost of materials handling is minimised. The scale of operations is such that although a single machine may cost several million dollars to purchase, the cost of operation outweighs this expense over several years. This motivates the need for a purchase and salvage policy, so that the optimal equipment replacement cycle can be achieved. Mining schedules often appear with multiple mining locations and dump-sites, where a dump-site can also represent a stockpile or a mill. Multiple periods must also be considered, which adds to the complexity of determining the optimal replacement policy for equipment. Further, some mines begin with a pre-existing set of equipment, and the subsequent fleet must be both compatible and satisfy the mill constraints. We also need to consider the possibility of a heterogeneous fleet. The equipment selection problem is cursed with a cascade of inter-dependent variables and parameters. For example, the cost of operating a piece of equipment depends on its utilisation; the utilisation depends on the availability of the equipment; and the availability depends on the age of the equipment. We formally define the equipment selection problem in the Introduction (Chapter 1) and further discuss the complexities of the problem. While numerous methods from Operations Research and Artificial Intelligence have been applied to this problem, optimal multiple period solutions remain elusive. Also, pre-existing equipment and heterogeneous fleets have largely been ignored. We present a comprehensive literature review in Chapter 2, outlining the methods applied and candidly discussing the successes and pitfalls of these approaches. We also organise the literature by linking related fields, such as Shovel-Truck Productivity and Mining Method Selection. In Chapter 3 we extend the match factor ratio, an important productivity index for the mining industry. Previously this ratio was restricted to homogeneous fleets and single location/dump. We provide several alternative ratios that incorporate heterogeneous trucks, heterogeneous loaders and multiple locations. These extensions are then
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paper_title: A construction algorithm for the selection and assignment of materials handling equipment

paper_content:

A model for selecting materials handling equipment and assigning it to departmental moves is presented. The problem is formulated as an integer program with the objective of minimizing the total operating and investment costs of the selected equipment. The constraints specify that each move is restricted to only one equipment type and the available operating time of each equipment type cannot be exceeded. The problem is solved using a construction heuristic algorithm that exploits, conceptually, some similarities to both the knapsack and the loading problems. The algorithm is computationally attractive and lends to achieve other goals, such as maximizing equipment utilization and minimizing the variations in equipment types, as well as the primary goal of cost minimization.
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paper_title: PRODUCTIVITY ESTIMATION IN BACK-ACTER/DUMP-TRUCK EARTH-MOVING OPERATIONS.

paper_content:

The importance of productivity estimation in earth-moving is explained, the values of hauler and loader cycle times are introduced and their use in the calculation of productivity is outlined. Existing methods of calculating hauler cycle time are discussed. Reductions in productivity due to mismatch and bunching are investigated and the associated match factor and bunching factor are explained. Field data has been collected. Using this data, alternative methods of estimating loader and hauler cycle times are discussed and these are used. A comparison with an actual operation is shown. Simulated values of bunching factor are then compared with actual field values. Guidelines to the use of these values and other methods introduced are given
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paper_title: Selecting earthmoving equipment fleets using genetic algorithms

paper_content:

This paper presents an application of simulation optimization in construction utilizing genetic algorithms. The paper focuses on the use of genetic algorithms (GAs) as a tool for optimizing the total cost of earthmoving operations accounting for available equipment models to contractors and their corresponding quantities. The developed genetic algorithm has a powerful computational utility that increases its efficiency. The fitness of generated chromosomes is calculated utilizing a simulation engine dedicated for earthmoving operations which is dynamically linked to the developed genetic algorithm. The impact of the algorithm's control parameters on its conversion is also examined. A numerical example is presented to illustrate the capabilities of the developed algorithm in selecting near-optimum fleet configurations.
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paper_title: Determination of Most Economical Scrapers Fleet

paper_content:

Scrapers are valuable construction equipment for large earthmoving operations. Their production rates vary widely as they depend on the equipment performance, operation’s travel time, and haul-road conditions. Determining the most economical selection of the size, model, and number of scrapers is a rather tedious process that involves repetitive calculations. A spreadsheet application was created in order to facilitate such calculations and select the most economical scraper from the list of available equipment for the job under consideration. The application is made of seven spreadsheets containing a scrapers’ database, performance charts, soil properties, and other supporting worksheets. The application provides a user interface to solicit all data entries specific to a project. Once the user enters the required data the system compares the production rate, time required for the job, determines the estimated unit cost for each scraper in the database, and recommends the most economical selection.
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paper_title: OR Practice - Design and Implementation of an Interactive Optimization System for Network Design in the Motor Carrier Industry

paper_content:

We describe the design and implementation of an interactive optimization system for routing freight over a less-than-truckload motor carrier network. We formulate a very large, mixed integer programming problem, and develop a decomposition strategy based partly on the mathematical structure of the problem as well as a range of important, real-world issues and constraints. Then we develop and implement a local improvement heuristic in such a way as to keep the “man-in-the-loop,” using the analyst to make judgments regarding certain complex constraints and tradeoffs. Important aspects of the system include a range of modeling approximations to keep the problem tractable and the way the analyst evaluates the quality of the different numbers. The package was implemented and is currently being used on an ongoing basis by a major motor carrier. An overview of the major elements of the package is given as well as a summary of important implementation issues that arose during the three year project.
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paper_title: The fleet assignment problem: solving a large-scale integer program

paper_content:

Given a flight schedule and set of aircraft, the fleet assignment problem is to determine which type of aircraft should fly each flight segment. This paper describes a basic daily, domestic fleet assignment problem and then presents chronologically the steps taken to solve it efficiently. Our model of the fleet assignment problem is a large multi-commodity flow problem with side constraints defined on a time-expanded network. These problems are often severely degenerate, which leads to poor performance of standard linear programming techniques. Also, the large number of integer variables can make finding optimal integer solutions difficult and time-consuming. The methods used to attack this problem include an interior-point algorithm, dual steepest edge simplex, cost perturbation, model aggregation, branching on set-partitioning constraints and prioritizing the order of branching. The computational results show that the algorithm finds solutions with a maximum optimality gap of 0.02% and is more than two orders of magnitude faster than using default options of a standard LP-based branch-and-bound code.
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paper_title: 0–1 reformulations of the multicommodity capacitated network design problem

paper_content:

We study 0-1 reformulations of the multicommodity capacitated network design problem, which is usually modeled with general integer variables to represent design decisions on the number of facilities to install on each arc of the network. The reformulations are based on the multiple choice model, a generic approach to represent piecewise linear costs using 0-1 variables. This model is improved by the addition of extended linking inequalities, derived from variable disaggregation techniques. We show that these extended linking inequalities for the 0-1 model are equivalent to the residual capacity inequalities, a class of valid inequalities derived for the model with general integer variables. In this paper, we compare two cutting-plane algorithms to compute the same lower bound on the optimal value of the problem: one based on the generation of residual capacity inequalities within the model with general integer variables, and the other based on the addition of extended linking inequalities to the 0-1 reformulation. To further improve the computational results of the latter approach, we develop a column-and-row generation approach; the resulting algorithm is shown to be competitive with the approach relying on residual capacity inequalities.
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paper_title: Integrated service network design for a cross-docking supply chain network

paper_content:

This paper considers an integrated service network design problem for a given set of freight demands that is concerned with integration of locating cross-docking (CD) centers and allocating vehicles for the associated direct (transportation) services from origin node to a CD center or from a CD center to the destination node. For the vehicle allocation, direct services (sub-routes) should be determined for the given freight demands, and then the vehicle allocation has to be made in consideration of routing for the associated direct service fulfillment subject to vehicle capacity and service time restriction. The problem is modeled as a path-based formulation for which a tabu-search-based solution algorithm is proposed. To guarantee the performance of the proposed solution algorithm, strong valid inequalities are derived based on the polyhedral characteristics of the problem domain and an efficient separation heuristic is derived for identifying any violated valid inequalities. Computational experiments are performed to test the performance of the proposed solution algorithm and also that of a valid-inequality separation algorithm, which finds that the solution algorithm works quite well and the separation algorithm provides strengthened lower bounds. Its immediate application may be made to strategic (integrated) service network designs and to tactical service network planning for the CD network.
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paper_title: Match factor for heterogeneous truck and loader fleets

paper_content:

The mining and construction industries have used match factor for many decades as an indicator of productivity performance. The term match factor is usually defined as the ratio of truck arrival rate to loader service time. This ratio relies on the assumption that the truck and loader fleets are homogeneous. That is, all the trucks are of the same type, and all the loaders are of the same type. In reality, mixed fleets are common. This paper proposes a method of defining match factor for heterogeneous fleets: in particular, a heterogeneous trucking fleet, a heterogeneous loading fleet, and the case where both truck and loader fleets are heterogeneous.
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paper_title: A combined transportation and scheduling problem

paper_content:

Abstract We consider a problem in which a given good has to be delivered from some origins (say production plants), to some destinations (say nodes at which the transportation mode is changed, or simply customers), during a workday, by means of a given fleet of trucks, at minimum cost. For the purpose of solution the problem is split into two levels, where, at the first level, the decision concerns the planning of trips in order to deliver goods, while, at the second level, the vehicles needed to operate the trips have to be scheduled. The solution approach presented here is based on Lagrangean Decomposition and makes use of a new algorithm for the approximate solution of the Lagrangean Dual. Computational results from a set of real life problems are presented
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paper_title: An integrated methodology for decision making of mining method selection

paper_content:

Mine enterprises increasingly depend on computerised decision support tools to improve decision-making in areas such as mining method selection, equipment selection and production scheduling. Information technology and management science are capable of improving the decision making of mining engineering, which have been integrated into a system we have developed. Selection of the mining method for ore deposits is extremely complex and it relies on several factors; the decision maker also confronts multiple conflicting objectives such as maximising benefits and safety, minimising cost, etc. In this paper, a methodology for developing an intelligent decision system for mining method selection integrated with expert systems and fuzzy evaluation based multi-attributes decision theory is described.
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paper_title: Estimation of large open pit haulage truck requirements

paper_content:

This paper examines the concept of a bare bones base case in the economic evaluation of a mineral property. This is the case that the banks like to see, and the paper examines why. The expression bare bones refers to a cash flow evaluation based on constant metal prices, constant dollars, no inflation, no debt, no interest, on a project basis and after tax. The paper looks individually at the impact of the various assumptions that go into an evaluation, and shows how these can be combined to show an exciting result that may not really exist. An example of an embellished case (the kind that one frequently sees when projects are being promoted) is developed and the cumulative impact is analyzed to show the actual project underneath. The paper also points out some areas to watch for overly optimistic assumptions such as prices, margins, and debt.
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paper_title: Applications of expert systems in equipment selection for surface mine design

paper_content:

ABSTRACT The MINDER system (MINe Design using Expert Reasoning), has been developed to a prototype level in the Department of Mining Engineering, University of Nottingham. The Xi-Plus shell system has been used to create a multi-level expert system capable of accessing and controlling both commercially available mine planning software and 'in-house' programs. The expert system is used primarily for surface mining method selection and excavation and haulage equipment selection. Methods of storing knowledge, interrogating and controlling external programs, and reaching conclusions using multiple knowledgebases have been discussed in previous papers by the authors, and will be dealt with only briefly in this paper. This paper concentrates on the methods used to rank equipment, including relational operations (both with the knowledgebase and in external databases) and fuzzy logic techniques. The paper will include an example of the ranking of hydraulic excavators under UK surface coal mining conditions.
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paper_title: Composite Variable Formulations for Express Shipment Service Network Design

paper_content:

In this paper we describe a new approach to solving the express shipment service network design problem. Conventional polyhedral methods for network design and network loading problems do not consistently solve instances of the planning problem we consider. Under a restricted version of the problem, we transform conventional formulations to a new formulation using what we termcomposite variables. By removing flow decisions as explicit decisions, this extended formulation is cast purely in terms of the design elements. We establish that its linear programming relaxation gives stronger lower bounds than conventional approaches. We apply this composite variable formulation approach to the UPS Next Day Air delivery network and demonstrate potential annual cost savings in the hundreds of millions of dollars.
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paper_title: A new earthworks estimating methodology

paper_content:

Earthworks and earthmoving operations are a major part of many civil engineering construction projects. Because of their labour and plant intensity, the planning and estimating of such operations is crucial to both the cost and duration of the project; earthworks are considered by many practitioners to be indicators to the success or failure of the project as a whole. Traditionally, a mixture of manufacturers' data (through published charts or computer databases) and historical company data are used in the estimating of earthworks. This process has two main drawbacks. First, plant haul velocity is dependent on the rolling resistance at the soil-wheel interface, which is notoriously difficult to determine; second, the stochastic interface between types of plant provides a non-deterministic system, resulting in estimates of output which may be unrealistically high. An alternative system of earthworks estimating is presented based on a combination of work undertaken in both the soil/vehicle and stochastic estimating fields. This system is demonstrated via a case study based on an actual highway project. The main conclusion to be drawn is that the traditional estimating approach results in a scheme costed well below realistic values.
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paper_title: Expert System for Equipment Selection

paper_content:

An expert system was developed for equipment selection for various unit operations in open pit mining. For each unit operation, it considers a wide variety of equipment and ranks them based on their suitability. A major difference between this system and other published expert systems in the considered domain is that it incorporates the uncertainty that is an inherent characteristic of the factors affecting equipment selection. It also allows users to specify the site-specific relative importance of each of the governing factors. This makes the system relatively flexible and allows its adaptation to different mining conditions. The programming features of the expert system include uncertainty databases and object oriented programming. The expert system is validated with a case study (Malanjkhand Copper Mine, India).
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paper_title: Service network design with management and coordination of multiple fleets

paper_content:

We present a new optimization model for the tactical design of scheduled service networks for transportation systems where several entities provide service and internal exchanges and coordination with neighboring systems is critical. Internal exchanges represent border crossings necessitating changes of vehicles, while the coordination with neighboring systems represents intermodal operations. For a given demand, the model determines departure times of the services such that throughput time of the demand in the system is minimized. The model is an extension of the design-balanced capacitated multicommodity network design model that we denote service network design with asset management and multiple fleet coordination to emphasize the explicit modeling of different vehicle fleets. Data from a real-world problem addressing the planning of new rail freight services across borders serves to illustrate the capabilities of the formulation. We analyze how synchronization with collaborating services and removal of border-crossing operations impact the throughput time for the freight. We identify a significant potential for system performance enhancement from synchronization among collaborating services for the problem studied.
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paper_title: A Stabilized Structured Dantzig-Wolfe Decomposition Method

paper_content:

We discuss an algorithmic scheme, which we call the stabilized structured Dantzig–Wolfe decomposition method, for solving large-scale structured linear programs. It can be applied when the subproblem of the standard Dantzig–Wolfe approach admits an alternative master model amenable to column generation, other than the standard one in which there is a variable for each of the extreme points and extreme rays of the corresponding polyhedron. Stabilization is achieved by the same techniques developed for the standard Dantzig–Wolfe approach and it is equally useful to improve the performance, as shown by computational results obtained on an application to the multicommodity capacitated network design problem.
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paper_title: Air Network Design for Express Shipment Service

paper_content:

Express shipment service requires that shipments be picked up and delivered within specified time intervals e.g., 24 hours, 48 hours or 3-5 days. In this paper, we describe the express shipment service design problem faced by a carrier and present a model and column generation approach for its solution. Our approach can find near optimal air service designs for a fixed aircraft fleet or for a fleet of unspecified size and make-up. In the latter case, the service design, fleet size and fleet composition are determined simultaneously. We have implemented our solution procedure, and a large carrier is using it to plan their air service operations and to evaluate various operating scenarios. The results indicate that service designs are generated that allow for improved service with a reduction in annual operating costs measuring in the millions of dollars.
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paper_title: A heuristic approach to long-haul freight transportation with multiple objective functions

paper_content:

This paper studies a long-haul freight transportation problem stimulated by a real-life application, whose underlying vehicle routing problem is a multi-objective one, where travel time and route cost are to be minimized together with the maximization of a transportation mean sharing index, related to the capability of the transportation system of generating economy scale solutions. In terms of constraints, besides vehicle capacity and time windows, transportation jobs have to obey additional constraints related to mandatory nodes (e.g., logistic platform nearest to the origin or the destination) and forbidden nodes (e.g., logistic platforms not compatible with the operations required). Based on the network definition, routes can be multimodal. To solve this problem, we propose a heuristic algorithm that can be applied in the tactical and the operational planning phase, and present the results of an extensive experimentation.
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paper_title: Preprocessing and cutting for multiple allocation hub location problems

paper_content:

Abstract In this paper we consider formulations and solution approaches for multiple allocation hub location problems. We present a number of results, which enable us to develop preprocessing procedures and tightening constraints for existing mixed integer linear programming formulations. We employ flow cover constraints for capacitated problems to improve computation times. We present the results of our computational experience, which show that all of these steps can effectively reduce the computational effort required to obtain optimal solutions.
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paper_title: A Simplex-Based Tabu Search Method for Capacitated Network Design

paper_content:

The fixed charge capacitated multicommodity network design problem is a well-known problem, of both practical and theoretical significance. This paper presents an efficient procedure to determine tight upper bounds on the optimal solution of realistically sized problem instances. Feasible solutions are obtained by using a tabu search framework that explores the space of the continuous flow variables by combining pivot moves with column generation, while evaluating the actual mixed integer objective. Computational experiments on a large set of randomly generated test problems show that this procedure outperforms the other available methods and is particularly suited to large problem instances with many commodities.
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paper_title: Service network design with asset management: Formulations and comparative analyses

paper_content:

In this paper, we address the service network design with asset management problem, which integrates asset management considerations into service network design models for consolidation-based freight carriers. We propose model formulations based on arc variables for both flow and design, as well as formulations with path flow variables and new cycle design variables. Problem instances reflecting actual planning problems are used in the computational study to analyze the strengths and weaknesses of the various model formulations and the impact of asset management considerations on the transportation plan and the computational effort. Experimental results indicate that formulations based on cycle variables outperform traditional arc-based formulations, and that considering asset management issues may significantly impact the outcome of service planning models.
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paper_title: A branch-and-cut algorithm for the pickup and delivery traveling salesman problem with LIFO loading

paper_content:

In the Traveling Salesman Problem with Pickup and Delivery (TSPPD) a single vehicle must serve a set of customer requests, each defined by an origin location where a load must be picked up, and a destination location where the load must be delivered. The problem consists of determining a shortest Hamiltonian cycle through all locations while ensuring that the pickup of each request is performed before the corresponding delivery. This article addresses a variant of the TSPPD in which pickups and deliveries must be performed according to a Last-In First-Out (LIFO) policy. We propose three mathematical formulations for this problem and several families of valid inequalities which are used within a branch-and-cut algorithm. Computational results performed on test instances from the literature show that most instances with up to 17 requests can be solved in less than 10 min, whereas the largest instance solved contains 25 requests. © 2009 Wiley Periodicals, Inc. NETWORKS, 2010
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paper_title: DRIVE: Dynamic Routing of Independent VEhicles

paper_content:

We present DRIVE (Dynamic Routing of Independent VEhicles), a planning module to be incorporated in a decision support system for the direct transportation at Van Gend and Loos BV. Van Gend and Loos BV is the largest company providing road transportation in the Benelux, with about 1400 vehicles transporting 160,000 packages from thousands of senders to tens of thousands of addressees per day. The heart of DRIVE is a branch-and-price algorithm. Approximation and incomplete optimization techniques as well as a sophisticated column management scheme have been employed to create the right balance between solution speed and solution quality. DRIVE has been tested by simulating a dynamic planning environment with real-life data and has produced very encouraging results.
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paper_title: Planning the Location of Intermodal Freight Hubs: an Agent Based Approach

paper_content:

Intermodal freight transportation is defined as a system that carries freight from origin to destination by using two or more transportation modes. In this system, hubs are one of the key elements that function as transferring points of freight between different modes. The location of hubs is one of the most crucial success factors in intermodal freight transportation and needs to be considered very carefully as it has direct and indirect impacts on different stakeholders including investors, policy makers, infrastructure providers, hub operators, hub users, and the community. There have been several attempts to evaluate intermodal freight hub location decisions by using conventional multi-objective evaluation models. Only a few studies take community's benefits into account next to the costs and it is difficult to assess the relationship between system level performance and the prefered solution for individual actors. This paper aims at developing an integral model for the evaluation of road-rail intermodal freight hub location decisions. The model comprises five dominant types of agents namely, hub operators, terminal operators, infrastructure providers, hub users, and communities. An agent based modeling approach is introduced to allow negotiation to happen in order to achieve a global objective. The paper outlines the methodology to be used. It presents a conceptual design and an illustrative case study for an agent based model for the decision making process for planning the location of intermodal freight hubs.
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paper_title: Strong Inequalities for Capacitated Survivable Network Design Problems

paper_content:

We present several classes of facet-defining inequalities to strengthen polyhedra arising as subsystems of network design problems with survivability constraints. These problems typically involve assigning capacities to a network with multicommodity demands, such that after a vertex- or edge-deletion at least some prescribed fraction of each demand can be routed.
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paper_title: Exact Algorithms for the Minimum Power Symmetric Connectivity Problem in Wireless Networks

paper_content:

In this paper we consider the problem of assigning transmission powers to the nodes of a wireless network in such a way that all the nodes are connected by bidirectional links and the total power consumption is minimized.Two mixed integer programming formulations are presented together with some new valid inequalities for the polytopes associated. A preprocessing technique and two exact algorithms based on the formulations previously introduced are also proposed.Comprehensive computational results, which show the effectiveness of the new valid inequalities and of the preprocessing technique are presented. The experiments also show that the exact approaches we propose outperform more complex methods recently appeared in the literature.
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paper_title: On cut-based inequalities for capacitated network design polyhedra

paper_content:

In this article, we study capacitated network design problems. We unify and extend polyhedral results for directed, bidirected, and undirected link capacity models. Valid inequalities based on a network cut are known to be strong in several special cases. We show that regardless of the link model, facets of the polyhedra associated with such a cut translate to facets of the original network design polyhedra if the two subgraphs defined by the network cut are (strongly) connected. Our investigation of the facial structure of the cutset polyhedra allows to complement existing polyhedral results for the three variants by presenting facet-defining flow-cutset inequalities in a unifying way. In addition, we present a new class of facet-defining inequalities, showing as well that flow-cutset inequalities alone do not suffice to give a complete description for single-commodity, single-module cutset polyhedra in the bidirected and undirected case – in contrast to a known result for the directed case. The practical importance of the theoretical investigations is highlighted in an extensive computational study on 27 instances from the Survivable Network Design Library (SNDlib). © 2010 Wiley Periodicals, Inc. NETWORKS, Vol. 57(2), 141–156 2011 © 2011 Wiley Periodicals, Inc.
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paper_title: Double-horizon based heuristics for the dynamic pickup and delivery problem with time windows

paper_content:

The dynamic Pickup and Delivery Problem with Time Windows (PDPTW) is faced by courier companies serving same-day pickup and delivery requests for the transport of letters and small parcels. This article focuses on the dynamic PDPTW for which future requests are not stochastically modelled or predicted. The standard solution methodology for the dynamic PDPTW is the use of a rolling time horizon as proposed by Psaraftis. When assigning a new request to a vehicle it may be preferable to consider the impact of a decision both on a short-term and on a long-term horizon. In particular, better managing slack time in the distant future may help reduce routing cost. This paper describes double-horizon based heuristics for the dynamic PDPTW. Computational results show the advantage of using a double-horizon in conjunction with insertion and improvement heuristics.
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Title: Equipment Selection for Surface Mining: A Review

Section 1: Introduction
Description 1: Provide a general background to surface mining and the parameters that can become important in the quest to find a good Equipment Selection Problem (ESP) solution.

Section 2: Equipment Selection Problem (mining)
Description 2: Define the Equipment Selection Problem (ESP) formally and discuss the inputs and outputs, highlighting the constraints and goals.

Section 3: Related Problems
Description 3: Outline problems in mining that are similar to the ESP and provide a summary of these related problems.

Section 4: Modeling and Solution Approaches
Description 4: Review both modeling and solution approaches for the ESP in mining, construction, and wider literature. Discuss specific methods and techniques used to address the problem.

Section 5: Discussion
Description 5: Contrast the simplicity and practicability of heuristic methods with more complex exact approaches, highlighting strengths and weaknesses in the context of surface mining.

Section 6: Future Research Directions and Conclusions
Description 6: Identify gaps in current research and suggest potential directions for future research, focusing on the need to generate robust solutions under uncertain parameters.