# Fleet Resilience: Evaluating Maintenance Strategies in Critical Equipment
## 1 Introduction
#### Fleet Resilience  
Capital-intensive organizations, such as those in the mining sector, require and use a lot of large and expensive equipment. This equipment is intended for the transport and processing of the material removed from the mine. Major investments in physical assets (capital expenditures--CAPEX), coupled with operation and maintenance costs (OPEX) can reach values of several hundred million dollars. The basic and fundamental components of any logistics infrastructure are all the resources that enable the storage, movement and handling of cargo units. This is supplemented by computer networks and decision support systems [19]. Typical open pit equipment consists of trucks, shovels, drills and other auxiliary units [20; 21] that develop activities that include drilling, loading, transport, unloading and other auxiliary services, such as road conditioning, among others [22; 23]. In a fleet-based system, all units in the system work together under a productive program with defined standards of availability and efficiency [24]. The transport of material is one of the most important aspects in open pit mining operations. The costs can reach up to 50% of OPEX, therefore, any improvement initiative in this area will have a significant economic impact on the organization [25]. Although some aspects of resilience have received attention in the transport sector, there is no unified definition for such a term. Based on the fundamental concepts of engineering resilience and ecological resilience, [PERSON] [18] defined'resilience in transport' as the quality that leads to recovery, reliability and sustainability. These attributes were integrated by [26] into three dimensions: Robustness, Redundancy and Recovery. Robustness is about the ability of system to resist when suffering disruptions. Redundancy provide the system with spare service capacity when some components or elements fails. Robustness and Redundancy concerns about the ability of maintain its service level or performance. Recovery concerns about the ability of a system restore its characteristic service level or performance [26]. The work of [27] investigates the role of network topology, and the characteristics of the topology, in the ability of a transportation system to cope with disruptive events. Specifically, the paper hypothesizes that the topological attributes of a transportation system significantly affect its resilience to disaster events. According to the authors, resilience explains not only the inherent ability of the system to absorb externally induced shocks, but also the effective and efficient adaptation measures that can be taken to preserve or re-establish performance post-event [27]. Many quantitative approaches have been proposed to measure the resilience of different transportation systems [16; 28], such as railway system [29], and freight transportation system [30]. [PERSON] et al. [31] provided a synthesis of the up-to-date literature on resilient transportation, focusing on concepts and methodologies. The main body of that review was devoted to the characterization of resilience metrics and mathematical models and to the strategies used to enhance resilience [31]. The authors suggested that through reliability investment, the organizations could achieve significant savings over a systems lifecycle. Thus, such reliability improved fleet availability and a larger fleet size can be used by the companies when needed. This work proposes the use of a resilience metric in the extraction fleet of an open-pit mine, using as a basis the availability of each of the elements, the topological structure of the fleets and the criticalities defined according to the reliability and maintainability of each of these pieces of equipment. A case study, using an example of a mine located in northern Chile, allows the validation of the concept and its usefulness in evaluating various maintenance strategies, as well as the impact of the topological structure of the system.