Traditionally, mining is viewed as a temporary land use, the value of mine sites being temporary and primarily tied to the extraction phase. Upon resource depletion or the cessation of economic viability, these sites are often abandoned. The neglect of proper rehabilitation strategies for these sites poses significant environmental risks, such as acid mine drainage (AMD) and contamination from tailings and waste piles
[1]. Estimates indicate a significant number of such neglected sites, with figures suggesting around 10,000 in Canada and 5500 in Japan
[2]. Recent years have witnessed increased engagement from academic and financial institutions in crafting frameworks for responsible mine closure
[3]. Current regulations necessitate the integration of closure and reclamation plans within mining operations, targeting the restoration of landscapes and the mitigation of environmental and socio-economic impacts
[4]. While essential, rehabilitation and restoration efforts categorize mine sites as transient land uses, generating no continual revenue but incurring restoration costs. This issue is particularly salient for vast, abandoned underground mines, where complete restoration is often impractical. Re-purposing these underground spaces provides an opportunity for sustained land use, potentially fostering industries capable of supporting the sites’ maintenance and rehabilitation costs
[5].
2. Smart Mining
The evolution of digital technologies has paved the way for a new era in mining, known as “smart mining”. Smart mining refers to the integrated approach to optimizing mine operations and improving productivity, safety, and environmental impact through real-time data analysis, automation, and advanced technologies
[7][8]. One crucial aspect of smart mining is the real-time monitoring and operational control enabled by the internet of things (IoT) and other connected technologies. Ikeda et al.’s (2021) exploration of sensor data communication in underground mining environments highlights the significance of robust and efficient data transmission systems. Their research compares and optimizes multiple installation sequences, contributing to the improvement of real-time data relay and decision-making processes underground
[9]. In addition to real-time data monitoring, smart mining also embraces innovative solutions for operational challenges. The work by Ikeda et al. (2019) underscores this aspect through the development of an underground in situ stress monitoring system using multi-sensor cells and Wi-Fi direct technology
[10]. This system not only enhances mining safety by providing immediate stress measurements but also improves operational efficiency. The integration of artificial intelligence (AI) and machine learning (ML) in smart mining operations has further transformed traditional practices. Deep learning techniques, for instance, are being utilized for estimating muckpile fragmentation. Ikeda et al. (2023) employed simulated 3D point cloud data for this purpose, demonstrating the potential of this technology in enhancing ore recovery and reducing waste
[8].
Smart mining, therefore, represents a multifaceted approach to modernizing mine operations. By leveraging digital technologies, mining companies can significantly improve operational efficiency, ensure the safety of mine workers, and minimize environmental impact. As this field continues to evolve, further advancements in IoT, AI, and automation are expected to drive the future of mining toward unprecedented levels of optimization and sustainability.
3. Digital Twin
A digital twin represents a real-time digital counterpart of a physical entity, process, or service. Unlike a prototype, a digital twin autonomously synchronizes data between the physical and digital models, reflecting any changes occurring in the physical model in the digital one. This synchronization is possible through the integration of various digital technologies, including but not limited to, the internet of things (IoT), cloud computing, analytics, and artificial intelligence (AI)—components of Industry 4.0. A digital twin comprises a physical object, its digital model, sensor-acquired time-series data, and the connections between them
[7][8][11].
Figure 1 illustrates the structure of a digital twin within a cyber-physical system.
Figure 1. Structure of a digital twin.
Data-driven decision making is enhanced by integrating simulation programs with the digital twin, linking physical systems to their digital counterparts. This integration creates a closed-loop known as a digital thread, autonomously updating the virtual model with data from sensors in the physical object. The data informs simulations essential for planning, design, and operations, enabling real-time, informed decision making and risk assessments. Moreover, integrating simulations facilitates the prediction of various outcomes, enhancing operational strategies.
The benefits of utilizing a digital twin include:
-
Real-time monitoring and control: With IoT, users can access the digital model of a physical entity or process from virtually anywhere.
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Enhanced safety and efficiency: Automated monitoring of remote or inaccessible areas.
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Predictive maintenance and scheduling: AI-driven solutions detect potential system faults, enabling pre-emptive maintenance and avoiding economic losses or safety hazards.
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Scenario and risk assessment: Simulations with varied input parameters allow the prediction and pre-emptive addressing of unforeseen scenarios.
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Improved documentation: Immediate access to real-time information enhances transparency for stakeholders.
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Streamlined operations: Data-driven decision making, bolstered by advanced analytics and interconnected intelligence networks, fosters synergies and collaborative efforts, boosting productivity.
4. Ventilation Simulation Programs
Ventilation control is crucial in underground environments, playing a significant role in the operational profitability of underground mining. The planning and optimization of underground ventilation systems demand rigorous analysis, as minor modifications can profoundly impact the entire system. This necessitates the exploration of various options and scenarios, entailing countless predictions related to the ventilation network, system design, and performance. Such complex predictions are unfeasible without the aid of precise and adaptable simulation tools capable of swiftly assessing multiple scenarios
[12]. Ventilation simulation programs facilitate the calculation and assessment of environmental variables—such as airflow, temperature, fog, and relative humidity—based on specified parameters like initial temperature, thermal output, and existing ventilation equipment
[13].
Previous studies, including those by Webber et al.
[13] and Sasmito et al.
[14], underscore the necessity of integrating ventilation simulation software for underground mine site monitoring, highlighting the critical role of simulations in enhancing underground systems. For instance, Sasmito et al.
[14] demonstrated the efficacy of simulation models in assessing thermal management’s impact within mines, focusing on the computational analysis of various thermal factors on underground tunnel airflow. Managing thermal conditions in underground environments is intricate, given the need to consider elements like geothermal gradients and internal heat loads from personnel, lighting, and equipment
[14].
5. Integrating Simulation Programs with Digital Twins
A well-calibrated digital twin of an underground environment mirrors the actual operational parameters of underground ventilation, incorporating real-time data from sensors within the specified area to offer an updated model of the subterranean conditions. This advanced approach significantly enhances the optimization processes of the ventilation systems. Previous studies have delved into the application of simulation programs for constructing digital twins, albeit in different contexts. For instance, Dahmen et al.
[15] explored this concept not for underground ventilation but for space missions, concentrating on the methodology behind digital twin development and its subsequent utilization for experimentation
[13].
Mine ventilation simulation software uniquely presents real-time data gathered from sensors deployed in underground mining locations. This real-time feature not only facilitates continuous monitoring but also autonomously updates the digital twin with fresh data from the mine, a capability explored by Sishi et al.
[16]. Similarly, Cheskidov et al.
[17] discussed the employment of monitoring systems to display real-time data regarding mining engineering structures, with in situ data analysis programs pinpointing inaccurately measured or calculated characteristics, such as slope safety factors or load-bearing capacities, within a nature-and-technology system. These programs then prompt further necessary measurements and computations. Both the study by Sishi
[16] and that by Cheskidov
[17] examined the use of digital twins’ as real-time monitoring platforms capable of immediate problem identification, yet neither delved into their application as simulation tools.
Jacobs
[18] offers an extensive review of the research conducted in this domain, identifying gaps, particularly in enhancing the methodology for digital twin development and its application as a simulation instrument for system evaluation (
Table 1).
Table 1. Different studies discussing integration of digital twin and simulation programs
[5].
Source
|
Development of Digital Twin
|
Digital Twin Used to Evaluate a System
|
Digital Twin Used as a Simulation Tool
|
[19][20][21][22]
|
F
|
F
|
F
|
[12][14][23][24][25][26]
|
F
|
F
|
T
|
[15][27][28][29][30][31][32]
|
T
|
F
|
T
|
[13][33][34][35][36]
|
T
|
F
|
T
|
[16][17]
|
F
|
T
|
F
|
6. Re-Purposing of Underground Spaces
The re-purposing of a mine site incorporates elements of the existing mining infrastructure and reconfigured landscape aspects for alternative activities post-closure. Such activity not only aids in transitioning the local economy but also mitigates the mine’s loss by fostering new forms of attachment to the site and region
[6]. An advantage of utilizing underground spaces lies in their stability. The conditions inside underground excavations remain unaffected by external weather conditions and are nearly constant, simplifying temperature and humidity control. Comfortable subsurface temperatures eliminate the necessity for additional insulation, thus conserving energy and reducing costs. Furthermore, underground structures sustain less damage compared to surface structures under earthquake loading
[5] and possess increased resistance to hurricanes, tornadoes, and most weapon system penetrations.
However, obstacles exist in re-purposing mine sites, including their susceptibility to flooding and the requirement for diverse skill sets. The location also poses a challenge, as mine sites are often situated in remote areas, far from communities and towns, leading to minimal community involvement that could otherwise motivate re-purposing. The stability and utility of these spaces must be continually re-evaluated and maintained throughout the re-purposing process to ensure safety. The geothermal gradient may cause temperatures inside the mined cavity to increase with depth, necessitating the utilization of pre-existing mine cooling systems for deep mine sites. Globally, examples of re-purposing are few compared to the number of closed mines. Out of the 1804 inactive mine sites documented in the S&P database, only approximately 141 operations have undergone some form of re-purposing
[6].
It is common for a mine site to serve multiple purposes after mining; post-mining transitions frequently encompass various categories of land use. Factors such as proximity to communities, infrastructure connectivity, and company policies also influence the re-purposing of mined underground spaces. The most prevalent re-purposing activities include wildlife habitats, historical museums or exhibitions, cultural or historical precincts, and parks or open green spaces
[6].
Table 2 illustrates other instances of mine re-purposing, like healthcare facilities such as Solotvyno’s Allergological Hospital in Ukraine, which specializes in treating patients with respiratory ailments.
Figure 2 depicts underground agriculture employing LED lights and hydroponic technology, while
Figure 3 and
Figure 4 present examples of a former salt mine in Germany, re-purposed for radioactive waste storage, and a former limestone mine, converted into a recreation center, respectively. With technological advancements and enduring demand for metals and other resources, the depth of underground mining sites is anticipated to increase. Re-purposing deeper mines will require considering the geothermal gradient—whereby underground mine temperatures rise with depth—and leveraging previous mine site cooling systems to maintain optimal temperatures.
Figure 2. Blast design at target site.
Figure 3. Drums with concrete shielding to reduce radiation exposure stored in Asse II, previously Asse salt mine. Adapted from
[34].
Figure 4. Former limestone mine in Louisville, Kentucky, restructured to create underground bike track. Adapted from
[35].
Table 2. Examples of mine re-purposing.
7. Data Centers
Data centers serve as pivotal infrastructure where organizations house critical applications and data. The paradigm has transitioned from traditional on-premises servers to sophisticated virtual networks, facilitating operations in multi-cloud environments
[37]. These centers underpin a myriad of applications and activities, encompassing virtual desktops, enterprise resource planning, and advanced realms like artificial intelligence and big data analytics.
Figure 5 illustrates the basic components in a data center facility, highlighting their complex architecture.
Figure 5. Basic components in a data center facility.
The year 2020 witnessed a 40% upsurge in global internet traffic, propelled by a proliferation in video conferencing, online gaming, and digital connectivity
[37]. Forecasts suggest that by 2024, remote work will be integral to over 90% of infrastructure operations, and centralized platform engineering will be embraced by more than half of enterprises by 2025
[38]. This digitalization trajectory accentuates the imperative for robust data accessibility and security protocols, challenging to internalize within organizations.
Power reliability is critical, with outages having substantial financial repercussions, potentially costing up to USD 17,244 per minute
[39]. Re-purposing underground mine sites as data centers presents a viable alternative, capitalizing on existing infrastructural elements like power lines and backup generators, essential for uninterrupted power supply (UPS) systems. The proposition for re-purposing the Osarizawa mine site underscores this potential.
Physical security complements cyber security in its importance, prompting some data centers to utilize underground facilities’ inherent security advantages
[37]. Examples include the Lefdal Mine Datacenter in Norway and the Bluebird Underground Data Center in Missouri, re-purposed from mining operations, offering natural cooling and fortified protection
[40][41].
Figure 6 shows the Lefdal Mine Datacenter, demonstrating its robust security features including a single point of entry.
Figure 6. Lefdal Mine Datacenter has a single point of entry
[21].
Innovative approaches extend to Microsoft’s underwater data center, Project Natick, and proposed extraterrestrial data centers, aiming to exploit the natural cooling properties of these environments to reduce energy consumption
[42][43].
Figure 7 captures the retrieval of Microsoft’s Northern Isles data center (Project Natick) in July 2020, showcasing its unique underwater environment.
Figure 7. Retrieval of Microsoft’s Northern Isles data center (Project Natick) in July 2020.
The integration of renewable energy sources and the conceptualization of data centers as heat sources for neighboring infrastructure further enhance their sustainability
[44].