Decision-Making Analysis of Ground Support Selection in a Critical Mine Infrastructure Tunnel

This research focuses on addressing the significant challenges faced by a critical mining infrastructure tunnel, an essential part of a mining company’s operations. Set against the backdrop of increasing global demand for copper, primarily driven by the rise in electric vehicle and renewable energy industries, the study underscores the vital role of copper. The objective is to ensure the efficient and sustainable functioning of this crucial mining infrastructure. The study employs a blend of qualitative and quantitative approaches, including Cost-Benefit Analysis (CBA) and the Analytic Hierarchy Process (AHP), to evaluate and prioritize ground support alternatives. These methodologies are chosen for their ability to assess the economic viability, safety, and sustainability of the tunnel. Facing the tunnel’s degradation, which threatens safety and efficiency, the goal is to stabilize the structure through 2041. Insights are drawn from expert opinions via the Delphi method and empirical data from site and geological surveys to devise strategic, sustainable solutions for tunnel maintenance and expansion. The study’s multifaceted approach using the Delphi technique, CBA, and AHP addresses the tunnel’s technical, economic, and sustainability challenges. It’s critical for the tunnel’s role in the global copper supply and the company’s operations. Through AHP, ground support Types C and D were identified as optimal, with Type C using Steel Sets and closer bolt spacing with shotcrete, ensuring stability. Type D is preferred for its economic efficiency but still considers the minimum factor of safety requirement. uses shotcrete arches and wider bolt spacing without additional shotcrete, aligning with a 27.3% priority score for cost-effectiveness. These methods balance the tunnel’s technical needs with safety and cost considerations. The Delphi method validated the AHP findings, reflecting an expert consensus on Type D’s suitability. CBA provided the financial rationale, emphasizing Type D’s lower costs. Ultimately, the choice of Type D reflects a strategic analysis of immediate and future needs, combining technical diligence, cost efficiency, and long-term planning into a coherent decision-making process informed by a breadth of expertise. For future research on the Critical Underground Mine Infrastructure Tunnel should encompass environmental and social factors, enhancing overall sustainability and impact. It’s crucial to involve a diverse range of stakeholders, ensuring broad perspectives are considered. This inclusive approach will improve the effectiveness, acceptance, and long-term viability of such engineering and construction projects.

Introduction

The escalating global demand for copper, often termed the “metal of electrification,” is intensifying due to the energy transition toward electric vehicles, power infrastructure, and renewable energy generation. This surge is pivotal in the context of the 2050 goal for net zero emissions. However, this rising demand underscores the critical need for a stable and efficient copper supply chain, which faces challenges, including the necessity for new copper sources to meet this demand (S&P, 2022).

The balance between the benefits and impacts of mining operations is crucial for sustainable development (UNDP, 2018). According to the International Council on Mining and Metals (ICMM, 2022), SME (2016) sustainable development in mining should ensure a net positive contribution to people and minimize environmental risks (UNDP, 2018; Hilson, 2002). The industry must ensure that the total benefits of mining outweigh its costs, supporting a broader balance of benefits and impacts.

In addressing global resource demands, sustainable mining practices are paramount. The Copper Gold Mining Company, a leader in mineral mining, specializes in extracting and processing copper, gold, and silver ores. Operating within the rich Grasberg minerals district in Papua, Indonesia, the company manages significant reserves. The Critical Underground Mine Infrastructure Tunnel, located in MP58 and spanning 1150 m, is vital for the company’s operations. It plays a crucial role in the efficient transportation of personnel and materials, which is essential for the smooth functioning of mining activities.

Ensuring the functionality and safety of the Tunnel is paramount. An effective ground support system is required to provide stability and structural integrity, safeguard the safety of personnel, and minimize risks associated with unstable conditions. Compliance with safety standards set by the Government of Indonesia (GOI), Reference Menteri (2018) and the Ground Control Management Plan (GCMP) is also crucial for operational integrity.

Company’s organizational structure includes various business units (Fig. 1), with the GeoEngineering and Environmental Division playing a critical role. This division, under an SVP, oversees geoscience and environmental-related practices and services. The Underground Geotechnical Services Department within this division is responsible for managing geotechnical aspects of mining operations, including the critical mine infrastructure Tunnel.

Fig. 1. Division structure of mining company.

The primary business issue for the company is the deteriorating condition of the Tunnel, impacting its functionality, safety, and viability. This deterioration, evident from historical incident data, poses challenges in structural integrity, safety, operational disruptions, maintenance costs, and long-term viability. Addressing these issues requires strategic decision-making, technical expertise, and collaboration with stakeholders, including the Company itself, Government regulation, and the surrounding society.

To comprehensively address these challenges, the company must engage in detailed research and analysis, focusing on ground support installation options and strategies. This research aims to ensure the tunnel’s long-term viability and sustainability, aligning with the company’s overarching goals and contributing to the broader objectives of sustainable mining and efficient resource management.

Furthermore, this research outlines the global context of copper demand, the principles of sustainable mining, the company’s role in the industry, and the critical importance of the Tunnel in the company’s operations. It sets the stage for a detailed examination of the technical, economic, and strategic considerations necessary to maintain the tunnel’s functionality and safety, emphasizing the need for a comprehensive approach to managing this essential mining infrastructure.

Literature Review

Ground Support

Ground support is essential to tunnel durability and sustainability; this is recognized in a number of industries, such as utilities, transportation, and mining. The literature emphasizes that ensuring the structural integrity and safety of tunnels is a major priority. An in-depth analysis of this literature clarifies the various technologies and approaches used in ground support while examining how they contribute to the longevity and efficiency of tunnel operations.

The fundamental components of ground support that are necessary for a tunnel’s long lifespan and sustainability are shown in Fig. 2. The figure emphasizes how crucial it is to have a well-designed ground support system that incorporates geotechnical engineering concepts to guarantee tunnel structures are safe and functioning for the duration of their intended lives. By using an integrative strategy, tunnels can efficiently serve their purpose and assist sustainable development practices while withstanding the harshness of their surroundings.

Fig. 2. Ground support elements (Kaiseret al., 1996).

The notion of the factor of safety is also included in the evaluation; this is an important element to make sure tunnels stay safe and operational for the duration of their intended life. These talks are especially relevant to the Critical Tunnel since they demonstrate company’s proactive approach to maintaining the structural integrity of the tunnel. In order to handle the wear indicators and possible failure modes found in the tunnel over time, the literature highlights the necessity of continual assessment and responsive ground support techniques.

One important instrument for the technical evaluation of tunnel ground conditions is the Q system (Fig. 3). It measures the quality of the rock mass and directs the choice of suitable ground support techniques. This methodology aids in the classification of the different rock stability levels in the Tunnel, showing where more robust methods, such as shotcrete or steel sets, are required for the weaker parts and where simpler techniques, such as rock bolts, are sufficient for the more stable zones. By matching ground support to the geological reality, the Q system is used to ensure tunnel longevity and safety.

Fig. 3. Rock mass quality and rock support chart (NGI, 2022).

Methodological Approaches for Tunnel Stability and Decision-Making

The RAND Corporation developed the Delphi technique in the 1950s with the initial goal of predicting the impact of technology on military operations. Since then, it has undergone modifications for use in a variety of fields, such as education, healthcare, and environmental studies. Using rounds of anonymous polling, expert panels are consulted to obtain an agreement on difficult topics. Experts contribute their ideas, see the group’s responses, and have the opportunity to revise their responses in subsequent rounds in order to bring their expertise together into a consensus.

The Delphi technique has been particularly useful in tunnel construction and rehabilitation, helping to gather expert assessments on the risks and required priorities for tunnel stability. In a Critical Tunnel project, this method involved experts in several rounds of surveys to pinpoint key factors that could lead to tunnel collapse, ensuring thorough and informed decision-making for the tunnel’s maintenance and advancement.

The Delphi technique can be implemented in tunnel construction or rehabilitation to address technical challenges. The Delphi survey technique was used to gather expert opinions on the factors that contribute to tunnel collapse risk and to prioritize these factors based on their importance (Kimet al., 2022).

For tunnel constructions, Cost-Benefit Analysis (CBA) is essential for assessing financial choices. It weighs the advantages and disadvantages of the project, taking into account unforeseen geological conditions that frequently result in cost overruns. Stakeholders can make decisions on the financial viability of tunneling projects with the use of a thorough CBA.

When choosing a ground support technique, a number of issues are assessed and prioritized using the Analytic Hierarchy Process (AHP). Fig. 4 taking into account the effects on the environment, economy, and technology. Pairwise comparisons and ratio scales are used in the procedure, which is crucial for making decisions about tunnel support, particularly in difficult geological situations. AHP aids in the selection of the best support techniques, which is essential for maintaining the integrity of the tunnel and ensuring user safety.

Fig. 4. Analytic hierarchy process diagram (Saaty, 2008).

Conceptual Framework

In addressing the complexities of modern tunneling projects, a strategic and holistic approach is essential for ensuring the longevity and sustainability of such critical infrastructure. The Critical Tunnel, an integral component of company’s mining operations, serves as a case study for the implementation of such an approach. Fig. 5 encapsulates the multifaceted strategy employed to confront the challenges presented by tunnel deterioration, cost management, and long-term operational demands.

Fig. 5. Conceptual framework for the critical mine infrastructure tunnel.

The framework depicted in Fig. 5 integrates advanced methodologies to create a cohesive plan that ensures the structural integrity and functional efficiency of the tunnel. The Delphi method, Cost-Benefit Analysis (CBA), and Analytic Hierarchy Process (AHP) are employed as key assessment and decision-making tools within this strategic framework. Each of these methods plays a crucial role in crafting a pathway toward sustainable tunnel operations, addressing immediate concerns while laying the groundwork for future adaptability and resilience.

Research Methodology

The research adopts a comprehensive approach, combining qualitative and quantitative methods. It utilizes Cost-Benefit Analysis (CBA) to evaluate the economic viability of different ground support alternatives, considering factors like construction and maintenance costs, and potential operational disruptions. Concurrently, the Analytic Hierarchy Process (AHP) is employed to offer a structured framework for decision-making, facilitating the prioritization of ground support methods based on their safety, economic feasibility, and sustainability (Alpay & Yavuz, 2009).

The data collection methodology is a robust blend of strategies aimed at capturing the full scope of the Tunnel’s condition and requirements. Experts are carefully selected based on their specific knowledge areas to provide targeted insights into the project’s multifaceted aspects. The Delphi method facilitates this by engaging these professionals in a structured survey, with the aim of harnessing their collective wisdom to identify and prioritize risks and solutions, as outlined in Fig. 6. Site inspections complement this expert survey by offering ground-truthing of the tunnel’s actual condition, allowing for a reality check against theoretical assessments. On the other hand, the technical perspective from experts on ground conditions forms the bedrock of the research design, where understanding the inherent geological challenges is paramount. In this project, the subterranean landscape presents a complex tapestry of rock formations, each with its own set of properties that dictate the suitability of various ground support alternatives. A meticulous assessment of these conditions, including rock strength, fracture patterns, and groundwater presence, is essential for selecting a ground support system that can withstand the stressors of the underground environment.

Fig. 6. Delphi flowchart.

The Delphi method taps into the deep well of expert knowledge to evaluate these geological intricacies, ensuring that the chosen support mechanisms are not only theoretically sound but also practically robust.

Qualitative data from these inspections add depth to the analysis, providing context to the numerical data from geological and financial reports. This rich tapestry of data forms the foundation for a nuanced understanding of the Tunnel’s operational and structural health. The quantitative analysis, detailed in Table I, delves into the hard numbers—cost reference, providing a clear-eyed view of the economic implications of each potential ground support strategy. The financial blueprint detailed here encompasses an array of support elements and their associated costs. By setting a baseline—the cost of 5.6 mm wire mesh per m², labeled “X”—it creates a standard unit cost against which all other support elements can be compared.

Table I. Cost Reference Based on Ground Support Element

Ground support element	Forecasted unit cost (Materials + Installation)	Cost variable
Bolting (Threadbar/Resin, MDX, Cable, D-Bolt)	Average cost for new and rehabilitation per bolt m	Table II
Fiber shotcrete 50 mm–75 mm	Total cost per m	48.3 X
Fiber shotcrete 100 mm–150 mm	Total cost per m	68.0 X
Wire mesh 5.6 mm	Cost per m2	1 X
Wire mesh 8.00 mm	Cost per m2	1.2 X
Steel sets	Cost per sets with current sets using 250 UC	223.2 X

Table II. Cost Reference for Bolting

Total bolt unit cost (Material + Installation)
Length (m)	Split set	MDX	Resin bars	Cable bolt
2.25	N/A	N/A	8.75 X	N/A
2.40	1.39 X	14.49 X	N/A	N/A
3.00	1.66 X	15.55 X	11.66 X	N/A
4.00	N/A	N/A	15.55 X	11.77 X
5.00	N/A	N/A	N/A	14.71 X
6.00	N/A	N/A	N/A	17.66 X
7.00	N/A	N/A	N/A	20.60 X
8.00	N/A	N/A	N/A	23.54
9.00	N/A	N/A	N/A	26.48
10.00	N/A	N/A	N/A	29.43

Conducting a Cost-Benefit Analysis (CBA) for evaluating the economic consequences of different ground support approaches in the critical mine infrastructure Tunnel project involves a detailed quantitative assessment of various financial factors. This analysis is crucial for determining the most economically viable ground support method. To form a robust foundation for the Cost-Benefit Analysis (CBA) concerning the Tunnel’s ground support, a meticulous data collection method for the financial aspects has been established. This approach focuses on collating comprehensive cost details and anticipated benefits, enabling an informed evaluation of the investment’s feasibility. as outlined in Fig. 7.

Fig. 7. CBA flowchart.

The AHP further refines the decision-making process by systematically ranking the various factors influencing ground support strategy. This process, visualized in Fig. 8, breaks down complex decisions into a hierarchy of simpler comparisons, facilitating clear, rational choices based on comprehensive criteria. Through the combination of these analytical methods, the study aims to formulate a ground support strategy that is not only technically sound and financially prudent but also sustainable over the long term.

Fig. 8. AHP flowchart.

The integration of these methods into a coherent analytical process ensures that the final recommendations for the Tunnel project are well-founded, robust, and aligned with strategic objectives.

Results

Ground Support Alternatives

Understanding the depth and complexity involved in guaranteeing the stability and efficiency of the tunnel is crucial as we set out on a thorough investigation of the tunnel project. This is a complex project that requires a variety of approaches and analyses, all of which are important for gaining a comprehensive grasp of and implementing the required ground support systems strategically. Each phase is vital in identifying the best course of action, from assessing the geological conditions with the Q system as part of the information to consulting experts using the Delphi technique and employing Cost-Benefit Analysis to balance technical requirements with financial viability. By balancing multiple aspects, the Analytic Hierarchy Process selects the best ground support method, further refining these judgments. Our journey through this research exposes the critical thought and planning needed for such a large-scale infrastructure project, in addition to the technical aspects. In order to provide a complete picture of the ground support plan for the Tunnel, let’s go into the in-depth analysis and reveal the subtleties of each method and choice.

The Q-system classifies the ground conditions within the Tunnel, indicating areas that require robust support due to “very poor to fair” ground conditions. Uniform support recommendations streamline the stabilization process (Fig. 9). Critical back wedge capacity checks ensure the support can handle expected loads, maintaining tunnel integrity. A combined strategy accommodating different ground conditions is suggested, aligning with the required Factor of Safety (FoS) (Table III).

Fig. 9. Evolution of consensus for each factor over the course of three survey rounds in the Delphi process.

Table III. Ground Support Design Based on Q-System

Rock mass classification	Ground support design
Very poor Q < 0.4	Shotcrete >15 cm
	Double layer shotcrete arches
	Bolt; 2.6 m length and 1.3 m–1.5 m spacing
Poor–Poor 0.4 < Q < 1	Shotcrete 12 cm–15 cm
	Single layer shotcrete arches
	Bolt; 2.6 m length and 1.5 m–1.7 m spacing
	Shotcrete 9 cm–12 cm
Poor–Fair 1 < Q < 4	Bolt; 2.6 m length and 1.7 m–2.1 m spacing
	Shotcrete 6 cm–9 cm
Fair–Good 4 < Q < 10	Bolt; 2.6 m length and 2.1 m–2.3 m spacing
	Bolt; 2.6 m length and 1.6 m–2.0 m spacing (without shotcrete)

In practical application, the ground support design for the tunnel must be adaptable to specific tunnel sections and material availability. Compliance with the required Factor of Safety (FoS) is essential to ensure the support system can handle the geological loads and uncertainties. As presented in Table IV, the ground support types A, B, C, and D are categorized based on Q-system classifications of rock mass quality: Very Poor (Q < 0.4), Very Poor-Poor (0.4 < Q < 1), Poor (1 < Q < 4), and Fair-Good (Q > 4). This classification guides the selection of support systems, ensuring safety and stability in varying ground conditions. The Q system is a widely used rock mass classification system developed by Bartonet al.(1974) and updated by NGI.

Table IV. Ground Support Type Based on Q-System

Q	Class	Ground support Type A		Ground support Type B		Ground support Type C		Ground support Type D
		GS element	FoS	GS element	FoS	GS element	FoS	GS element	FoS
Q < 0.4	Very poor	Steel Sets with spacing 1.5 m	>3.0	Steel Sets with spacing 1.5 m	>3.0	Shotcrete > 15 cmDouble layer shotcrete archesBolt; 3.0 m length and 1.3 m spacing + WM	>1.8	Shotcrete > 15 cmDouble layer shotcrete archesBolt; 3.0 m length and 1.3 m spacing + WM	>1.8
0.4 < Q < 1	Very Poor-Poor	Steel Sets with spacing 1.5 m	>3.0	Shotcrete 12 cm–15 cmSingle layer shotcrete archesBolt; 3.0 m length and 1.3 m spacing + WM	>1.7	Steel Sets with spacing 1.5 m	>3.0	Shotcrete 12 cm–15 cmSingle layer shotcrete archesBolt; 3.0 m length and 1.3 m spacing + WM	>1.7
1 < Q < 4	Poor	Shotcrete 9 cm–12 cmBolt; 3.0 m length and 2.0 m spacing + WM	>1.5	Shotcrete 9 cm–12 cmBolt; 3.0 m length and 2.0 m spacing + WM	>1.5	Shotcrete 9 cm–12 cmBolt; 3.0 m length and 2.0 m spacing + WM	>1.5	Shotcrete 9 cm–12 cmBolt; 3.0 m length and 2.0 m spacing + WM	>1.5
Q > 4	Fair-Good	Shotcrete 6 cm–9 cmBolt; 3.0 m length and 2.3 m spacing + WM	>1.5	Bolt; 3.0 m length and 1.5 m spacing + WM	>1.5	Shotcrete 6 cm–9 cmBolt; 3.0 m length and 2.3 m spacing + WM	>1.5	Bolt; 3.0 m length and 1.5 m spacing + WM	>1.5

Delphi Approach

The Delphi method has been used to consolidate expert opinions on this Tunnel project. Through iterative rounds of surveys, experts have refined their consensus, contributing to a strategic planning process that accommodates geological, technical, and operational factors. The convergence of expert agreement across rounds indicates a reliable decision-making process. The evolution of consensus for each factor over the course of three survey rounds in the Delphi process is provided in Fig. 9.

Cost Benefit Analysis

For the Critical Mine Infrastructure Tunnel project, the cost-benefit analysis (CBA) acts as a financial compass, directing decision-makers toward the most economically sensible ground support options. The comprehensive benefit and cost analysis (CBA) methodically lists and weighs the advantages and disadvantages of each possible solution. Paraskevopoulouet al.(2022), this gives a quantitative basis on which the project’s economic viability may be determined. A careful trade-off is made between the immediate and continuous financial costs and the longer-term, more comprehensive advantages, including improved safety protocols, uninterrupted operations, and environmentally friendly practices. This analytical procedure is essential to guarantee that the infrastructure expenditures made in the tunnel are not only warranted but also complement the project’s strategic goals and yield the greatest possible return on investment during the project’s lifetime.

Table V provides a comprehensive financial breakdown and helps evaluate the economic impact of each system by providing precise cost-per-meter information for each type of ground support. Table VI provides an overview of the advantages of each form of ground support, including safety, operational efficiency, and sustainability. This completes the detailed cost-benefit analysis of the ground support systems of the Tunnel.

Table V. Cost per M for Each Ground Support Type

Ground support type	Old tunnel		New tunnel		Combine
	Total cost (X)	Cost/m (X)	Total cost (X)	Cost/m (X)	Total cost (X)	Cost/m (X)
Type A	116,890.1	263.9	668,353.8	500.4	785,243.9	764.2
Type B	68,046.4	153.6	324,544.1	243.0	392,590.5	396.6
Type C	121,929.5	275.2	471,461.4	353.0	593,390.9	628.2
Type D	68,046.4	153.6	277,742.1	207.9	345,788.5	361.5

Table VI. Benefit Consideration of Each Type of Ground Support

Ground support type	Safety improvements	Operational continuity	Sustainability
Type A	The higher FoS on each ground support element according to ground Class. Expected to be no failure.	Maximizes uptime and reduces the risk of costly operational halts; ensures consistent economic output from tunnel operations.	Long-term durability reduces the need for frequent repairs or replacements; potential for using environmentally friendly materials.
Type B	Moderate improvement in safety due to sturdy construction; lowers the chance of minor incidents.	Sufficiently reliable to maintain regular operations with minimal interruptions.	Designed with recyclable materials or methods that minimize environmental impact.
Type C	Combined ground support element to get higher FoS from the limit. Makes it is stable on each ground class.	High-quality construction likely to prevent significant operational disruptions.	incorporates innovative, long-lasting materials.
Type D	Basic safety features that meet standard requirements.	Stable enough to ensure regular operations but may require occasional maintenance.	Utilizes traditional materials with known longevity.

Analytic Hierarchy Process

For a critical Mine Infrastructure Tunnel project, the Analytic Hierarchy Process (AHP) is a strategic technique that is used during the decision-making process, particularly when choosing the best ground support system. This systematic process decomposes the difficult choice into a hierarchical framework that includes a number of criteria and sub-criteria. These consist of operational effectiveness, safety, economic viability, and technical feasibility. The ground support options are thoroughly examined and ranked using Analytic Hierarchy Process (AHP), which offers a lucid and organized framework to direct the decision procedure.

Table VII represents a structured framework for evaluating and prioritizing various aspects critical to the project’s success. It breaks down the decision-making process into a hierarchical format, comprising different levels of criteria and sub-criteria, each with its assigned weight and global priority.

Table VII. Decision Hierarchy

Level 0	Level 1	Weight	Level 2	Weight	Glb Prio.	Type A	Type B	Type C	Type D
Optimize ground support system	Technical feasibility	0.226	Geotechnical adequacy	0.484	10.90%	0.363	0.326	0.163	0.148
			Flexibility and adaptability	0.187	4.20%	0.096	0.146	0.391	0.367
			Expert consensus	0.329	7.40%	0.124	0.141	0.321	0.415
	Economic viability	0.159	Initial cost	0.255	4.10%	0.094	0.134	0.358	0.414
			Maintenance cost	0.142	2.30%	0.356	0.326	0.194	0.124
			Cost-efficiency	0.603	9.60%	0.078	0.125	0.306	0.492
	Safety and stability	0.510	Factor of safety	0.503	25.70%	0.33	0.33	0.2	0.14
			Risk of failure	0.279	14.20%	0.128	0.142	0.348	0.383
			Durability	0.218	11.10%	0.363	0.326	0.163	0.148
	Operational effectiveness	0.104	Installation time	0.225	2.30%	0.128	0.158	0.295	0.419
			Ease of implementation	0.227	2.40%	0.363	0.326	0.163	0.148
			Operational disturbance	0.548	5.70%	0.076	0.127	0.384	0.414
Total					100%	23.20%	23.70%	25.80%	27.30%

During this procedure, Types C and D have been determined to be especially advantageous possibilities. Their ability to strike a balance between cost-effectiveness and operational efficiency makes them stand out and fits in nicely with the project’s overall objectives. The Analytic Hierarchy Process (AHP) not only streamlines the process of comparing various ground support technologies but also incorporates a wide range of considerations into the decision-making process. This guarantees a thorough and balanced assessment that considers all factors that are essential to the tunnel project’s sustainability and success.

Based on the AHP analysis, Types C and D have emerged as the leading alternatives, with global priority scores of 25.8% and 27.3%, respectively. These scores suggest that these two types of ground support systems align closely with the project’s objectives, particularly the emphasis on cost-effectiveness and operational efficiency.

Discussions

The decision-making process favors Types C and D ground support based on the Analytic Hierarchy Process (AHP) outcomes and project priorities. Type C is recognized for adaptability, and Type D for its cost-effective suitability for budget-limited sections. The emphasis on the ‘Factor of Safety’ in line with company and government regulations underpins this choice, advocating a conservative approach to tunnel support. Literature on infrastructure projects supports this strategy, stressing the importance of lifecycle costs over initial expenditures. The methods align with best practices and are backed by research suggesting their effectiveness in operational efficiency. However, the application of these methods requires expert validation to tailor them to the tunnel’s unique challenges, with ongoing monitoring for safety and operational excellence.

Based on Company and government regulation regarding Factor of Safety standard on tunnel safety and stability, emphasizes the importance of the ‘Factor of Safety’ and robustness against failure, which supports the prioritization of these factors in the AHP analysis. Also, the design guidelines for steel arch support, which suggest a factor of safety in the range of 1.7-1.8, indicate a cautious and conservative approach to tunnel support (Mitri & Khan, 1991), affirming the importance given to safety and stability in the AHP analysis.

The selection of efficient tunnel support methods requires the consideration of both technical and non-technical factors, which is a recurrent theme in the literature on infrastructure projects. The focus on lifecycle costs, rather than just initial expenses, underpins the prioritization of cost-effectiveness in the evaluation process (Tomaet al., n.d.).

The preference for Types C and D ground support systems, based on AHP analysis and informed by best practices such as the Wienerwald tunnel and the Gotthard tunnel and research from Chalmers University (Marklund, 2022), indicates that these methods are well-suited to the project’s goals, especially concerning cost-effectiveness and operational efficiency. The literature supports the use of such methods, with the understanding that these choices should be validated by additional expert opinions to ensure they provide the best fit for the unique challenges of the crucial mining infrastructure Tunnel project.

Conclusion and Recommendation

The Analytic Hierarchy Process (AHP) provided a structured framework for decision-making regarding the Tunnel’s ground support system, leading to the identification of Types C and D as suitable ground support systems. Type D emerged as the preferable choice with a 27.3% global priority score, aligning with the project’s focus on cost-effectiveness and operational efficiency (Fig. 10). This preference is supported by its economic advantages and balance between cost savings and functional performance. The iterative consensus-building process of the Delphi method validated the selection of Type D, leveraging collective expertise to inform the decision-making process. Cost-Benefit Analysis (CBA) further complemented the AHP and Delphi method findings, showing that Type D’s financial benefits, such as lower initial and maintenance costs, outweighed its expenses more significantly than other types. The decision to select Type D addressed technical challenges, economic implications, and long-term needs. Continuous monitoring of geotechnical conditions, rigorous testing of the support system’s resilience, and maintaining a contingency plan are crucial. The economic advantages of Type D include cost-effectiveness, affordability, and minimal operational disruptions. For long-term needs, Type D is expected to ensure tunnel safety and operational efficiency, aligning with sustainable mining practices.

Fig. 10. Business solution result.

The strategies developed for the Critical Mine Infrastructure Tunnel project offer comprehensive recommendations applicable to various engineering and construction initiatives. These strategies emphasize the importance of expert validation and advisory, flexible and detailed planning, strategic procurement, effective installation and monitoring, and post-installation monitoring and maintenance. Additionally, comprehensive risk management, workforce training and safety culture, financial oversight and cost efficiency, stakeholder communication, and documentation and knowledge management are critical. These strategies form a scalable and adaptable framework for various projects, with room for future enhancements to incorporate environmental and social considerations more comprehensively. The limitation of the study lies in its potential shortfall in capturing all stakeholder viewpoints, suggesting the need for inclusive engagement processes in future projects. Integrating continuous stakeholder engagement will enhance the overall effectiveness and acceptability of projects like a critical mine infrastructure Tunnel, making the framework robust and responsive to diverse stakeholder interests in engineering and construction projects.

For future directions, the research on the Critical Underground Mine Infrastructure Tunnel indicates a need to expand beyond technical and managerial aspects, incorporating environmental and social considerations into mining practices. This holistic approach would address broader sustainability concerns, enhancing the project's impact. The study also highlights the importance of inclusive stakeholder engagement. Future projects should focus on capturing diverse viewpoints, ensuring that a wide range of interests and concerns are addressed. This inclusive approach will enhance the overall effectiveness, acceptability, and sustainability of such infrastructure projects, making them more robust and responsive to dynamic stakeholder interests in the field of engineering and construction.