Restoration of the Nanjing Circumvallation in Sustainable Urban Planning: Application of Environmental Ethical Decision-Making Model

Abstract

The Nanjing Circumvallation has been severely damaged due to natural factors, human interference, and urban expansion. Restoring this edifice serves not only as a preservation of historikcal and cultural values, but also as an advancement towards sustainable urban development. This research proposes an environmental ethical decision-making model (EEDM) grounded in sustainable urban development indicators. The model is then applied to the restoration of the Nanjing Circumvallation. Based on feedback from the research trial section, the renovation of the Circumvallation trial segment, guided by the EEDM, effectively embodies the core principles of sustainable urban development. By extending this model to the entire restoration project, it is feasible to achieve a harmonious balance between heritage preservation and urban sustainability. This methodology offers a novel framework for the restoration of similar heritage sites, ensuring the concurrent achievement of conservation and sustainable development goals. Furthermore, this approach holds considerable promise for fostering sustainable urban progression.

1. Introduction

Circumvallation, a prominent military and civil structure in ancient times, offers insights into historical production and lifestyles due to its enduring construction. These structures can be categorized into two main types: ordinary and fortified. The ordinary ones are static, primarily designed for defensive purposes with a simple configuration. In contrast, fortified versions encompass sophisticated elements such as water gates, moats, city gates, and barbicans, forming a complete urban defense system. Historically, these fortified structures safeguarded cities. Currently, they function as channels for historical and cultural interactions, bolstering tourism economies. The Nanjing Circumvallation stands as a prime example of ancient, fortified architecture in China. Built between A.D. 1366 and A.D. 1393 during the Ming Dynasty, this impressive structure is one of the best-preserved antiquities in China [1]. Constructed primarily from durable bricks and stones, the fortification showcases exceptional physical properties such as density, hardness, and resilience. Intriguingly, many of its bricks bear engraved texts and patterns, enhancing its distinctive worth. However, modern activities threaten such monumental sites. Addressing the challenge of mitigating these adverse effects and guaranteeing the appropriate conservation and usage of these historical resources has emerged as an urgent public issue.

The preservation of historical sites signifies a dedication to safeguarding cultural assets and a strategic investment in urban sustainable development. Sustainability is defined as the capacity to address present needs without hindering future generations from fulfilling theirs. As urbanization advances, pursuing sustainability has emerged as a primary objective at the city scale [2,3]. Sustainable urban development ensures the fulfillment of current residents’ fundamental needs without jeopardizing the needs of future generations. Initiated in 1991, the Sustainable City Program (SCP) by the United Nations Human Settlements Programme and the Department of Environmental Planning set a novel direction for urban evolution. In light of this, researchers have investigated the features of New Urbanism and its convergence with sustainability. While New Urbanism provides a pathway to achieve sustainable urban development, it occasionally diverges from practical sustainability principles [4,5]. In Williams’ study, he highlighted diverse strategies for sustainable urban development and identified the associated challenges [6]. Sustainable development has significantly influenced urban planning policies in numerous countries and regions, as highlighted by Rydin [7]. Subsequently, researchers examined the relationship between urban and rural areas to assess its influence on sustainable urban development. According to Xue et al., considering the city as a combination of urban and rural characteristics improves urban sustainability [8]. Furthermore, researchers have proposed specific strategies. Peter and Yang believed that integrating master planning with diverse facets of urban development can foster sustainable urban growth [9]. The Nanjing Circumvallation serves as a prominent marker of the city’s cultural and historical heritage, offering unique opportunities for sustainable development. Therefore, it is imperative to safeguard this ancient fortress as a crucial aspect of sustainable urban development planning.

Since the 20th century, the Nanjing Circumvallation has undergone continuous maintenance and preservation. To preserve the authenticity and durability of this cultural monument, the government has initiated various renovation endeavors, such as masonry restoration and structural fortification. Nevertheless, China grapples with significant obstacles in historical heritage preservation. The historic integrity of certain old cities has been affected due to economic-driven changes [10,11]. The restoration of these historic defenses has garnered considerable focus. Challenges encompass preserving historical monuments and facilitating their harmonious integration into contemporary urban environments [12,13]. For instance, despite the efforts to restore the old town of Pingyao, there are still certain areas of its construction that are at risk of collapsing [14]. To address these issues, the researcher adopted the Microbially Induced Carbonate Precipitation (MICP) technique to mend fractures, demonstrating its efficacy [15]. These accomplishments suggest a possible change in restoration approaches, highlighting the significance of technological progress. Heritage preservation encounters governance and institutional challenges both domestically and internationally [16]. It is imperative for developing nations to prioritize the safeguarding of traditional craft heritage [17]. These findings indicate that incorporating sustainable urban development concepts is crucial to effectively conserve and utilize cultural heritage [18,19], both domestically and internationally, to achieve sustainable urban growth.

Sustainable urban development strategies have been effectively implemented in domains such as infrastructure development, public transportation design, and green building construction [9,20,21,22]. Nevertheless, their integration into historical preservation, namely in the protection and revival of historic city fortifications, is still restricted. This study investigates the implementation of sustainable urban development concepts in preserving and rehabilitating these historic structures, with a specific focus on the Nanjing Circumvallation as a case study. This presentation provides a comprehensive analysis of the restoration methods, materials, implementation, and results of a particular section of the rehabilitation project. This investigation underscores the significance of sustainable urban development strategies in maintaining the historical and cultural essence of such ancient fortifications and establishes their practicality for such restorations. In conclusion, this study validates the potential and importance of leveraging sustainable urban development principles in heritage conservation, introducing a novel research approach to the domain. This research methodology seeks to investigate the practical implementation of sustainable urban development principles in the context of urban conservation and building, with a specific focus on the preservation of the Nanjing Circumvallation. The methodology incorporates six essential components of sustainable urban development: cultural preservation, social harmony, resource conservation, infrastructure development, economic growth, and environmental safeguarding. Additionally, it evaluates three critical urban development indicators: economic, social, and environmental sustainability. To comprehensively examine these aspects, an EEDM was developed, in accordance with sustainable urban development indicators. This model functions as a comprehensive structure to address the ethical considerations related to environmental aspects in the context of urban growth and the preservation of cultural heritage. The process comprises six stages: collection of environmental data, stakeholder engagement, application of environmental ethical principles, evaluation and selection of EEDM, implementation and monitoring, and result evaluation and feedback. By employing this model, the project offers a comprehensive guide for the restoration of the Nanjing Circumvallation, facilitating its integration into modern urban development and achieving a harmonious equilibrium between the preservation of cultural heritage and the advancement of urban development. Moreover, this methodology presents a replicable model for sustainable development applicable to other cities, worldwide. It enables researchers to enhance their comprehension of the economic, social, and environmental dynamics in urban development.

2. Research Subjects and Methods

2.1. Engineering Background

The Nanjing Circumvallation, constructed during the Ming Dynasty, comprises four distinct sections: the Royal Palace, the Imperia, the Metropolitan, and the Outer defensive walls [23]. Noteworthy is the fact that Nanjing is the only city, globally, to exhibit all four categories of these defensive structures preserved [24]. However, some negative factors such as natural erosion and inadequate conservation practices have led to its significant deterioration. Taking the section of the Circumvallation from Dongshuiguan to Wudingmen as an example, researchers have conducted multiple field investigations on this section. The schematic diagram of this section is shown in Figure 1.

Field inspections have enabled researchers to collect pertinent data on the damage sustained by these historical walls. This data encompasses an assessment of the structure physical integrity, the damage scope, and the adjacent environment characteristics. Detailed findings are provided below:

• The surface on the Circumvallation has subsided and deformed. Researchers measured the elevation of this section revetment surface. The results indicate that the revetment along the entire length of this section still shows noticeable subsidence, with the maximum subsidence amounting to 56 mm.
• The structure of the Circumvallation is swollen and deformed. This section of the fortification exhibits obvious swelling deformation, as shown in Figure 2. Figure 2a displays the inner side between markers 0 and 2, revealing a bulging deformation spanning approximately 46 m in length and covering the full height of the structure. Conversely, Figure 2b presents a segment of the outer side between markers 1 and 2, with a bulging deformation approximately 2 m in length and 9 m in height.

3.

The cracks are splitting. The upper surface of the Circumvallation exhibits fractures in bricks, detachment of mortar joints, and cracks in both parapets and battlements, as delineated in Figure 3 (with crack extents indicated). Typically, crack widths range from 1.5 mm to 2.0 mm and occur in both vertical and diagonal orientations.

4.

The drainage system of the Circumvallation exhibits notable deficiencies. This extensive damage undermines the structural integrity, posing a significant risk to its long-term stability. An on-site assessment revealed blockages and deterioration in the drainage channels, resulting in reduced drainage capacity. Consequently, rainwater accumulates on the structure surface, elevating the structure humidity and hastening the corrosion of its brick and stone materials.

A detailed restoration approach has been developed to address the problems in this part of the wall. This strategy encompasses deconstructing and reconstructing the wall extended segments, mending the mortar joint fissures in the lateral walls, and preserving the drainage infrastructure. A critical component of this plan is the real-time surveillance of the wall structural alterations to guarantee safety throughout the restoration. The overarching objective is to restore the structural soundness and safeguard its historical significance, thereby contributing to the city sustainable evolution.

2.2. Method

2.2.1. The Concept of Sustainable Urban Development

The “Sustainable Urban Development Program”, initially proposed by the United Nations Centre for Human Settlements and the Environment Planning Agency, primarily focused on ecological concerns. This concept has undergone development since its inception, with a significant milestone reached with the 1994 “Aalborg Action Plan”, introduced at the Sustainable Cities Conference in Europe. The plan emphasized the significance of green urbanism, ecological communities, and pedestrian-friendly urban centers, offering a framework for cities worldwide [6,25,26]. The principles of this initiative received widespread acceptance during the 1992 United Nations Conference on Environment and Development in Rio de Janeiro [27]. Rivero Moreno’s analysis of European historic cities underscored the role of cultural heritage in fostering adaptable and democratic urban development [28]. He presented cities as hubs for both tangible and intangible cultural and creative exchanges. Al Ani highlighted the sustainability of cultural heritage, using the Erbil Citadel in Iraq as an illustrative example to demonstrate its significance in promoting sustainable urban development [29]. Bogdan concentrated his efforts on the medieval city of Brașov, Romania, proposing a blend of heritage conservation and restoration practices with heritage planning [30]. This approach emphasized the integration of conservation techniques with urban planning. Stefanović, in the context of Serbia, discussed the crucial impact of spatial and urban planning on sustainable development and the preservation of cultural heritage [31]. He argued that the current approach to cultural heritage conservation is still incomplete and lacks appropriate integration with landscape planning and conservation plans. Al-Alawi examined the interplay between the development of small- and medium-sized cities and cultural heritage knowledge. He emphasized the protection of architectural heritage through regional and local cooperation, particularly in the German–Polish border area.

Figure 4 depicts the chronological development of sustainable urban development, highlighting significant milestones and improvements throughout its history. The flowchart demonstrates that the notion goes beyond simple environmental protection and includes a comprehensive and diverse approach. By employing case studies, this research showcases the ways in which different regions and cities successfully combine sustainable economic and social development with the preservation of cultural heritage. The concept of urban sustainable development has undergone significant global evolution, transitioning from a focus on environmental protection to the implementation of the Aalborg Action Plan. Practices across various countries have highlighted the profound impact of this evolving concept.

The concept of sustainable urban development has gained significant traction, encompassing six fundamental dimensions: cultural preservation, social harmony, resource conservation, infrastructure development, economic growth, and environmental safeguarding. Globally, cities are integrating this paradigm into their developmental agendas. For instance, Copenhagen has transitioned to renewable energy sources, emphasizing wind power and bolstering public transport [32,33,34,35]. Vilnius has been examining the enduring effects of creative industries on its urban economy, integrating this inquiry into its sustainable urban development strategy [36]. This approach has also been effectively employed in melding historical heritage conservation with contemporary urban landscapes. For example, on the Strait of Messina coastline (Italy), sustainable regional development is being fostered through the adaptive reuse of historical fortresses, steered by an exhaustive evaluation framework for cultural heritage advancement [37]. Undeniably, the evolution of sustainable urban development strategies has led to the emergence of more environmentally friendly, healthier, and increasingly habitable models for forthcoming urban landscapes.

2.2.2. An Environmental Ethical Decision-Making Model Constructed on the Basis of Sustainable Urban Development Indicators

The Nanjing municipal government devoted significant efforts to address the challenge of preserving Nanjing Circumvallation amidst modern urban development. Nevertheless, this undertaking brought attention to a clash between the preservation of historical elements and the current requirements of urban development. The critical question arises: how might the historic city wall be incorporated into the contemporary urban framework? How can we achieve a harmonious compromise between the conservation of the city wall and the requirements of contemporary urban development? These issues necessitate us to surpass conventional development notions and embrace the notion of sustainable urban development. This concept must encompass environmental, cultural, social, and economic dimensions. Central to this concept, as Molina emphasizes, is a multifaceted focus on sustainability, transcending mere environmental protection to include cultural conservation, social harmony, and efficient resource utilization [38]. Guzman’s research exemplifies this, employing a mixed methodology to identify key urban development indicators crucial for world heritage city preservation. Similarly [39]. Bănică’s analysis of Târgu Ocna town in Romania discusses specific sustainable urban development indicators [40]. Bakier’s empirical studies on international institutions and organizations contribute a set of tailored indicators for urban development [41]. Pupphachai underscores the significance of these sustainability indicators in facilitating adaptive governance in urban development [42]. Kou’s sustainability assessment model, encompassing heritage preservation, stakeholder involvement, economic growth, and planning and governance, is particularly instructive [43]. This model features twelve primary indicators and twenty-seven subsidiary ones. Utilizing the amalgamation of these works and notions, the study suggests the subsequent indicators of sustainable urban development. First, economic sustainability indicators: this indicator seeks to achieve a harmonious equilibrium between the conservation of historical and cultural heritage and the promotion of economic development. The stipulation emphasizes that economic development policies should not only prioritize the speed and scale of growth, but it should also guarantee the adequate protection and transmission of historical and cultural heritage. Second, social sustainability indicators: this indicator focuses on the involvement of individuals in society and the fair distribution of resources, emphasizing inclusivity and fairness in the process of urban development. It guarantees that all inhabitants benefit from urban development and participate in decision-making processes related to planning. Third, environmental sustainability indicators: this indicator assesses the correlation between the conservation of city walls and the promotion of environmental sustainability, investigating methods of integration. The scope of the study includes an assessment of the sustainability of city wall restoration, integration of environmental protection measures in urban planning, and optimization of energy use. These indicators provide a structure to promote sustainable urban growth, emphasizing the importance of city walls in the economic, social, and environmental dimensions.

This research introduces an EEDM informed by sustainable urban development indicators. Comprising six components (Figure 5), the model aligns with and extends previous research in the field. Notably, Bibri’s comprehensive model, derived from empirical studies on strategic sustainable urban development, merges the ideas of ecological and data-driven smart cities [44]. This enhances the applicability and relevance of our model. Additionally, Zhang et al. developed a hierarchical model to delineate urban personality traits, facilitating the comparison of sustainable development approaches in various Chinese cities [45]. This model enriches our environmental ethics decision-making framework by offering macro-level insights into urban sustainability evaluation. Complementing this, Shao’s system evaluates the sustainable environmental quality of Chinese cities using six dimensions and 29 criteria [46]. These elements, when integrated into our model, provide specific assessment indicators and methodologies for informed decision-making. Moreover, Moroke’s Successful Neighborhood Model assesses neighborhood sustainability, offering a micro-level perspective to our EEDM [47]. Furthermore, Hoefle et al. incorporates the principles of radical ecology and political ecology, analyzing the interplay between the environment, agriculture, and cultural landscapes [48]. This interdisciplinary approach broadens our understanding of urban sustainability and underpins comprehensive decision-making processes. Upon integration of these discoveries, the EEDM proposed in this study constitutes a multifaceted and all-encompassing model. The main objective is to enhance our understanding of and promote the sustainable growth of urban areas.

• Collection of environmental data. This process entails the aggregation of quantitative data related to urban environments using sustainable urban development indicators. Such data serve as the bedrock for the environmental ethics decision-making model, providing a distinct viewpoint on the city environmental condition and supplying tangible proof for decision-making.
• Stakeholder engagement. Stakeholders, including individuals, groups, or organizations impacted by or interested in environmental decisions, play a pivotal role. Sustainable urban development indicators capture data from both the social and the economic dimensions directly related to these stakeholders. Their perspectives and requirements are paramount in the ethical decision-making process.
• Application of environmental ethical principles. Sustainable urban development indicators are rooted in critical environmental ethical principles, namely environmental justice, sustainability, precaution, and humility. Environmental justice focuses on safeguarding vulnerable communities, ensuring equity in environmental decisions. The principle of sustainability prioritizes long-term environmental impact assessments and promotes the judicious use of resources to benefit both current and future generations. By emphasizing preventive actions, the precautionary principle aims to mitigate environmental risks and ambiguities. Finally, the humility principle underscores the symbiotic relationship between humans and the environment. Integrating these principles into decision-making models fosters ethically robust choices when balancing diverse factors.
• Evaluation and selection of environmental ethical decision-making. It is imperative for decision-makers to evaluate the ecological consequences, hazards, and advantages of different alternatives [49,50,51,52,53]. Sustainable urban development indicators offer measurable criteria to contrast these options.
• Implementation and monitoring. An effective implementation plan is essential. Decision-makers must monitor and appraise the unfolding process. Sustainable urban development indicators not only guide decisions, but also gauge the efficacy of implementations and ensure the objectives of environmental ethics are met. Continuous monitoring is vital to ascertain the sustainability of the chosen approach.
• Results and feedback. Decision-makers must assess the impacts of their decisions and collect feedback for refinement. Indicators for sustainable urban development offer an objective framework to evaluate these impacts. Comparing outcomes with these indicators facilitates ongoing enhancement of environmentally ethical decision-making models.

2.3. Restoration Project

The segment of the Nanjing Circumvallation between Dongshuiguan and Wudingmen has exhibited disruptions and fissures in its upper reinforced concrete waterproof layer, attributed to natural erosion and inadequate maintenance. Certain sections have displayed indications of expansion and fracturing, introducing potential hazards to both the structure and adjacent transportation. Immediate maintenance and preservation measures are imperative. Restoration primarily focuses on prolonging the physical lifespan of a heritage object and safeguarding its historical significance, rather than simply duplicating its initial appearance. This process differs from reconstruction or maintenance, as it entails the creation of a new structure that is not identical but similar to the original, in cases when the original structure has been damaged or lost. Maintenance, in contrast, is a proactive procedure that involves routine examination, cleansing, and minor repairs.

The subsidence of the surface on the Circumvallation and the cracking issue of the rigid waterproof layer originate from the soaking of loess by rainwater during the process of backfilling with crushed stone soil. When loess encounters water, its strength markedly diminishes. The side of the structure, composed of block stones, strip stones, and bonding materials, exerts a retaining effect on the crushed stone soil. Consequently, in the immediate future, the seafloor subsidence and the waterproof layer cracks do not jeopardize the structural safety. However, substantial damage to the waterproof layer allows for persistent rainwater infiltration into the core, weakening its integrity and augmenting the lateral pressure on the side walls. Therefore, these disruptions significantly impact the safety, requiring proactive measures to mitigate the infiltration of precipitation and the deformation induced by soil subsidence. The primary objective of the renovation project is to substitute the compromised concrete waterproof layer with a resilient, eco-friendly, waterproof surface and explore sustainable repair solutions. For this purpose, super molecular polymers, renowned for their superior water absorption and adhesion, are integrated with lime and clay. This lime blend will be amalgamated with clay and positioned at the base of the waterproof layer, and also employed to mend the cracks in the surrounding structures.

3. Results and Discussion

3.1. The Conservation History of the Nanjing Circumvallation

Over the past thirty years, the Nanjing Circumvallation Administration has committed to extensive maintenance, successfully restoring the historical facade of the Nanjing Circumvallation and its adjoining moat. During this time, the introduction of “The Nanjing Circumvallation Protection Management Measures” and the receipt of the “Chinese Human Settlement Environment Exemplary Award” has underscored the commitment and accomplishments of the restoration initiative. In 2014, following its acknowledgment as a World Heritage Site, the Nanjing municipal government introduced stricter conservation standards. These policies precluded construction and development within the vicinity of the historical wall and its buffer zone, placed stringent limits on tourist numbers, and have been responsible for the enforcement of the “Protection Regulations of the Nanjing Circumvallation” since 2015. More recently, attention has turned toward the seamless integration of this vital cultural heritage with the urban development of contemporary cities. Consequently, the ongoing preservation and rehabilitation efforts for this ancient structure require a solid sociological approach.

3.2. Application of the Environmental Ethical Decision-Making Model

3.2.1. Environmental and Durability of Restoration Materials

Restoration materials containing organic polymers represent an emerging environmentally friendly material class. When these polymers are integrated with lime, they demonstrate pronounced film-forming capabilities, commendable water resistance, and elevated viscosity. In the present study, a controlled indoor assessment of durability post-immersion was undertaken. This investigation included three distinct binding materials: pure lime, silty clay combined with organic polymers, and lime combined with organic polymers. The organic polymers were incorporated at a concentration of 3% relative to the lime or powdery clay content. Bricks were bonded using these three different binders and subsequently submerged in water to evaluate the durability of each formulation.

Figure 6 illustrates the outcomes of each experimental condition after a 96 h immersion. The pure lime sample exhibited diminished bonding capability (Figure 6a). While the silty clay and organic polymer sample also showed reduced bonding, it retained its structural integrity (Figure 6b). The lime and organic polymer mixture retained its adhesive characteristics and exhibited noticeable tensile strength (Figure 6c).

To assess the robustness (strength index) of the specimen treated by organic polymers, this study evaluated the unconfined compressive strength and water stability of standard limed paste specimens. Cubic specimens of 70.7 mm side length were prepared using pure lime paste and a mixture of lime paste with organic polymers, as illustrated in Figure 7a. These specimens were cured under standardized conditions for 7 days, followed by an unconfined compressive strength test, presented in Figure 7b. Results indicated that the average strength of limed specimens is 415kPa, whereas for the limed specimens with polymers is 470 kPa. This suggests that the organic polymers enhance the compressive strength of limed specimens. After 60 days of water immersion and subsequent testing, the limed paste specimens were obviously damaged, resulting in loss of strength, as shown in Figure 7c. Conversely, the polymer-mixed specimen retained an average strength of 342 kPa. Despite a marked reduction from its initial strength, this value remains within the design specifications.

Based on the findings, organic polymer compounds effectively increased the strength and durability of limed specimens. The incorporation of these compounds not only diminishes lime consumption, but also markedly decreases the need for subsequent repairs post-renovation. Consequently, these repair materials exhibit commendable environmental and longevity attributes.

3.2.2. Ethical Assessment

The project highlighted the crucial function of the environmental ethics decision model in effectively balancing stakeholder interests and addressing ethical dilemmas during the restoration of the city wall. The model facilitated the involvement of all relevant stakeholders in the decision-making process. For example, in the Nanjing Circumvallation restoration, the local government represented economic and development interests, but grappled with budgetary constraints. Collaborating with the Cultural and Tourism Bureau, they secured subsidies from the National Cultural Heritage Administration, therefore alleviating budgetary constraints. At the oversight meeting, the cultural heritage department championed a limit on commercial activities, prioritizing the conservation of cultural integrity alongside economic pursuits. The Urban Planning Department places a high importance on the promotion of sustainable urban functionality and the preservation of cultural assets. In order to minimize the impact on inhabitants’ everyday routines, a phased building approach was implemented, guided by numerous on-site inspections. This strategy addresses potential disturbances, such as noise pollution and traffic congestion, which significantly impact local residents. The project team implemented comprehensive communication and coordination measures with the affected community in response to these challenges. These included arranging community gatherings, administering surveys, and distributing questionnaires to identify residents’ primary concerns. Following initial data collection, the team facilitated a series of community meetings for direct, face-to-face engagement with the residents. To ensure inclusive participation, the team disseminated notices about these meetings well in advance, targeting complete community awareness and involvement. Meeting venues, typically located in or near community centers, were strategically chosen for their accessibility. The scheduling of these meetings was deliberately planned to align with residents’ work schedules and lifestyle preferences, typically during evenings or weekends, maximizing potential attendance. During the discussion, the project team presented the construction plan and its anticipated effects, allowing ample time for locals to express their thoughts and ask questions. This strategy ensured the active involvement of every attendee. After the discussion, the team improved the construction plan by incorporating feedback to minimize disturbance and execute tactics to reduce noise. They chose to use environmentally sustainable materials and implement energy-efficient procedures in response to environmental concerns. The implementation of these measures showcased the team’s dedication to resolving community issues and guaranteeing the advancement of construction. In summary, the team followed the environmental ethical decision-making paradigm and placed importance on incorporating input from stakeholders. Efficient communication facilitated collaboration among citizens, government agencies, and organizations dedicated to the preservation of cultural assets.

The project team successfully integrated environmental ethics into their approach and techniques while reconstructing Nanjing Circumvallation. Strict adherence to the principles of environmental justice was of utmost importance. The team developed effective communication channels with the local community, placing a high priority on the well-being of residents in order to minimize the negative effects of construction. This method demonstrated a conscientious consideration and equitable weighing of many interests, exemplifying the principles of environmental justice. Following that, driven by the principle of sustainability, the team assessed and implemented materials and techniques that had little impact on the environment. The restoration project focused on prioritizing sustainable materials and practices, with the goal of minimizing energy use and waste. Simultaneously, they optimized the construction timeline to minimize inconvenience to the local community, showcasing a dedication to sustainable progress. In the first stages of the project, the team diligently adhered to the precautionary principle by completing a thorough risk assessment to identify and minimize any potential environmental risks. Emphasis was placed on safeguarding the surrounding ecosystem, particularly in preventing construction-related damage to local flora. Such foresight in planning effectively minimized initial risks. Furthermore, embodying the principle of humility, the team meticulously integrated local historical and cultural considerations into their choice of technologies and methods. They opted for a restoration approach that minimally altered the original structure of the ancient city walls, thereby preserving historical integrity. As the project progressed, a robust feedback mechanism was established, ensuring steadfast adherence to environmental ethics. This was exemplified by the creation of a trial section within the restoration process, which facilitated the ongoing evaluation and adaptation of practices based on real-time feedback, thereby reinforcing the commitment to environmental ethics.

Moreover, the project also exemplifies ethical considerations in various facets. Primarily, it encompasses the notion of social fairness. The project adhered to the environmental ethical decision-making paradigm, which considers the needs and rights of different stakeholders to ensure that its implementation does not harm any particular groups. Furthermore, the fundamental aspect of ethical behavior lies in the transparency of the decision-making process. The project employed the EEDM to ensure that the decision-making process incorporated the viewpoints of community members. This guarantees that the decision-making process is not only based on solid scientific principles, but also characterized by fairness and transparency. Finally, it is essential to strike a balance between economic factors and moral considerations. When choosing refurbishment materials and technology, we took into account both the cost-effectiveness and the long-term environmental impact. Not only does this have advantages in terms of efficient resource utilization, but it also conforms to ethical norms. By thoroughly examining these factors, we can effectively illustrate the significance of ethics in promoting sustainable urban development. This encompasses not only the utilization of ecologically sustainable materials and the involvement of diverse stakeholders, but also more profound deliberations in the societal, economic, and regulatory spheres.

3.2.3. Feedback of Test Section

Guided by an environmental ethics decision model, the project targeted specific structures for thorough experimentation and evaluation. A preliminary and thorough evaluation was conducted, specifically examining the visual elements of the trial piece of the city wall that had been reconstructed. The comparison investigation revealed that the refurbished part successfully preserved its historical and artistic integrity. The project also assessed the structural integrity of this part, determining that novel restoration procedures improved its resistance to environmental and human influences. Furthermore, the proposal guaranteed the seamless incorporation of the wall into its surroundings. The repaired part regained its historic attractiveness and stimulated educational and tourism development potential in Nanjing. The knowledge gained from these insights has been incorporated into the following stage of the restoration endeavor. The potential challenges identified in the experimental phase of the project have attracted attention from pertinent departments. This attention establishes a robust basis for the future development and sustainable management of the city wall. The project encompasses the incorporation of sensors to oversee the execution, accompanied by a meticulous strategy designed to synchronize with the building schedule. This plan covers critical phases from engineering analysis to project completion. Detailed workflows and contents for each stage are outlined in Figure 8. The objective of this thorough monitoring strategy is to guarantee the enduring protection and sustainable management of the cultural relics.

3.2.4. Result

The implementation of the EEDM in the Nanjing Circumvallation Restoration Project resulted in a set of tangible results. Firstly, the collection of environmental data. The collection of environmental data has provided accurate reference points for the project, improving the renovation and traditional restoration materials. Additionally, pre- and post-restoration environmental data collection confirmed the efficacy of novel materials and technologies. Investigations focused on organic polymer materials in the restoration field have identified these materials as an environmentally beneficial choice, distinguished by their capacity to resist corrosion and their commitment to environmental sustainability. Secondly, stakeholder engagement. The Nanjing Circumvallation rehabilitation project effectively achieved a balanced equilibrium among various interests through the utilization of an EEDM. The local government secured national fiscal subsidies by collaborating with the Cultural and Tourism Bureau, alleviating budgetary burdens. The Cultural Relics Protection Department’s proposal to restrict commercial activities near the ancient fortifications safeguarded cultural heritage integrity. The urban planning department’s implementation of a phased building method mitigated interruptions to the lives of residents. Crucially, the project team engaged with residents, addressing concerns through community meetings and surveys. Adjustments included the alteration of construction times and usage of eco-friendly materials. These measures minimized the influence on residents’ lives, promoting the project progress and fostering harmony within the community. Thirdly, application of environmental ethical principles. The concepts of environmental ethics have significantly influenced the project teams’ approach while dealing with restoration issues. Environmental justice ensures inclusivity by engaging the team in review meetings, community consultations, and surveys to take into account a wide range of interests. The precautionary principle aids in proactively identifying and mitigating potential risks. For instance, the project prioritized ecological preservation near the city historic boundaries during construction, successfully preventing damage to adjacent vegetation. The preservation of the historical integrity of these ancient structures with little damage is guided by humility in choosing restoration approaches. Finally, the sustainability concept forms the foundation of a more scientific approach to the restoration process. This is apparent through the use of effective scheduling, minimized resource inefficiency, and optimum time in construction. These efforts were implemented to mitigate the impact on the daily life of local populations. Fourthly, evaluation and selection of environmental ethical decision-making. Following a comprehensive assessment of several refurbishment procedures, the team opted for the most ecologically conscious alternative. This method entailed substituting traditional materials with more durable alternatives that align more closely with environmental preservation standards. Fifthly, implementation and monitoring. Throughout the monitoring phase of the test segment, the crew implemented careful structural surveillance by deploying embedded sensors. These sensors monitored enhancements in the structure capacity to endure compression, its longevity, and its eco-friendliness following restoration. This outcome validates the effectiveness of polymer absorbent resins in bolstering the structure durability against environmental elements. Sixthly, results and feedback. The evaluation of the examination portion of the urban fortification indicated that its renovation preserved its historical and artistic genuineness and enhanced its visual attractiveness, durability, and practicality. The assessment of visual aesthetics definitively verified the conservation of the historical core of the structure. The structural safety analysis showed improved stability due to the implementation of advanced technology. Furthermore, the functionality analysis highlighted the growing significance of the structure in the fields of education and tourism. Moreover, the comments collected identified precise locations that require enhancement in the restoration procedure. The feedback offered valuable insights to improve the decision-making model for environmental ethics.

3.3. Discussion Based on the Environmental Ethical Decision-Making Model

The successful implementation of this project underscores the critical role of the EEDM, particularly in addressing ethical challenges during the restoration of city walls. This approach facilitated effective solutions while ensuring comprehensive stakeholder engagement in the decision-making process. Consequently, it allowed for a balanced representation of diverse stakeholder concerns and perspectives, contributing to the project inclusiveness and fairness. The renovation of the Nanjing Circumvallation has effectively preserved its historical authenticity and charming simplicity. Moreover, the transformation of the wall into a key recreational site promoted social cohesion and stability. Additionally, effective management of construction waste was a significant achievement. The implementation of environmental ethical concepts within the project produced extraordinary outcomes. By adhering to the principle of environmental justice, the project promoted local community involvement and safeguarded their interests, strengthening community bonds and social acceptance. The sustainability principle guided a more scientific, reasonable, and environmentally friendly construction process. By applying the precautionary principle, we were able to anticipate and address potential environmental hazards, effectively protecting the surrounding natural ecosystem. Ultimately, implementing the humility principle showcased reverence towards the local culture and heritage, thereby augmenting the historical significance and worth of the restoration. Finally, guided by the EEDM, the project achieved successful construction in alignment with planned specifications and quality standards. This was facilitated by real-time monitoring through embedded sensors. The analysis of the monitoring data revealed that the inclusion of innovative materials improved the structural integrity and longevity of the wall, hence promoting resource conservation. Continuous monitoring throughout the construction process ensured accuracy and safety and facilitated the timely identification and resolution of potential issues. During the assessment and feedback phase, evaluations showed marked improvements in the renovated city wall, specifically in visual appeal, structural integrity, and functionality. These findings were instrumental in the ongoing refinement of the project and established a foundation for its sustainable management. In conclusion, the renovation of the Nanjing Circumvallation exemplified the principles of resource conservation, cultural preservation, social harmony, and environmental safeguarding under the EEDM. These principles are integral to sustainable urban development. The initiative not only conserved the historical culture but also significantly contributed to the advancement of contemporary urban development.

In addition to its prospective applications, the model may be utilized for sustainable development initiatives in contemporary cities. For instance, research by Alekseeva et al. examined the comprehensive impacts of urban greening, encompassing the ecological, social, and cultural dimensions [54]. This study examined existing methods for the evaluation of urban greening and assessed their effectiveness in practical situations. Utilizing the EEDN could ensure that urban greening initiatives realize maximal benefits across the ecological, social, and cultural domains. This comprehensive approach would lead to the creation of a healthier, sustainable, and more harmonious urban environment. In Spain, for instance, Arab–Muslim architecture possesses substantial historical significance. By employing advanced computer graphics, it is possible to digitally reconstruct buildings that have been previously destroyed [55]. This endeavor exemplifies the prowess of contemporary technology and emphasizes the importance of respecting and conserving historical and cultural legacies. Implementing the EEDM in such contexts can effectively safeguard historical and cultural assets. Guided by principles of environmental ethics, the model can steer heritage restoration efforts, promoting a balanced relationship between humanity and the natural world. Such a comprehensive decision-making strategy is instrumental in perpetuating Spain’s profound historical and cultural heritage. Hamurcu and colleagues developed a multi-criteria decision-making process to prioritize public transportation projects in Kırıkkale, a developing city [56]. Their approach included an EEDM, enhancing the multi-dimensionality of the evaluation. This guarantees that selected initiatives are not only financially viable, but also environmentally and socially sustainable. Culwic and team’s analysis of two Johannesburg housing projects in South Africa unveiled various motivations and logics influencing sustainable fairness [57]. Implementing an EEDM in this context has the potential to help integrate environmental ethical principles into decision-making, aligning sustainability with social justice. Gharehbaghi and colleagues investigated sustainable urban development strategies in Melbourne [58]. By utilizing the EEDM, they could analyze Melbourne’s urban development and transportation infrastructures, focusing on environmental data. This model aids in decision assessment and guides exploration of diverse urban planning and transportation solutions. Kowarik and colleagues examined the significance of urban biodiversity [59]. By employing the EEDM, they could assess the current state of urban biodiversity using environmental data. This approach also highlights biodiversity intrinsic value and its contribution to human wellbeing. Wang and colleagues delved into the trends and challenges of sustainable urban design in the digital era [60]. By applying the EEDM, they focused on collecting environmental data to understand the impact of digital technology on urban sustainability. The model decision assessment and selection phases enable the examination of ecological implications associated with different technical solutions.

The EEDM offers extensive global benefits and is highly relevant across diverse cultural and environmental landscapes, particularly between Eastern and Western contexts. Influenced by distinct cultural and historical elements, urban areas encounter unique sustainability challenges. This model navigates such variances by delivering tailored strategies that enhance sustainable development. Central to the model is environmental ethical principles; these vary in expression and significance among cultures. Consequently, the EEDM is especially adept at balancing the complexities arising from global and local pressures. Specifically, the EEDM prioritizes environmental justice and public engagement by ensuring that decisions go beyond technical aspects and take into consideration community opinions and concerns. This crucial element, sometimes overlooked in competing frameworks, is essential to this approach. The strategy enhances project success by promoting broad stakeholder engagement and by strengthening social approval. The EEDM also prioritizes long-term factors and adheres to the precautionary principle. It diverges from methods that prioritize immediate financial gains or focus on economic aspects by facilitating the early detection and mitigation of potential environmental and societal hazards. Conventional decision-making frameworks frequently lack a proactive and forward-thinking approach. Lastly, the EEDM adequately resolves the dilemma arising from the interplay between globalization and localization. It can integrate globally recognized environmental ethical concepts with the distinct socio-cultural contexts of various countries and regions, tailoring solutions to fit their distinctive circumstances. Models that are inflexible or monocultural in their outlook face challenges. In essence, the model demonstrates significant viability and practical utility in attaining sustainable urban development goals. With the growing focus on sustainability, there is a possibility for the extensive implementation and endorsement of the EEDM.

4. Conclusions

The study investigates the integration of Nanjing Circumvallation restoration into sustainable urban development strategies, striving for an equilibrium between heritage conservation and sustainable growth through the utilization of the EEDM. This restoration project encompasses both the preservation of historical and cultural heritage and the promotion of sustainable urban development. This research facilitates both the sustainable development of the city and the safeguarding and continuation of cultural heritage.

The study demonstrates that implementation of the EEDM in the Nanjing Circumvallation restoration project not only led to the safeguard of cultural heritage, but also to the sustainable development of the city. The study discovered that the EEDM was successful in providing excellent guidance for the repair effort, as demonstrated by a small-scale pilot restoration project. The efficacy of the EEDM was apparent in a preliminary restoration, emphasizing its role in enabling equitable and comprehensive decision-making. This method considered the viewpoints of different stakeholders, guaranteeing the preservation of the authenticity of the historical site while promoting social cohesion. The incorporation of environmental ethical values, such as environmental justice, sustainability, precaution, and humility, have rendered the construction methods more scientific and pragmatic. The application of environmental justice has bolstered community involvement and enhanced the project social acceptance. The restoration process has been guided by the concepts of sustainability and precaution, which prioritize environmental consciousness and scientific rigor. Lastly, the principle of humility has been crucial in preserving the site authenticity, thereby retaining its historical and cultural significance. The implementation of real-time monitoring was crucial in guaranteeing the safety and precision of the construction process. The evaluation results indicate a significant improvement in the visual attractiveness, structural soundness, and practical usefulness of the ancient fortifications following renovation. This initiative contributes substantially to the preservation of the cultural and historical significance of Nanjing Circumvallation. It also serves as a noteworthy implementation of modern urban development and environmental protection concepts. It embodies the principles of sustainable urban development, which prioritize the conservation of resources, preservation of culture, promotion of societal peace, and protection of the environment. Applying an EEDM successfully aligns the goals of preserving cultural heritage with promoting sustainable urban development.

The research findings present innovative viewpoints and approaches for restoring the Circumvallation. Traditional heritage conservation approaches predominantly emphasize physical restoration and protection. However, this study effectively introduces a method that integrates sustainable urban development concepts into heritage preservation. Notably, the exploration of innovative materials was undertaken. These materials ensure the protection and repair of monuments while also preserving resources and enhancing durability. This combination of traditional and modern technologies showcases the possibility of incorporating advanced technological principles into the preservation of cultural heritage. This study provides a novel approach to urban heritage restoration and establishes a distinctive path in heritage conservation that encompass sustainable urban development. Although the EEDM in this study may be influenced by existing Chinese cultural heritage regulations, it is hypothesized that this model can offer a more organized and systematic approach to urban sustainable development. Moreover, the implementation and promotion of sustainable urban development strategies in heritage protection are expected to be adopted in many cities.

The methodology and strategies utilized in this study offer valuable insights and guidance for regions worldwide grappling with similar challenges. This study demonstrates the delicate balance existing among the preservation of cultural legacy, maintenance of ecological equilibrium, and promotion of economic advancement, which are widespread concerns in various regions worldwide. It highlights the utilization of eco-friendly materials, the adoption of energy-conserving techniques, and community engagement through direct interaction and interest mediation as practical solutions that may be applied in various cultural and geographical settings. The successful execution and attainment of these solutions in specific endeavors underscore their global importance and efficacy in tackling analogous problems.