Evaluation of the Suitability of Cultural Heritage Protection and Utilization in the Process of Underground Space Development: A Case Study of Xuzhou City

Abstract

Utilizing underground space has become a means to address urban issues; however, heritage protection in underground development has become an unavoidable challenge. Whether to proceed with underground development in a heritage site requires a suitability study that considers various influencing factors to guide comprehensive protection planning. Therefore, conducting a suitability study for underground development in heritage sites is a critical issue that must be addressed before policy and planning decisions. Based on preliminary research, this study identifies and summarizes the influencing factors of underground heritage development suitability, innovatively constructs the “Underground Resource Development Suitability Index System of Cultural Heritage, URDSIS-CH”, and employs the “Dependency Analytic Process, DAP” method for evaluation. It explores spatial development issues arising from underground heritage development and clarifies the relationship mechanisms between relevant influencing factors. This study seeks to resolve the contradiction between underground space development and cultural heritage protection through technological and methodological approaches, providing insights for a more scientific approach to underground heritage preservation and utilization.

1. Introduction

Globally, the trend of utilizing underground space has evolved from early-stage spatial utilization to a means of solving urban problems. This has become an inevitable path for urban renewal [1,2,3,4]. However, urban heritage is inherently vulnerable in the face of large-scale exploitation and construction. The historical value of urban heritage is accumulated over time, with much of it buried underground and irreplaceable. A lack of attention during underground development may lead to irreversible destruction.

Heritage protection in underground resource development is an unavoidable issue, as it is about not just preserving the past for the past’s sake, but respecting the past for the present [5]. In European countries such as the UK, France, and Germany, the purpose of underground space utilization is to protect the urban environment, natural landscapes, and historical sites. Hence, a fundamental principle of urban infrastructure construction in Europe is to place facilities that would otherwise obstruct cityscapes underground [6]. Scholars have conducted extensive research in this field, which can be categorized into four areas: (1) Comprehensive Underground Resource Development in Historic Cities: Archer argues that if underground heritage is neither fully utilized nor well understood, even a cultural metropolis like Paris cannot effectively manage its vast underground space [7]. Varriale emphasizes the importance of strengthening underground cultural spaces as valuable resources for urban identity and tourism advancement [8]. (2) Underground Development and Protection of Individual and Clustered Heritage Sites: Salvarani states that urban underground spaces are often symbolically used for rituals and memorial ceremonies and are closely linked to local community culture [9]. Hiroi systematically analyzed the integrated and multifunctional underground development of historic Japanese cities [10]. (3) Heritage Protection Near Underground Rail Transit: Giuseppe suggests that underground transport development should be designed to minimize its impact on heritage buildings in historic city centers [11]. (4) Underground Archeological Site Protection: Bayraktar and Ayşe propose that developing archeological parks can preserve ancient landscapes in open spaces while promoting heritage conservation and tourism, thereby driving economic growth [12]. Varriale notes that reconstructing underground building heritage (UBH) for sustainable reuse is becoming increasingly popular and is a key focus of several internationally funded projects [13]. He also highlights that underground archeology can utilize and repurpose abandoned underground cultural heritage, contributing to cultural, social, and urban renewal [8]. These studies demonstrate that from a holistic urban perspective, cultural heritage remains inseparable from urban underground development. Ultimately, the issue revolves around the efficient and integrated use of underground space while balancing exploitation and preservation concerns.

The suitability of underground resource development is a highly complex and interdisciplinary issue, involving not only geological factors such as geological structures but also economic, social, transportation, and locational factors [14]. Since the laws and regulations related to underground development and heritage protection formulated by different countries vary, our research is mainly based on the project “Special Planning for the Development and Utilization of Urban Underground Space in Xuzhou City, China (2021–2035)”. Therefore, while recognizing the relevant heritage protection conventions issued by the UNESCO World Heritage Committee and the CIDOC CRM data, etc., we have referred more to the relevant policies and evaluation standards formulated by China. Many scholars have already studied and constructed various evaluation systems for the suitability of urban underground space development [15,16,17,18,19,20]. However, there is an inherent contradiction between the practical needs of urban underground development and the objective necessity of cultural heritage protection. A lack of respect and understanding of historical preservation, local cultural context, and the spirit of place often arises [21]. Compared to regular urban land, cultural heritage areas are more fragile and possess unique heritage value. Therefore, underground resource development in heritage sites must consider not only the factors typically involved in underground development but also the intrinsic value of the heritage itself and the impact of utilization on it. Many heritage sites are located in old urban districts, where underground development could potentially alleviate urban issues such as traffic congestion, parking shortages, and inadequate infrastructure—problems that otherwise threaten the historical landscape. Existing research on heritage underground resource development evaluation [22,23] has mainly focused on heritage impact assessment [24,25]. For example, Wang Qian argues that a rapid and accurate risk assessment of the impact of China’s rapidly burgeoning urban rail transit systems on surrounding architectural heritage is crucial [26].

Clearly, there is an inherent contradiction between the demand for urban underground development and the protection of cultural heritage areas. Overemphasizing underground development at the cost of urban heritage or excessively prioritizing heritage preservation at the expense of urban comfort and ecological balance can both hinder the harmonious and organic growth of a city. However, underground resource exploitation in heritage sites does not necessarily lead to destruction; it can be transformed into a means of protecting heritage and utilizing its value. Whether a heritage site should undergo underground development requires an understanding of the influencing factors affecting both development and preservation. A comprehensive approach that integrates all relevant factors must be taken to formulate a protection plan for the entire heritage site. Therefore, evaluating the suitability of underground development in heritage areas is a crucial issue that must be addressed before making policy and planning decisions.

A scientific and comprehensive feasibility assessment of underground cultural heritage resource development will provide a strong basis for guiding such projects. This study examines the factors influencing the suitability of underground heritage development and analyzes their impact on decision-making. By constructing an indicator system and using the authors’ “Dependency Analytic Process, DAP” [27] to determine factor weights, this study explores heritage underground development and protection. The contributions of this research, compared to previous studies, are as follows: (1) It conducts an in-depth analysis of the factors influencing the suitability of heritage underground development and constructs an evaluation index system along with scoring standards. (2) It carries out an on-site investigation of heritage sites in the old city of Xuzhou, incorporating the current state of heritage, discussions with local government officials and experts, and identified heritage protection issues to prepare for subsequent evaluation work. (3) Two typical case studies are selected, evaluated using the author’s previously developed DAP, and analyzed for factor interrelationships. These case studies further demonstrate the practicality, superiority, and innovation of the method. (4) Based on the evaluation results, this study discusses the interconnections between factors influencing underground heritage utilization and provides targeted policy recommendations. In summary, this research aims to provide technical guidance for underground heritage resource development while also showcasing the applicability and comprehensiveness of the DAP in holistic evaluations.

2. Methods

2.1. Establishment of Evaluation System

Through a comprehensive analysis of domestic and international research on heritage protection and utilization in underground development [28,29,30,31], it is evident that cultural heritage areas possess unique heritage value. Therefore, the suitability of underground development for heritage sites should not only consider conventional underground exploration factors but also the intrinsic value of the heritage, its feasibility for utilization, indirect impact factors, and the spatial needs of local residents. Many heritage sites are located in old urban districts, where underground development could help alleviate urban issues such as traffic congestion, parking shortages, and inadequate infrastructure, which threaten the historical landscape. Feasibility and indirect impact factors primarily refer to the systematic evaluation of advancement resistance and potential benefits, all of which affect utilization suitability. This study asserts that the influencing factors should not be evaluated in isolation but rather in terms of their interdependencies and mutual support, forming the principles of this evaluation system.

Based on the “Principles for the Conservation of Heritage Sites in China” and “Law of the People’s Republic of China on Protection of Cultural Relics” and respecting existing research [22,32,33,34,35], an initial framework for assessing the suitability of underground resource development of cultural heritage has been established, as shown in Figure 1. This framework consists of four core values: intrinsic value, current status value, reuse value, and impact value. Intrinsic value means that the higher the heritage protection level, the less suitable it is for underground exploitation. Current status value means whether the current function of the heritage site is reasonable, whether it has already been developed, whether it is above or underground, and the preservation status, quality, and scale of the remains. Reuse value refers to the location, transportation, development potential, environmental, and ecological values, which influence future protection and utilization. Impact value is the future growth value of the heritage, including its economic and commercial value, public recognition, transportation development, and urban planning significance.

To refine the evaluation system, at approximately 20 cultural heritage sites in Xvzhou surveys were conducted [36], and discussions were held with experts, scholars, and planners on aspects such as the current state of heritage sites, heritage protection status, and future planning design. As a result, a three-tier evaluation index for underground resource development of cultural heritage suitability was formulated, as shown in

Table 1. Underground Resource Development Suitability Index System of Cultural Heritage (URDSIS-CH).

Objective Layer	First-Level Indicator	Indicator Code	Second-Level Indicator
Suitability of Underground Resource Development of Cultural Heritage	Heritage Value (A)	A1	Heritage Protection Level
		A2	Historical Value
		A3	Archeological Value
	Heritage Development Characteristics (B)	B1	Heritage Building Density
		B2	Heritage Control Zone
		B3	Heritage Protection Method
		B4	Heritage Quality
	Heritage Environmental Condition (C)	C1	Spatial Location
		C2	Current Function of Underground Space
		C3	Accessibility of Underground Transportation
		C4	Ground Transportation Condition
		C5	Infrastructure facilities
	Existing Construction Status of Heritage (D)	D1	Height of Ground Buildings
		D2	Scale of Heritage Site
		D3	Depth of Underground Development
		D4	Condition of Underground Remains
		D5	Underground Rail Transit Lines
	Natural Conditions (E)	E1	Geological Disasters
		E2	Water Quality Conditions
		E3	Engineering Geological Conditions
	Future Development Value (F)	F1	Economic Status
		F2	Commercial Economic Value
		F3	Sense of Identity Among User Groups
		F4	Rationality of Current Use of Heritage
		F5	Transportation Development (Urban Planning) Value

. These indicators determine the methods and strategies for future heritage protection and utilization.

2.2. Establishment of Scoring Criteria

The URDSIS-CH comprehensive evaluation system proposed in this study includes many indicators that can be accurately scored, such as heritage protection level, zoning control, building density, and construction status. However, some indicators are difficult to quantify precisely and can only be represented within a fuzzy range, such as the commercial economic value of heritage conservation and transportation (urban planning) value. To standardize evaluation, this study adopts a direct quantitative scoring approach, using quantifiable indicators as the benchmark for defining scoring standards. According to China’s Cultural Relics Protection Law, Chapter 1, Article 3, heritage protection levels in China are divided into National Key Cultural Relics Protection Units, Provincial-Level Cultural Relics Protection Units, and Municipal and County-Level Cultural Relics Protection Units. Heritage zoning control areas are categorized as strict construction restriction zones, limited construction zones, appropriate construction zones, and developed zones. Protection methods are classified into preservation, restoration, renovation, and reconstruction. According to the occupied area scale and type of heritage, they are divided into tomb clusters and city sites, large sites, historical and cultural districts, individual historical buildings, and cultural relics protection sites. At the same time, by combining with the evaluation criteria in the existing evaluation systems referred to during the process of screening indicators when creating Table 1. Based on the characteristics of the evaluation system, the assessment levels are divided into five grades using a five-point scale (5, 4, 3, 2, 1). The URDSIS-CH evaluation system takes heritage value as its foundation and the feasibility of underground development as its objective, assigning scores to different factors based on the characteristics of each heritage site, thus establishing the corresponding scoring standard, as shown in

Table 2. Scoring criteria for suitability evaluation of underground resource development of cultural heritage.

Evaluation Sub-Item Indicators	Scoring Criteria
	5	4	3	2	1
A1 Heritage Protection Level	Cultural Relics Protection Site	Municipal/County Level	Provincial Level	National Level	World Level
A2 Historical Value	Aboveground Sites
	No significant commemorative value or historical value is common nationwide	Minor historical research value	Certain historical value	Commemorates significant historical events and figures, with high historical value	Strongly associated with significant historical events and figures, high historical value
	Underground Sites
	Strongly associated with significant historical events and figures, high historical value	Commemorates significant historical events and figures, with relatively high historical value	Certain historical value	Minor historical research value	No significant commemorative value or historical value is common nationwide
A3 Archeological Value	Highly related to significant historical information, high archeological value	Relatively highly related to significant historical information	Somewhat related to significant historical information	Low archeological value	No significant archeological value and common nationwide
B1 Heritage Building Density	High density, requires underground space to supplement ground functions	Relatively high density	Moderate density	Low density	Square or open space
B2 Heritage Control Zone	No zoning	Built-up area	Suitable construction area	Restricted construction area	Cautious construction area
B3 Heritage Protection Method	No protection needed	Reconstruction category	Renovation category	Restoration category	Protection category
B4 Heritage Quality	Abandoned, unusable	Dilapidated buildings	Average	Basically intact	Well preserved
C1 Spatial Location	City center	Sub-center	Some distance from city center	Deviates from city center	Far from city center
C2 Current Function of Underground Space	Fully functional	Many functions but incomplete	Some functional spaces, with civil defense facilities	Sparse point-like underground spaces	None
C3 Accessibility of Underground Transportation	Complete pedestrian, vehicular, and rail transit	Rail transit available	Pedestrian and vehicular underground transport available	Pedestrian underground transport available	None
C4 Ground Transportation Conditions	High traffic volume, parking difficulties	Relatively high traffic volume, parking relatively difficult	Moderate traffic volume and average parking	Low traffic volume, parking easier	Low traffic volume, easy parking
C5 Infrastructure Support for Heritage	No supporting facilities, requires underground space to compensate for functional deficiencies	Few supporting facilities	Moderate supporting facilities, some impact on historical appearance	Many supporting facilities, some impact on historical appearance	Complete supporting facilities, no impact on ground historical appearance
D1 Height of Ground Buildings	Bungalow (<4.5 m)	Low-rise (<9 m)	Multi-story (9–18 m)	Mid-rise (18–27 m)	High-rise (>27 m)
D2 Scale of Heritage Site	Tomb clusters, city sites, etc.	Large sites	Historical and cultural districts	Individual historical buildings	Cultural relics protection sites
D3 Depth of Underground Development	Shallow	Sub-shallow	Medium	Sub-deep	Deep
D4 Condition of Underground Remains	None	Identified, with general historical value	Identified, with significant historical value	Unidentified but confirmed historical value	Unidentified but confirmed minor historical value
D5 Underground Rail Transit Lines	Three or more subway transfer stations	Two subway transfer stations	Normal transfer station	No subway station	No subway
E1 Geological Disasters	Almost no disasters	Rare disasters, earthquake magnitude <5	Few disasters, earthquake magnitude 5–6	Prone to disasters, earthquake magnitude 6–7	Frequent disasters, earthquake magnitude >7
E2 Water Quality Conditions	Non-erosion zone	Weak decomposition zone	Weak decomposition erosion zone	Weak crystalline erosion zone	Weak crystalline decomposition composite zone
E3 Engineering Geological Conditions	High soil bearing capacity, low compression	Relatively high soil bearing capacity	Moderate soil bearing capacity	Low soil bearing capacity	Soil does not meet development requirements
F1 Economic Status	Good economic status, supports development	Relatively good economic status, supports development	Moderate economic status, supports limited development	Poor economic status, supports minimal development	Poor economic status, does not support development
F2 Commercial Economic Value	Enhances commercial value of the entire area	Significant impact on surrounding commercial value	Moderate impact on surrounding commercial value	Minor impact on surrounding commercial value	No impact
F3 Sense of Identity Among User Groups	Significantly improves production and living environment	Relatively improves production and living environment	Improves basic production and living environment	Partially meets production and living needs	No impact
F4 Rationality of Current Use of Heritage	Deteriorated appearance, requires overall improvement	Somewhat unreasonable use	Average functional utilization	Utilized but needs improvement	Reasonable function, harmonizes with surrounding appearance
F5 Transportation Development (Urban Planning) Value	Enhances overall city image and reputation, solves traffic congestion	Improves overall traffic and appearance of the area	Improves traffic and appearance of the heritage site	Solves traffic congestion at the heritage site	No significant improvement

. Using this standard, data are collected through field surveys, random interviews, and structured discussions, providing a foundation for data calculation and result analysis.

The evaluation results are categorized into different levels according to the standards of being highly suitable for development, moderately suitable for development, development with due caution, and not suitable for development. The development suitability is then segmented into four tiers, corresponding to the evaluation grade intervals of 4, 3, 2, and 1, respectively, as shown in

Table 3. Grading criteria for suitability evaluation of underground resource development of cultural heritage.

Development Suitability	Score Range
Suitable for Development	$Y$> 4
Developable	3 ≤ $Y$< 4
Cautious Development	2 ≤ $Y$< 3
Not Suitable for Development	1 ≤ $Y$< 2

.

2.3. Comprehensive Evaluation

Once the URDSIS-CH evaluation system and scoring standards are established, a comprehensive assessment can be conducted to determine whether a cultural heritage site is suitable for underground development. This study investigates the current use of underground space in Xuzhou’s more than 20 cultural heritage areas, organizes findings from field research [36], and applies the DAP, which was established by the author to refine heritage protection and utilization evaluation. Given the interdependencies and interactions between evaluation indicators, the DAP method is well suited for optimizing decision-making in heritage conservation and utilization.

2.3.1. Constructing the Incidence Matrix

There are multiple indicators in the comprehensive evaluation, set as ${\mathrm{a}}_1,{\mathrm{a}}_2,\cdots {\mathrm{a}}_{\mathrm{n}}$. Generally, these indicators are not completely independent but have a certain dependency on each other. If 10% of the contribution to ${\mathrm{a}}_{\mathrm{i}}$ comes from ${\mathrm{a}}_{\mathrm{j}}$, then define the dependency degree of ${\mathrm{a}}_{\mathrm{i}}$ to ${\mathrm{a}}_{\mathrm{j}}$ as ${\mathrm{s}}_{\mathrm{i}\mathrm{j}}=0.1$. Thus, the matrix is obtained as follows:

$$B=\left(\begin{array}{ccc}{s}_{11}& \cdots & s_{1n}\\ ⋮& \cdots & ⋮\\ s_{n1}& \cdots & s_{nn}\end{array}\right)$$

(1)

Usually, ${\mathrm{s}}_{\mathrm{i}\mathrm{j}}$ is not necessarily equal to ${\mathrm{s}}_{\mathrm{j}\mathrm{i}}$. We take the degree of correlation between ${\mathrm{a}}_{\mathrm{i}}$ and ${\mathrm{a}}_{\mathrm{j}}$ as ${\mathrm{r}}_{\mathrm{i}\mathrm{j}}$:

$${\mathrm{r}}_{\mathrm{i}\mathrm{j}}={\displaystyle \frac{{\mathrm{s}}_{\mathrm{i}\mathrm{j}}+{\mathrm{s}}_{\mathrm{j}\mathrm{i}}}{2}}={\mathrm{r}}_{\mathrm{j}\mathrm{i}}$$

(2)

constructing the following incidence matrix:

$$A=\left(\begin{array}{c}\begin{array}{cc}{\mathrm{r}}_{11}& {\mathrm{r}}_{12}\\ {\mathrm{r}}_{21}& {\mathrm{r}}_{22}\end{array} \begin{array}{cc}\cdots & {\mathrm{r}}_{1\mathrm{n}}\\ \cdots & {\mathrm{r}}_{2\mathrm{n}}\end{array}\\ \begin{array}{cc}⋮& ⋮\\ {\mathrm{r}}_{\mathrm{n}1}& {\mathrm{r}}_{\mathrm{n}2}\end{array} \begin{array}{cc}⋮& ⋮\\ \cdots & {\mathrm{r}}_{\mathrm{n}\mathrm{n}}\end{array}\end{array}\right)$$

(3)

Since matrix $A$ fully reflects the correlation among the indicators, it is called $A$ as the incidence matrix. $A$ is a real symmetric matrix with a main diagonal of 1 and other elements within (0.1).

The sum of the dependency of an indicator on other indicators should be less than 1; otherwise, from the perspective of evaluation, this indicator is redundant and can be eliminated. If the sum of the dependency of an indicator on other indicators exceeds 1, it indicates that the dependencies are unreasonable. Therefore, further requirements can be imposed:

$$\sum _{\mathrm{j}=1}^{\mathrm{n}}{\mathrm{r}}_{\mathrm{i}\mathrm{j}}-{\mathrm{r}}_{\mathrm{i}\mathrm{i}}<1,\mathrm{i}=\mathrm{1,2},\dots \mathrm{n}$$

(4)

Therefore, $A$ is a real symmetric matrix with a main diagonal element of 1 and is strictly diagonally dominant. Thus, $A$ is a positive definite matrix, and all its eigenvalues are greater than zero.

2.3.2. Calculating Dependency

(a)

Calculate the sum of the interdependency between the indicator ${\mathrm{a}}_{\mathrm{i}}$ and other indicators, denoted as ${\mathrm{b}}_{\mathrm{i}}$:

$${\mathrm{b}}_{\mathrm{i}}=\sum _{\mathrm{j}=1}^{\mathrm{n}}{\mathrm{r}}_{\mathrm{i}\mathrm{j}}-{\mathrm{r}}_{\mathrm{i}\mathrm{i}},\mathrm{i}=\mathrm{1,2},\cdots \mathrm{n}$$

(5)

the larger ${\mathrm{b}}_{\mathrm{i}}$ is, the more important the corresponding indicator ${\mathrm{a}}_{\mathrm{i}}$ is, and thus the greater the weight of indicator.

(b)

Arrange ${\mathrm{b}}_{\mathrm{i}}$ descending order and denote it as ${\mathrm{c}}_1\ge {\mathrm{c}}_2\ge \cdots {\mathrm{c}}_{\mathrm{n}}$. In other words, the largest ${\mathrm{b}}_{\mathrm{i}}$ is ${\mathrm{c}}_1$, the second largest ${\mathrm{b}}_{\mathrm{i}}$ is ${\mathrm{c}}_2$, and so on; the smallest one is ${\mathrm{c}}_{\mathrm{n}}$.

2.3.3. Determine Weight

Assume that the eigenvalues of the incidence matrix $A$ are sorted in descending order as follows: ${\mathsf{\lambda }}_1,{\mathsf{\lambda }}_2,\cdots {\mathsf{\lambda }}_{\mathrm{n}}$. Establish the following order:

$${\mathsf{\beta }}_{\mathrm{i}}={\displaystyle \raisebox{1ex}{${\mathsf{\lambda }}_{\mathrm{i}}$}\!\left/ \!\raisebox{-1ex}{$\sum _{\mathrm{j}=1}^{\mathrm{n}}{\mathsf{\lambda }}_{\mathrm{j}},\mathrm{i}=\mathrm{1,2},\cdots \mathrm{n}$}\right.}$$

(6)

If ${\mathrm{c}}_{\mathrm{i}}$=${\mathrm{b}}_{\mathrm{k}}$, record the score of the indicator ${\mathrm{a}}_{\mathrm{k}}$ as ${\mathrm{a}}_{\mathrm{k}\mathrm{i}}$; then, the weight of the indicator ${\mathrm{a}}_{\mathrm{k}}$ is taken as ${\beta }_{\mathrm{i}},\mathrm{i}=\mathrm{1,2},\cdots \mathrm{n}$.

Assign the weight of the indicator ${\mathrm{a}}_{\mathrm{k}\mathrm{i}}$ corresponding to ${\mathrm{c}}_{\mathrm{i}}$ as ${\beta }_{\mathrm{i}},\mathrm{i}=\mathrm{1,2},\cdots \mathrm{n}$.

2.3.4. Calculate the Evaluation Result

Calculate the total evaluation value:

$$Y={\beta }_1{\mathrm{a}}_{\mathrm{k}1}+{\beta }_2{\mathrm{a}}_{\mathrm{k}2}+\cdots +{\beta }_{\mathrm{n}}{\mathrm{a}}_{\mathrm{k}\mathrm{n}}+\mathsf{\epsilon }$$

(7)

$\mathrm{Y}$ is the evaluation result, ${\beta }_1,{\beta }_2,\cdots {\beta }_{\mathrm{n}}$ is the weight vector calculated from the second step above, and ${\mathrm{a}}_{\mathrm{k}1},{\mathrm{a}}_{\mathrm{k}2},\cdots {\mathrm{a}}_{\mathrm{k}\mathrm{n}}$ is the reordering of ${\mathrm{a}}_1,{\mathrm{a}}_2,\cdots {\mathrm{a}}_{\mathrm{n}}$ based on its dependencies on other indicators, and also the scores of each indicator. $\mathsf{\epsilon }$ is a control variable, and it is used to account for the occurrence of special circumstances. For example, the decision of whether to proceed with the utilization ultimately requires the local government’s administrative department to comprehensively consider various other factors such as the overall urban planning and financial situation, or there may be unavoidable factors that render the project unfeasible.

This method utilizes the dependency matrix to reflect the importance of indicators, i.e., the magnitude of the weights. The greater the dependency on other indicators, the greater the corresponding weight, and the smaller the dependency, the smaller the weight. The weight vector is determined by relying on the eigenvalues of the incidence matrix. The score in the second-level indicator represents the level of support for the selected mode, and calculating the support for each factor in the first-level indicators is performed via the same method as above, determining the weight vector for the first-level indicators and obtaining the final evaluation result (Figure 2).

3. Research Area

3.1. Case Investigation

Xuzhou City has a large number of heritage sites, making it essential to conduct exploitation suitability assessments to prevent irreversible damage to cultural heritage. However, not all heritage sites require underground development, as decisions should consider factors such as heritage protection level, physical condition, transportation accessibility, economic value, and urban planning significance.

Heritage site investigation and evaluation involve a multidisciplinary approach. During the initial assessment, detailed records of heritage attributes, the natural environment, and the social environment according to

Table 4. Content of cultural heritage status survey records.

Survey Item	Record Content
Heritage Overview	Protection level, heritage type, heritage quality, current use
Heritage Ownership	Control zones, protection methods, restrictions
Heritage Features	Heritage scale, spatial layout, feature characteristics
Historical Information	Heritage history, regional history, historical events
Location	Urban location, transportation conditions, infrastructure
Environmental Landscape	Surrounding environment, cultural characteristics, geographical conditions
Social Attributes	Economic status, commercial status, popularity, cultural sentiment

were compiled. To enhance research and analysis, multiple structured meetings were held with local authorities to supplement and refine survey records, as shown in Figure 3. These discussions provided insights into local protection policies, management conditions, socio-economic conditions, and planning designs, ensuring that the evaluation was scientifically robust and free from future controversies that could arise in heritage protection and utilization decisions.

Through the aforementioned work, we determined that both the “Xuzhou Underground City Site” and the “Ancient buildings of Hu Bu Shan” are of considerable scale and are highly regarded by the local government and the public (Figure 4). Whether to carry out underground development at these two heritage sites is a subject with significant discussion value. As a result, we decided to select these two cases for in-depth research.

3.2. Xuzhou Underground City Site

The author strives to provide an intuitive and accurate assessment by integrating theories on the underground development, protection, and utilization of cultural heritage, consulting the relevant literature and conducting on-site investigations, structured interviews, and visits to local cultural heritage authorities together with the project team. Through this process, the following information about the Xuzhou Underground City Site in Xuzhou has been gathered:

(1)

Heritage Value: The Xuzhou Underground City Site is a municipally protected cultural heritage unit in Xuzhou. Based on the city’s 2600-year urban history, the site displays the unique phenomenon of layered urban development, known as the “city beneath the city, streets beneath streets, wells beneath wells”. This extraordinary stratification vividly showcases the deep historical and cultural heritage accumulated over millennia of urban construction. The site is vast and rich in content, with well-preserved residential layouts and street scales that clearly reflect the spatial organization and functional characteristics of Ming Dynasty dwellings. The discovery of Han Dynasty drainage systems and flood control dikes fully illustrates flood defense infrastructures in commoner districts during the Ming period. The smoothly finished walls of the Han Dynasty wells are also of significant archeological value.

(2)

Heritage Development Characteristics: The site is located within a buried cultural relics zone. It was discovered during the construction of Xuzhou’s central commercial district, and the area has since been protected and excavated for archeological purposes, ensuring the site’s excellent preservation.

(3)

Heritage Environmental Condition: The Xuzhou Underground City Site is situated at Pengcheng Square, the central hub of Xuzhou, serving as a key area for commerce, culture, and entertainment. It also functions as the interchange station for Metro Lines 1 and 2, offering convenient underground transportation and complete supporting infrastructure.

(4)

Existing Construction Status of Heritage: The rooftop plaza of the site’s museum has been designed as an open space to enhance the urban landscape. This approach not only ensures the protection of the underground heritage but also accommodates the development of the city’s surface infrastructure and environmental improvement.

(5)

Natural Conditions: Xuzhou is located in the Yellow River floodplain. Historically, the ancient city has been repeatedly flooded and rebuilt on the same site, giving rise to the unique layered urban landscape known as the city beneath the city.

(6)

Future Development Value: During the investigation, it was found that the Xuzhou Underground City Site, located in the city center, lies beneath the intersection of two subway lines. It is a municipal-level cultural relics protection unit, well known locally, and a key project in Xuzhou’s 14th Five-Year Plan for Cultural and Tourism Development. Given the government’s interest in its underground development, assessing its suitability for underground development is crucial for its future protection, cultural education initiatives, and urban ecological landscape improvement.

3.3. The Ancient Buildings of Hu Bu Shan

The Ancient buildings of Hu Bu Shan (1624), located in Hu Bu Shan, Xuzhou, were designated as a National Key Cultural Relics Protection Unit in 2006 (sixth batch). The site consists of 13 well-preserved ancient residential courtyards and over 500 traditional dwellings, offering high historical and cultural research value.

(1)

Heritage Value: The Ancient buildings of Hu Bu Shan are a nationally protected cultural heritage site, preserving over 500 traditional residential buildings. Most of the architecture consists of traditional “Siheyuan (courtyard houses)”, with spatial layouts built along the mountain’s slope. The buildings feature exquisite decorative carvings and distinctive styles, representing the architectural characteristics of Xuzhou during the Ming and Qing dynasties. Historically, Hu Bu Shan was a gathering place for many prominent and wealthy families, leading to the local saying “Poor in Beiguan, rich in Nangguan, the wealthy live on Hu Bu Shan.” In ancient times, the area surrounding Hu Bu Shan was a bustling commercial district and the largest goods distribution center at the junction of Jiangsu, Shandong, Henan, and Anhui provinces, giving it high historical reference value.

(2)

Heritage Development Characteristics: The ancient architectural complex is located in a restricted construction zone and is categorized as a restored cultural heritage site. In 2021, the “Environmental Improvement Plan for the Ancient buildings of Hu Bu Shan (Hunan Xiang Block)” was developed, proposing protection measures in areas such as restoration, renovation, adaptation, and reintegration. The overall historical area is well preserved, although the authenticity is somewhat compromised due to traces of restoration in a few spots.

(3)

Heritage Environmental Condition: The complex is situated in a sub-center of Xuzhou city, within walking distance of the Houbushan Station on Metro Line 2. Currently, only surface-level parking is available, which affects the historical appearance of the area to some extent.

(4)

Existing Construction Status of Heritage: The ancient buildings are primarily low-rise “Siheyuan” courtyard houses. Based on current archeological findings, there are no underground remains.

(5)

Natural Conditions: Due to the elevated terrain of Hu Bu Shan, the area is minimally affected by flooding.

(6)

Future Development Value: The site is currently well developed, with enclosed “Siheyuan”-style dwellings as the main feature. It also hosts a folk culture museum and other functional facilities that are reasonably laid out and harmonize with the surrounding historical setting. Adjacent to the site is the Hu Bu Shan Historical and Cultural Street, home to snack shops and souvenir stores that attract a large number of tourists. The main current issue is a shortage of parking space.

Based on on-site investigations and comprehensive analyses of Xuzhou’s old city heritage sites, these two sites were selected for underground development suitability evaluation using the DAP.

4. Results

4.1. Underground Development of Xuzhou Underground City Site

After conducting on-site investigations and data collection for the Xuzhou Underground City Site, discussions were held with the project team to refine the original evaluation materials and scoring. Having thoroughly familiarized ourselves with the heritage site, six professionals (including two heritage protection experts, two architectural designers, and two urban planners) assigned scores regarding its development suitability. Their assessment took into account both the intrinsic value of the heritage itself and the factors related to the feasibility and indirect impacts during underground development. By adhering to the evaluation criteria presented in Table 2, the evaluation scores for the underground development suitability of the “Xuzhou Underground City Site” were derived (as shown in

Table 5. Suitability score of underground development of Xuzhou Underground City Site, Xuzhou City.

Objective Layer	First-Level Indicator	Indicator Code	Second-Level Indicator	Score
Suitability of Underground Resource Development of Pengcheng Subterranean Ruins, Xuzhou City	Heritage Value (A)	A1	Heritage Protection Level	4
		A2	Historical Value	3
		A3	Archeological Value	5
	Heritage Development Characteristics (B)	B1	Heritage Building Density	5
		B2	Heritage Control Zone	1
		B3	Heritage Protection Method	1
		B4	Heritage Quality	3
	Heritage Environmental Condition (C)	C1	Spatial Location	5
		C2	Current Function of Underground Space	5
		C3	Accessibility of Underground Transportation	4
		C4	Ground Transportation Condition	4
		C5	Infrastructure facilities	3
	Existing Construction Status of Heritage (D)	D1	Height of Ground Buildings	5
		D2	Scale of Heritage Site	4
		D3	Depth of Underground Development	5
		D4	Condition of Underground Remains	3
		D5	Underground Rail Transit Lines	4
	Natural Conditions (E)	E1	Geological Disasters	3
		E2	Water Quality Conditions	3
		E3	Engineering Geological Conditions	4
	Future Development Value (F)	F1	Economic Status	4
		F2	Commercial Economic Value	5
		F3	Sense of Identity Among User Groups	5
		F4	Rationality of Current Use of Heritage	2
		F5	Transportation Development (Urban Planning) Value	5

).

Following the support evaluation for the underground development of cultural heritage, the six professionals analyzed and rated the interdependencies among evaluation indicators. The DAP method was applied to calculate the weighting of these dependencies. For example, within the first-level indicator heritage value (A), the second-level indicator heritage protection level (A1) has a self-dependency score of 1. For the Xuzhou Underground City Site, during the determination of the heritage protection level (A1), expert evaluations suggest that 30% of its contribution can be attributed to its historical value (A2). Consequently, the dependence of indicator A1 on indicator A2 is calculated as 0.3. The heritage protection level (A1) contributes 10% due to its archeological value (A3), so the dependency degree of indicator A1 on A3 is 0.1. Similarly, the dependency degree of indicator A2 on A1 is 0.3, A2 on A2 is 1, and A2 on A3 is 0.2. The dependency degree of A3 on A1 is 0.3, A3 on A2 is 0.3, and A3 on A3 is 1. This results in the mutual dependency scores among the second-level indicators within the first-level indicator of heritage value (A), as shown in

Table 6. The mutual dependency degree among the second-level indicators within heritage value (A).

	A1	A2	A3
A1	1	0.3	0.1
A2	0.3	1	0.2
A3	0.3	0.3	1

.

The degree of dependence between two indicators is determined by the influence exerted by one indicator on the other. Using the DAP algorithm, within first-level indicator A, heritage protection level (A1) depends on archeological value (A3), with a dependency score of 0.1. Archeological value (A3) depends on heritage protection level (A1), with a dependency score of 0.3. Thus, the correlation score between A1 and A3 is 0.2. Through this method, the second-level correlation matrix for the first-level indicator heritage value (A) is established.

$$A=\left(\begin{array}{ccc}1& 0.3& 0.2\\ 0.3& 1& 0.25\\ 0.2& 0.25& 1\end{array}\right)$$

The sum of the correlation degrees of indicators $a_1, a_2, a_3$ with other indicators are as follows: $b_1=0.5,b_2=0.55,b_3=0.45$. ${\mathrm{b}}_1,{\mathrm{b}}_2,{\mathrm{b}}_3$ are sorted from largest to smallest as ${\mathrm{c}}_1,{\mathrm{c}}_{2,}{\mathrm{c}}_3;$ then, ${\mathrm{b}}_2=0.55$ is the largest, so the indicator corresponding to ${\mathrm{c}}_1$=${\mathrm{b}}_2$ is ${\mathrm{a}}_2,{\mathrm{b}}_1=0.5$, which is the second largest, so the indicator corresponding to ${\mathrm{c}}_2$=${\mathrm{b}}_1$ is ${\mathrm{a}}_1,$… Following this logic, the indicators ranked by descending correlation degrees are $a_2,a_1,a_3,$ and the score values are recorded as ${\mathrm{a}}_{21},{\mathrm{a}}_{12},{\mathrm{a}}_{33}$.

The eigenvalue of A calculated by MATLAB R2024a is:

$${\mathsf{\lambda }}_1=1.5022,{\mathsf{\lambda }}_2=0.8066, {\mathsf{\lambda }}_3=0.6912,$$

The sum of the eigenvalues of a matrix is equal to the sum of its diagonal elements, and the weight vector of the second-level indicators is:

$${\beta }_1={\displaystyle \frac{{\lambda }_1}{{\displaystyle \sum _{i=1}^3{\lambda }_i}}}={\displaystyle \frac{1.5022}{3}}=0.5007,{\beta }_2=0.2689, {\beta }_3=0.2304,$$

The scores of indicators $a_1, a_2, a_3$ are 4, 3, and 5, respectively, as shown in Table 5, so ${\mathrm{a}}_{21}$=3$,{\mathrm{a}}_{12}=4,{\mathrm{a}}_{33}=5$. Therefore $,$ the score of indicator A is calculated as follows:

$$Y_1={\beta }_1{a}_{21}+{\beta }_2{a}_{12}+{\beta }_3{a}_{33}=3\times 0.5007+4\times 0.2689+5\times 0.2304=3.7297$$

By analyzing the dependency degrees of the second-level indicators within other first-level indicators, the incidence matrix of the second-level indicators is calculated as follows:

The incidence matrix of heritage development characteristics (B) is:

$$\mathrm{B}=\left(\begin{array}{cccc}1& 0& 0& 0.05\\ 0& 1& 0.15& 0.05\\ 0& 0.15& 1& 0.35\\ 0.05& 0.05& 0.35& 1\end{array}\right)$$

The incidence matrix of heritage environmental condition (C), existing construction status of heritage (D), natural conditions (E) and future development value (F) is calculated as follows:

$$\mathrm{C}=\left(\begin{array}{ccccc}1& 0.05& 0.2& 0.2& 0.1\\ 0.05& 1& 0.1& 0.05& 0.1\\ 0.2& 0.1& 1& 0.25& 0.1\\ 0.2& 0.05& 0.25& 1& 0.1\\ 0.1& 0.1& 0.1& 0.1& 1\end{array}\right)$$

$$\mathrm{D}=\left(\begin{array}{ccccc}1& 0& 0.15& 0& 0\\ 0& 1& 0& 0& 0\\ 0.15& 0& 1& 0.05& 0.2\\ 0& 0& 0.05& 1& 0.15\\ 0& 0& 0.2& 0.15& 1\end{array}\right)$$

$$\mathrm{E}=\left(\begin{array}{ccc}1& 0.1& 0.15\\ 0.1& 1& 0.15\\ 0.15& 0.15& 1\end{array}\right)$$

$$\mathrm{F}=\left(\begin{array}{ccccc}1& 0.2& 0& 0.05& 0.2\\ 0.2& 1& 0.15& 0.15& 0.3\\ 0& 0.15& 1& 0.15& 0.2\\ 0.05& 0.15& 0.15& 1& 0.2\\ 0.2& 0.3& 0.2& 0.2& 1\end{array}\right)$$

Using the same method, the evaluation scores for other first-level indicators are calculated as follows:

$$Y_2=2.1364, Y_3=4.1655, Y_4=4.24, Y_5=2.8226, Y_6=4.3519$$

The interdependence among the factors in the first-level index layer is shown in

Table 7. The mutual dependency degrees of factors within the first-level indicators.

	A	B	C	D	E	F
A	1	0	0	0	0	0
B	0.3	1	0.1	0	0	0.1
C	0	0.1	1	0.2	0.2	0.2
D	0	0	0.2	1	0.2	0.1
E	0	0	0	0.1	1	0
F	0.3	0.2	0.1	0.2	0.1	1

.

The correlation matrix of each factor in the first-level indicators is calculated:

$$G=\left(\begin{array}{cccccc}1& 0.15& 0& 0& 0& 0.15\\ 0.15& 1& 0.1& 0& 0& 0.15\\ 0& 0.1& 1& 0.2& 0.1& 0.15\\ 0& 0& 0.2& 1& 0.15& 0.15\\ 0& 0& 0.1& 0.15& 1& 0.05\\ 0.15& 0.15& 0.15& 0.15& 0.05& 1\end{array}\right)$$

Using the same method as for the first-level indicators, the eigenvalues of $G$ calculated with Matlab are:

$${\mathsf{\lambda }}_1=1.4805,{\mathsf{\lambda }}_2=1.1864, {\mathsf{\lambda }}_3=0.9222,{\mathsf{\lambda }}_4=0.8729,{\mathsf{\lambda }}_5=0.7821,{\mathsf{\lambda }}_6=0.7558$$

The weight vector of the underground development suitability index of the Pengcheng Subterranean Ruins in Xuzhou City is calculated as follows:

$${\beta }_1=0.2468,{\beta }_2=0.1977,{\beta }_3=0.1537,{\beta }_4=0.1455,{\beta }_5=0.1304,{\beta }_6=0.1260$$

The sum of the correlation degrees of each indicator is 0.3, 0.4, 0.55, 0.5, 0.3, and 0.65, respectively, the corresponding indicators are ranked as $a_6, a_3, a_4, a_2, a_1, a_5,$ and the indicator score values are ${\mathrm{a}}_{61}=Y_6,{{\mathrm{a}}_{32}=Y}_3,{{\mathrm{a}}_{43}=Y}_4,{{\mathrm{a}}_{24}=Y}_2,{{\mathrm{a}}_{15}=Y}_1,{{\mathrm{a}}_{56}=Y}_5$. The total score is:

$$\begin{gathered} Y={\beta }_1{a}_{61}+{\beta }_2{a}_{32}+{\beta }_3{a}_{43}+{\beta }_4{a}_{24}+{\beta }_5{a}_{15}+{\beta }_6{a}_{56}+\epsilon ={\beta }_1{Y}_6+{\beta }_2{Y}_3+{\beta }_3{Y}_4+{\beta }_4{Y}_2+{\beta }_5{Y}_1+{\beta }_6{Y}_5+ \\ \epsilon =0.2468\times 4.3519+0.1977\times 4.1655+0.1537\times 4.24+0.1455\times 2.1364+0.1304\times 3.7297+0.1260\times 2.8226+0=3.7021 \end{gathered}$$

In special circumstances (e.g., policy shifts, technical constraints, or extreme outliers), control variables $\epsilon$ are used to adjust the evaluation. Generally, these control variables receive a score of 0, unless a critical issue arises. For instance, if a geological hazard is severe enough to make underground development entirely unfeasible, a negative score is assigned (a veto factor). However, in most cases where underground cultural relics exist, geological conditions are not severe enough to make exploitation impossible. Moreover, within this case, the government places significant emphasis on the development of the Xuzhou Underground City Site, and there are no financial issues. As a result, no unavoidable factors are present.

The final evaluation score for Pengcheng Subterranean Ruins exceeds 3. According to the grading criteria in Table 3, underground development is recommended for the Xuzhou Underground City Site in Xuzhou, and advancement strategies should be formulated. The underground museum, subway system, underground commerce spaces, and pedestrian pathways should be integrated into a cohesive structure, creating a “Hub + Landmark + Museum” complex. This will enable the entire underground space to ensure efficient pedestrian flow and transit connections in the city center while protecting and showcasing the underground heritage.

4.2. Underground Development of Ancient Buildings of Hu Bu Shan

Similarly, after conducting on-site investigations and collecting relevant information of the Ancient buildings of Hu Bu Shan, and based on a comprehensive understanding of the heritage site, the same six professionals evaluated the suitability of underground development. The resulting evaluation scores for the Ancient buildings of Hu Bu Shan are presented in

Table 8. Suitability score of underground development of Ancient buildings of Hu Bu Shan, Xuzhou City.

Objective Layer	First-Level Indicator	Indicator Code	Second-Level Indicator	Score
Suitability of Underground Resource Development of Hubu Mountain Ancient Architecture Complex, Xuzhou City	Heritage Value (A)	A1	Heritage Protection Level	2
		A2	Historical Value	2
		A3	Archeological Value	3
	Heritage Development Characteristics (B)	B1	Heritage Building Density	3
		B2	Heritage Control Zone	1
		B3	Heritage Protection Method	2
		B4	Heritage Quality	1
	Heritage Environmental Condition (C)	C1	Spatial Location	4
		C2	Current Function of Underground Space	2
		C3	Accessibility of Underground Transportation	1
		C4	Ground Transportation Condition	4
		C5	Infrastructure facilities	3
	Existing Construction Status of Heritage (D)	D1	Height of Ground Buildings	4
		D2	Scale of Heritage Site	3
		D3	Depth of Underground Development	5
		D4	Condition of Underground Remains	5
		D5	Underground Rail Transit Lines	3
	Natural Conditions (E)	E1	Geological Disasters	3
		E2	Water Quality Conditions	3
		E3	Engineering Geological Conditions	4
	Future Development Value (F)	F1	Economic Status	4
		F2	Commercial Economic Value	4
		F3	Sense of Identity Among User Groups	2
		F4	Rationality of Current Use of Heritage	2
		F5	Transportation Development (Urban Planning) Value	3

.

Similarly, we use the URDSIS-CH indicator system constructed in this article and apply the DAP method to calculate the score of each level of indicators. For the first first-level indicator, heritage value (A), the scores ${\mathrm{a}}_1,{\mathrm{a}}_2,{\mathrm{a}}_3$ of the three second-level indicators are 2, 2, and 3, respectively (see Table 8). Their degrees of correlation are sorted in the order of ${\mathrm{a}}_2,{\mathrm{a}}_1,$ and ${\mathrm{a}}_3,$ and the score values are recorded as follows: ${\mathrm{a}}_{21},{\mathrm{a}}_{12},{\mathrm{a}}_{33};$ therefore,${\mathrm{a}}_{21}=2,{\mathrm{a}}_{12}=2,{\mathrm{a}}_{33}=3,$ and through calculation, we obtain $Y_1={\beta }_1{\mathrm{a}}_{21}+{\beta }_2{\mathrm{a}}_{12}+{\beta }_3{\mathrm{a}}_{33}=2.2304$. Using the same method, we calculate that $Y_2=1.6668,Y_3=2.6201,Y_4=4.1006,Y_5=3.4226,Y_6=2.4017$.

Represent the six first-level indicators with ${\mathrm{a}}_1,{\mathrm{a}}_2,{\mathrm{a}}_3,{\mathrm{a}}_4,{\mathrm{a}}_5$, and ${\mathrm{a}}_6$, respectively. The sums of the degrees of correlation of each indicator are 0.3, 0.4, 0.55, 0.5, 0.3, and 0.65, respectively. After sorting according to the size of the degree of correlation, the order is ${\mathrm{a}}_6,{\mathrm{a}}_3,{\mathrm{a}}_4,{\mathrm{a}}_2,{\mathrm{a}}_1,{\mathrm{a}}_5$. Indicator ${\mathrm{a}}_6$ corresponds to the maximum weight ${\beta }_1,$…, Indicator ${\mathrm{a}}_5$ corresponds to the minimum weight ${\beta }_6,$ and the indicator score values are ${\mathrm{a}}_{61}=Y_6, {\mathrm{a}}_{32}{=Y}_3, {{\mathrm{a}}_{43}=Y}_4, {{\mathrm{a}}_{24}=Y}_2, {{\mathrm{a}}_{15}=Y}_1, {{\mathrm{a}}_{56}=Y}_5$. Therefore, the total score is:

$$\begin{gathered} Y={\beta }_1{\mathrm{a}}_{61}+{\beta }_2{\mathrm{a}}_{32}+{\beta }_3{\mathrm{a}}_{43}+{\beta }_4{\mathrm{a}}_{24}+{\beta }_5{\mathrm{a}}_{15}+{\beta }_6{\mathrm{a}}_{56}+\mathsf{\epsilon }={\beta }_1{Y}_6+{\beta }_2{Y}_3+{\beta }_3{Y}_4+{\beta }_4{Y}_2+{\beta }_5{Y}_1+{\beta }_6{Y}_5+\mathsf{\epsilon } \\ =0.2468\times 2.4017+0.1977\times 2.6201+0.1537\times 4.1006+0.1455\times 1.6668 \\ +0.1304\times 2.2304+0.1260\times 3.4226+0=2.7056 \end{gathered}$$

According to the evaluation results, the necessity for underground resource development in the Hubu Mountain Ancient Architecture Complex is relatively low, and should be approached with caution. The primary consideration could be the addition of underground parking facilities to alleviate ground-level parking congestion without disrupting the heritage site’s structure.

5. Discussion

The results of the underground development suitability evaluation for the Xuzhou Underground City Site and Ancient buildings of Hu Bu Shan reveal several key insights: (1) Heritage protection level does not determine the necessity of underground resource development, and not all national-level protected sites require underground development. (2) The urban and commercial centers influence the economic value and clustering effect of an area. Heritage sites located in city centers are often considered landmarks, enhancing urban image and attracting attention from governments and the public. (3) Existing underground spaces should be integrated and improved as part of heritage conservation planning. (4) The demand for underground development is proportional to surface-level functional needs and deficiencies. (5) The decision to develop underground resources is linked to the current state of heritage preservation. These conclusions underscore the holistic nature of comprehensive evaluations, where multiple interdependent factors must be considered.

When applying the evaluation system established in this research, the following points should be noted: (1) The evaluation criteria should adopt a broad perspective, integrating historical landscapes, the ecological environment, urban planning, and cultural continuity, ensuring a comprehensive assessment of heritage protection and utilization. (2) This evaluation system is not a conventional assessment of heritage intrinsic value. Instead, it focuses on non-use values, with multiple indicators aimed at protection and utilization, such as environmental value and economic use value, which are closely tied to the use value derived from heritage conservation efforts. (3) Whenever possible, evaluation criteria should be quantified as much as possible. For instance, heritage protection level and current condition should have clear quantifiable standards. For less tangible indicators (e.g., natural conditions and future development potential), evaluations should be based on research, field surveys, and expert consultation to approximate reality. (4) The three-tier indicator system presented in this study includes representative indicators, but it can be refined and expanded in actual evaluations. (5) If the project involves factors such as geological hazards, water quality conditions, and engineering site conditions that are unsuitable for underground development, a “one-vote veto” decision-making power can be applied, preventing underground development in unsuitable locations. (6) The final evaluation score should not be the sole determinant of underground development feasibility. Instead, it should serve as a scientific reference for cultural heritage underground development and related protection strategies. In practice, multidisciplinary research and analysis will be involved, requiring collaborative efforts from various fields.

Through the analysis of the indicator system, some indicators, such as Height of Ground Buildings, Scale of Heritage Site, and Depth of Underground Development, pose challenges in determining their relative importance. Many indicators are interdependent, requiring a structured analysis. For instance, heritage protection level is closely related to historical value and archeological value significance. Higher historical and archeological value often lead to a higher heritage protection level. Therefore, when evaluating such an indicator system, to address such interdependencies, the authors’ created the DAP, which addresses the theoretical challenge of determining the importance of indicators.

Heritage protection is a highly specialized field, and any underground development must comply with local laws and regulations. Currently, in China, national and local planning standards rarely mention heritage site underground development explicitly. Only the Cultural Relics Protection Law and related cultural relics protection plans include legal references for the protection of underground sites. However, this study goes beyond underground archeological site protection to discuss comprehensive underground development, including old city underground developments, subsurface utilization of individual and clustered heritage sites, and heritage protection around underground transit systems. To guide underground space development in historic districts, restrictive policy frameworks should be established. Protection planning should prioritize integrating underground development with heritage protection, coordinating aboveground and underground design, ensuring authenticity protection for immovable cultural relics, defining underground archeological zones based on archeological findings, creating systematic plans for dispersed heritage sites, and strengthening connectivity between underground and surface heritage sites to preserve urban cultural continuity, and ultimately promote the restoration of heritage landscape in historical areas.

Several limitations in this study warrant discussion. Firstly, this research is based on the context of China’s heritage protection laws, planning regulations, and policy environment. The strategies proposed are China-specific and may not be directly applicable to other countries. Heritage status, geographic conditions, conservation experience, policy frameworks, and cultural beliefs vary globally, affecting underground development feasibility. Developing nations, in particular, face unique challenges in this regard. Secondly, our analysis of Xuzhou’s heritage sites combines field investigations, government-published information, research institution findings, media observations, and data obtained from consultations with institutions such as the Natural Planning Bureau. However, time constraints may have led to gaps in observation, potentially affecting the accuracy of our judgment on heritage information. Further research should incorporate more objective data sources to enhance accuracy. Lastly, while this study focuses on the suitability factors in underground development at heritage sites in Xuzhou, the results indicate that heritage underground development is a multidimensional issue involving social, economic, environmental, and cultural factors. These factors include the current function of underground space, the accessibility of underground transportation, commercial economic value, the sense of identity among user groups, and the rationality of the current use of the heritage. These aspects are critical in determining underground development feasibility and should be explored in future research.

6. Conclusions

The author believes that the social value of underground development in cultural heritage sites is not only an opportunity for urban spatial progress but also a means to ensure the preservation of urban cultural heritage while providing cultural and educational value to society. This study organizes, selects, expands, and refines evaluation factors based on the research objectives, initially constructing a relatively comprehensive URDSIS-CH framework for assessing the suitability of the underground development of cultural heritage. By applying this evaluation system to empirical analysis, using the DAP method previously created by the author, this study aims to resolve the conflict between underground space development and cultural heritage protection through technical and methodological approaches, ensuring a more scientific approach to heritage protection and utilization.

The research findings of this paper are expected to contribute to the future development of underground resources by integrating feasibility assessments into heritage protection strategies. This would help address many challenges faced in cultural heritage protection, balancing modern urban development with historical and cultural preservation. Moreover, it is hoped that these findings will provide valuable planning insights for the overall protection of the cultural landscape in Xuzhou’s old town, which is characterized by large-scale heritage sites and historical relics, as well as for other similar historic urban areas striving to achieve urban renewal and sustainable development through heritage protection and utilization.