A Narrative of Urban Underground Pipeline System Disasters in China in 2021: Spatial and Temporal Distribution, Causal Analysis, and Response Strategies

Abstract

In recent years, there have been frequent disasters and accidents in the underground pipeline system of Chinese cities, posing a continuous threat to the safety of life and property of the public and the order of urban operations. This article uses statistical data on the spatiotemporal distribution of major underground pipeline disasters in various provinces of China in 2021. By using Pearson’s correlation coefficient and regression analysis, a causal analysis model for urban underground pipeline accidents is constructed, and the correlation between urban underground pipeline accident rate and economic and social indicators is analyzed. From the analysis, it has been found that the correlation coefficients of gross domestic product (GDP) per capita, the pipeline density in the built-up area, and the urban pipeline accident rate reach −0.4019 and −0.4275, respectively, showing a negative correlation. Further, the regression analysis results show that the underground pipeline accident rate shows a decreasing trend as the per capita GDP and the density of pipelines in the built-up areas increase. Among them, the results of the power function fitting model show that the GDP per capita accounts for 48.10% of the urban underground pipeline accidents, whereas the pipeline density of the built-up area accounts for 58.27% of these accidents. The construction of underground pipeline regulations is influential in reducing underground pipeline disaster accidents. In this study, the role and effectiveness of the factors, such as the construction of professional regulations in maintaining the safe operation of urban underground pipelines, has been discussed, and suggestions and methods to improve the problems that need to be solved, such as the construction of a municipal supporting emergency management system in the safe operation of underground pipelines in the future, have been proposed.

1. Introduction

As the economy and society of China continue to develop rapidly, the urbanization process has been promoted rapidly. Owing to this, the aging urban underground pipeline system is subjected to frequent disasters, which poses a serious threat to public safety and causes great trouble to the normal operation of social order. The urban pipeline system is buried underground in the city, and the buried pipelines can be deformed or even damaged due to road construction and other factors [1,2,3]. In addition, underground pipelines can also be affected by the surrounding soil environment, natural disasters, and other complex environmental factors, and disaster accidents can occur during the long-term burial process due to various reasons, such as failure [4], posing grave threats to public safety, and even resulting in loss of life and property [5]. The urban flooding events and gas pipeline system disasters related to underground drainage pipeline systems that occurred in 2021 in China caused significant human and property losses, of which two main representative events occurred as follows:

• Six–Thirteen Major Gas Explosion in Shiyan City

On 13 June 2021, at approximately 6:42 P.M., a major gas explosion occurred at a market in the Yanhu community of Zhangwan District, Shiyan City, Hubei Province, resulting in 26 deaths, 138 injuries, including 37 serious injuries, and a direct economic loss of CNY 53,954,100 (see Figure 1). The cause of this most tragic accident in the history of China’s city gas industry was historical in terms of corroded and aging natural gas pipelines as well as illegal construction and caused by human error due to improper handling of the accident [6].

• Zhengzhou ‘7.20’ rainstorm event

From 18:00 to 0:00 on 18 July 2021, a rare and continuous heavy precipitation occurred in Zhengzhou City, Henan Province, with heavy to very heavy rainfall all over the city and a cumulative average precipitation of 449 mm. This caused a serious incident of death and the disappearance of 390 people (see Figure 1 and Figure 2). Upon investigation, it was found that comprehensive management measures for the fragmentation of heavy rainfall and flooding emergency management include promoting the need for the articulation and integration of flood control and emergency systems, implementing flood control drills and realizing the entire emergency management process, optimizing the organizational design of flood control and emergency response, improving the coordination mechanism, establishing a flood control information sharing platform, using advanced technology to obtain more comprehensive disaster information, strengthening emergency training, and changing leadership thinking to promote emergency and promoting the matching of authority and responsibilities. The cultural integration of flood control awareness is aimed at achieving parity and breaking the dualistic concept and system of emergency services [7].

Many studies have been conducted in recent years to analyze the causes of urban underground pipeline accidents. Studies and analyses are available on the common causes of pipe-borne liquid leaks and their significant negative consequences, which provide the relevant personnel with the opportunity to implement effective corrective and safety measures [8,9]. Analyses of natural gas pipeline accidents have also been conducted, which point out that the casualties caused relate to the population and the extent of their accompanying secondary disasters that occur after the accident [10]. Studies that use data mining of underground pipeline accidents in the United States have been conducted to illustrate the trends, causes, and consequences of different pipeline accident types [11,12]. Some studies have also used the 2013 pipeline accident in Qingdao, China, as an example to analyze the accident from a systems engineering perspective based on the systems theory accident model and process and applied the game theory to explore the roles of the government and businesses in urban pipeline accidents [13]. Accidents involving urban underground pipelines have a clear impact on the lives of city dwellers and endanger urban public safety. Many studies have focused on the rational planning of urban above-ground buildings and underground pipelines, balancing the urban development rate and underground pipeline load, strengthening safety inspection and safety hazard investigation, the timely replacement of old underground pipelines, and developing an integrated information management system for underground pipelines [14,15,16]. Some scholars have developed probability-based integrated pipeline management systems to help municipal engineers make decisions in planning pipeline maintenance and rehabilitation projects for the purpose of protecting pipeline networks [17]. A complex qualitative criterion for determining the quality of the pipelines has also been proposed for underground metallic pipelines with respect to their life and quality assessment under corrosion fatigue conditions [18].

Furthermore, some researchers have compared and analyzed the detection effects of near-spaced parallel pipelines, nonmetallic pipelines, and deeply buried pipelines using various detection methods and test parameters in conjunction [19]. The use of a geo-radar instrument to detect the spatial distribution of underground pipelines, extracting location information from urban underground pipelines, and mapping underground utility pipelines has become a regular means of maintaining the safety of underground pipelines [20,21,22,23]. In recent years, China has solved some of the key problems and algorithms in the urban underground pipeline management system, as well as perform functions such as underground pipeline analysis and auxiliary decision making [24]. China has proposed countermeasures for the regulatory system, development planning management, supervision mechanism, investment construction and operation mechanism, and investment construction and operation mechanism [25], as well as expanded scientific and technological means to protect underground pipelines [26]. For example, the nonlinear law of the interaction between underground pipelines and soil has been studied using the linear elasticity of soil shear strain, viscoelasticity law, and Coulomb’s law. Thus, the seismic resistance of underground pipelines has been calculated [27] and the shell model, the finite element method, has been used to analyze the deformation of underground pipelines with large deformation [28].

With the development of geographic information systems (GIS) application technology, the establishment of a scientific three-dimensional (3D) pipeline system has become a research direction [29]. By constructing a system, users can browse underground pipelines in 3D [30]. Studies have also been conducted on the 3D numerical simulation of the underground space, in which a 3D finite element analysis model of the tunnel support structure–soil–underground pipeline coupling has been established, the construction process has been simulated, and the safety of the underground pipelines has been predicted [31]. In terms of professional pipeline research, the safety of urban heating underground pipelines has become a key issue in the research of municipal underground pipeline safety [32]. Urban gas management units, on the other hand, have summarized management points such as pipeline retesting and pipeline guardianship for underground gas pipelines in order to prevent external damage accidents and ensure the gas operation and maintenance safety [33]. To reduce the number of field inspections in underground pipeline inspection, some researchers proposed a method to predict the external corrosion rate based on a combination of six soil parameter measurements and reduced inspection corrosion rate data [34]. Models for assessing and predicting the condition of oil and gas pipelines with multiple factors, including corrosion, have also been developed using regression analysis techniques to help decision makers assess and predict the conditions of the existing oil and gas pipelines to prioritize their inspection and rehabilitation programs [35]. Studies have also been conducted to identify leak locations and monitor underground natural gas leaks by deploying sensor networks to detect methane gas concentrations [36]. Various pipeline fault detection methods have been compared in order to discuss their applicability [37]. To address the issue of underground pipeline inspection, researchers have designed and developed pipeline inspection robots which can work in inaccessible areas [38].

With the deepening of urbanization, the risk assessment of the safe operation of underground pipelines has become a research hotspot. Some researchers have developed a GIS-based fuzzy integrated risk assessment method for underground gas pipelines, created a fuzzy integrated evaluation model, calculated the relative risk values of pipelines in the region, and visualized them in a 3D geographical scene [39]. A water pipeline risk assessment method using the feedforward backpropagation neural network has also been developed to assess the adverse risk of water pipeline systems [40]. Some studies have also provided a framework structure based on machine learning and predictive algorithm models of digital twins to analyze and predict the risk probability of oil pipeline systems [41]. Studies that focus on the relationship between the consequences of pipeline failures and the underlying pipeline design variables have also been conducted, providing a valuable contribution to pipeline risk modeling [42]. Studies have been conducted to model the uncertainty involved in pipeline risk assessment problems using a combination of the relative risk scoring approach (one of the most popular techniques in pipeline risk assessment) and fuzzy logic [43]. Soft computing techniques based on fuzzy inference systems have also been developed to deal with data imprecision, uncertainty, and fuzziness in risk analysis and modeling of buried pipeline systems [44]. In a case study on Colombia’s oil transportation network, an artificial intelligence inference system has also been proposed to reduce the uncertainty of traditional risk assessment methods in pipelines [45].

The research presented in this paper involves urban underground pipeline accidents, including operation and maintenance disaster accidents such as underground pipeline bursts and urban flooding, as well as urban municipal road pavement collapse accidents that are closely related to underground pipeline operation. The purpose of this research is to analyze the current underground pipeline systems in each province of China via quantitative representation using GIS and computer mapping of the spatial and temporal distribution statistics of major municipal pipeline disasters across China in 2021 to investigate the causes of disaster accidents. Furthermore, this paper, through research steps such as spatiotemporal distribution analysis of China’s underground pipeline accident disasters in 2021, analysis of the main categories of underground pipeline problems, and correlation analysis of the causes of underground pipeline disasters, aims to examine the influence of subjective and objective factors, such as built-up area density and GDP per capita, in urban pipeline accidents by developing a correlation evaluation model to examine their potential causes, characteristics, and current status of hazards. On this basis, the development trend of underground pipeline accidents has been predicted, their role in future urban construction has been studied, and some problems and suggestions for underground pipeline accident prevention have also been proposed.

2. Spatial and Temporal Distribution of Underground Pipeline Accident Disasters in China in 2021

2.1. Data Sheet

The year 2021 was one of frequent underground pipeline disasters in Chinese cities. In 2021, the Underground Pipeline Professional Committee of the China Society of Surveying, Mapping and Geoinformation and the Beijing Research Center for Comprehensive Management of Underground Pipelines provided excellent statistical data on underground pipeline accidents in China. The research data were from a credible and authoritative source. The data used in this study are from the China Underground Pipeline Accident Statistical Analysis Report (2021). This annual report focuses on the accident information in China for the year 2021 and analyzes the types of accidents, the time distribution, the location distribution, and the causes of accidents. The data can enhance the understanding of the researchers from the point of view of the accident pattern and safety status of the underground pipelines in China, as well as the importance of underground pipeline safety management. The common types of underground pipeline disaster accidents that occurred in China in 2021 are shown in Figure 3.

2.2. Accident Statistics and Analysis

A total of 1723 underground-pipeline-related accidents were collected in China in 2021. Among them were 1355 underground pipeline damage accidents, accounting for 78.64% of the total number of underground-pipeline-related accidents, 347 roadway collapse accidents, accounting for 20.14% of these accidents, and 21 other types of accidents, accounting for 1.22% of these accidents. The accidents caused 76 fatalities and 317 injuries. The statistical chart of various types of underground-pipeline-related accidents in China in 2021 is shown in Figure 4.

2.2.1. Main Types of Accidents

(1)

Manifestation of accidents

Based on the manifestation of accidents, 12 categories of underground-pipeline-related accidents were collected in 2021, namely, leakage, cable failure, explosion, fire, blockage, manhole cover type accident, equipment and facility damage, road collapse, poisoning and asphyxiation, fall, urban flooding, and integrated pipeline corridor accident.

Among them, water supply, drainage, gas, and heat pipeline leaks had the highest number of accidents, reaching 1076, accounting for 62.45% of the total number of pipeline-related accidents in the city. Explosion accidents caused the highest number of casualties, resulting in 45 deaths and 235 injuries. The percentage of various types of underground-pipeline-related accidents in China in 2021 is detailed in Figure 5.

(2)

Underground pipeline damage accidents.

Underground pipeline damage accidents can be divided into eight categories depending on the type of pipeline facilities: electricity, telecommunications, water supply, drainage, gas, heat, industrial pipeline accidents, and manhole cover accidents. Among them, the number of water supply line damage accidents was the largest, with 719 cases, accounting for 53.06% of the total number of underground pipeline damage accidents. A total of 61 people were killed, and 271 people were injured in these accidents. The number of underground pipeline vandalism accidents and casualties of each category are detailed in Figure 6.

2.2.2. Main Causes of Accidents

(1)

Underground pipeline damage accidents.

Underground pipeline damage accidents are caused by four factors: structural hazards, external damage, environmental factors, and management flaws. Underground pipeline damage accidents caused by their own structural hazards were the most common, accounting for 783 cases and accounting for 57.79% of all underground pipeline damage accidents. Accidents caused by external damage were the second most frequent, reaching 441 cases, 32.55% of the total number of underground pipeline damage accidents. There are 58 underground pipeline damage accidents with unknown causes due to the lack of information collected or lack of understanding of their causes.

In the different types of underground pipelines, accidents of water supply lines, drainage lines, heat pipelines, industrial pipelines, and manhole covers are mainly caused by their own hidden structural problems. Gas pipelines, power cables, and telecommunication cables are mainly damaged by external forces. See Figure 7 for more details on the causes of underground pipeline damage accidents of various types.

(2)

Pavement collapse accidents

Based on the statistics, the causes of pavement collapse accidents can be classified into five categories, namely, underground pipeline problems, engineering construction, soil disease, natural disasters, and gravity load. Among the pavement collapse accidents with clear causes, the maximum number of pavement collapse accidents caused by underground pipeline problems reached 65, accounting for 18.73% of the total number of underground pipeline damage accidents. Due to the lack of information collected or the cause of the accident to be investigated, there were 204 roadway collapse accidents with unknown causes. The percentage of causes of roadway collapse accidents is detailed in Figure 8.

2.3. Time Distribution Trend

In terms of accidents occurring in different months, the maximum number of underground-pipeline-related accidents occurred in November 2021, reaching 220 accidents, corresponding to 12.77% of the total number of underground-pipeline-related accidents. The month-wise distribution of these accidents is detailed in Figure 9.

2.3.1. Underground Pipeline Damage Accident

Out of the 1355 underground pipeline vandalism accidents, the highest number of accidents, namely 195, occurred in November 2021, accounting for 14.39% of the total number of underground pipeline vandalism accidents.

Out of the 116 power cable accidents, the highest number of accidents occurred in August 2021, with 14 accidents accounting for 12.07% of the total number of power cable accidents. Out of the 27 telecommunications cable accidents, the highest number of accidents occurred in February 2021, with 5 accidents accounting for 18.52% of the total number of telecommunications cable accidents. Out of the 719 water supply line accidents, the highest number of accidents occurred in November 2021, with 94 accidents accounting for 13.07% of the total number of water supply line accidents. Out of the 94 drainage line accidents, the most accidents occurred in May 2021, totaling 15 accidents, accounting for 15.96% of the total number of drainage line accidents. Out of the 230 gas line accidents, the most accidents occurred in November 2021, totaling 34 accidents, accounting for 14.78% of the total number of gas line accidents. Out of the 142 heat line accidents, the most accidents occurred in November 2021, with a total of 49 accidents accounting for 34.51% of the total number of accidents in thermal pipelines. Out of the 22 accidents in the category of manhole covers, the most accidents occurred in May 2021, with a total of 4 accidents accounting for 18.18% of the total number of accidents in this category. In the case of industrial pipeline accidents, a total of five accidents occurred in four months in the rare gas and crude oil industries.

The monthly distribution of underground pipeline damage accidents of various categories is detailed in Figure 10.

2.3.2. Road Cave-In Accidents

Among the 347 roadway collapse accidents, August 2021 had the highest number of accidents, with a total of 46 accidents, thus accounting for 13.26% of the accidents of this type. A total of 196 roadway collapse accidents occurred cumulatively from June to October 2021, accounting for approximately 56.48% of the total number of roadway collapse accidents. The monthly distribution of these accidents is detailed in Figure 11.

2.4. Spatial Distribution

2.4.1. Scope Distribution

Among the 1723 underground-pipeline-related accidents, 1405 occurred within the city roads, accounting for 81.54%, whereas 318 occurred outside the city roads, accounting for 18.46% of the total number of accidents.

2.4.2. Province Distribution

In China, there are various factors that can affect the safety of underground pipelines, and different geographic environments may also affect the safety of urban underground pipelines. First, the economic development level and investment in pipeline construction and information technology are determined by the different geographical locations of cities, which in turn affect the safety of urban underground pipelines. At the same time, different geological environments in cities where underground pipelines are located may have varying impacts on the safety of underground pipelines. From the distribution of provinces, a total of 32 provincial areas (including municipalities directly under the Central Government, autonomous regions, and special administrative regions) recorded underground-pipeline-related accidents in 2021. Among them, a large number of accidents occurred in Shandong Province, Henan Province, and Guangdong Province, with the number of accidents being 141, 140, and 128, respectively, corresponding to 8.18%, 8.13%, and 7.43% of the total number of underground-pipeline-related accidents. The Tibet Autonomous Region and the Macao Special Administrative Region were not counted in underground-pipeline-related accidents. The distribution of underground pipeline accidents in each provincial area is detailed in Figure 12.

The largest number of road collapse accidents occurred in Henan Province, Shaanxi Province, and Guangdong Province, with the number of accidents being 41, 36, and 27, corresponding to 11.82%, 10.37%, and 7.78% of the total number of underground pipeline damage accidents (Xinjiang Uygur Autonomous Region, Tibet Autonomous Region, Hong Kong Special Administrative Region, Macao Special Administrative Region, and Taiwan Province did not record road collapse accidents). Other accidents occurred in Jiangsu Province, Anhui Province, Shandong Province, Guangdong Province, Chongqing Municipality, Sichuan Province, and 15 other provincial areas (including municipalities, autonomous regions, and special administrative regions). The main accident types were poisoning and asphyxiation, urban flooding, and falls.

The statistics of the number of underground pipeline damage accidents, the number of road collapse accidents, and the number of other accidents according to different provinces (administrative regions) in China in 2021 are detailed in Figure 13.

3. Analysis of the Main Types of Underground Pipelines in China in 2021

3.1. Problems of Main Types of Underground Pipelines

3.1.1. Underground Water Supply Pipeline

The urban water supply pipeline is mainly composed of pressurized pipelines. The reasons for the frequent accidents of underground water supply pipelines are mainly manifested in the following three aspects: the urban underground water supply pipelines generally have poor pipe quality, poor operation environment, long-term over-limit operation, long-term disrepair, aging equipment, and serious corrosion. These factors result in pipe bursts and various forms of open and hidden leakage. In addition to the historical reasons for the imperfect pipeline system and pipeline aging, pipeline maintenance is not in place, and pipeline siltation, blockage, corrosion, leakage, and other hidden diseases are present that cannot be found and eliminated in time. These are also important reasons for the occurrence of underground water supply pipeline accidents. In addition, the lack of basic data on underground water supply pipelines, especially nonmetallic underground pipelines, leads to unclear positioning of the pipelines and accidents of broken pipelines due to external construction occurring from time to time.

3.1.2. Underground Drainage Pipeline

Drainage pipeline accidents can be divided into three categories: leakage, blockage, and collapse. From a comparison of the number of accidents occurring within the three categories, it can be seen that pipeline collapse occurs more frequently than leakage and blockage. Pipeline corrosion, well damage, perforation, pipeline deformation, pipeline damage, joint dislocation, joint leakage, well cracks, bottom hole damage, cracks, wall damage, and so on are the 15 categories of drainage pipeline accidents. Because the drainage pipeline is scoured and corroded during use, pipeline corrosion and cracks are the most common accidents. The drainage pipeline is typically installed beneath the road and bears specific soil and ground loads. Uneven stress is easily caused by uneven load, resulting in rupture and leakage. Pipeline damage is primarily caused by poor construction during the urban construction process [46,47,48].

3.1.3. Underground Gas Pipeline

There are many reasons for the occurrence of gas accidents. In the process of gas transmission and distribution, inadequate management or weak safety awareness will cause accidents, which will have a negative impact on people’s body and mind, property and social stability, and development. Therefore, it is necessary to understand every link in the gas operation process that may have hidden dangers and affect the reliability of the overall gas supply system, summarize and conclude the safety accidents, analyze the causes of hidden dangers and risks, and conduct control and management to avoid the occurrence of accidents [49]. Underground gas pipeline problems include illegal operation, pipeline aging and corrosion, temperature change and soil settlement, nonstandard construction management, and illegal occupation.

3.2. Road Collapses

In recent years, road collapses caused by underground pipeline incidents have become increasingly frequent in China. Field investigations and scientific research on urban road collapse disasters have shown that the vast majority of collapse disasters can be attributed to three causes: aging and leakage of underground pipelines, disturbances caused by construction activities related to underground space development, and natural damage. Most of the underground pipelines in most Chinese cities were installed after the reform and opening-up policy, and their lifespan has reached the “mid-to-late stage.” Due to the lack of maintenance and repair for a long time, the pipelines have been damaged and leaked. In addition, overloading operations of the underground pipeline, combined with problems in the foundation layer, can easily cause road collapse disasters. Especially with the rapid development of cities, a large amount of underground space has been developed, causing significant disturbance to the underground environment. In particular, it can severely damage the collapsible soil structure below ground. When the collapsible soil is soaked under a certain pressure, the strength of the soil layer decreases, the soil loses its viscosity, and large additional sinking may occur, leading to ground subsidence and potential road collapse. Moreover, underground pipeline networks often experience leakage, which can easily create voids in the ground. The causes of road collapses in urban areas are complex, with various factors interacting and compounding with each other, but without a doubt, underground pipelines are one of the important causes of these disasters.

4. Correlation Analysis of the Causes of Underground Pipeline Disasters

From a macro perspective, the construction and management of urban underground pipelines are closely related to the level of urban economic development. The development of urbanization promotes the construction of underground pipelines. At the same time, with the improvement of the economy, an increasing amount of attention is being paid to the safety of underground pipelines. The planning and design of underground pipelines are scientific and based on the selection of technical methods that are more conducive to safety in terms of pipeline materials, laying methods, and construction quality. Therefore, studying the relationship between underground pipeline accidents and economic and social indicators will help to provide a basis for decision making on underground pipeline construction management.

4.1. Index Selection

In this study, the rate of pipeline accidents in each province and city was used as the evaluation index of the severity of the underground pipeline accident disaster in each province and city. The per capita GDP of each province and city and the pipeline density of the built-up area were selected as the economic and social indicators for the correlation analysis.

The rate of pipeline accidents is generally expressed by the number of accidents per unit length of pipeline per year and is usually expressed in the units of km⁻¹ × a⁻¹. The total pipeline length has been calculated in this study based on the length data on the water supply pipeline, gas supply pipeline, artificial gas supply pipeline, liquefied petroleum gas supply pipeline, heat pipeline, and drainage pipeline of each province (city, district) at the end of 2021 given in the ‘2021 China Urban—Rural Construction Statistical Yearbook’. Despite the lack of pipeline data, such as power and communication, the total length of the pipeline is still representative.

The rate of pipeline accidents, per capita GDP, and built-up area pipeline density calculation results are outlined in

Table 1. Underground pipeline accident rate, per capita GDP, and pipeline density of built-up area in each province (city, district).

Provinces and Cities	Ten Thousand Kilometers Pipeline Accident Rate (km−1 × a−1)	Per Capita GDP (Million Yuan)	Pipeline Density of Built-Up Area (km/km2)
Beijing	2.60	18.40	104.40
Tianjin	0.98	11.43	107.06
Hebei	3.77	5.42	58.19
Shanxi	4.17	6.49	60.44
Inner Mongolia	7.48	8.55	50.46
Liaoning	3.87	6.52	58.36
Jilin	6.35	5.57	50.62
Heilongjiang	5.62	4.76	40.72
Shanghai	2.37	17.36	78.00
Jiangsu	1.59	13.68	67.15
Zhejiang	2.34	11.24	64.74
Anhui	4.43	7.03	43.16
Fujian	4.36	11.66	41.32
Jiangxi	3.42	6.56	42.24
Shandong	3.98	8.17	53.58
Henan	9.24	5.96	32.78
Hubei	6.17	8.58	50.02
Hunan	5.21	6.96	43.64
Guangdong	3.05	9.81	49.30
Guangxi	6.82	4.91	35.80
Hainan	8.72	6.35	50.41
Chongqing	3.23	8.68	45.13
Sichuan	4.18	6.43	53.30
Guizhou	6.31	5.08	37.37
Yunnan	8.51	5.79	38.46
Shaanxi	8.18	7.54	39.25
Gansu	6.95	4.11	35.70
Qinghai	0.00	5.63	55.82
Xinjiang	2.62	6.17	40.16
Tibet	0.00	5.68	54.10
Ningxia	23.36	6.24	12.10

.

4.2. Method

4.2.1. Pearson’s Correlation Coefficient

The correlation coefficient is an important indicator that statistically describes the correlation characteristics of various monitoring parameters and indicates the degree of influence of a variable changing with another variable. Its value is between −1 and 1. A correlation coefficient greater than 0 indicates a positive correlation, less than 0 indicates a negative correlation, and 0 indicates no correlation. In other words, the greater the absolute value of the correlation coefficient, the higher the correlation between the variables. Its calculation formula is as follows:

$$r=\frac{\Sigma \left(x-\overline{x}\right)\left(y-\overline{y}\right)}{\sqrt{\Sigma {\left(x-\overline{x}\right)}^2\cdot \Sigma {\left(y-\overline{y}\right)}^2}}$$

where the value of $r$ is [−1,1], x represents the independent variable, i.e., the economic and social index, y represents the dependent variable, i.e., the pipeline accident rate, and $\overline{x}$, $\overline{y}$ represent the mean values of each variable, respectively.

4.2.2. Regression Analysis

Regression analysis focuses on the law of quantity change between the variables, i.e., using continuous curves to approximately describe or provide an analogy of the functional relationship between the coordinates represented by discrete point groups on the plane and then determining the degree of influence of one or more variables on another variable. The goal of regression analysis is to minimize the distance between the predicted and observed values on the regression line. In general, the deviation between the regression line fitted by the least-squares method and the sample data which point in the vertical direction is the lowest.

4.2.3. Coefficient of Determination

$R^2$ represents the coefficient of determination of the regression equation whose value is between 0 and 1. The closer it is to 1, the stronger the explanatory power of the independent variable to the dependent variable. It is calculated as follows:

$$R^2=1-\frac{\Sigma {\left(y-\widehat{y}\right)}^2}{\sum {\left(y-\overline{y}\right)}^2}$$

where y represents the dependent variable, i.e., the actual value of the pipeline accident rate, $\widehat{y}$ represents the predicted value of the pipeline accident rate, and $\overline{y}$ represents the mean value of the actual value of the pipeline accident rate.

4.3. Results

Because some provinces and cities are significantly affected by environmental factors (Henan Province and Shaanxi Province had more rainfall in 2021, Xinjiang had less rainfall, with an annual rainfall of only 154 mm, and the length of underground pipelines in Ningxia, Qinghai, and Tibet are shorter), it is impossible to accurately reflect the relationship between the rate of underground pipeline accidents and the economic and social indicators. Therefore, in this study, the samples that are greatly affected by accidental factors, such as weather and insufficient pipeline length, were eliminated, and 25 provinces (cities and districts) were taken as the samples for the simulations.

4.3.1. Results of the Correlation Analysis

From the calculation, it has been observed that the correlation coefficient between the pipeline accident rate and the per capita GDP reaches −0.4019, and the correlation coefficient between the pipeline accident rate and the pipeline density reaches −0.4275, i.e., the pipeline accident rate is negatively correlated with the per capita GDP and the pipeline density in the built-up area.

4.3.2. Results of the Regression Analysis

As shown in Figure 14 and Figure 15, the power function was used to fit the pipeline accident rate as a function of the per capita GDP and pipeline density in the built-up area. It is observed that with the increase in the per capita GDP and pipeline density in the built-up area, the pipeline accident rate shows a rapid downward trend. This shows that through reasonable planning and design, the safety of pipeline operation can still be ensured in the case of increasing pipeline density.

Table 2. Fitting results of pipeline accident rate as a function of the per capita GDP and pipeline density.

	Linear Fitting		Power Function Fitting
	Formula	${\mathit{R}}^2$	Formula	${\mathit{R}}^2$
Per capita GDP	$y=-0.3522x+7.612$	0.4019	$y=27.124x^{-0.918}$	0.4810
Pipeline density	$y=-0.0733x+8.6454$	0.4275	$y=932.45x^{-1.371}$	0.5827

presents the simulation results.

5. Discussion

5.1. Main Causes of Urban Underground Pipeline Disasters in China in 2021

The problem of underground pipeline disasters in China in 2021 is the epitome of the social problems brought about by the rapid urbanization of Chinese society in recent years. After considering the statistics of disasters in China’s underground pipeline system, a correlation analysis of the typical cases was carried out. Studying the statistical analysis report on the national underground pipeline accidents (2021), it was found that the number of accidents related to underground pipelines collected in 2021 increased by 484 compared to those in the year 2020, indicating a growth rate of 39.06%. The number of deaths caused by accidents decreased by 8, and the number of injuries increased by 88. Among them, the collected underground pipeline damage accidents increased by 422, a growth rate of 45.23%, and the collected road collapse accidents increased by 84, showing a growth rate of 31.94%. Other accidents collected were observed to be reduced by 22. The above data indicate that with the acceleration of urbanization, an increasing number of problems have been exposed to the development of underground space. For example, extreme rainstorm events exceed the urban drainage capacity, resulting in waterlogging incidents in some public places, and drowning caused by the inability of personnel in the subway to be transferred in time. Similarly, in gas pipelines, improper operation by staff often leads to disasters at the cost of life. The aforementioned examples illustrate that while carrying out the large-scale construction of underground pipelines, the pipeline management department should also enhance their awareness of prevention in advance, such as strengthening training programs for related personnel to deal with unforeseen events such as pipeline disasters.

5.2. Trend of Underground Pipeline Disasters in China

Based on the data on underground pipeline accidents in China in the past three years, from the investigation performed in this study, it has been observed that the number of accidents related to underground pipelines collected in 2021 is 484, more than that in 2020, with a growth rate of 39.06%. The number of deaths caused by accidents has decreased by 8, whereas the number of injuries has increased by 88. Among them, the collected underground pipeline damage accidents have increased by 422, a growth rate of 45.23%, and the collected road collapse accidents have increased by 84, with a growth rate of 31.94%. Other accidents have reduced by 22. The number of accidents related to underground pipelines collected in 2019, 2020, and 2021 increased every year, with an average annual growth rate of 87.90%. Among them, the average annual growth rate of underground pipeline damage accidents is 97.89%, and that of road collapse accidents is 80.93%. From 2019 to 2021, the number of accidents related to underground pipelines and the casualties collected are shown in Figure 16, and the monthly distribution of these accidents is shown in Figure 17. The above data indicate that with the accelerated urbanization process in China, there has been a certain increase in underground pipeline accidents and casualties. In the future, urban management work needs to pay attention to the damage caused by road construction to underground pipelines and strengthen preventive measures against issues such as road collapse. These are the aspects that need to be emphasized in the future management of underground pipelines in Chinese cities.

5.3. Causes and Countermeasures

In the past 30 years, China’s urbanization process has occurred rapidly. With the expansion of cities, government departments have been paying an increasing amount of attention to the use of underground space. On analyzing a few underground space accidents in China in this study, it has been observed that the improvement of the social management system is very important for the safe operation of the urban underground pipeline system. For example, in the face of extreme rainstorm weather, the urban managers should comprehensively enhance the drainage capacity of the city’s facilities, especially in weak areas. It is necessary to upgrade drainage facilities and improve drainage capacity to make up for the shortcomings of urban construction. In addition, it is necessary to build refuge and escape infrastructures such as underground tunnels, underground passages, subways, and underground parking lots in vulnerable areas and set eye-catching escape and refuge indication signs. Finally, a comprehensive investigation of the high-risk hidden danger areas should be carried out, and preventive measures and emergency management should be set up in advance. In particular, emergency management and disposal plans, mass evacuation routes, and strategies in the face of different levels of rainstorm and flood disasters should be developed, and the soft power of risk management and control should be enhanced. Another example is the gas explosion accident. When combing the accident reflection, it can be seen that many accidents cause serious casualties because preventive safety countermeasures are not in place. The information held by the emergency rescue department is incomprehensive when the accident occurs. The units responsible for the dangerous pipelines have not submitted pipeline burial status to the local government in order for them to make a record of this, thus resulting in a lack of clarity in the government regarding the underground pipeline situation, easy misjudgment, and failure to take effective control measures in time to reduce risks. The aforementioned issues all need to be avoided in future work.

5.4. Future Management of Urban Underground Pipelines

• Underground pipeline safety life cycle management.

At present, safety life cycle management has become the main means of the construction, management, and maintenance of underground pipelines in China. Underground pipeline safety life cycle management (product life cycle management) refers to the information and processes involved in the entire life cycle of underground pipeline management, beginning with demand and ending with recycling and disposal. Concurrent design, agile manufacturing, collaborative design and manufacturing, networked manufacturing, and other advanced design and manufacturing technology are all supported. To ensure the safety of urban underground pipeline construction and operation in the future, underground pipelines will be efficiently supervised by safety life cycle management. For example, monitoring the entire safety life cycle of subway tunnels during the construction process can ensure the operation of the entire safety life cycle of subway tunnels to a certain extent.

• Information management based on digital twin technology.

Digital twin technology is currently widely used in the construction of underground pipelines in China. The digital twin technique fully utilizes information technology to create a physical model of underground pipeline objects, integrates sensors, operation history, and other data, completes entity mapping in virtual space, and employs simulation technology to represent the entire life cycle process of the corresponding entity equipment. The safe operation of urban underground space in the ‘virtual world’ is promoted by simulating the operation status of underground pipelines.

• Regulations on underground pipeline construction, management, and informatization development.

China’s urban underground pipeline regulatory development work is gradually underway and has had a national impact. As shown in

Table 3. Summary of local regulations on underground pipelines in some Chinese cities.

Number	Province/City	Local Regulations on Underground Pipelines	Publishing Unit	Implementation Date
W	Hebei Province	Regulations on Underground Pipelines in Cities of Hebei Province	Standing Committee of Hebei Provincial People’s Congress	1 September 2015
2	Taiyuan City	Regulations on Underground Pipelines in Cities of Taiyuan	Standing Committee of Taiyuan Municipal People’s Congress	1 May 2016
3	Nanjing City	Pipelines Management Regulations in Nanjing	Standing Committee of Nanjing Municipal People’s Congress	1 September 2018
4	Huai’an City	Regulations on Underground Pipeline Management in Huai’an City	Standing Committee of Huaian Municipal People’s Congress	1 November 2017
5	Hangzhou City	Regulations on Urban Underground Pipeline Construction and Management in Hangzhou	Standing Committee of Hangzhou Municipal People’s Congress	1 January 2009
6	Hefei City	Regulations on Underground Pipeline Management in Hefei City	Standing Committee of Hefei Municipal People’s Congress	1 March 2019
7	Qingdao City	Regulations on Underground Pipeline Management in Qingdao City	Standing Committee of Qingdao Municipal People’s Congress	1 November 2016
8	Zibo City	Regulations on Underground Pipeline Management in Zibo City	Standing Committee of Zibo Municipal People’s Congress	1 January 2017
9	Changsha City	Regulations on Underground Pipeline Management in Chongqing City	Standing Committee of Changsha Municipal People’s Congress	1 January 2017
10	Zhuhai City	Regulations on Archives Management of Urban Underground Pipeline Engineering in Changsha City	Standing Committee of Zhuhai Municipal People’s Congress	1 May 2005
11	Chongqing City	Regulations on Underground Pipeline Management in Zhuhai City	Standing Committee of Chongqing Municipal People’s Congress	1 August 2009
12	Yibin City	Regulations on Urban Pipeline in Chongqing City	Standing Committee of Yibin Municipal People’s Congress	1 January 2017
13	Kunming City	Regulations on Underground Pipeline Management in Yibin City	Standing Committee of Kunming Municipal People’s Congress	1 October 2018
14	Shaanxi Province	Regulations on Underground Pipeline Management in Kunming City	Standing Committee of Shaanxi Provincial People’s Congress	1 March 2013
15	Ningxia Hui Autonomous Region	Regulations on Underground Pipeline Management in Shaanxi Province	Standing Committee of Ningxia Hui Autonomous Regional People’s Congress	1 October 2013
16	Yinchuan City	Regulations on Urban Underground Pipeline Management in Ningxia Hui Autonomous Region	Standing Committee of Yinchuan Municipal People’s Congress	1 September 2017

, some Chinese cities will have implemented underground pipeline legislation by 2021. These local laws and regulations have had some success in preventing underground pipeline accidents, and thus the number of underground pipeline disasters has decreased in many cities.

6. Conclusions

This article uses Pearson’s correlation coefficient and regression analysis to construct a model for analyzing the causes of urban underground pipeline accident disasters. Through correlation analysis between the accident rate of urban underground pipelines and economic and social indicators, the study found that per capita GDP, density of pipelines in built-up areas, and urban pipeline accident rate showed a significant negative correlation. This study shows that owing to urbanization, urban underground pipeline disaster accidents are closely related to urban expansion, social and economic development, population growth, pipeline facilities aging, and other issues. These disasters are inevitable in a certain period of time, but they can be efficiently controlled mainly by means of strong construction rules and regulations, from the stage of planning, design, operation, and maintenance mode to supervise the entire safety life cycle of underground pipelines in order to promote the safe operation of the pipeline.

The use of new technologies in the control of underground pipeline disasters has become very important in recent years. First, geophysical prospecting technology can objectively find the buried status of the underground pipelines, thus enabling the control and monitoring of these pipelines. In addition, the application of underground pipeline information technology can enable most cities in China to have the ability of underground pipeline information management which, to a certain extent, ensures the safe operation and maintenance of these pipelines. Finally, the detailed application of underground pipeline information can accurately predict the construction and operation risks of underground pipelines, especially in the application of safety evaluation, promoting scientific rationality in urban underground pipeline construction and, to some extent, reducing the occurrence of underground pipeline accidents.

At the same time, underground pipeline management plays a critical institutional role. At the moment, many cities in China are gradually establishing relevant laws and regulations on urban underground pipeline informatization, which protects the construction and safe operation and maintenance of underground pipelines, avoids accidents, and improves accident handling capacity and methods.