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As the strategy for building China's strength in transportation continues to advance, people's demand for the quality of travel is increasing. Rail transit has become the lifeline for high-quality development in urbanization. Especially for intercity railways, suburban railways, and metros, which are mainly built through urban areas and are mostly laid underground, resulting in numerous urban tunnels. Due to the complex urban environment, tunnels inevitably pass above, below, or alongside existing buildings and structures such as railways, metros, highways, main urban roads, and high-rise buildings (hereinafter referred to as close-spaced engineering). How to ensure the normal operation and safety of close-spaced engineering during tunnel construction, as well as how to reasonably determine the deformation control standards for close-spaced engineering, are the focus, difficulty, and control points of urban tunnel construction. This article categorizes by adjacent railway, highway, urban rail transit, and underground pipelines, systematically sorts out the standards of related industries, and proposes protection ranges and requirements for tunnels in different environments, deformation control standards for close-spaced engineering construction. Based on the control standards and engineering experience, a set of design and construction control measures for close-spaced engineering are proposed: During the survey phase, it is necessary to ascertain the surrounding environment and geological conditions. During the design phase, on the basis of reasonably designing the route scheme and keeping enough safe clearance, adopt reasonable construction methods and reliable supporting structures, and set up effective isolation, protection, and reinforcement measures. During the construction phase, strengthen tunnel geological prediction and monitoring, and establish perfect contingency plans. [ABSTRACT FROM AUTHOR]

Using phosphogypsum (PG) as the aggregate of cemented backfill is an economical and effective method of PG utilization. However, the stability and performance of cemented backfill are challenged by the rich fluoride content in PG. In this study, the effects of citric acid pretreatment on PG defluorination, backfill performance and environmental behavior were investigated by washing PG with different concentrations of citric acid and washing times. The results showed that the citric acid pretreatment could significantly reduce the fluoride content in PG and promote the hydration reaction with the binder, thus greatly reducing the usage and cost of the binder in actual production. Considering the efficiency of defluorination, the optimal citric acid concentration and washing times were determined to be 4% and 7–8 times, respectively. In addition, after citric acid pretreatment, the viscosity and setting time of the backfill slurry and the porosity of the backfill reduced, and the strength of the backfill improved, which was conducive to slurry pipeline transportation and underground mine stability. Finally, a further analysis of environmental behavior was conducted and it was found that the citric acid washing greatly reduced the content of fluoride in the bleeding water of slurry and the backfill leachate, which met the integrated wastewater discharge standard in China. The results of this study can provide important guidance for the large-scale recycling and environmental management of PG. [ABSTRACT FROM AUTHOR]

Urban ground collapse is a common geological disaster characterized by its invisible nature, particularly in China, and results in significant socioeconomic losses and even loss of life. Underground pipeline breakage is the most common factor leading to urban ground collapses. Hence, it is essential to study how different types of pipeline breakages initiate the collapse mechanism. In this study, an indoor model test was conducted to directly observe the process of collapse due to broken pipe leakage. A broken pipe was put into a model box and tested by an experimental device. The results showed that among the different pipeline breakage types, vertical damage had the greatest influence on the degree of cavity development and ground collapse. Similarities were observed in the patterns of cavity evolution development and the extent of ground collapse as well, further revealing the significance of the cavity evolution process in predicting ground collapses. [ABSTRACT FROM AUTHOR]

Urban ground collapse (UGC) is becoming more common in China, resulting in significant socioeconomic losses and even personal casualties. The frequency of UGC accidents is highest in the east coastal area owing to developed urbanization, while it is lowest in the northeast area because of its smallest land area. Natural causes (such as geological conditions and rainfall) and artificial causes (such as groundwater withdrawal, underground pipeline breakage, underground engineering, and other reasons) all contribute to UGC accidents in China. Groundwater influences most factors that lead to UGC. Adverse geology, such as collapsible loess and karst geology, is sensitive to groundwater. The groundwater environment is vulnerable to rainfall, pipeline leakage or groundwater withdrawal. Under the action of groundwater, the steady state of the soil may change, which finally leads to UGC. Groundwater control, which is essential for mitigating the risk of UGC, can be implemented through detailed geological surveys, sponge city and utility tunnel construction, and groundwater–level control measurement. [ABSTRACT FROM AUTHOR]

In the past several years, the high frequency of cave-in failures of urban roadways has posed a serious threat to the safety of traffic, pedestrians, and existing structures and facilities in China, and they have often led to fatalities, injuries, and significant economic losses. First, this study collates 379 cases to characterize roadway cave-in failures. Then the major causes associated with these events are classified, which includes damage and defects on preexisting underground structures and facilities, washout and erosion of roadway subgrade by seepage water, underground construction, loose subgrade, excessive lateral wall movement and through-wall leaking of deep excavations adjacent to roadways, and rapid decline in water table levels. Then four enormously influential failure cases are described as typical examples. Finally, the primary characteristics of the cave-in failures are discussed, including their temporal and spatial distributions, sizes, and morphologies, as well as the number of casualties and injuries involved. This review concludes that it is of paramount importance to inspect healthy conditions of aging underground structures and pipelines and to adopt or develop reliable measures to check unseen loose zones, voids, and cavities underneath urban roadways, in particular those adjacent to construction sites, with erodible subsurface conditions, or frequently subject to disturbing forces (seepage flow and vibration). [ABSTRACT FROM AUTHOR]

Land reclamation has become an important way to take land from the sea or wetlands, in order to create much more living space in over-crowded coastal areas. However, there is serious soil salinization of hydraulic fill, where most offshore sediments are added into the surrounding seawater with a generally high salt content. The hydraulic fill project also causes the groundwater discharge path to be extended. These impacts have posed a great challenge on the efficiency of investment and the speed of ecological environmental recovery. Therefore, it is very necessary to accurately predict the desalination process, rate and duration for land use planning and ecological environment restoration in reclaiming coastal areas. Taking the coating finishing project in the eastern new area of Taizhou in Eastern China as a research area, a DRAINMOD-S model was extended to the simulation and prediction of natural desalination process in hydraulic reclamation. The hydrological and desalination process in the model were calibrated using the hydrological and salt data from the regional monitoring points after one year of reclamation. Two modes were selected to implement the field test, including the natural desalination and the specific desalination process under comprehensive control measures. In natural desalination, the salt of dredger fill under the rainfall was discharged from the soil along the drainage into the nearby river. In specific desalination, the comprehensive treatments were mainly composed of the water conservancy, supplemented by biological control measures, thereby to speed up the output of salt. The results show that the DRAINMOD-S model better simulated the hydrological process and the salt leaching of hydraulic fill. The variation of groundwater level was basically consistent with the measured value. Specifically, the average deviation was -3.4 cm, while the average absolute deviation was 6.9 cm, and the root mean square error was 8.60 cm and the correlation coefficient was 0.79, as well as, the average deviation of soil salt concentration was -0.08 g/L, while the average absolute deviation was 0.20 g/L, and the root mean square error was 0.24 g/L and the correlation coefficient was 0.91. The soil salt of hydraulic fill was slowly decreasing under the natural rainfall and river drainage, where the annual average desalination rate was 0.45 g/L, while, the duration for the soil to reach the desalination standard was about 27 a. In contrast, the comprehensive treatments greatly shortened the desalination of dredger fill, where the average annual desalination rate increased to 0.73-1.80 g/L, while the desalination time reduced to 3-13 a. As such, the comprehensive treatments can be technically feasible to rapidly leach and drain the salt. In theoretical case, the better leaching can be achieved in the deeper buried depth and the smaller distance between underground pipelines, but the investment cost would be relatively high. Therefore, an optimal strategy can be further selected to balance multiple factors, such as the actual needs of project and investment budgets. The proposed model can be expected to serve the preliminary prediction for the land-building projects, land use management, and ecological environment reconstruction. [ABSTRACT FROM AUTHOR]

Soil erosion is a serious hazards occurring in overlaying diluvial fans of shallow underground pipelines. To learn the extent of soil erosion in such landforms, we propose a method of susceptibility assessment of soil erosion based on a case study of the Chaka diluvial fan, Qinghai Province, China. First, we conducted a field investigation at 24 sites, to obtain the land surface properties. Then, vital information such as soil anti-scouribility, permeability, density, sectional water volume, and pipeline burial depth was collected. The slope grade and the vegetation index were determined with the geographic information system (GIS) technology. Further, the analytic hierarchy process (AHP) was used to determine the weight of various indices on the potential susceptibility of shallow underground pipelines. The susceptibility classification of the study area soil erosion was obtained based on the GIS overlay analysis tool. Lastly, the susceptibility classification was compared with the results of the field investigation. Their consistency indicates that the proposed method can be successfully implemented to accurately assess soil erosion. The erosion mechanism indicates that occlusion and cementation have an important influence on the susceptibility intensity in overlaying diluvial fans of shallow underground pipelines. [ABSTRACT FROM AUTHOR]

To invert mine subsidence parameters and predict the timing of associated risk to underground pipelines passing through mining areas with incoherent subsidence information, this study proposes a model based on combining the advantages of interferometric synthetic aperture radar (InSAR) technology, the probability integral method (PIM), segmented Knothe time function, and genetic algorithm. Firstly, InSAR technology is used to analyze a time series of surface deformation in a mining area, circle the range of large-gradient deformation, and distinguish the subsidence edge from the subsidence center. In the case of the subsidence edge (small-scale deformation), InSAR results are retained, whereas in the case of the subsidence center (large-scale deformation), subsidence parameters, such as the subsidence coefficient and influence radius, are obtained via the genetic algorithm. The subsidence of the working face in the mining area is determined by combining InSAR information and the PIM parameter inversion-based basin model. This allows us to obtain continuous surface subsidence information, study surface subsidence trends over time, and predict future pipeline subsidence. The researchers subsequently test the efficacy of this model in the Qinchi mining area in Shanxi Province, China. Sentinel-1A images were used as the data source, combine the PIM and segmentation time function, and use the genetic algorithm to obtain the subsidence mining parameters. The inversion results show that the subsidence coefficient is 0.5917 (with an error of 2%), and the main influence angle tangent value is 1.927 (with an error of 2.18%), indicating high inversion accuracy. Based on this model, the study predict that subsidence in the Qinchi mining area will threaten the structural integrity and operation of the intersecting pipeline by November 2025. • A new parameter inversion method of probability integral method is proposed. • This model based on combining InSAR, PIM, Knothe time function, and GA. • This model can be used for inversion using incoherent SAR data. • This model can predict the dynamic change of surface displacement • This model can predict the timing of structure subsidence risk. [ABSTRACT FROM AUTHOR]

In the process of urban expansion and development, "asset-heavy and invisible" infrastructure construction is playing an increasingly important role, which also makes people realize the importance of the diffusion of policies that need collective institutional action among Chinese cities. We examine what drives the diffusion of the new underground utility tunnel (UUT) policy with an analysis of 242 prefecture-level cities in China. The results show that horizontal competition, central government pressure and incentives, international resource utilization and image pressure, urban economic development, and administrative rank are positively and significantly associated with policy diffusion, whereas urbanization, population density, and existing underground pipelines are not significant. • The diffusion of the underground utility tunnel policy is a novel process. • Its diffusion is driven by horizontal, central and international dynamics. • Economic development and administrative rank matter in policy diffusion. [ABSTRACT FROM AUTHOR]

• Bayesian network model for buried gas pipeline failure analysis is presented. • The pipeline failure caused by corrosion and external interference is analyzed. • Failure frequency and leakage size are analyzed based on pipeline characteristics. • The pipeline in the city of Hefei is used to state the practicability of the model. • Critical pipeline parameters can be identified using this model. The unintentional release of urban buried gas pipeline may cause crucial consequences to the economy, society and environment. Corrosion and external interference are primary causes of pipeline failure incidents. Due to the complexity and unpredictability of outside influence on the buried gas pipeline, this paper presents an approach to analyze pipeline failure frequency and leakage size caused by corrosion and external interference based on pipeline characteristics. Bayesian network method is used to construct a knowledge model. Pipeline characteristics statistics and failure data are collected to build the relationships among variables in the model and verify the applicability of the model. Results show that the proposed model can estimate buried gas pipeline failure frequency and leakage size caused by corrosion and external interference. It is also capable of highlighting the critical parameters to pipeline failure. Practical application of the model is demonstrated on the underground gas pipeline in the City of H, China. Results indicate that proposed model can explicitly quantify uncertainties and then put forward practical measures for buried gas pipeline parameter design, laying plan and operating maintenance. [ABSTRACT FROM AUTHOR]

With rapid urbanization in China, many underground utility tunnels have been established these years. This huge underground construction facilitates city life, but may introduce societal risks due to the installation of high‐risk pipelines. Natural gas pipelines have the potential to cause catastrophic accident if a gas leakage and a subsequent explosion occurs. The potential hazards in the gas compartments of a utility tunnel are quite different from those in conventional directly buried gas pipelines. This study developed a dynamic quantitative risk analysis method for natural gas pipelines in a utility tunnel. First, potential accident scenarios of natural gas pipelines situated in a utility tunnel were identified and implemented in a Bow‐tie diagram based on case studies of typical gas pipeline accidents and expert experience. Then, a Bayesian network was established from the Bow‐tie diagram using a mapping algorithm. Based on a comprehensive analysis of the results of probability updating and sensitivity analysis, critical influencing factors were identified. The proposed framework provides a predictive analysis of the gas pipeline accident evolution process from causes to consequences and examines key challenges in gas pipeline risk management in utility tunnels. © 2019 American Institute of Chemical Engineers Process Saf Prog: e12051 2019 [ABSTRACT FROM AUTHOR]

The article discusses the need for open data infrastructures to compare information on materials failures as part of an effort to prevent disasters, relative to the explosions of pipes in Qingdao and Kaohsiung, China that resulted to several deaths and injuries. Topics mentioned include the lack of understanding of the corrosion and degradation of underground pipes, the Materials Genome Initiative (MGI), and industry involvement through partnerships with academia.