Tunnel Operation Research Articles

Dynamic response analysis of the process of the utility shield tunnel under-passing the operating subway tunnel

In order to analyze the interaction between the operating subway tunnel and the utility tunnel under construction during the utility tunnel under-passing the subway tunnel, an operating tunnel-stratum-utility shield tunnel coupled dynamic calculation model is established taking the utility tunnel under construction under-passing the Guangzhou-Foshan line subway project as an example. And the interaction between the existing tunnel and utility tunnel was studied. The results show that the amplitude change of the vertical displacement, acceleration and additional vertical stress are most influenced by the under-passing shield tunnel when the train operating on one line, and the max changes are 0.01 mm, 0.03m/s2 and 1.5kPa, respectively. The vertical displacement and acceleration response generated by the train operation during the excavation of the new tunnel can be neglected, but the vertical additional stress will have the max change of 2.1kPa. The closer the distance between the train load to the new and old tunnel structures are, the greater the displacement, acceleration and additional stresses of the new and old tunnel structures are when the trains are running in different lines. Structural safety calculations show that the old and new tunnel structures are safe during the utility shield tunnel under-passing. The study can provide useful reference for the construction and operation of similar tunnels.

Digital Twin-enabled and Knowledge-driven decision support for tunnel electromechanical equipment maintenance

Urban tunnel infrastructure plays critical roles in sustaining the wellbeing of a society. The operation of tunnels relies on a diverse range of tunnel electromechanical equipment (TEE), such as ventilation, drainage, and the lighting system. However, effectively and proactively maintaining TEE to prevent unforeseen failures using limited resources remains an unresolved challenge. The utilization of digital twin technology, which combines Building Information Modeling (BIM), Internet of Things (IoT) and Semantic Web technologies, offers a knowledge-rich environment for the development of improved maintenance strategies. This study proposes a digital twin-enabled and knowledge-driven decision support method for proactive TEE maintenance. Initially, a digital twin conceptual framework for proactive TEE maintenance is presented, which integrates a knowledge-driven approach to support decision making. Subsequently, a controlled vocabulary-based method is developed to extract and update maintenance knowledge. Finally, a novel combinatory reasoner, including a rule selection algorithm and an inference algorithm, is devised to automatically generate maintenance schemes. Based on the proposed method, a decision support tool was developed and applied to Wenyi Road Tunnel in Hangzhou, China. The results demonstrated the effectiveness of the method, which can continuously update maintenance knowledge and assist fault detection and TEE state prediction with the combinatory reasoner. Moreover, the inference efficiency achieved by our method surpasses that of traditional approaches by approximately 162 ms.

How to Guarantee the Sustainable Operation and Maintenance of Urban Utility Tunnels? From the Perspective of Stakeholder and the Whole Life Cycle

Urban utility tunnels (UUTs) have become an important infrastructure for sustainable urban development. However, numerous uncertainties brought by the complex stakeholder groups seriously hinder sustainable operation and maintenance (O&M) of UUT projects, which make it necessary to plan the development of UUT projects in advance. Previous studies mostly identified and analyzed the influencing factors from the partial life cycle perspective and neglected the limitations of exploring the complex whole life cycle factors from one single perspective. This paper comprehensively considered the perspectives of stakeholder roles and the whole UUT project life cycle and proposed a factor identification and analysis framework. In the factor identification section: (a) literature surveys were conducted to identify all influencing factors of stakeholders at each stage; and (b) 21 types of factors were identified through semi-structured interviews. In the factor analysis section: (a) the hierarchical structure of the factors was analyzed by introducing the Decision-Making Trial and Evaluation Laboratory (DEMATEL) approach and Interpretative Structural Model (ISM); (b) the various factors were divided into linkage, dependent, autonomous, and driving factors to clarify their influence degrees; and (c) the core influencing factor was determined based on the above analysis results and the two perspectives. The results indicated that (1) the pricing and charging mechanism is the decisive factor affecting the sustainable O&M of UUTs, the government should focus on establishing a standardized and transparent pricing and charging mechanism; (2) policy support to encourage social capital and user participation should be actively explored; and (3) UUT development must rely on the strong promotion of the government, and the needs of all stakeholders throughout the life cycle should be paid attention to. This study can provide useful insights for guaranteeing the sustainable O&M of UUTs in China and similar regions.

Experimental investigation of strength repairing effects of chemical grouting on fractured porous sandstone under different temperature conditions

Investigation of the seepage characteristics and the corresponding repairing effects of slurry on fractured rock mass is of great significance to grouting theory and operation parameters designing. Several chemical grouting tests under different temperatures and grouted pressures were conducted and the seepage processes were monitored by the LF-NMR (low field nuclear magnetic resonance) technique. The influence of temperature on the flow properties, grouted volume and permeability of slurry were comprehensively studied through the analysis of the NMR T2 response. The effects of temperature on the mechanical performance of grouted specimens after curing were investigated through the directly shear tests. The results indicated that the temperature has an obvious impact on the seepage characteristics, the higher the temperature, the lower the permeability. The mechanical performance of grouted specimen is closely dependent on the grouting temperature, the inter friction angle φ and the cohesion c exponentially decrease as the temperature increases. A temperature dependent shear strength mechanical model of slurry bonding layer was proposed and verified. The findings of this study are useful for the parameters designing of grouting operation in deep-buried tunnels.

Development of a Test Rig for the Measurement of Small Wind Turbines in a Wind Tunnel

Abstract This paper describes the development, design and function of a test rig for the measurement of small wind turbines in a wind tunnel and presents the first exemplary measurements of the performance characteristics of various horizontal and vertical rotors. A central part of this test rig is the developed control system with an electronic load, which enables an automated recording of the measured values for the evaluation of the power coefficients (cp) and tip-speed ratio (λ) values. Another challenge emerges owing to the known differences in the power spectrum, because the power coefficients of drag rotors (<20%) are different from those of buoyancy rotors (<40%). The system was adapted to the different ranges by means of a stepless switching using various resistors. The entire control and regulation unit was compactly implemented using a programmable logic controller (PLC) and dynamically linked to the operating parameters of the wind tunnel. This enables an automated operation of the wind tunnel during the determination of the performance parameters of the investigated wind turbines.

Crystallization blockage damage in tunnel drainage system and suggestions for its prevention and control

The functionality of drainage systems in highway tunnels is of paramount importance for the structural safety and efficient operation of the tunnels. This study investigated the operation, management and maintenance of tunnels on Renxin Expressway and Yinghuai Expressway in Guangdong Province, and conducts tunnel disease statistics and analyzes the types of tunnel diseases under different geological bodies, and proposes prevention and control suggestions. The results showed that (1) water leakage at the linings and construction joints accounted for over 90% of all pathological conditions, (2) water samples collected from the sites had an alkaline pH level greater than 7, with 74% of samples exceeding 9, and (3) the dominant components of the crystalline substances collected from the sites were calcite and aragonite (CaCO3 crystals), accounting for 97% of the total. Based on the field investigation and data analysis, this paper presents many effective measures to control crystalline blockages for tunnels’ drainage systems.

Risk Assessment Mmodel of Karst Tunnel Flood Based on Distance Discriminant Weighting and Set Pair Cloud

Flood has become the main hidden threat to the safety of the karst tunnel. Scientific and reasonable flood classification assessment and prevention measures have also become the main problems to be solved urgently in the construction and operation of tunnels. Aiming at the problems of multiple influencing factors, complex index systems, and linear processing of the connection degree of set pair analysis, a set pair cloud model based on cloud theory eigenvalues is proposed to optimize the connection degree of set pair analysis. Regarding the uncertainty of the evaluation system and the ambiguity of the evaluation grade boundary, firstly, the ridge-type membership function is used to determine the basic probability distribution of each measured index. Secondly, the distance discrimination weighting theory based on the index distance is also established, so that each measured index can assign the dynamic weight of the evaluation system. It can comprehensively determine the weight of the cloud connection degree for the system, and draw the cloud level diagram to determine the tunnel flood risk level. Finally, the proposed model is verified with tunnel flood. The results show that the evaluation results are consistent with other evaluation models and actual tunnel conditions. This model can provide guidance for flood prediction and prevention in karst tunnels.

Research on the Design and Construction of Inclined Shafts for Long Mountain Tunnels: A Review

In recent years, inclined shafts have been widely used in long mountain tunnels, but the corresponding design and construction technical specifications need to be improved. By means of literature statistics and actual cases, a comprehensive and systematic review is made on the tunnel profile, lining structure, construction and operation ventilation, construction methods, and machinery of inclined shafts for long mountain tunnels. The results show that: (1) The design of a gentle slope section of an inclined shaft with large longitudinal slope needs to be further improved; (2) When an inclined shaft is only used for ventilation in the operation stage, it is necessary to make full use of the natural wind and eliminate its adverse effects; (3) It is suggested to study the supporting parameters of an inclined shaft in order to realize the standardised design of the supporting parameters; (4) The space of an inclined shaft is narrow, and it has practical demand in improving the automation, intelligence, management, and dispatching level of transport vehicles. In the future, it is an inevitable trend for electric vehicles to replace fuel vehicles. It is necessary to carry out further research on inclined shaft longitudinal slope design, construction and operation ventilation design, and transportation mode.

Comparative Study of the Rock-breaking Mechanism of a Disc Cutter and Wedge Tooth Cutter by Discrete Element Modelling

The operation of a shield tunnel boring machine (TBM) in a high-strength hard rock stratum results in significant cutter damage, adversely affecting the thrust and torque of the cutter head. Therefore, it is very important to carry out the research on the stress characteristics and optimize the cutter parameters of cutters break high-strength hard rock. In this paper, the rock-breaking performance of cutters in an andesite stratum in the tunnel of Qingdao Metro Line No. 8 was investigated using the discrete element method and theoretical analysis. The rock-breaking processes of a disc cutter and wedge tooth cutter were simulated by software particle flow code PFC3D, and the rock-breaking degree, stress of the cutter, and rock-breaking specific energy were analyzed. The rock damage caused by the cutter in a specific section was divided into three stages: the advanced influence, crushing, and stabilizing stages. The rock-breaking degree and the tangential and normal forces of the wedge tooth cutter are larger than that of the disc cutter under the same conditions. The disc cutter (wedge tooth cutter) has the highest rock-breaking efficiency at a cutter spacing of 100 mm (110 mm) and a penetration depth of 8 mm (10 mm), and the rock-breaking specific energy is 11.48 MJ/m3 (12.05 MJ/m3). Therefore, two types of cutters with different penetration depths or cutter spacing should be considered. The number of teeth of wedge tooth cutters can be increased in hard strata to improve the rock-breaking efficiency of the shield. The research results provide a reference for shield cutterhead selection and cutter layout in similar projects.

Development of a non-Gaussian copula Bayesian network for safety assessment of metro tunnel maintenance

The operation and maintenance of metro systems play a crucial role in urban development, with a focus on ensuring the serviceability and safety of metro tunnels. Accurate evaluation of the condition of these tunnel states requires investigating the complex interaction of multiple factors that impact their safety state. This study developed a hybrid model that integrates pair copula constructions (PCCs) and Bayesian networks (BN) to assess the safety state of metro tunnels, considering complex dependencies among these factors. First, key performance indicators (KPIs) were selected to assess tunnel safety, based on six failure modes. Then, an improved copula-based PC algorithm was employed to learn the non-Gaussian bayesian network model, which eliminated the normality assumption in the marginal densities of the KPIs. Finally, a combination of forward reasoning and GM(1,1) was utilized to predict the safety state of the metro tunnel in time series, facilitating the formulation of effective operation and maintenance plans. Furthermore, the proposed approach was applied to a real case study of the Wuhan metro system to demonstrate its effectiveness and applicability. The results highlighted the significant influence of some KPIs, such as convergence deformation, dislocation displacement, and stripping area, on metro tunnel safety. These KPIs emerged as key factors requiring focused attention in the operation and maintenance of metro tunnels.

Model Test of Surrounding Rock Temperature Field under Different Drainage Structures and Insulation Conditions in High Cold Tunnel

Improper layout of drainage structures and inadequate insulation measures in high-altitude cold areas have resulted in varying degrees of frost damage in numerous tunnels during operation. To address this issue and propose a viable drainage structure layout scheme, this paper analyzes and studies the temperature field distribution characteristics of the lower surrounding rock and drainage structure around high-altitude cold tunnels, as well as the layout of the central drainage ditch and anti-cold water leakage hole. Based on physical model test results of cold area tunnels, the distribution characteristics of the temperature field around the tunnel drainage structure under different insulation conditions are obtained, and a control equation of temperature change along the depth direction is proposed. By comparing and analyzing the differences in temperature field and water flow characteristics of drainage structures under different insulation methods, the setting conditions of different drainage structures are determined. Furthermore, the function relationship between the freezing depth of the lower surrounding rock of the tunnel arch and the air temperature inside the tunnel is established, and the curve of the on-site tunnel freezing depth change is predicted. This study provides valuable insights into the design and construction of drainage structures and insulation measures for high-altitude cold tunnels, ultimately contributing to the prevention of frost damage and ensuring safe and efficient tunnel operation.

A survey of fire accidents during the process of highway tunnel operation in China from 2010 to 2021: Characteristics and countermeasures

China has the largest number of highway tunnels in the world and the most rapid development in this scope. Along with the advancement of highway tunnels, fire incidents continue increasing, causing significant damages to life and property safety. The knowledge of characteristics of highway tunnel fire accidents is essential for the fire authorities to update their safety policies on tunnels and also useful for the scholars to carry out basic and applicable researches. Previous studies have been performed on fire accident statistics in highway tunnels before 2016. The dataset after 2016 are unknown. To solve this problem, the present study examined total 256 fire incidents in Chinese highway tunnels during 2010–2021 based on police-reported database. The results showed that the fire number in 2017–2021 is almost three times that in 2010–2016. The fires occur more in spring and summer. The majority of fires occur in the long and extra-long tunnels (80%), in the one-way tunnels (90%), in the curved tunnels (70%), in the interior zone of tunnels (67.2%) and in the low altitude areas (60%). The top two burning vehicle types are heavy goods vehicles (HGVs, 38.1%) and passenger cars (37.2%). A total of 81.2% of fatalities in highway tunnel fires are associated with HGVs. The head of vehicle (41.8%), tire (25.3%) and goods (15.3%) are the top three causes of fire. Despite the fact that 92.7% of cases are single fire category while spread fire category only accounts for 7.3%, the spread fire has a more than 7 times higher casualty rate than the single fire. Based on the results, some useful fire safety measures for highway tunnels are proposed. It is hoped that this work could provide some data supports and references for tunnel fire safety and relative policy-making.

Study on Traffic Accident Forecast of Urban Excess Tunnel Considering Missing Data Filling

Urban highway tunnels are frequent accident locations, and predicting and analyzing road conditions after accidents to avoid traffic congestion is a key measure for tunnel traffic operation management. In this paper, 200 traffic accident data from the YingTian Street Tunnel in Nanjing city were analyzed and encoded to extract the main factors affecting tunnel traffic conditions from three aspects: time, traffic flow, and tunnel environment. Next, graph convolution long short-term memory networks were used to predict and fill in missing traffic flow data. Finally, seven independent variables selected by Pearson correlation analysis were input into the constructed BP neural network and random forest model to predict tunnel traffic conditions during accidents and accident duration. Experimental results show that the accuracy of random forest and BP neural networks in predicting traffic flow is 83.39% and 82.94%, respectively, and that the absolute error of the two models in predicting accident duration is 75% and 60% within 25 min, respectively. Both models perform well in predicting traffic conditions, and the random forest models perform better in terms of robustness and generalization in predicting crash duration. The experimental results have important implications for tunnel operation management during accidents.

Computer Vision-based Monitoring Method for Differential Settlement of Shield Tunnels

Shield tunnels in soft soils are inevitably subject to large differential settlement during construction and long-term operation, which can lead to various diseases and then impair structural safety and durability. Due to the inefficiency of traditional inspection methods, timely and accurate monitoring methods are necessary to ensure the safe operation and long-term maintenance of tunnels. In this study, a computer vision-based monitoring method for differential settlement of shield tunnels was developed and implemented. The monitoring area is located in an interval tunnel of a subway line in Shanghai during the freezing construction of its side channel. The influence of camera position’s micro-change was considered. The field equipment mainly consists of high-resolution industrial CMOS (complementary metal oxide semiconductor) digital camera sets, LED (light emitting diode) lights and power modules. The differential settlement relative to datum points are obtained and vertical displacement of one ring acquired by total station is compared with the proposed method to verify the feasibility of the monitoring system. The results indicate that the monitoring system is reliable and can be further applied.

Mechanical performances of shield tunnel segments under asymmetric unloading induced by pit excavation

To explore the stress and deformation responses, as well as the failure characteristics of the shield tunnel segment of Hangzhou Metro under the influences of pit excavation and other surrounding projects, a self-developed “shield tunnel segment hydraulic loading system” was used to carry out full-scale loading tests on the three-ring staggered assembled segments. The structural performances and failure process of the tunnel segment under step-by-step asymmetric unloading were studied. A safety index was proposed to describe the bearing capacity of the segment. Next, a finite element model (FEM) was established to analyze the bearing capacity of segment using the test results. Finally, the effect of reinforcement with a steel plate on the deformation and bearing capacity of the segment was analyzed. The results showed that under asymmetric unloading, the peak value and amplitude of the bending moment on the near unloading side converged with a greater value than those on the far side. The concrete internal force exhibited a directional transformation at different load stages. Cracks first appeared at the 180° inner arc surface of the bottom standard block and then expanded to both sides, while the rate of crack propagation of the outer arc surface was relatively lower. The bearing capacity of the segments can be evaluated by the combination of the factors, e.g. the residual bearing capacity coefficient, moment transfer coefficient, and characterization coefficient. The segments approaching failure can facilitate the increase in the residual bearing capacity coefficient by more than 50%. This can provide guidance for the service assessment of metro tunnel operations.

Ground movements induced by shield tunnelling in sand layers, Ho Chi Minh City mass rapid transit Line 1

AbstractThe EPB shield tunnelling for mass rapid transit (MRT) Line 1 of Ho Chi Minh City (HCMC) is the first tunnel excavation in Vietnam to use a tunnel boring machine (TBM). A comprehensive instrumentation programme was developed for safety control and to obtain a better understanding of the characteristics of induced ground movement and the forecasts. The observed ground surface settlement is summarized and interpreted with respect to the tunnelling operation parameters. The settlement trough is compared with the forecast data by applying the empirical Gaussian function and numerical 2D finite‐element analysis (FEA). The trough width parameter in the city's sandy subsoil is determined. The relation between the volume loss of the ground surface and that of the tunnel (contraction ratio) is identified. The result of the investigation is useful for future shield tunnel projects in HCMC and elsewhere in Vietnam.

Thermal Insulation, Antifreeze, and Anti-Drainage Technology for Tunnels in the Cold Area of Jinpen Bay

There are a large number of tunnels built in permafrost regions every year in China. When investigating the road tunnels that have been in operation in cold regions, it was found that most of these tunnels have various freezing damages. Therefore, in the design, construction, operation, and maintenance of tunnels in cold regions, there are still many technical problems that need to be solved urgently. Among them, the problems of heat preservation, anti-freezing, and anti-drainage are the key technical problems to determine whether the tunnels in cold regions are affected by freezing damage. The project was based on the completed highway tunnels in Inner Mongolia. Given a series of special problems faced by the construction and management of tunnels in cold regions, a large number of reference documents were consulted. This paper designed thermal insulation, antifreeze, and anti-drainage technology for tunnels in the cold area of Jinpen Bay. The research in this paper can effectively reduce the probability of the occurrence of tunnel freezing damage, ensure the safety of the long-term operation of the tunnel lining structure, and greatly reduce maintenance costs, which have good economic and social benefits.

Working mechanism and testing of emergency reinforced airbag used for blocking in tunnels

During the construction and operation of tunnels, disasters, such as groundwater leakage, gushing water, and toxic gas diffusion, occasionally occur. The frictional resistance between an emergency airbag and the tunnel is used to resist external pressure, and gases or fluids can be isolated on one side of the airbag. Thus, more time can be gained for rescue and emergency repair. The external pressure that conventional airbags can resist is limited by their internal pressure, but increasing the internal pressure requires higher material strength and is uneconomical. Based on research on the force characteristics and failure mechanism of conventional airbags, a method for improving the blocking ability by reinforcing conventional airbags is proposed. A force analysis model of the reinforced airbag under external pressure is established, the reinforcement mechanism is revealed, and the calculation formula for the critical external pressure is obtained. Through model tests and full-scale field tests, the effect of improving the blocking ability of the reinforced airbag is verified, and the accuracy of the theoretical calculation formula is proved. The research shows that the reinforcement method is economical and effective, can greatly improve the blocking ability, and provides a theoretical analysis and practical application basis for emergency airbag design.

Analysis of drivers’ preferences toward content and message format of variable message signs during tunnel emergency evacuation: A case study of Niayesh tunnel in Tehran

In the event of an emergency evacuation of a tunnel, variable message signs are one of the tools available to tunnel operators to communicate with tunnel users and play an important role in guiding them. In this study, the primary focus is to determine the most appropriate message for variable message signs in terms of content and format for tunnel emergency evacuations. This study evaluates the responses of drivers to the visual comparison between variable message signs by using stated choice methods. Using a binary logit model, the results indicate that drivers prefer the text message “Turn off the car, exit the tunnel” in two lines on the right side of the sign along with the green image of the emergency exit on the left side. Therefore, it is anticipated that the findings obtained and their application at the time of the tunnel disaster will reduce the likelihood of catastrophic accidents and mitigate their consequences.

Safety Evaluation of Plain Concrete Lining Considering Deterioration and Aerodynamic Effects

With an increase in the service time of high-speed railway tunnels, various defects caused by construction-quality defects in the secondary lining begin to appear. How to evaluate the safety of such tunnels and take countermeasures is very important for the safe operation of tunnels. Based on the load-structure method and a numerical simulation, this paper studied the short-term and long-term safety of the missing section of anti-crack reinforcement mesh in the plain concrete lining of a high-speed railway mountain tunnel. The short-term safety evaluation considered the influence of negative pressure caused by aerodynamic effects. The long-term safety evaluation considered the combined influence of the surrounding rock and concrete deterioration and the negative pressure and concrete fatigue damage caused by aerodynamic effects. The results showed that under the negative pressure generated by aerodynamic effects, the minimum tensile safety factor of the lining in the defective section increased by 3.8%, while the minimum compressive safety factor of the lining decreased by 7.9%. The negative pressure generated by the aerodynamic effects had little impact on the short-term safety of the lining in the defective section. During the long-term safety evaluation, the overall safety of the defective section decreased significantly, and the minimum tensile and minimum compressive safety factors of the lining decreased by 59.4% and 66.8%, respectively. The calculation results for the initial design do not meet the long-term design requirements and cannot guarantee the long-term safe operation of the tunnel. Finally, two new strengthening methods of galvanized steel mesh-short bolts and galvanized corrugated steel plate-short bolts were proposed to strengthen the defective section of the concrete lining, so as to improve the ultimate bearing capacity and toughness of the plain concrete lining structure.