Tunnel Operation Research Articles

Laser-based intelligent perception method for tunnel invasion

Laser-based visual perception technology is an effective way to enhance the intelligent level of tunnel operation and maintenance, which could improve the efficiency of the automatic identification and intelligent positioning of different diseases. Although various sensing and data processing methods for tunnel inspection have been studied, the research on invasion detection based on laser scanning technology is still rare. In this paper, the invasion detection of the tunnel and train is carried out based on terrestrial laser scanning data. A feature-based registration is proposed in order to fuze the tunnel and the train models accurately and automatically in the unified coordinate system, where the local contact points are set as the features and identified by means of the normal vector descriptor. The invasion analysis is achieved with the convex points, which are paired through the convex hull and polar principle. A complete and comprehensive image of the invasion analysis is generated, which offers a reality model base for the design and decision-making. The method proposed can be extended to other similar scale scenarios of invasion analysis and spatial position inspection. It is a reference for the engineering applications of the intelligent operation and maintenance of the tunnel.

Safety inspection system and comprehensive evaluation method for concrete structure of gas pipeline tunnel based on fuzzy mathematics

Regular safety inspections are an important guarantee to ensure the high-quality operation of concrete structures of tunnels. The Chinese West-east Gas Pipeline Project is large in scale and complex in construction environment. These tunnels are equipped with gas pipelines, and the concrete structural defects of the tunnels are continuously exacerbated during the long-term operation. There are few studies on the safety evaluation methods of concrete structures of gas tunnels. Based on the characteristics of the operation of the gas tunnels, this paper proposes the establishment of a structural safety comprehensive inspection system from the following seven aspects, that is, the void between the concrete lining and surrounding rock, the strength of the concrete lining, the thickness of the protective layer of the reinforced concrete lining, the carbonization depth of the concrete lining, the deformation of the tunnel section, the cracks in the concrete lining, and the auxiliary concrete structure of the tunnel. In addition, a corresponding quantitative determination method and safety level classification standard are established. Based on the fuzzy mathematics theory and a structural safety comprehensive inspection system, a five-level safety evaluation method for tunnel concrete structures is proposed. Finally, a comprehensive inspection and evaluation were carried out for a tunnel running across the mountain.

Laboratory Test of EPB Shield Tunneling in Mixed-Face Conditions

Field measurements and laboratory tests were carried out to study the mechanical behaviors of soil in response to earth pressure balance (EPB) shield tunneling in mixed-face conditions, i.e., layers of granite and sand. Specifically, an experimental investigation was carried out using a laboratory-scale model to replicate the EPB tunneling operations in such ground conditions. The effects of the ratio of rock/sand at the tunnel face (Tr/Ts) and the cover-to-diameter ratio (C/D) on the soil pressure in the chamber, ground displacement, and volume loss were examined. The results show that the soil's response to the mixed-face conditions differs significantly from that in the homogenous ground and highly depends on the ratio of rock/sand, especially for relatively shallow tunnels. As the ratio of rock/sand at the tunnel face increased, the pressure gradient in the chamber became more inconsistent. The translated cumulative curve does not always provide a good fit in the mixed-face conditions, particularly in cases when the rock/sand ratios are high. A smaller width of settlement trough has been observed for cases with a large rock/sand ratio compared to that in clay and cohesionless soil.

A Numerical Study on Axial Pump Performance for Large Cavitation Tunnel Operation

In this paper, a numerical investigation was carried out on the performances of a designed axial flow pump for a large cavitation tunnel. From this, the flow characteristics, force, and torque performance of the axial flow pump were investigated, and the rotating speeds of the impeller satisfying the test section speed performances required in the large cavitation tunnel were estimated. The axial flow pump was modeled such that the impeller, stator, and nacelle were located in a cylindrical tunnel. The calculations were carried out for incompressible steady-state turbulent flow considering the impeller rotating. The performance of the pump was confirmed, finding that the head gain was caused by the pressure jump downstream of the pump. The performance of the stator was confirmed to be good enough to refine the tangential flow due to the impeller rotating. To investigate the operating performance of the large cavitation tunnel, the head loss of the entire tunnel without the pump was obtained from a numerical analysis. The operating points were estimated from the specific speed–head coefficient curves, and it was found that the present numerical results were in good agreement with the experiments.

A Novel Approach to Automated 3D Spalling Defects Inspection in Railway Tunnel Linings Using Laser Intensity and Depth Information.

The detection of concrete spalling is critical for tunnel inspectors to assess structural risks and guarantee the daily operation of the railway tunnel. However, traditional spalling detection methods mostly rely on visual inspection or camera images taken manually, which are inefficient and unreliable. In this study, an integrated approach based on laser intensity and depth features is proposed for the automated detection and quantification of concrete spalling. The Railway Tunnel Spalling Defects (RTSD) database, containing intensity images and depth images of the tunnel linings, is established via mobile laser scanning (MLS), and the Spalling Intensity Depurator Network (SIDNet) model is proposed for automatic extraction of the concrete spalling features. The proposed model is trained, validated and tested on the established RSTD dataset with impressive results. Comparison with several other spalling detection models shows that the proposed model performs better in terms of various indicators such as MPA (0.985) and MIoU (0.925). The extra depth information obtained from MLS allows for the accurate evaluation of the volume of detected spalling defects, which is beyond the reach of traditional methods. In addition, a triangulation mesh method is implemented to reconstruct the 3D tunnel lining model and visualize the 3D inspection results. As a result, a 3D inspection report can be outputted automatically containing quantified spalling defect information along with relevant spatial coordinates. The proposed approach has been conducted on several railway tunnels in Yunnan province, China and the experimental results have proved its validity and feasibility.

Anti-Blocking Mechanism of Flocking Drainage Pipes in Tunnels Based on Mathematical Modeling Theory

Crystalline pipe plugging in tunnel drainage systems is one of the causes of tunnel lining cracking and water leakage. Therefore, effective prevention of crystalline pipe blockage in tunnel drainage systems is very important to ensure the safety and stability of the lining structure during tunnel operation. Combined with the theories of fluid mechanics, structural mechanics and basic physics, the flocking and anti-blocking mechanism of drainage pipe was comprehensively analyzed by using the method of mathematical modeling, including: (1) the calculation expression of average velocity of the flocked section of a flocked drainage pipe v = Q/(C1 − C2(r + r′)) and the calculation formula of flowing water pressure under the action of groundwater Fw = KAγQ2/(2g(C1 − C2(r + r′))2); (2) the flow velocity v0 in the flocked drainage pipe shall meet v2 < 4gπrlτ1/γKA, crystals will be attached to the fluff and the crystals will maintain dynamic balance; (3) the flow velocity v0 in the flocked drainage pipe shall meet v2 ≥ 4gπrlτ1/γKA, crystals will not adhere to the fluff and the flocked drainage pipe will remain unobstructed. The research on the mechanism of preventing blockage of flocking drainage pipes fills the gap in research theory in this regard, contributes to the popularization and application of blocking prevention technology of flocking drainage pipes, reduces the maintenance cost during operation of tunnel drainage systems and ensures the safe and normal operation of tunnels.

A digital twin-based decision analysis framework for operation and maintenance of tunnels

Digital twins are at the core of urban infrastructure maintenance, operation and evaluation. In modern cities, digital twins can be established to integrate the life cycle spatio-temporal data of tunnels, as well as analyze the potential causes and effects of abnormalities in civil structures or electromechanical equipment. This will provide reasonable and feasible countermeasures to guide and optimize the operation and maintenance (O&M) management. This paper proposes a digital twin-based decision analysis framework for the O&M of tunnels. The framework defines an extended COBie standard-based organization method for the tunnel twin data, and uses Semantic Web technologies to achieve fusion at the data, object and knowledge levels. In addition, a rule-based reasoning engine has been developed by establishing a large rule base. The framework has been utilized for the fault cause analysis of fans in Wenyi Road Tunnel in Hangzhou, China to demonstrate its decision analysis process and validity. The application results show that the framework can provide efficient and automatic decision analysis support for the O&M of tunnels.

Psychophysiological Predictors of Soldier Performance in Tunnel Warfare: A Field Study on the Correlates of Optimal Performance in a Simulation of Subterranean Combat.

Tunnel operations produce unique psychophysiological activation that is correlated with cognitive impairment and lower performance. This study introduces a new concept: subterranean operational potential (SOP) and assesses its psychophysiological correlates for performance prediction in underground spaces. 138 soldiers of elite infantry battalions, with/without previous experience, who participated in a simulation of tunnel warfare. Physical, psychological, cognitive style, and performance measures were collected. SOP has three sub-components: performance, leadership, and orientation. Leadership and performance both were negatively correlated with perceived stress. Claustrophobia was negatively correlated with leadership. The cognitive style was positively correlated with performance. Saliva cortisol levels were significantly higher before the simulation. Inexperienced and experienced differed in the change in before-after saliva cortisol levels.

Evaluation and Deformation Control Study on the Bias Pressure of Layered Rock Tunnels

In the process of tunnel construction, the bias of layered rock mass tunnels has always been a prominent problem that troubles the construction and safe operation of tunnels. In this paper, a comprehensive method that combines monitoring technology and discrete element (3DEC) numerical simulation is proposed to analyze the deformation characteristics of the surrounding rock in the layered rock tunnel and the deformation law of the bias tunnel. The results indicate that the tunnel surrounding rock deformation in the study area showed the characteristics of bias. Based on the bias mechanism, the surrounding rock deformation law, the construction deformation control, and the optimization measures of layered rock mass in the bias tunnel were studied by means of combining monitoring technology with discrete element (3DEC) numerical simulation. Based on the research results, appropriate methods for controlling the deformation of the surrounding rock of the tunnel with comprehensive consideration of the anchor rod length, anchor rod angle, and anchor rod layout spacing were proposed. The method proposed in this paper could visually reveal the deformation characteristics of the surrounding rock of layered rock tunnels and the deformation law of bias tunnels. It could also better solve the problem of deformation control in the tunnel construction process. This approach provides a novel idea for special layered rock mass tunnel bias evaluation and deformation control parameter optimization and serves as a valuable reference for analogous engineering cases through engineering case analysis.

A Secure Link-Layer Connectivity Platform for Multi-Site NFV Services

Network Functions Virtualization (NFV) is a key technology for network automation and has been instrumental to materialize the disruptive view of 5G and beyond mobile networks. In particular, 5G embraces NFV to support the automated and agile provision of telecommunication and vertical services as a composition of versatile virtualized components, referred to as Virtual Network Functions (VNFs). It provides a high degree of flexibility in placing these components on distributed NFV infrastructures (e.g., at the network edge, close to end users). Still, this flexibility creates new challenges in terms of VNF connectivity. To address these challenges, we introduce a novel secure link-layer connectivity platform, L2S. Our solution can automatically be deployed and configured as a regular multi-site NFV service, providing the abstraction of a layer-2 switch that offers link-layer connectivity to VNFs deployed on remote NFV sites. Inter-site communications are effectively protected using existing security solutions and protocols, such as IP security (IPsec). We have developed a functional prototype of L2S using open-source software technologies. Our evaluation results indicate that this prototype can perform IP tunneling and cryptographic operations at Gb/s data rates. Finally, we have validated L2S using a multi-site NFV ecosystem at the Telefonica Open Network Innovation Centre (5TONIC), using our solution to support a multicast-based IP television service.

Emergency preparedness for tunnel fires – A systems-oriented approach

Efficient emergency response is key to preventing major losses in tunnel fires. Our general concern in this paper is the degree to which tunnel systems are prepared and the means by which we can be prepared for a major fire in a single-tube road tunnel. Conformance to prescriptive regulations dominates existing practice in the area of emergency preparedness. Risk-based approaches exist but have little influence on emergency preparedness designs for tunnel systems. A successful emergency response to tunnel fires is dependent on many actors collaborating under serious time constraints. Safety becomes a matter of controlling critical processes necessary to keep the system in a safe state. Efficient decision-making in situations of major uncertainty is vital, to achieve safety goals. This essentially means that efficient emergency preparedness for road tunnels is a matter that needs attention in the early design phases and continuous improvements during the operational phase. To achieve high-performance emergency preparedness against tunnel fires, there is a need for radical changes to the design and operation of tunnels. In this paper, it is claimed that a system-theoretic approach is appropriate to deal with the tunnel system’s complexity and to drive the design of appropriate control structures for critical processes, from the design phase to the actual emergency. It is shown how system theoretic approaches will change the safety management practices for tunnels and how this will increase consistency between potential fire scenarios and associated control actions.

Theoretical and Experimental Investigation of Vehicle-Mounted Transient Electromagnetic Method Detection for Internal Defects of Operational Tunnels

With the durable operation of high-speed railway tunnels in China, many tunnel defects successively appeared in the tunnel lining structure and gradually threatened the safe operation of the tunnels. In the limited maintenance time of high-speed railways, it is urgent to find out and maintain tunnel defects, especially internal defects. We propose an applied detection technology called the vehicle-mounted transient electromagnetic method (TEM). The detection technology aims to rapidly detect and locate the internal defects of the lining structure throughout the entire tunnel. Firstly, we investigate tunnel defects in detail and introduce the rapid detection method. Secondly, we analyze the principle and process of vehicle-mounted TEM. Thirdly, the rationality and applicability of vehicle-mounted TEM are verified by three different methods, including theoretical analysis, numerical simulation, and laboratory experiment. Finally, we compare the inversion results of experimental data under the two conditions. The results illustrate that tunnel surface defects are the external manifestations and characteristics of tunnel defects, while the forms of surface defects are directly related to internal defects. This detection method is suitable for the significant resistivity difference between tunnel defects and surrounding rocks, and its rationality is effectively validated. Furthermore, the apparent resistivity results reveal that there is a low resistivity region in front of the transmitter coil, and that the relative position can be preliminarily judged. The research results can provide a potential and significant application technology for the rapid detection of tunnel defects.

Stochastic event simulation model for quantitative prediction of road tunnel downtime

Given the importance of road tunnels in a transportation network, it is essential to quantitatively assess and predict tunnel functionality loss due to disruptive events. In this study, a stochastic event simulation model was developed to evaluate the resilience of tunnel infrastructure, quantified using a functionality metric as a function of loss in traffic capacity and its duration. The model consists of individual modules to account for disruptive events that cause tunnel closures. In this paper, the mechanism and probabilistic models used for each simulation module are presented. A simulation for Eisenhower tunnel, Colorado, was conducted using the proposed method as a validation case study. The results showed that the proposed model could simulate realistic tunnel operation status. While the validation was made for a specific tunnel, the model was designed to be applied to the resilience analysis of any road tunnel with defined design and operation parameters.

Thermal Environment Simulation and Ventilation Strategy in Tunnels for Heating Pipes and Power Cables

The thermal environment of the utility tunnel is important for the safe operation and maintenance of the pipeline system. When the power cables and heat pipelines are installed in the utility tunnel at the same time, the compatibility of thermal environment and the ventilation scheme need to be studied. Therefore, in this paper, the temperature field and the effect of air change rates in the utility tunnel were studied by using numerical simulation method. Numerical results show that the heat pipelines and the power cables have good thermal compatibility in the same compartment. Moreover, reducing ventilation volume is an effective way to increase the temperature and the optimal air change rate is between 3h−1-4 h−1. Therefore, it provides reference for safety operation and standardization study of the utility tunnel.

Corrosion Level of Rock Bolts Exposed to Aggressive Environments in Nordic Road Tunnels

For road tunnels in most Nordic countries, temporary rock support installed during tunnel excavation usually becomes a part of the permanent rock support. Rock bolts are the most common rock support measure in road tunnels excavated in hard rock, and their conditions over the period of tunnel operation play a significant role in the safety of these tunnels. The rock bolt types and aggressive environmental conditions considered in this research are focused on those used and observed in Norwegian and Swedish road tunnels. Findings elsewhere in similar environments are included to highlight the different kinetics of degradation. Based on the collected data, the corrosion levels in these road tunnels are comparable to those in the most polluted industrial areas. Aggressive groundwater conditions for rock bolts include a groundwater pH below four (which can be caused by sulfuric acid formation due to the oxidation of the mineral pyrite in the rock), marine groundwater, and flowing groundwater with a high concentration of dissolved oxygen. Furthermore, chloride-bearing deicing salts commonly used on roads located in cold climate regions during winter can promote corrosion in rock bolts from the tunnel room. For these environments, this research proposes a lognormal probability function to quantify the expected steel corrosion level for 25, 50, and 100 years of exposure time. The corrosion protection given by cement grouting, hot-dip galvanizing and epoxy coating are also addressed to explore their contributions to the lifespan extension of rock bolts in acidic and chloride-rich environments.

Study on the Progressive Deterioration of Tunnel Lining Structures in Cold Regions Experiencing Freeze–Thaw Cycles

The linings of tunnels in cold regions with long service lives usually have cracks, with parts of the structure peeling and falling off, which seriously threatens the tunnel safety and operation. The unsaturated freeze–thaw cycle of concrete, which is the main cause of structural deterioration, has not received much research attention. During the service life of tunnels in cold regions, unsaturated freeze–thaw cycles deteriorate the quality of the concrete, and its degree presents a gradual distribution in the circumferential and longitudinal directions. An experiment system was adopted to simulate the distribution of the progressive deterioration of tunnel lining concrete. The test results of the temperature field of the model show the distribution law of freeze–thaw cycles, and the gradual deterioration of the lining concrete was realized. Then, the bearing capacity of the model was tested after the progressive deterioration. The results show that the ultimate load of the model decreases with an increase in the number of freeze–thaw cycles. Finally, a numerical simulation was carried out to discuss the influence of the gradual deterioration of the lining. The gradual deterioration of lining concrete will encourage the gradual development of cracks, leading to serious cracking of the lining structure and even block spalling. Through this study, we hope to provide useful information for the prevention and control of tunnel frost damage in cold regions.

Efficiency of methods of strengthening foundations of environmental buildings with a significed influence from the construction of the metroline line

A section of the Syretsko-Pecherska metro line is being built in Kyiv. Subway line tunnels are built in a partially open way. In the area of the picket PK-2 pit construction of the subway is an existing building on Ave. Truth 68, which is located in the zone of possible influence. The impact on the construction of surrounding buildings occurs at different stages of the existence of subway tunnels: the construction of tunnels with open pits and the stage of operation of subway tunnels with vibration during train traffic.
 At the stage of construction of subway tunnels, deformations of the soil base under existing buildings occur during the development of soil in the middle of the pit, which leads to uneven subsidence of buildings. The article investigates the effectiveness of methods of strengthening the foundations of the surrounding buildings with a certain impact from the construction of the subway line.
 To determine the most effective option of strengthening the foundations of the house in the construction of tunnels of the subway line, variable calculations were performed using different schemes of strengthening the foundations to determine the optimal ratio of labor costs to ensure strength and minimize deformation in each way. Taking into account the constructive scheme of the building, engineering and geological conditions of the construction site and technological possibilities of non-destructive reinforcement of the foundations, the following reinforcement options were considered: installation of the foundation slab; injection of reinforcing solution of the foundation base; arrangement of micropiles.
 Calculations of the system "pit - soil - building" were performed in the software and calculation complex "PLAXIS 2D" by the finite element method.
 Given that the greatest influence on the occurrence of defects in the structures of the building will give the parameter of non-uniformity of deformations, the comparison of the reinforcement efficiency was determined by this parameter.
 The smallest non-uniformity of deformations was provided by means of strengthening by a base plate. Compared to this method, the reinforcement of the foundation foundation injection with 89% more non-uniform deformations gave the reinforcement solution, and 296% more non-uniform deformations with micro-field reinforcement. The most effective way to strengthen the foundations of the building is to install a foundation slab with a compaction of the base with a self-expanding polymeric material.

Deformation failure characteristics of weathered sandstone strata tunnel: A case study

Appropriate countermeasures are required after extreme deformation failure of rock mass to ensure the safety of the tunnel construction and operation, especially in a tunnel that through strongly weathered sandstone strata. The load bearing capacity is further weakened by the permeation of water in complicated geological conditions, which can frequently cause collapse and result in budget overruns during the construction period. This paper provides a case study about the process of the extreme deformation that occurred in the Piancheng Tunnel based on in situ monitoring. Based on the analysis of on-site deformation monitoring data, combined with the engineering practice characteristics, the factors affecting the deformation were analyzed, further, the countermeasures were put forward and its effectiveness was analyzed. The maximum settlement reached 1046.3 mm and the convergence reached 876.4 mm, and the seepage, rock strength and bias load were considered the main cause of extreme deformation. As a means to maintaining the structural integrity, countermeasures such as temporary steel arch, vertical bracing, diagonal bracing and the temporary inverted arch combination were used for strengthening the tunnel’s structure, hence, effectively preventing the development of extreme deformation. The manuscript records the whole process from occurrence to countermeasures of extreme deformation of surrounding rock, which provide experience for future similar projects.

Simplified Analytical Method for Predicting the Lateral Ground Displacements due to Shield Tunnelling

Earth pressure balance or slurry shield tunnelling will squeeze the subsoils and lead to lateral outward ground displacement. However, current methods to estimate the shield tunnelling-induced ground displacements generally use the methods based on the face unsupported tunnelling (e.g., New Austrian tunnelling and open shield excavation), which cannot predict the lateral ground movement due to shield tunnelling. In this paper, a novel simplified analytical method is proposed to predict the ground lateral displacement during the shield advancing process. The key shield tunnelling operation factors, including the additional pressure of cutter head, the friction forces around shield body, the back-fill grouting pressure, and the soil volume loss are all considered. The lateral ground displacements induced by the four former factors are calculated by using Mindlin’s solutions. The soil volume loss-induced lateral ground displacement is calculated by employing the expression introduced by Pinto and Whittle. Combining with the displacement obtained from all the factors, the analytical method for lateral ground displacement induced by shield tunnelling is obtained. The applicability of the proposed analytical approach is verified with three well-documented case histories involving slurry shield and EPB shield machines.

Numerical Analysis of the Hydraulic Fracturing of Pressure Tunnel Lining Based on the 2P-IKSPH Method

In order to investigate the fracture mechanisms of the pressure tunnel lining under water-stress coupling, based on the traditional smoothed particle hydrodynamics (SPH) method, the solid-water particle interaction method, and the particle damage conversion algorithm are proposed to realize the hydraulic fracturing process, which is called the 2P-IKSPH method. The “particle domain searching method,” the “birth-and-death particle method,” and the “group discrimination searching method” have also been proposed to realize the simulations of complex processes of excavation, lining, and operation of the hydraulic tunnel. Taking the Guzeng hydraulic tunnel as an engineering example, the hydraulic fracturing of tunnel lining under different conditions is numerically simulated. Results show the following: (1) the 2P-IKSPH method can dynamically reflect the stress wave propagation processes of surrounding rock and the damage process of tunnel lining. (2) The lining damage mainly occurs on the vault and the arch foot. (3) The critical internal water pressure increases with the increase of the tunnel buried depth and the thickness of lining, but increases first and then decreases with the increase of the surrounding rock mass grade. The research results can provide some references for the optimization designs of tunnel lining and reinforcement of similar projects. Meanwhile, developing 3D parallelization program based on 2P-IKSPH will be the future research directions.