Tunnel Section Research Articles

Flow measurement in a wind tunnel with blockage screens

The small and medium-scale wind turbine development have been improved due to their adaptability in offshore and onshore localities for wind farm applications. Blockage effects caused by numerous impediments restrict the flow-field near the turbine and impact the turbine's performance. The testing and optimization of turbines in such conditions at laboratory-level are challenging due to the unavailability of customized wind tunnel configurations with blockage screens. The present work focuses on the design, development and evaluating aerodynamic performance of wind tunnel with and without blockage screens. A comprehensive design is established by evaluating losses in each section, uncertainties, velocity, forces, and turbulence intensity in the wind tunnel through the experimental analysis. The novel blockage screens are arranged to maintain 5% and 10% blockage percentage for wind velocity range of 2 to 14 m/s. The maximum velocity reduction with 5% blockage is 41.40% and this drop reaches to 67.84% for 10% blockage. Consequently, available wind power is seen to undergo a maximum reduction of 79.88% and 96.67%, respectively.

A spatio-temporal forecasting method of fracture distribution using dynamically exposed rock images in tunnel: Methodology and application

Forecasting the geometric characteristics of rock fractures in unexcavated tunnel sections is crucial for construction arrangements. This paper presents a method for predicting fracture distribution near the tunnel face from a spatiotemporal perspective. We Innovatively analogize the tunnel excavation mileage as the time series data. Using fractal geometry and geostatistics, we extract geometric features of peripheral rock fractures and establish a spatiotemporal dataset for dynamic prediction. The SCINet model, a spatial-aware recursive neural network, is employed for deterministic-stochastic dynamic prediction. Numerical simulations are conducted to validate the predictive accuracy of the model for various distributions, including trace length, dip angle, and density. Notably, the Mean Absolute Percentage Error (MAPE) for trace length prediction is remarkably low at 5.49 %, and the Kullback-Leibler (KL) divergence is as low as 4.81 %. The method is further applied to an underground oil storage cavern, China, revealing structural surface information. By incorporating continuously exposed fracture data, prediction accuracy is progressively improved, demonstrating the method's potential as a predictive tool for enhancing tunnel construction safety and efficiency.

Research on the Stability of Lining Structures Under Different Fault Moments Based on FDM-DEM

Currently, research on employing finite difference method and discrete element method (FDM-DEM) coupling to assess the stability of tunnel lining structures is limited. This study utilized the FDM-DEM coupling approach, with the F2 fault of the East Tianshan Tunnel as a case study, to develop a numerical model in conjunction with PFC3D 6.0 and FLAC3D 6.0 software. We conducted a comprehensive analysis of the displacement deformation and crack progression of the tunnel lining structure under varying dislocation momentum conditions, unveiling the underlying mechanisms. The findings indicated that as the dislocation increased, the extent of damage to the vault intensified, and the particle contact force within the tunnel lining shifted from compression to tension, significantly contributing to the crack formation. Fault dislocation influenced the gradual expansion of cracks from the vault to the spandrel and arch waist, with the crack width increasing alongside the rising dislocation momentum. In particular, under substantial dislocation momentum, the overall stability of the tunnel lining was markedly diminished. The safety factor at the tunnel section declined progressively as the dislocation momentum escalated, with values of 2.53, 2.49, 2.43, 2.39, and 2.32 corresponding to dislocation momenta of 0.01 m, 0.05 m, 0.1 m, 0.15 m, and 0.2 m, respectively. This research offers valuable insights and a reference framework for investigating the stability of tunnel lining structures in proximity to fault dislocations, pinpointing potential failure points, and bolstering the structural integrity of tunnels.

Study on Engineering Properties and Mechanism of Loess Muck Grouting Materials

Shield tunneling generates a massive amount of muck, and achieving the on-site reuse of muck is an urgent need in the field of shield tunneling. This study, based on a section of the Xianyang diversion tunnel in a loess stratum, aims to optimize the mix ratios of loess muck grouting materials to meet specific performance requirements. Laboratory tests were conducted to analyze the effects of the bentonite content and water–solid ratio on the properties of grout. The engineering properties, cost, and environmental impact of the optimized loess muck grouting materials were compared with those of traditional grouting materials. Additionally, XRD, SEM, and CT were employed to investigate the solidification mechanism of loess muck grouting materials. The results show that the bleeding rate, setting time, fluidity, and consistency of loess muck grouting materials decreased with increasing bentonite content, while these properties increased as the water–solid ratio rose. The compressive strength reached 0.26 MPa and 1.05 MPa at 3 d and 28 d, respectively. Compared to traditional grouting materials, the economic cost and carbon emissions of loess muck grouting materials were reduced by 49.46% and 37.17%, respectively. As the curing time increased, gel filling and particle agglomeration reduced the number of pores. The dense microstructure is the primary factor for the improvement of strength.

Tricolored Bat (Perimyotis subflavus) microsite use throughout hibernation

Abstract White-nose syndrome (WNS) has caused dramatic population declines in several bat species, including the Tricolored Bat (Perimyotis subflavus). Several studies have documented bats using colder roosting temperatures after infection; however, this strategy may have costs such as increased freezing risks or greater predation risks and it is unknown when during hibernation bats begin to utilize these colder temperatures. Our aim was to examine Tricolored Bat roost locations in a WNS-positive site in relation to roost microclimate and other environmental conditions throughout the hibernation season. We conducted monthly censuses of tricolored bats across 2 hibernation seasons (November to March 2020 to 2021 and October to March 2021 to 2022) in a WNS-positive hibernaculum in northwestern South Carolina and recorded skin and adjacent wall temperature, tunnel section, and distance from the entrance for each bat species. We continuously measured hibernacula temperature and relative humidity during both hibernation seasons. Most bats roosted in the back part of the tunnel where temperatures were warmer and more stable, and vapor pressure deficit (VPD) and human disturbance were low. However, >20% of bats roosted in the front, where roost temperatures were significantly colder and VPD was higher but more variable; human disturbance was also higher in this section. The proportion of bats in each tunnel section did not vary among months and we did not find evidence of significant movement to the front section of the tunnel as hibernation progressed based on marked bats; however, bats in the front section roosted higher on the wall suggesting that they may be avoiding human disturbance or predators. Our results support the notion that no optimum hibernation temperature exists for tricolored bats and that high VPD and disturbance are likely important factors driving microsite use. Protection of Tricolored Bat hibernacula that offer a range of microclimates or a network of sites in close proximity that offer different microclimates may be helpful for recovery of this species.

Multisource information fusion for safety risk assessment in complex projects considering dependence and uncertainty.

The success of tunneling projects is crucial for infrastructure development. However, the potential leakage risk is particularly challenging due to the inherent uncertainties and fuzziness involved. To address this demanding challenge, a hybrid approach integrating the copula theory, cloud model, and risk matrix, is proposed. The dependence of multiple risk-related influential factors is explored by the construct of the copula-cloud model, and the diverse information is fused by applying the risk matrix to gain a crisp risk result. A case study is performed to test the applicability of the proposed approach, in which a risk index system consisting of nine critical factors is developed and Sobol-enabled global sensitivity analysis (GSA) is incorporated to investigate the contributions of different factors to the risk magnitude. Key findings are as follows: (1) Risk statuses of the studied three tunnel sections are perceived as under grade I (safe), II (low-risk), and III (medium-risk), respectively, and the waterproof material aspect is found prone to deteriorating the tunnel sections. Furthermore, the proposed approach allows for a better understanding of the trends in the risk statuses of the tunnel sections. (2) Strong interactions between influential factors exist and exert impacts on the final risk results, proving the necessity of studying the factor dependence. (3) The developed neutral risk matrix presents a strong robustness and displays a higher recognition capacity in risk assessment. The novelty of this research lies in the consideration of the dependence and uncertainty in multisource information fusion with a hybrid copula-cloud model, enabling to perform a robust risk assessment under different risk matrices with varying degrees of risk tolerance.

Prediction Models and Feature Importance Analysis for Service State of Tunnel Sections Based on Machine Learning

Prediction Models and Feature Importance Analysis for Service State of Tunnel Sections Based on Machine Learning

Wind tunnel testing and modelling of a rod-airfoil setup: validation and 3D acoustic imaging

This work revisits the rod-airfoil benchmark experiment from Jacob et al. (2004) with the aim of performing a detailed numerical validation in the nearfield and far field as well as to perform 3D acoustic imaging. The setup consists of a rod near the leading edge of a NACA-0012 airfoil and is placed in a semi-open wind tunnel in anechoic conditions. In addition to a far-field microphone array, the setup is equipped with two planar microphone arrays as well as wall-mounted microphones on the closed wind tunnel section and on the airfoil. The setup is modelled using a second-order finite volume method, and particular attention is devoted to including installation effects and sensor response properties in order to guarantee simulation accuracy. Validation examples are provided, including single microphone spectra as well as the acoustic field reconstructed on the test object by means of 3D acoustic imaging using the planar microphone arrays. Finally, the experimentally-validated numerical model is used as a means to gain further insight into the tested object. For instance, the model allows to separate acoustical and turbulent effects present in the sensors located within the flow section.

Design of experimental section of a water tunnel for simulation of heat dissipation condition of seawater-activated battery

Abstract A water tunnel is a crucial experimental apparatus in hydrodynamic research, as the traditional water tunnel has drawbacks such as a small cross-sectional area of the test section and higher costs, which makes it difficult to meet the requirements of a water tunnel for simulating the heat dissipation conditions of the seawater-activated battery. This paper proposes a water tunnel specifically designed for simulating the heat dissipation conditions of seawater-activated batteries, and the water tunnel consists of an external cooling water circulation system and an internal electrolyte circulation system. The experimental section’s design determines the water tunnel’s size and key technical indexes. The temperature distribution contour maps of the experimental section were obtained using Ansys Fluent software simulation. The cooling effect was analyzed, and a cooling water flow rate of 10 m/s was selected. Pressure and velocity contour maps were obtained by simulating the experimental section of the water tunnel. The results show that when the cooling water velocity is 10 m/s, the pressure drop of the experimental section is approximately 1.76 atmospheres. The flow field is uniform and stable, and the heat dissipation power can reach 45.5 kW, meeting the technical requirements.

Analytical Solution to Estimate the Effect of Underlying Tunnel Excavations on the Existing Tunnel

ABSTRACTThe tunneling underlying inevitably leads to the displacement of adjacent soil, greatly influencing the deformation of the tunnel above. Most theoretical studies primarily concentrate on analyzing the mechanical equilibrium of individual tunnel sections, ignoring the energy generated by the system during tunnel deformation. Based on this, in view of the energy relationship, the overlying tunnel's deformation is simulated by using the Rayleigh–Ritz method. Further, its potential energy equation can be established based on the Vlasov foundation. The corresponding energy variational solution is solved according to the minimum potential energy principle, leading to an analytical solution for the shield tunneling‐induced overlying tunnel's response. The efficacy of the suggested method is verified by contrasting it with centrifuge experiments and field case studies derived from prior studies. Relative to the Winkler foundation model, which deviated from the suggested approach, the results derived from the suggested method show a closer correlation with the collected measurement data. Further parameter studies show that the vertical clearance and skew angle between two tunnels, the volume loss rate, and elastic modulus are significant factors affecting the tunnel behaviors due to tunneling underneath. The suggested theoretical model can be applied to forecast potential risks that an existing tunnel may encounter during the excavation of a new tunnel underlying in similar engineering projects.

Effects of folded fissure properties on tunnel model failure: Experiments and numerical simulations

Natural folded fissures commonly exist rather than simple straight fissures in rock masses surrounding tunnels. The presence of folded fissures significantly affects the fracture processes and failure modes of tunnel structures, thereby affecting their safety and stability. However, the research in this area is limited. Given this, this study fabricates city-gate section tunnel specimens containing folded fissures of various dip angles (α) and orientation angles (β), utilising 3D sand printing with sand and furan resin as matrix materials. Uniaxial compression fracture tests were conducted at a loading rate of 0.3 mm/min on these specimens using a digital image correlation technique to assess the impact of folded fissures on the mechanical properties and failure modes of the tunnel structures. Additionally, the improved smoothed particle hydrodynamics (SPH) method was used for damage evolution simulations during interactions between folded fissures and tunnels, and the simulation results were compared with the experimental results to verify the correctness of the method. The results show that for folded fissures, wing cracks and anti-wing cracks initiate not only from the ends but also from the bends of the fissures, whereas for straight fissures, they appear only at the fissure ends. Except for β = 0°, the interaction between folded fissures and tunnels generally results in the formation of a crack connecting the folded fissure upper end with tunnel, and the connection position varies with β. Different β values of folded fissures also influence the appearance and morphologies of top major cracks, underside major cracks, side cracks, and corner cracks around tunnels. As α increases, the overlap point of the crack and the tunnel moves from the tunnel corner to the tunnel crown. Moreover, folded fissures significantly affected the peak strength of the tunnel structures. As β increases, the peak strength first decreases, then increases, and finally decreases, reaching a minimum of 3.58 MPa at β = 90°. However, the peak strength differences are not evident under different α values. Finally, the influence of folded fissures on the cracking mechanism of the tunnel models is discussed in detail. This study provides insights into the impact of folded fissures on tunnel fracture modes and offers a reference for the application of SPH to reveal the underlying failure mechanisms of tunnel structures.

Surface settlement induced by frictional force of epb shield tunneling in sandy gravels.

The excavation of Earth Pressure Balance (EPB) shield can be divided into two distinct stages, i.e. advancing and lining installation. The frictional force applied on surrounding soils reverses at these two stages, which is harmful to the settlement control. Based on Mindlin's method, a new model of surface settlement is derived to involve the reversed friction. A closed form formula is then obtained for the major type of metro tunnels. Main operational parameters are also used as input of the formula. Numerous operational data and measured settlements are collected from EPB tunnels of Chengdu Metro, Line 7. The proposed formula is validated against these field data in sandy gravels. It is shown that the new formula gives reasonable prediction of surface settlement along the tunnel sections. The accuracy of new formula is significantly higher than that of Peck's formula. This study provides a new vision in settlement control of EPB shield tunneling. The increase of chamber pressure will induce higher negative friction during the lining installation. Therefore, surface settlement of EPB tunneling cannot be controlled by just increasing chamber pressure. A balanced relationship between the chamber pressure and the thrust should be maintained instead.

Prescribed performance dynamic surface control based on dual extended state observer for 2-dof hydraulic cutting arm

In tunnel section forming operations, the boom-type roadheader tracking target trajectory with high precision is greatly significant in avoiding over and under excavation and improving excavation efficiency. However, there exist complex cutting loads, measurement noise, and model uncertainties, seriously degrading the tracking performance of traditional nominal model-based controllers. Hence, this study first fully analyzes the kinematics of all members of the cutting mechanism and establishes its complete multi-body dynamic model using the Lagrange method. Furthermore, a dual extended state observer is designed to estimate the mechanical system’s angular velocity and unmodeled disturbances and actuators’ uncertain nonlinearities. In particular, introducing a nonlinear filter replaces the traditional first-order filter in dynamic surface technology, overcoming the “explosion of complexity” while attenuating the conservatism of gains tuning. Then, a dual extended state observer-based prescribed performance dynamic surface controller is developed for roadheaders for the first time. Simultaneously, integrating an improved error transformation function into controller design effectively avoids the online computational burden caused by traditional logarithmic operations. Utilizing Lyapunov theory, the cutting system’s prescribed transient response and steady-state performance are guaranteed. Finally, the proposed controller’s effectiveness is verified by comparative experiments on the roadheader.

Experimental study on the influence of extremely broken surrounding rock grade on the mechanical characteristics of tunnels

To study the significant deformation and distortion issues in certain sections of the Qinyu tunnel extremely fragmented surrounding rock under identical conditions, six tunnel sections with the same depth of burial and lithology were selected for on-site monitoring of stress. The experimental data were then used to explore the impact of gradation on the mechanical characteristics of the extremely fragmented surrounding rock tunnels. The results indicate that the tunnel experiences larger stresses at the crown and smaller stresses at the side walls and invert, showing the influence of gradation on the stress behavior of extremely fractured surrounding rock. A dual-fractal structure model was employed to quantitatively describe the gradation of the surrounding rock, yielding fitting coefficients above 0.9. The model demonstrated good applicability for extremely fractured rock with significant particle size differences. Additionally, the relationship between fractal model parameters and the maximum rock pressure at various tunnel sections was discussed, revealing an exponential correlation between the absolute difference in fractal dimensions of coarse and fine particles and the maximum rock pressure. To further understand the factors and the influence of gradation on tunnel rock pressure, indoor model tests were conducted using six different gradations. The experimental results once again confirmed the importance of gradation on the stress behavior of highly fragmented rock tunnels and validated the functional relationship between the absolute difference in fractal dimensions and rock pressure. The results can provide guidance for the design of tunnels with extremely fractured surrounding rocks in the future.

Continuous Slag Discharge Construction Technology for Shield Tunneling in Narrow Space Environment

The shield tunneling method is the main construction method in subway tunnel construction, which has the characteristics of safety, efficiency, mechanization, and high degree of automation. However, the shield tunneling equipment is huge, the supporting facilities are numerous, and the site requirements are high. In response to the problems of slow slag removal speed and low construction efficiency in shield tunneling under the construction conditions of small wellhead shield tunneling sections in urban subways, taking the shield tunneling section of Guangzhou Metro Line 13 Phase II as the background,This article introduces the main components, working principles, installation and transportation processes, fault handling, and benefit analysis of the continuous belt conveyor slag removal system,This article elaborates on the method of using a continuous belt conveyor in the tunnel combined with a vertical lifting system at the wellhead to achieve continuous slag removal during underground shield tunneling construction in a narrow wellhead construction site. This not only improves excavation efficiency but also reduces construction costs, solves construction problems, and provides reference for similar projects in the future.

Numerical Modeling for Tunnel Lining Optimization

The construction of tunnels excavated by the conventional method in densely populated urban environments requires an adequate characterization of the loads acting on the primary lining during the excavation process, to ensure that the ground is deformed and stresses around the tunnel are relieved, simultaneously complying with the failure and serviceability limits of international standards while minimizing damage to nearby structures. In this paper, common lining design criteria are revisited, through the numerical simulation of an instrumented tunnel section which is part of a 4.5 km long metro line currently under construction in Mexico City. Key needs for improvement in current design approaches are identified. The tunnel was instrumented with load cells, extensometers, and topographical references for convergences and divergences. A three-dimensional finite difference model of the instrumented section was developed, and the load transfer mechanisms between the excavated soil and the primary lining were analyzed. Then, the numerical simulation of the contribution of the secondary lining in the overall stability for sustained load was established, along with the expected ground settlements, which can significantly affect nearby structures. Results gathered from this research are key for updating lining design criteria for urban tunnels built in stiff brittle soils.

Study on the Stress and Deformation of Surrounding Rock and Support Structure of Super Large Section Tunnels Based on Different Excavation Methods

Study on the Stress and Deformation of Surrounding Rock and Support Structure of Super Large Section Tunnels Based on Different Excavation Methods

How do different seasonal environmental colors of highway tunnel entrances and dominant colors of portal walls affect the driver’s vehicle control ability?

The entrance section of the highway tunnel is a high-risk area for traffic accidents, and its traffic accident rate has significant seasonal differences. However, the dominant causes of this difference are still lacking in targeted research. On the other hand, due to the lack of a mature design system and normative guidance, the landscape design of tunnel entrances is more and more random, landscape elements tend to be complex, and color design tends to be diversified. The influence of tunnel entrance landscape design on driving behavior and its applicability in different seasonal environments needs to be studied. Given this, this study focused on two main variables − the typical seasonal environmental colors and different portal colors, and designed 12 schemes composed of three seasonal environments (green spring, golden yellow and red autumn, and white winter) and four portal colors (gray, blue, red, and tawny). Thirty subjects were invited to conduct a driving simulation experiment to study the influence of different seasonal environmental color characteristics and tunnel portal color on the amplitude and stability of driving behavior. The results show that the drivers’ behavior amplitude is large in spring and winter, and the traffic safety risk is relatively high. The typical color characteristics of the environment in different seasons are one of the reasons for the seasonal difference in the traffic accident rate. The driver’s operational stability is relatively poor in the autumn environment, which is related to the high scene complexity of the season. Compared with the grey portal scheme, the color design of the portal will increase the driver’s driving speed and the driving safety risk. However, its influence on the stability of driving behavior is bidirectional, and the color design coordinated with the environment can improve the stability of driving. When the portal is ready for landscape decoration, it is recommended to use a color scheme that is in harmony with the environment.

Study on the smoke mass flow in T-shaped tunnel fire

Smoke mass flow rate (SMFR) is an important factor for smoke control in tunnel fire. The presence of bifurcation structure can lead to the flow redistribution and distinctive characteristics. In the current study, a relational expression for the SMFR in branched tunnel was theoretically derived. A series of numerical simulations with Fire Dynamics Simulator(FDS) were conducted to investigate the effects of multiple factors on the smoke mass flow and validate the predictions. The results indicated that for a T-shaped tunnel, the amount of smoke flowing into the branch is mainly depends on the thickness and temperature of the incoming smoke flow from mainline, affecting by heat release rate(HRR) and tunnel section size, while the influence of the bifurcation angle and longitudinal position of fire source is unremarkable. Fairly good agreement was achieved between the predictions and simulation results. This research can be instrumental in estimating the SMFR in T-shaped tunnel fire scenarios and offer valuable insights for smoke management strategies.

A comprehensive evaluation of the frog effect on drivers in mountain highway tunnels – The effect of low-volume intermittent information

Objective The driver’s inability to fully absorb and react to operational cues while driving is like boiling a frog in warm water. With intermittent, low-volume information, drivers can underreact by ignoring these minor but continuous changes. This paper aims to provide an opportunity to test the effects of intermittently occurring low-volume information on drivers. Methods A real vehicle test with naturalistic driving was used to collect driving speed data from 40 drivers on a highway tunnel section in Chongqing, China, where nine tunnels are located. Drivers were classified into three categories according to the degree of compliance of their driving speed with the speed limit required by traffic signs, and drivers were analyzed in terms of their sensitivity to traffic signs and their reaction to driving maneuvers. Results Conservative drivers are the most absorbent of low-volume intermittent information, and the cumulative effect of the frog effect does not exceed 2.00 km; eager drivers tend to ignore this information, and the cumulative effect of the frog effect reaches 2.91 km; and the general type of driver is in the middle of these two types of drivers, and the frog effect gradually penetrates the driving speed in a weakly increasing manner, up to a maximum of 9.8 km. Conclusion At the beginning of a journey, drivers are most sensitive to traffic signs, and low-volume intermittent information can also play a role in guiding driving operations effectively at this time. However, as the driving distance increases, the effect of the frog effect on different types of drivers gradually increases, even exceeding the effect caused by the black-and-white hole effect, especially when driving in tunnel groups. Considering the driving characteristics of different types of drivers to improve the deployment of low-volume intermittent information and reduce the distance of the frog effect can effectively improve driving safety.