Tunneling Behavior Research Articles

Evaluating the Time-Dependent Behavior of Deeply Buried Tunnels in Soft Rock Environments and Relevant Measures Guaranteeing Their Long-Term Stability

The time-dependent behavior and long-term stability of deep-buried tunnels in soft rocks have received lots of considerations in tunnel engineering and allied sciences. To better explore and deepen the engineering application of rock creep, extensive research studies are still needed, although fruitful outcomes have already been obtained in many related investigations. In this article, the Weilai Tunnel in China’s Guangxi province is studied, taking its host rocks as the main research object. In fact, aiming at forecasting the time-varying deformation of this tunnel, a novel elasto-visco-plastic creep constitutive model with two variants is proposed, by exploiting the typical complex load–unload process of rock excavation. The model is well validated, and good agreements are found with the relevant experimental data. Moreover, the time-dependent deformation rules are properly established for the surrounding rocks, by designing two new closed-form solutions based on the proposed creep model and the Hoek–Brown criterion. To investigate the effects of the major creep parameters and the geological strength index (GSI) of the surrounding rocks on the time-dependent trend of the tunnel, an in-depth parametric study is carried out. It is shown that the convergence deformation of the surrounding rocks is remarkably influenced by the GSI and creep parameters. The convergence deformations calculated from the closed-form solutions conform well to the on-site monitoring data. In only 27 days after excavation, the creep deformation of the Weilai tunnel overtakes 400 mm, which is enormous. To guarantee the long-term stability of this tunnel, a robust support scheme and its long-term monitoring with appropriate remote sensors are strongly suggested.

Stress-induced collapse in horizontally layered rock and a yielding support strategy: A case study

Squeezing problems pose a serious challenge for tunnel engineers because they can slow down a project, increase the project budget, and potentially lead to catastrophic collapse. The choice of an adequate support is also often difficult owing to complex geological environments. Lack of sufficient understanding of geological conditions such as high geostress and horizontal layered rock mass could cause tunnel collapse and further lead to economic loss and endanger human life. In an attempt to deal with in-situ squeezing problem, this paper focus on the investigation of the mechanical behavior of tunneling in horizontal layered rock mass with high geostress and the proposal of proper engineering measures. A tunnel collapse incident occurred in northeastern China is analyzed using comprehensive methods including photographing, laboratory tests, discrete element numerical simulations, and site monitoring. The discrete element method was applied to investigate the tunneling mechanical behavior under high-geostress conditions in a horizontally layered rock mass. Numerical simulations show that the dominant horizontal stress and joints cause the maximum deformation at the corner of the arch region. The effect of horizontal joints and horizontal dominant stress were analyzed and found to be the main causes of the collapse. Based on the simulation results, an innovative, simple and efficient tangential yielding element is developed and implemented to test its applicability in a tunnel engineering scenario. Load-displacement curves of the tangential yielding element were obtained through laboratory tests and introduced to the numerical model using the 3D discrete element method. The performance of the developed tangential yielding element was validated in the simulation. Site monitoring was also conducted to determine the in-situ performance of the yielding support using the tangential yielding element. The monitored settlement at the crown region is in agreement with the simulation. The in-situ tests show that the yielding element was considerably deformed while the tunnel remained stable, which confirms the applicability of this technique. The effectiveness of the yielding element is also confirmed in terms of a comparative cost analysis of the yielding and resistant support schemes.

Numerical modelling and field observations on the failure mechanisms of deep tunnels in layered surrounding rock

Tunnelling through layered rock mass with high geo-stress often leads to large deformation disasters, including rock collapses and structural failures. This study investigates the asymmetrical deformation and failure behaviors of deep tunnels in layered phyllite strata in Chengdu-Lanzhou railway (China). It has been observed that the mechanical behavior of these tunnels exhibits evident correlations with the orientations between geo-stress conditions and bedding plane. For in-depth analysis, a modeling method was first proposed considering the difference between interlayer bedding planes and intralayer joints. The excavation disturbance behaviors of unsupported tunnels with various bedding angles, such as deformation characteristics, crack generation and propagation, and stress distribution, were simulated and compared with on-site phenomena. Afterward, the crack distributions were classified into four typical types based on simulation results, and their causes, differences, characteristics, and evolutionary process mechanisms were also systematically analyzed. Additionally, the asymmetric failure caused by the weak plane effect was investigated and discussed. The results revealed that the bedding angle, the direction of principal stress and the effect of layer thickness primarily influenced the failure patterns of layered surrounding rock, which resulted in variations in both the direction and depth of failure. Engineering practice demonstrated that the classification method, based on the proposed numerical modeling approach, can serve as a valuable reference for tunnel support design.

A Diffuse-Interface Description of Electron Tunneling across Solid Electrolyte Interphases

Solid electrolyte interphase (SEI) is an electronically insulating layer on battery electrode due to electrolyte decomposition, which critically affects the battery performance. Electron tunneling is a key short-term electron transport mechanism that controls the SEI thickness and its growth behavior. The electron tunneling behavior is governed by the static Schrödinger equation and the tunneling barrier of SEIs, which shows an exponential decay of electron probability across the SEI layer. Here we develop a diffuse-interface description of electron tunneling behavior by formulating a phase-dependent tunneling barrier, so that the electrode/SEI and SEI/electrolyte interface positions do not need to be explicitly tracked when numerically solving the Schrödinger equation. We will show that this diffuse-interface description can accurately and efficiently predict the electron tunneling behaviors in 2D and 3D especially when the electrode/SEI and SEI/electrolyte interfaces are highly nonuniform. Furthermore, we will show that it can be seamlessly integrated with the phase-field simulation of electrodeposition and SEI growth in lithium-ion batteries, providing guidance for controlling the SEI morphology and improving the battery performance.

Simulation of the role of agglomerations in the tunneling conductivity of polymer/carbon nanotube piezoresistive strain sensors

A 3D Monte Carlo method paired with a percolation model is carried out to predict the electrical resistivity and piezoresistive sensitivity of carbon nanotube (CNT)-polymer piezoresistive sensors. CNTs are randomly dispersed into the insulating layer of a polymer matrix having agglomerated morphologies in some parts. The electrical resistivity of nanocomposite with a defined agglomeration state is determined by considering the tunneling effect between each connected pair of CNTs. The influence of various parameters such as agglomeration radius, percentage, intrinsic properties and geometries of CNTs are investigated. A comparison was made between the analytical results and experimental data. Considering the tunneling behavior in the vicinity of the percolation transition, a good agreement is obtained between the analytical results and experimental data. Monte Carlo simulations indicated that the tunneling resistance with a random distribution of CNTs depends on the level of agglomeration. Results revealed that piezoresistive sensitivity was diminished by larger agglomerations.

Analytical solutions for bolted tunnel structures with voids behind the lining

Understanding the mechanical behaviour of tunnels reinforced by end-anchored bolts and lining with voids behind the lining is crucial in determining the appropriate supporting measures. In this study, we constructed a geometric model for a tunnel with a single or double void. We used the substructure method and point matching method to obtain the elastic analytical solutions for the model. We examined the stress, internal force, and deformation characteristics of the tunnel and support structure under the influence of single and double voids. To validate the analytical model, we established a numerical model using the finite difference method. Additionally, we compared and analyzed the mechanical behaviour of tunnels reinforced by bolts and lining versus lining-only, and determined the contribution factor of the bolts.

Optimization of Underground Cavern Sign Group Layout Using Eye-Tracking Technology

Efficient sign layouts play a crucial role in guiding driving in underground construction caverns and enhancing transportation safety. Previous studies have primarily focused on evaluating drivers’ gaze behavior in tunnels to optimize individual traffic sign layouts. However, the lack of a theoretical framework for visual perception of visual capture and information conveyed by sign groups hinders the measurement of drivers’ comprehensive visual perception and the layout optimization of sign groups. To address this gap, this study introduces a calculation method for sign group information volume and a visual cognition model, establishing a comprehensive evaluation approach for sign group visual cognition. Eye movement data, collected using eye-tracking technology, were utilized to evaluate the comprehensive visual perception and optimize the layout of sign groups. The findings indicate that a low information volume fails to enhance recognition ability and alleviate the psychological burden. Conversely, excessive information may result in overlooking signs positioned on the left and top. Furthermore, drivers are unable to improve cognitive efficiency and driving safety even with self-regulation when faced with an information volume exceeding 120 bits within a 100 m span. Overall, this study demonstrates the effectiveness of the proposed method in promoting the long-term safety effect of temporary signage layouts in underground construction areas.

Tunnelling with Full-Face Shielded Machines: A 3D Numerical Analysis of an Earth Pressure Balance (EPB) Excavation Sequence Using the Finite Element Method (FEM)

Urban tunnelling can be highly challenging, especially in areas where limited ground settlements and environmental disturbance is required. Mechanised tunnelling is usually preferred in such ground environments, specifically Slurry or EPBM (Earth Pressure Balance Machine), depending on the ground properties. Being able to predict the anticipated tunnel behaviour at the preliminary stages of the project can be very beneficial in optimising not only the design, but also control the construction activities and completion times. In practice, the short-term excavation response and support performance focus primarily on design, since most site characterisation inputs are focused on material properties gained from short-term testing. Although the analysis of tunnelling is a three-dimensional (3D) problem, conventional approaches and design methods employed during the design and construction of underground openings are often based on the ground’s static response in two dimensions (2D). In this paper, an initial 2D model is generated in PLAXIS2D and RS2 (Rocscience) to test advanced constitutive models and compare transverse settlement profiles; subsequently, a complete 3D FEM numerical model in RS3 (Rocscience) was used to simulate an Earth Pressure Balance (EPB) excavation sequence. The 3D numerical model simulates the relevant EPB components such as face pressure, TBM shield, backfilling of the tail void (time-dependent hardening of the grout) and gradual segmental lining erections in the longitudinal direction. The presented numerical approach can be used by tunnel designers and engineers to predict the soil response in EPBM tunnelling.

Parametric Investigation of Interaction between Soil-Surface Structure and Twin Tunnel Excavation: A Comprehensive 2D Numerical Study

The growing demand for transportation tunnels in densely populated urban areas has led to the widespread adoption of twin tunnel configurations in contemporary infrastructure projects. This research focuses on investigating the complex interaction between soil, structures, and the excavation of twin tunnels. The study employs the tunnel boring machine (TBM) method and utilizes two-dimensional numerical modeling based on the finite element method (FEM). The numerical model is validated by comparing its results with field measurements obtained from a twin tunnel project in Italy, specifically the New Milan Metro Line 5. A comprehensive parametric study is conducted to analyze various parameters that influence soil–structure interaction during tunnel excavation. These parameters include the positioning of the tunnels in relation to each other, the spacing between them, the presence of structures above the tunnels, eccentricity between the structure axis and tunnel axis, and tunnel depth and diameter. Moreover, a comparative analysis is performed between scenarios with and without structures to elucidate the impact of structure presence on the interaction phenomenon. The research findings provide valuable insights into the intricate behavior of twin tunnels and their interaction with the surrounding soil and structures.

An analytical approximate solution for stress and displacement around a shallow circular tunnel excavated under concave slope topography

For shallow buried tunnels under slope, overloading on the ground surface and unloading of excavation both significantly influence the stability of the tunnel surrounding rock and slope. This study proposes an analytical approximate solution for the stress and displacement around shallow buried circular tunnel under slope boundary. In derivation process, the original problem is divided into two models: Model A is a slope plane without any holes subjected to gravity and surcharge load along the ground surface, and Model B is a tunnel contained in a slope plane loaded by released stresses along the tunnel boundary. Furthermore, Model B is decomposed into another two models: Model B1 represents a slope without holes subjected to virtual surface force along the ground surface, and Model B2 is an infinite domain containing a tunnel loaded by another virtual surface force along its boundary. Two sets of virtual surface forces are then achieved by an iterative calculation. The solution, which strictly meets all stress boundary and compatibility conditions of the original problem, are ultimately solved by superposing the solution of Models A, B1 and B2, respectively obtained by the method proposed by the authors (Models A, B1) and complex variable theory (Model B2). The convergence of iteration process and good agreement between the derived and numerical results under the same assumptions verify the correctness of the proposed solution. Furthermore, a parametric investigation is performed to investigate the influence of surcharge load position, slope topography and tunnel position on the stress and displacement around the tunnel and near the ground. The proposed solution is of great value for the conceptual understanding of mechanical behavior of shallow tunneling in slope terrain and for verifying the numerical models. Moreover, the solution is useful for the preliminary design of tunnels at shallow depth under slope topography.

Numerical investigation of water inflow and seepage characteristics in a tunnel crossing two overlapped parallel faults

Water inflow is one of the main geohazards that threaten the safety of tunnels and other underground engineering projects. Faulted zone is one of the important geological triggers for such events. Numerical investigations on the evolution of flow behavior in tunnels across fault zones are of significance to the predication and prevention of this type of geohazards. In this work, a numerical investigation model with two overlapped parallel faults is established at a steady stage according to the "Three Zones" fault structure theory. The rapid turbulent flow in the fault zone is simulated by using the improved Darcy-Brinkman seepage model, while the slow laminar flow in ordinary rock zone is described by Darcy equation. The effect of relative position and distance between the tunnel excavation face and overlapped parallel faults to the groundwater pore pressure and flow velocity is studied through several scenarios, and the water inflow rate into the tunnel is calculated. The numerical investigation results reveal that while the tunnel face is excavated into the fault center core, the fractured zone, the ordinary rock zone, and the center of the overlapped faults, the pore pressure value ahead of the excavation face increases while the flow velocity decreases sequentially. The inflow rate is the largest while the tunnel face is excavated to center of the fault center core, which is closely related to the range of the overlapped area. The investigation results offer a practical reference for predicting early warning of water inflow geohazard when a tunnel cross two overlapped parallel faults.

Structural Behaviors of Large-Section Mine Tunnels Undercrossing Existing Metro Lines

To meet the operational requirements of a new metro line in Guangzhou, China, a complex tunneling project was undertaken in a business area surrounded by high-rise buildings and underground utility pipelines. Two large-section mine tunnels, with a maximum excavation span of 15.6 m, were constructed, crossing beneath the existing metro line 7 in close proximity. To ensure construction safety, extensive field monitoring was conducted, investigating the deformation and stress characteristics of the newly built tunnel lining structures and settlement of existing tunnels during various construction stages. The findings indicate that the structural integrity of the newly built tunnels may be compromised by the ground pressure resulting from deep-hole grouting, which is aimed at protecting the existing metro line above. The primary lining of the new tunnels is particularly susceptible to stress at the arch waist, where it experiences significantly higher stress compared to the arch crown and arch foot. While constructing the secondary lining before removing temporary diaphragm supports can be advantageous in controlling ground settlement, the stress levels within the secondary lining can fluctuate significantly once the temporary supports are removed. Once the tunnels are completed as closed loops, the stress conditions in both the primary and secondary lining tend to stabilize. The secondary lining primarily undergoes flexural stress, with internal force diagrams roughly symmetrical to the cross-section center line, and the most vulnerable position being at the left arch waist or invert. This investigation provides valuable insights for the design and construction of similar engineering projects in the future.

Numerical investigation into the composite behaviour of over-deformed segmental tunnel linings strengthened by bonding steel plates

Bonding steel plate has been used as a strengthening approach to repair disrupted segmental lining of operational tunnels. This paper introduces numerical investigation into the composite behaviour of the initially deformed segmental tunnel linings strengthened by bonding steel plates using finite element modelling. Cohesive zone modelling was used to simulate the interface bonding behaviour between the segmental linings and steel plates. The full history of the tunnel behaviour before and after strengthening were simulated, where the segmental tunnel lining is initially loaded to create some deformation, then after bonding steel plate, the strengthened tunnel is reloaded until failure occurs. By comparing the results with experimental data from the literature, the proposed model was proved to be capable of simulating the strengthened lining behaviour and able to capture the strengthening failure process in terms of the interface debonding. Subsequently, the segmental lining response and interface shear stress distribution and propagation were analysed to interpret the interaction and failure mechanism of the steel plate strengthened segmental linings. The influence of the initial deformation and the steel plate thickness were investigated and discussed in terms of the strengthened stiffness and capacity. It has been found that the interface shear stress concentration occurred at the positions of the segment joints, where bond damage first initiated. The ultimate failure of the steel plate strengthening happened suddenly once a local debonding zone close to the segmental joint was formed. In addition, the predicted results indicate that a delay in strengthening would result in an increase in strengthened capacity but a decrease in strengthened stiffness. By using thicker steel plates, the strengthened stiffness was improved, while the strengthened capacity could be improved only if the thickness was relatively thin.

Device Simulation on GaN‐LED Operating in Noncarrier Injection Mode for Performance Improvement by Enhancing the Tunneling Effect in Multiquantum Wells

AbstractNoncarrier injection (NCI) operation mode is an emerging driving mode for nanoscale light‐emitting diodes (LEDs) for application in nanopixel light‐emitting displays. However, the luminescence intensity of the NCI‐LED with traditional epitaxial structure is relatively low because of the absence of external carrier injection. Therefore, improving the luminescence intensity by optimizing the epitaxial structure of the LED is an important technical measure. In this work, the tunneling behavior of the NCI‐LED under reverse bias, which plays a key role in increasing the luminescence intensity, is studied through modeling and simulation. The dynamic variation of carrier concentration in each voltage cycle is studied to explore the working process of the NCI‐LED. Results show that the luminescence output of the NCI‐LED is highly sensitive to doping concentrations, and reducing the number of multiquantum wells can increase the probability of interband tunneling so as to improve dramatically the carrier number contributing to luminescence. This simulation work can deepen the understanding of the NCI mode and serve as an important guidance for the rational design of the NCI‐LEDs.

A bending-shear-torsion resistant beam foundation model for segmental tunnels in longitudinal direction

Segmental tunnels constructed by Shields / TBMs are easily subjected to uneven longitudinal cross-sectional torsion because of asymmetric external loads or deformations along the tunnel. However, the conventional models for soil-tunnel interaction in the longitudinal direction generally regard the tunnel as a one-dimensional beam on elastic springs, ignoring its cross-sectional torsion. To mitigate this gap, the paper proposed a bending-shear-torsion-resistant beam foundation model to explore the effects of cross-sectional torsion on tunnel performance. Firstly, an analytical solution for the longitudinal bending-shearing-torsion stiffness of a segmental tunnel was derived, then a soil-tunnel interaction model based on torsional Timoshenko beam on Winkler foundation was proposed with three-dimensional soil reactions incorporated. The present model is verified by comparing it with the Finite Element program and other published methods based on two case studies. The new contributions and findings are as follows: (1) The longitudinal torsional stiffness is proposed, and it is found that it is greatly affected by the number of bolts and segment size. (2) The governing differential equations and the closed-form solution for the soil-tunnel interaction model under bending-shear-torsion mode are derived, regarding arbitrary loading and two typical boundary conditions. (3) By considering the sectional torsion and three-dimensional soil reactions, the proposed method is proved to be actually more reasonable than the existing analytical methods. (4) A parametric analysis for the proposed solution was conducted to investigate the influence of key parameters on the torsional performance of segmental tunnels, which revealed the effect of torsional stiffness, soil resistance and elastic boundary conditions. The proposed solution and results could promote tunnel engineers better understand the anti-torque behaviors of segmental tunnels and improve the tunnel design in case of complicated circumstances.

Corporate governance, moral hazard, and financialization

Corporate governance, by mitigating managers' moral hazard problems and affecting firms' operational efficiency, significantly influences firms' allocation of funds between investing in internal projects and financial investments. We develop a model for how better corporate governance influences firms' financialization through increasing managerial efforts and suppressing extravagant consumption and tunneling behavior. We then manually collect data on China's non-financial firms' financialization including investing in entrusted loans and wealth management products (WMPs) to empirically test the effects of corporate governance. The results show that enhanced corporate governance can suppress non-financial firms' financialization.

Two tigers cannot live on the same mountain: The impact of the second largest shareholder on controlling shareholder's tunneling behavior.

Under the current corporate governance model, the second largest shareholder (SLS) is a very special, common and important presence, which becomes an important counterweight to the controlling shareholder (CS). Through a game matrix, this paper explains whether the SLS will supervise the CS's tunneling behavior. Based on this, we empirically examine the effect of the SLS on CS's tunneling behavior in Chinese listed firms between 2010 and 2020. The results indicate that the SLS significantly inhibits CS's tunneling behavior. In addition, the heterogeneity analysis reveals that the negative effect of the SLS on CS's tunneling behavior is concentrated in non-state-owned enterprises (NSOEs) and enterprises located in regions with better business environment. This paper provides a reference for resolving the current "conflict of interest" among multiple large shareholders (MLSs), as well as evidence to support the governance role of the SLS in listed firms with MLSs.

Similar model test of a mudstone-interbedded–sandstone-bedding rock tunnel

Herein, for the Zhengzhou–Wanzhou high-speed railway mudstone-interbedded–sandstone-bedding rock tunnel, the mechanical parameters of the surrounding rock were tested via uniaxial and triaxial compression tests, and these were converted into rock mass parameters according to the Hoke–Brown theory. Various similar mudstone, sandstone, and tunnel lining materials were prepared in accordance with the similarity theory and orthogonal tests. Based on a similar model test, the effects of the bedding structure and different burial depths on the tunnel lining were simulated. The displacement and contact pressure along the normal direction of the tunnel bedding were evidently greater than those along the tangential direction of the surrounding rock. Further, increasing the burial depth of the bedding tunnel first resulted in longitudinal cracking at the lining invert. Simultaneously, floor heaving occurred in the lining invert, and longitudinal cracks appeared at the lining arch waist corresponding to the normal position of the bedding structure. The similar model test results were found to be in good agreement with the tunnel field test results, indicating that the test model could simulate the mechanical behaviour of bedding rock mass tunnels.

Dependence of the tunneling properties on an anisotropic factor in a graphene-like system

In analogy with the Klein tunneling in an isotropic linear energy graphene system, we reveal an anisotropic Klein tunneling in an anisotropic two dimensional (2D) linear energy system. The chirality and the absence of the back scattering leads to the Klein tunneling. The tunneling characteristics can be tuned by the barrier structure, the incident energy and angle, and more importantly the anisotropic parameter and different potential direction. The controllable Klein and side tunneling peaks can be understood by the carrier states and the phases in barrier/well regions. This interesting tunneling behaviors enrich the 2D tunneling properties and broaden the studies on the three-dimension tunneling features which will enlarge its electronic applications.

The Contamination of the Lower Layer in Sloped Tunnel Fires

Fires in tunnels are a major concern due to the casualties they may cause. Therefore, forced ventilation is mandatory in long tunnels, despite the significant associated costs. In shorter tunnels, however, natural ventilation may be sufficient to comply with safety regulations. Accordingly, the analysis of natural fire smoke flow is relevant for tunnels shorter than 1000 m. This paper presents a computational investigation of the influence of the tunnel slope on the contamination of the cold lower layer with smoke and discusses how it impairs the user’s egress. Large-eddy simulations of the smoke propagation show three different regimes, namely, a quasi-horizontal tunnel behavior for a slope of 0.5%, a transitional behavior for slopes in the range of 1% to 5% and a quasi-forced ventilation behavior for a slope of 7%. The computational results are compared with the application of 1D equations to predict the upper layer temperature, the average mass flow rate, the upper layer mass flow rate, the upper layer velocity and the lower layer velocity. The distance from the fire to the location where the lower layer contamination with smoke starts is accurately predicted by the one-dimensional model for slopes of 2% and 3.5%. However, in the case of lower or higher slopes, the one-dimensional model performs poorly and needs further improvement.