Tunneling Behavior Research Articles

Long‐term time‐dependent deformation and stability analysis of the machine hall of an underground powerhouse cavern using microseismic monitoring

AbstractThe geomechanical behaviour of the main tunnel of an underground powerhouse structure in the Himalayan region after its construction is a challenge for the geotechnical experts due to the issues of time‐dependent deformation and failure of the rock mass support system. The machine hall of the underground powerhouse of Tala Hydropower Plant facing such issues needs demarcation of the failure zone in advance, as well as parameters to assist in the proper support redesign using a real‐time continuous monitoring system. Seismic source parameters deduced using a three‐dimensional microseismic monitoring network at this powerhouse cavern provide information on the deformation zone in the machine hall and its stability status using spatio‐temporal analysis of seismic potency displacement, Gutenberg–Richter relation and log–log (energy–moment) relationship. Sectional analysis demarcates the deformation zone in the upstream and downstream wall of the machine hall and planar analysis at regular intervals of the machine hall has provided a path of propagation of deformation. This analysis has helped to increase the stability of this underground powerhouse, and the same methodology may be applied to other underground structures for marking their deformation zone to increase their long‐term stability in the Himalayan region.

The influence of lateral ambient wind speed on fire smoke behavior in tunnel with unpowered ventilation caps shaft

The influence of lateral ambient wind speed on fire smoke behavior in tunnel with unpowered ventilation caps shaft

Field investigation of fire and smoke spreading characteristics in the high-altitude tunnel with strongly longitudinal ventilation

Evolution of the fire combustion and propagation of smoke plume in the high-altitude area is likely to perform different features compared to those fires burned in flatlands. Currently, limited experiments have been conducted to analyze the fire and smoke behavior in the high-altitude tunnels. Motivated by such knowledge gap, the present work conducted a set of burning tests at the altitude of 3200 m. The flame spreading characteristics, as well as the propagation of smoke plume, were studied. Meanwhile, comparison with the data derived from urban tunnel fires was made to quantify the influence of tunnel altitude. Results suggest that the longitudinal ventilation speed has vital influence on the flame behavior and smoke movement. Burning rate of heptane pool fires firstly decreases and then increases with the wind velocity. The peak drop of burning rate caused by the wind cooling effect exceeds 70 %. At a certain ventilation speed, the flame titled angle at high-altitude area is found to be smaller than that predicted for the fires in flatlands. As the ventilation velocity increases, plume bifurcation results in a sharp decrease of ceiling temperature. The maximum temperature is found to decrease at a very low speed when the ventilation velocity is within 0.40 m/s ∼ 1.10 m/s. Thermal stratification loses its stability due to the strong wind while the corresponding temperature rise at human height is still below the safety limit. According to the comparison with literature models, more exploration regarding tunnel fires in the high-altitude area shall be conducted since the existing formulae may lose their effectiveness if applying to such conditions.

Enhanced performance of hafnia self-rectifying ferroelectric tunnel junctions at cryogenic temperatures

The advancement in high-performance computing technologies, including quantum and aerospace systems, necessitates components that operate efficiently at cryogenic temperatures. In this study, we demonstrate a hafnia-based ferroelectric tunnel junction (FTJ) that achieves a record-high tunneling electroresistance (TER) ratio of over 200,000 and decade-long retention characteristics. By introducing asymmetric oxygen vacancies through the strategic use of indium oxide (InOx) layer, we enhance the TER ratio without increasing off-current, addressing the longstanding issue of low on-current in hafnia-based FTJs. Unlike prior approaches that led to leakage currents, our method optimizes tunneling behavior by leveraging the differential oxygen dissociation energy between InOx and hafnium zirconium oxide (HZO). This results in asymmetric modulation of the tunnel barrier, enhancing electron tunneling in one polarization state while maintaining stability in the opposite state. Furthermore, we explore the intrinsic characteristics of the FTJ at cryogenic temperatures, where reduced thermal energy minimizes leakage currents and allows the maximization of device performance. These findings establish a new benchmark for TER in hafnia-based FTJs and provide valuable insights for the integration of these devices into advanced cryogenic memory systems.Graphical

Influence of shells on the charge tunneling behavior in quantum-dot light-emitting diodes

Abstract Due to the advances in quantum dot (QD) synthesis and device design, quantum-dot light-emitting diodes (QLEDs) have gained much progress in luminance, efficiency, and operational stability. However, fabricating high-performance QLEDs remain to be empirical, lacking full understanding of the electroluminescent mechanism of QDs. The formation and recombination of excitons is one of the most crucial charge-carrier dynamics in determining device design and performance. As a fingerprint, the ideality factor of diodes is used here to evaluate the transportation and recombination of charge carriers in QLEDs. The ideality factor of the current for QLEDs deviates significantly from 2, indicating that tunneling behavior dominates the charge injection and transportation processes in the low driving region. The ideality factor of the luminance strongly depends on the core-shell structure of the QDs. For QLEDs with I-QDs that have an alloying shell, the luminance ideality factor falls between 1 and 2, suggesting the coexistence of both trap-assisted recombination and Langevin bimolecular radioactive recombination processes. In contrast, for II-QDs with a sharp core-shell structure, the luminance ideality factor is approximately 2, indicating that trap-assisted recombination prevails in the device.

Two-Dimensional Numerical Analysis of the Effects of Different Construction Methodologies on Tunnel Behavior

Abstract: The growth of urban populations necessitates the construction of robust infrastructure, including highways, public transportation systems, sanitation networks, and housing. Consequently, underground space utilization becomes pivotal, prompting the construction of tunnels, access shafts, and galleries. However, such construction encounters challenges due to the unpredictable geotechnical and geological characteristics of the excavation site, especially when sensitive structures are nearby. This study examines the impact of various tunnel construction methodologies on earth mass behavior, with a particular focus on deformations, surface displacements, and forces exerted on linings. To this end, numerical simulations were conducted utilizing ABAQUS finite element software under plane strain conditions. These simulations were designed to simulate conditions akin to a tunnel project in Florianópolis. The numerical model encompasses four layers of soils and rocks, spanning approximately 70 meters in depth and 190 meters in width. The tunnels, with an excavated area of 161.29 m², are situated 20 meters below ground and are equipped with primary and secondary linings. The soils/rock and linings are modeled using Mohr-Coulomb and linear elastic failure criteria, respectively. The soil domain was modeled with CPE4 elements, while the linings domain employed CPE4I elements. The study initially examines the convergence and confinement curves to incorporate the three-dimensional effects of construction, considering the degree of mass relaxation during lining application. The construction sequences for single and twin tunnels entail full-section excavation, subsequent placement of the definitive crown and inverted arch, and side drift associated with half-section and inverted arch. The results discuss and highlight earth mass deformation patterns, critical areas during construction, surface displacement basins, and forces exerted on linings at various excavation phases. The effectiveness of various construction methodologies in reducing deformations and enhancing project safety is evaluated. The conclusions drawn from the numerical analyses offer valuable insights for tunnel project professionals, facilitating the development of more efficient and safer construction practices.

Structural behaviour of tunnels exposed to fire using numerical modelling strategies

Structural behaviour of tunnels exposed to fire using numerical modelling strategies

Study on the blast mitigation behavior of metakaolin-based foam geopolymer (MKFG) as tunnel cushioning layer against external blasts

In this study, the similarity model contact blast test and numerical simulations were carried out to investigate the protective behavior of tunnels with a metakaolin-based foam geopolymer (MKFG) cushioning layer under blast impacts. In contact blast test, Rock-Foam Geopolymer-Concrete Tunnel (RFGCT) structures with various densities (400, 600 and 800 kg/m3) of MKFG were tested against a blast impact of 100 g TNT. In numerical simulations, several parameters covering TNT equivalent as well as density and thickness of cushioning cladding, were comprehensively discussed. Test results show that the attenuation rate of cushioning cladding to the blast wave is enhanced from 34.7 % to 71.0 % with the reduction of the density of MKFG from 800 kg/m3 to 400 kg/m3. Meanwhile, the reflected tensile wave generated by blast wave falls from 1.85 MPa to 0.66 MPa. When the density of MKFG exceeds 600 kg/m3, the cladding exists obvious defects in energy absorption at the bottom of mid-span and free end, which gradually disappear as the TNT equivalent and cushioning thickness increases. Increasing thickness of the MKFG-400 can lead to excessive overall displacement of the tunnel lining. Full-size uncertainty analysis shows that at TNT equivalents of 2000 kg, the thickness of MKFG-800 as cushion is recommended to be 2–3 times that of the lining.

Effect of seismic interaction between twin tunnels on internal forces

The objective of this paper is to investigate the effects of seismic interaction between twin adjacent tunnels on internal forces. A 2D numerical analysis was conducted, considering position, distance, and seismic components as key parameters. The results of this paper demonstrate that as the separation distance between tunnels decreases, internal forces increase, except for the normal force, which decreases. The total principal stresses around the tunnels exhibits the same behaviour. Additionally, the position of the adjacent tunnel clearly influences the internal forces, decreasing in vertically aligned tunnels case and increasing in scenarios where the tunnels are inclined or horizontally aligned. The magnitude of distance and position effects is related to the seismic components, with the influence of the vertical seismic component being greater than that of the horizontal component. The presence of overloading can influence the interaction between the twin tunnels, either augmenting or reducing the values of internal forces. This influence is contingent upon the specific position scenarios and seismic components involved. This study provides a comprehensive perspective on the seismic behaviour of twin tunnels by systematically examining the interplay between tunnel separation distance, orientation, and seismic loading. These findings yield essential insights for guiding design strategies in seismic-prone regions.

Diagnosing the Charge Dynamic Behaviors in Quantum-Dot Light-Emitting Diodes by Temperature-Dependent Measurements.

Distinguishing and understanding the nonradiative recombination of charges are crucial for optimizing quantum-dot light-emitting diodes (QLEDs). Auger recombination (AR), a well-known nonradiative process, is widely recognized to occur in QLEDs. However, it has not yet been directly observed in a real working QLED. Here, the AR effect is verified in the QLED at temperatures of <150 K. At low temperatures, the QLED exhibits a unique S-shaped external quantum efficiency (EQE) evolution as the driving current density increases. Experimental and modeling results indicate that this S-shaped EQE results from the asynchronous changes in the behavior of injection of electrons and holes into the quantum-dot emission layer. At low driving voltages, both electron and hole currents are limited by the Fowler-Nordheim (F-N) tunneling behavior. The relatively low barrier for electrons leads to overwhelming electron injection and seriously imbalanced charges in the quantum dots, triggering the AR process. As the voltage increases, the electron current within the emission layer is no longer governed by F-N tunneling but limited by space charges. Then, charge injection becomes balanced, and the EQE increases. These results offer valuable insights into the charge injection and recombination processes within QLEDs, as well as implications for device design.

Experimental study on the seismic behavior of tunnels with distinct surface roughness in liquefiable soils

Earthquake-induced liquefaction poses grave safety risks to the underground structures. In this study, 1-g shaking table tests were conducted to investigate the uplift behaviors and soil-structure interaction (SSI) of a two-part tunnel located in liquefiable soils, with special attention paid to the influence of structural surface roughness. Two parallel tests, including a free-field test and a soil-tunnel test, were carried out to investigate the field responses and the effect of SSI during liquefaction induced by various input motions. The test results indicate that the ground partially liquefied during the first shaking event, and then experienced full liquefaction in the subsequent events with higher loading amplitude and longer loading duration. The excess pore pressure and horizontal acceleration responses around the tunnel were significantly altered due to the presence of the tunnel, which also led to different patterns of acceleration amplification and strain development in its vicinity. While structural surface roughness influenced the aforementioned responses to some extent, it played a more dominant role in the uplift behavior of the tunnel. The segment with lower surface roughness experienced significantly greater uplift compared to the rougher counterpart. Furthermore, it was found that the structural uplift behavior can be divided into distinct stages that feature different patterns of pore pressure development, and such behavior was notably different under varied loading conditions. The findings in this research emphasize the importance of incorporating the considerations of surface roughness in future numerical or experimental studies so that the structural uplift can be better captured.

The Effect of Blast Loading on the Behavior of Shallow Tunnels

The Effect of Blast Loading on the Behavior of Shallow Tunnels

Basic Cells Special Features and Their Influence on Global Transport Properties of Long Periodic Structures.

In this contribution, we address quantum transport in long periodic arrays whose basic cells, localized potentials U(x), display certain particular features. We investigate under which conditions these "local" special characteristics can influence the tunneling behavior through the full structure. As the building blocks, we consider two types of U(x)s: combinations of either Pöschl-Teller, U0/cosh2[αx], potentials (for which the reflection and transmission coefficients are known analytically) or Gaussian-shaped potentials. For the latter, we employ an improved potential slicing procedure using basic barriers, like rectangular, triangular and trapezoidal, to approximate U(x) and thus obtain its scattering amplitudes. By means of a recently derived method, we discuss scattering along lattices composed of a number, N, of these U(x)s. We find that near-resonance energies of an isolated U(x) do impact the corresponding energy bands in the limit of very large Ns, but only when the cell is spatially asymmetric. Then, there is a very narrow opening (defect or rip) in the system conduction quasi-band, corresponding to the energy of the U(x) quasi-state. Also, for specific U0's of a single Pöschl-Teller well, one has 100% transmission for any incident E>0. For the U(x) parameters rather close to such a condition, the associated array leads to a kind of "reflection comb" for large Ns; |TN(k)|2 is not close to one only at very specific values of k, when |TN|2≈0. Finally, the examples here-illustrating how the anomalous transport comportment in finite but long lattices can be inherited from certain singular aspects of the U(x)s-are briefly discussed in the context of known effects in the literature, notably for lattices with asymmetric cells.

Analytical study on plastic loosening zone of weak surrounding rocks tunnel in high cold areas

AbstractThe analysis of plastic loosening zone of tunnels with cold condition, high in situ stress, and weak stratum is the key scientific problem of tunnel construction in cold areas. Based on the unified strength theory and considering the coupling effect of high in situ stress and low‐temperature field, the analytical model of the plastic loosening zone of tunnel surrounding rocks was proposed, and the influence laws of physical parameters (initial ground stress, freezing temperature, excavation radius, and intermediate principal stress) was explored. The results illustrate that: (1) with the coupling of low temperature and stress fields, the in‐situ stress has a more significant effect on the radius of the plastic loosening zone of the tunnel surrounding rocks, showing a nonlinear correlation. When the in situ stress is small, the influence of the temperature field on the radius of the plastic loosening zone is more obvious. (2) The radius of the plastic loosening zone of the tunnel surrounding rocks increases synchronously with the excavation radius and gradually decreases with the increase of the intermediate principal stress. (3) The greater the temperature difference in the low‐temperature field, the tunnel stability has a more significant response to the intermediate principal stress and is positively correlated with the coefficient of the intermediate principal stress. (4) In the actual project, the proposed model can well describe the mechanical behavior and deformation characteristics of tunnel surrounding rocks in low‐temperature environment, showing applicability. The research results are expected to provide a theoretical basis for the study of tunnel stability in cold areas.

Ground Behavior of Parallel Tunnels in Response to Variations in Groundwater Flow

With the steady expansion of urban development, the importance of tunnel design and construction has increased, particularly with respect to changes in the groundwater level. Excavation without considering groundwater variations can destabilize tunnels; and this problem has been exacerbated by recent climate change-induced groundwater level fluctuations. This study evaluates the impact of various factors, such as filler width, lateral earth pressure coefficient, and groundwater flow, on tunnels by analyzing the ground behavior around parallel tunnels in Korea. The findings reveal that an increase in filler width reduces settlement and displacement, while the coefficient of lateral earth pressure affects convergence displacement to a higher degree than other settlements. Moreover, steady flow conditions are observed to wield a more pronounced impact on ground behavior than unsteady ones. These findings emphasize the importance of thoroughly evaluating groundwater flow characteristics during tunnel excavation and provide essential data for the future design and construction of parallel tunnels.

Absence of Additional Stretching-Induced Electron Scattering in Highly Conductive Cross-linked Nanocomposites with Negligible Tunneling Barrier Height and Width.

The intrinsic resistance of stretchable materials is dependent on strain, following Ohm's law. Here the invariable resistance of highly conductive cross-linked nanocomposites over 53% strain is reported, where additional electron scattering is absent with stretching. The in situ generated uniformly dispersed small silver nanosatellite particles (diameter=3.6nm) realize a short tunneling barrier width of 4.1nm in cross-linked silicone rubber matrix. Furthermore, the barrier height can be precisely controlled by the gap state energy level modulation in silicone rubber using cross-linkers. The negligible barrier height (0.01eV) and short barrier width, achieved by the silver nanosatellite particles in cross-linked silicone rubber, dramatically increase the electrical conductivity (51710Scm-1) by more than 4 orders of magnitude. The high conductance is also maintained over 53% strain. The quantum tunneling behavior is observed when the barrier height is increased, following the Simmons approximation theory. The transport becomes diffusive, following Ohm's law, when the barrier width is increased beyond 10.3nm. This study provides a novel strain-invariant resistance mechanism in highly conductive cross-linked nanocomposites.

Charge-Selective 2D Heterointerface-Driven Multifunctional Floating Gate Memory for In Situ Sensing-Memory-Computing.

Flash memory, dominating data storage due to its substantial storage density and cost efficiency, faces limitations such as slow response, high operating voltages, absence of optoelectronic response, etc., hindering the development of sensing-memory-computing capability. Here, we present an ultrathin platinum disulfide (PtS2)/hexagonal boron nitride (hBN)/multilayer graphene (MLG) van der Waals heterojunction with atomically sharp interfaces, achieving selective charge tunneling behavior and demonstrating ultrafast operations, a high on/off ratio (108), extremely low operating voltage, robust endurance (105 cycles), and retention exceeding 10 years. Additionally, we achieve highly linear synaptic potentiation and depression, and observe the reversibly gate-tunable transitions between positive and negative photoconductivity. Furthermore, we employed the VGG11 neural network for in situ trained in-sensor-memory-computing to classify the CIFAR-10 data set, pushing accuracy levels comparable to pure digital systems. This work could pave the way for seamlessly integrated sensing, memory, and computing capabilities for diverse edge computing.

Numerical study on the mechanical and deformation behavior of a shield tunnel under different geological conditions

Investigating the mechanical and deformation response of a shield tunnel to nearby cavities has a significant importance on the structural safety assessment and protection. Limited to the laborious modelling and analysis barriers, the refined structural model including lining segments and connecting bolts are proposed by the BIM-based parametric modelling technology, using which the geometric properties can be adjusted through one-click operation. The pretreatment algorithm has also been developed to impose springs on the numeric nodes effectively and accurately, forming an elaborate numerical simulation method. Numerical analysis has been exerted and verified considering the homogeneity of the excavation geological condition. Results show that for the shield tunnel excavated in the homogeneous stratum, the mechanical and deformation responses of the lining structure are symmetrical about the vertical central plane. The lining ring deforms from a circle to an elliptic shape. To inquire the effect of the geological cavity, three sceneries for cavity at various positions are studied. Numerical results reveal that the lining segments deform towards the cavity side significantly, leading to over 100 times the deformation increment at the vault and invert, even over 1000 times at the cavity side for the unilateral cavity. At the cavity(ies) side(s), the internal forces of the lining segments increase, and the stress states change from compression on the outer surface to tension. The stress of connecting bolts also indicates the stress concentration for the supporting structures at the cavity side. Reinforced supports are needed for the concrete linings near the geological defects.

Stationary scattering for the nonlinear Schrödinger equation with point-like obstacles: exact solutions

AbstractWe solve the Nonlinear Schrödinger Equation (NLSE) in 1D in presence of one, two and several Dirac delta potentials. With the help of an equivalent central force problem we obtain the analytical solutions in terms of a biparametric family containing the Jacobi functions. Elliptic Jacobi functions are already reported in the literature but they have not been used in the context of a scattering problem under causal boundary conditions. In the simplest examples of one or two Dirac deltas we analyze how the nonlinear term of the equation affects the modulus and phase profiles of the wave function. We also study the transmission curves under the nonlinear modification of the tunneling behavior for the first time. For a Fabri-Perot configuration made of two deltas, we obtain the effect of nonlinear coupling in the positions of the local maxima (resonances). We lay the foundations for nonlinear Anderson localization of 1D BECs in a speckle field. Upon redefinition of parameters these novel results describe the dynamics of a stationary Higgs field in 1D. Finally, we discuss the conditions for soliton formation under the influence of a Dirac comb potential, giving rise to fully correlated locations and intensities of the defects.

Investigation on in-situ thermal behavior of tunnel surrounding rock based on the thermal probe test

Heat-transfer mechanism of energy tunnel is different from that of conventional borehole heat exchanger, where the thermal flux flows along perpendicular to the tunnel circumferential direction. However, the existing measurement methods cannot directly detect the in-situ thermal behavior and thermal conductivity of surrounding rock of tunnel circumferential direction. Hence, a thermal probe test (TPT) equipment was developed and the TPT was performed to investigate the in-situ thermal behavior of surrounding rock, the thermal conductivity measurement methods of tunnel surrounding rock was proposed and compared with laboratory measurement methods. The results showed that the developed TPT equipment achieved to directly detect the in-situ thermal behavior and thermal conductivity of circumferential surrounding rock. There was a significant variation in thermal response curves of different test areas due to the fact that joint development affected the transfer paths of the thermal flux, the temperature difference between test point 1 and test point 2 could reach up to 11.4 °C. The thermal conductivity tested by TPT was reliable and reflected the in-situ thermal behavior, the deviation was 6.99 % and 1.08 %, respectively, compared with laboratory measurement results. The joint development of the surrounding rock had a major impact on the thermal conductivity, where the thermal conductivity ranged from 0.66 to 2.91 W/m K in the 1# borehole and 1.96 to 3.66 W/m K in the 2# borehole. The local thermal conductivities were difficult to apply to an energy tunnel design, hence, the comprehensive thermal conductivity model of surrounding rock with joints was proposed based on series–parallel theory and was simplified according to the heat-transfer mechanism of energy tunnel. The comprehensive thermal conductivity model provided a new idea for obtaining the heterogeneity of thermal-physical properties of tunnel surrounding rock, which improved performance predictions and optimized design strategies for energy tunnel projects, enhancing their efficiency and reliability in various applications.