Transmission Tunnel Research Articles

Study of Superconducting Transmission Lines and Tunnel Junctions for Signal Detection at Frequencies above 1 THz

Study of Superconducting Transmission Lines and Tunnel Junctions for Signal Detection at Frequencies above 1 THz

A Hybrid Prediction Model for Local Resistance Coefficient of Water Transmission Tunnel Maintenance Ventilation Based on Machine Learning

Multiple ducts in the working shaft and main body of tunnels form a combined tee structure. An efficient and accurate prediction method for the local resistance coefficient is the key to the design and optimization of the maintenance ventilation scheme. However, most existing studies use numerical simulations and model experiments to analyze the local resistance characteristics of specific structures and calculate the local resistance coefficient under specific ventilation conditions. Therefore, there are shortcomings of low efficiency and high cost in the ventilation scheme optimization when considering the influence of the local resistance. This paper proposes a hybrid prediction model for the local resistance coefficient of water transmission tunnel maintenance ventilation based on machine learning. The hybrid prediction model introduces the hybrid kernel into a relevance vector machine to build the hybrid kernel relevance vector machine model (HKRVM). The improved artificial jellyfish search algorithm (IAJS), which utilizes Fuch chaotic mapping, lens-imaging reverse learning, and adaptive hybrid mutation strategies to improve the algorithm performance, is applied to the kernel parameter optimization of the HKRVM model. The results of a case study show that the method proposed in this paper can achieve the efficient and accurate prediction of the local resistance coefficient of maintenance ventilation and improve the prediction accuracy and prediction efficiency to a certain extent. The method proposed in this paper provides a new concept for the prediction of the ventilation local resistance coefficient and can further provide an efficient prediction method for the design and optimization of maintenance ventilation schemes.

Study on Temperature Field Distribution Law and Mechanical Properties of Hydraulic Tunnel-Surrounding Rock under the Action of Large Temperature Differences

This study aims to explore the temperature field and mechanical characteristics of hydraulic tunnels during operation in an area with large temperature differences throughout a year. By relying on the measured displacement field change results of a water transmission tunnel in Xinjiang, a finite element calculation model applicable to the hydraulic tunnel-surrounding rock under the action of large temperature differences was established. Then, the FEM model was used to analyze the temperature field distribution and stress field variation of hydraulic tunnel-surrounding rock under the effect of large temperature differences. The results showed that, under the action of large temperature differences, the displacement of the cave top was the largest, followed by the cave bottom, and finally the cave waist. The obtained displacement field data using the calculation model in this study were basically consistent with the on-site measured data, and the displacement field change law was the same, indicating that the established finite element calculation model is reliable. When the ambient temperature was below zero, the freezing front gradually expanded to the depth of the surrounding rock along the tunnel radial direction, while the frozen rock at the intersection of the lining and the surrounding rock melted first when the ambient temperature was above zero. The stress in various parts of the surrounding rock of the hydraulic tunnel increased continuously. To be specific, the growth rate of the tensile stress at the cave bottom, the tensile stress at the cave top, and the compressive stress at the cave waist of the tunnel reached 0.052 MPa/year, 0.053 MPa/year, and 0.096 MPa/year, respectively, in the first year, but the increasing rate subsequently tended to slow down continuously. Therefore, in actual projects, attention should be focused on the effect of large temperature differences on the stress growth of tunnel-surrounding rocks at an early stage, especially the growth of compressive stress at the cave waist. Notably, there are a large number of symmetrical and asymmetric phenomena related to engineering in this study.

Flow–Solid Coupling Analysis of Ice–Concrete Collision Nonlinear Problems in the Yellow River Basin

Yellow River ice is the most prominent and significant natural disaster in winter and spring in China. During the drift ice period, water transmission tunnels located in this area tend to be hit by water–drift ice coupling. Thus, it is an important issue to reduce water transmission tunnel damage by drift ice, ensure the safety of operation and maintenance, and prevent engineering failure. In this paper, a numerical simulation of the collision process between ice and the tunnel is carried out by using the fluid structure coupling method and ANSYS/LS-DYNA finite element software. In addition, a model test with a geometric scale of 1:10 is carried out to verify the numerical simulation results, and the mechanical properties and damage mechanism of drift ice impacting the tunnel concrete lining in water medium are studied. The results show the following: the experimental values of maximum equivalent stress and X-directional displacement of the flow ice on the water transfer tunnel have the same trend as the simulated values, both of which show an increasing trend with an increase in flow ice velocity. It is shown that the ice material model parameters, ALE algorithm, and grid size used in this paper are able to simulate the impact of drift ice on the water transfer tunnel more accurately. With an increase in drift ice collision angle and drift ice size, the fitted curves of equivalent stress and peak displacement in X-direction all show relationships of exponential function. The peak value of displacement in the X-direction and maximum equivalent stress decrease with an increase in the curvature of the tunnel structure. It is also shown that the influence of change in drift ice size on the tunnel lining is greater than that of a change in tunnel section form. It is found that a high-pressure field will be formed due to extrusion of flowing ice, which should be fully considered in the numerical simulation. The research method and results can provide technical reference and theoretical support for prevention and control of ice jam disasters in the Yellow River Basin.

Modelling and Stress Analysis of Shaft Work Subsidence of Underground Power Transmission Line Tunnel

This research presents an analysis of soil subsidence around shaft work under its construction process and drilling tunnel by finite element method (FEM). The study is focused on the underground power transmission tunnel in the Chao Phraya River construction project (Southern Bangkok Station to Suksawat Road, Thailand) of the Metropolitan Electricity Authority. This research aims to provide information for designing shaft work and preventing drilling tunnel problems. The research analyzed the soil subsidence around shaft work with 12 m of inside diameter and 1 m of thickness that located 33 m underground during constructing a tunnel chimney by sinking method. It is assumed that the analyzed horizontal reaction is the net resistance of the lateral earth pressure around the shaft work. This study found that the subsidence of soil around shaft work during the construction and drilling process had the value between 0.80 - 53.30 mm. In the part of the base slab, the soil subsidence value is between 3.40 - 16.00 mm. It can be concluded that the top of shaft work during the construction and drilling process had a soil subsidence value of 53.30 mm with dmax/H ratio of 0.00162.
 HIGHLIGHTS
 
 The Metropolitan Electricity Authority has an underground power transmission tunnel in the Chao Phraya River Construction (Southern Bangkok Station to Suksawat Road, Thailand) project which used to distribute electricity from the source station to the other side of the Chao Phraya River
 This research studied the behavior of the shaft work in sinking reinforced concrete shaft work and drilling tunnel process by finite element method (FEM) with the Midas Gen 2021 program
 The analysis results of the maximum soil subsidence around the shaft work wall occurred in the top area (very soft to medium stiff clay layer)
 
 GRAPHICAL ABSTRACT

Analysis of Surface Deformation and Settlement Characteristics Caused by Tunnel Excavation and Unloading

Aiming at the problems of surface deformation and unloading settlement caused by urban tunnel construction, the basic characteristics of surface deformation caused by tunnel construction, the main influencing factors of surface deformation and settlement, and the temporal and spatial evolution law of stress field and displacement field of surface deformation and settlement are studied by using the comprehensive methods of evaluation factor analysis, theoretical research, and numerical simulation. The results show that the surrounding rock deformation of the tunnel is mainly concentrated in the arch crown and arch bottom, and the deformation gradually decreases from the center of the tunnel to the periphery. The surrounding rock of arch crown has sudden settlement, large deformation rate and amount, and poor stability of surrounding rock, and is prone to engineering accidents such as block falling and even collapse. The farther away from the tunnel, the smaller the degree of settlement. As the time step of tunnel excavation increases, the influence area of surface deformation and settlement increases gradually. After the tunnel adopts reasonable lining support, it can effectively prevent soil deformation transmission and restrain tunnel instability deformation, so as to prevent surface deformation and settlement by improving the self stability of surrounding rock and taking lining support and other measures.

Hydrogeological assessment and estimation of groundwater inflow into the water transmission tunnel to Urmia Lake, Northwestern Iran

Hydrogeological assessment and estimation of groundwater inflow into the water transmission tunnel to Urmia Lake, Northwestern Iran

Virus transmission by ultrasonic scaler and its prevention by antiviral agent: An in vitro study.

BackgroundIt is well recognized that dental procedures represent a potential way of infection transmission. With the COVID‐19 pandemic, the focus of dental procedure associated transmission has rapidly changed from bacteria to viruses. The aim was to develop an experimental setup for testing the spread of viruses by ultrasonic scaler (USS) generated dental spray and evaluate its mitigation by antiviral coolants.MethodsIn a virus transmission tunnel, the dental spray was generated by USS with saline coolant and suspension of Equine Arteritis Virus (EAV) delivered to the USS tip. Virus transmission by settled droplets was evaluated with adherent RK13 cell lines culture monolayer. The suspended droplets were collected by a cyclone aero‐sampler. Antiviral activity of 0.25% NaOCl and electrolyzed oxidizing water (EOW) was tested using a suspension test. Antiviral agents' transmission prevention ability was evaluated by using them as a coolant.ResultsIn the suspension test with 0.25% NaOCl or EOW, the TCID50/mL was below the detection limit after 5 seconds. With saline coolant, the EAV‐induced cytopathic effect on RK13 cells was found up to the distance of 45 cm, with the number of infected cells decreasing with distance. By aero‐sampler, viral particles were detected in concentration ≤4.2 TCID50/mL. With both antiviral agents used as coolants, no EAV‐associated RK‐13 cell infection was found.ConclusionWe managed to predictably demonstrate EAV spread by droplets because of USS action. More importantly, we managed to mitigate the spread by a simple substitution of the USS coolant with NaOCl or EOW.

Full scale tests and a progressive failure model to simulate full mechanical behavior of concrete tunnel segmental lining joints

In the context of segmental concrete linings for tunneling, segmental joints are the most vulnerable parts of the lining. Most existing segmental joint models cannot evaluate the full mechanical behavior of segmental joints from the elastic deformation to the inelastic damage and failure. However, in some actual field cases, segmental joint damage and failure can occur. In this study, full-scale tests on the segmental joint adopted by a gas transmission tunnel are presented. The segmental joint is continuously loaded until it reaches its ultimate capacity. The internal force, deflection and failure characteristics of the segmental joint during the loading process are reported and compared with those of previous studies tested with flat segments. The relationships between the internal force, deflection and damage to the segmental joint are systematically analyzed. The tests reveal that the full mechanical behavior of the segmental joints can be divided into three progressive phases with four critical points. Based on the test observations, a progressive failure model that consists of a multiple stress states is proposed to simulate the full mechanical behavior of the segmental lining joints. The proposed model is ultimately compared with the full-scale test results.

Substantial and stable magnetoresistance and spin conductance in phosphorene-based spintronic devices with Co electrodes.

Designing devices with excellent spin-polarized properties has been a challenge in physics and materials science. In this work, we report a theoretical investigation of the spin injection and spin-polarized transport properties of monolayer and bilayer phosphorene devices with Co electrodes. Based on the analysis of transmission coefficients, spin-polarized current, magnetoresistance (MR) (or tunnel MR) ratio and spin injection efficiency (SIE), both devices show superior spin-polarized transport properties. As phosphorene in the device is changed from monolayer to bilayer, the charge carrier type can be tuned from n-type to p-type. For the monolayer phosphorene device, the tunnel MR ratio reaches about 210% and the SIE is about 80.7% at zero bias. Notably, the SIE and tunnel MR ratio maintain almost constant values against bias voltage and gate voltage, which makes it suitable for magnetic sensors. As for the bilayer phosphorene device, it not only exhibits a considerable tunnel MR ratio, but also shows significantly enhanced conductance, beneficial to the sensitivity of spintronic devices. Further analysis shows that the improvement of conductance is attributed to the low barrier height between the bilayer phosphorene channel and Co electrodes. According to our results, the studied phosphorene devices with Co electrodes demonstrate superior spin injection and transport properties. We believe that these theoretical findings will be a strong asset for future experimental works in spintronics.

A Numerical Investigation of TBM Disc Cutter Life Prediction in Hard Rocks

There is a direct relationship between the efficiency of mechanized excavation in hard rocks and that of disc cutters. Disc cutter wear is an important effective factor involved in the functionality of tunnel boring machines. Replacement of disc cutters is a time-consuming and costly activity that can significantly reduce the TBM utilization and advance rate, and has a major effect on the total time and cost of the tunneling projects. When these machines bore through hard rocks, the cutter wear considerably affects the excavation process. To evaluate the performance of the cutters, first, it is essential to figure out how they operate the rock cutting mechanism; secondly, it is important to identify the key factors that cause the wear. In this work, we attempt to introduce a comprehensive numerical method for estimation of disc cutter wear. The field data including the actual cutter wear more than 1000 pieces and the geological parameters along the Kani-Sib transmission tunnel in the northwest of Iran are compiled in a special database that is subjected to a statistical analysis in order to reveal the genuine wear rule. The results obtained from the numerical method indicate that with an increase in the wear of disk cutter up to 25 mm, the applied normal and rolling forces can be multiplied by 2.9 and 2.7, respectively, and by passing the critical wear, the disk cutters lose their optimal performance. This method also shows that confining pressure will increase the wear of the disc cutter. By the proposed formulation, the cutter consumption rate can be predicted with a high accuracy.

Comparison of predicted and actual states in tunnels: lessons to be learned from the Gerede Water Transmission Tunnel, Turkey

The Gerede Tunnel is a large inter-basin project in Turkey. As with many long tunnels, some of the predictions in the project report and the tender contract have not been realized. Completion of the tunnel has been delayed for more than twice the time given in the tender contract. Unexpectedly complex geological–tectonic–hydrogeological conditions and the selection of tunnel-boring machines (TBMs) are the main reasons for this long delay. There were some discrepancies between the predicted and actual geology. The groundwater pressure encountered was much higher than expected. Plastic clays in the limestone and breccia and loose agglomerates with a high water pressure in the faults decreased the advance rate and led to several long stoppages. One of the three double-shield TBMs became stuck in the tunnel and could not be recovered. The last quarter of the tunnel was excavated more slowly, but without severe problems, by a modified earth pressure balance shield TBM. As a result, the TBM type, drive direction, length, route, cost and completion date of the Gerede Tunnel have all changed.

Growth controlling behavior of vertically aligned MoSe2 film

Vertical layered MoSe2 nanosheets have been synthesized via rapid selenization of a magnetron sputtered Mo film with a large number of penetrating microcracks. The phase microstructure and morphologies of Mo and MoSe2 films were evaluated by X-ray diffractometer, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The results indicate that a relatively high argon pressure during the sputtering process allows Mo films to deposit with a multi-crack structure. The microcracks increase the inner surface area of Mo films and provide a rapid transmission tunnel for selenium diffusion, which allows MoSe2 nanosheets to grow vertically with a c-axis // substrate texture. The growth mechanism for vertically aligned MoSe2 films has been proposed based on the experimental results. The growth orientation of MoSe2 film can be precisely controlled by adjusting the density of Mo film precursor under the same selenization condition. These findings provide a new strategy for the preparation and application of highly orientated MoSe2 film.

Investigation of the ultimate bearing capacity of a staggered assembly segmental lining for an urban gas transmission tunnel

This paper presents a local prototype compression-bending test to investigate the specific failure process, failure characteristics and the ultimate bearing capacity of a staggered assembly segmental lining for an urban gas transmission tunnel. The results indicate that the initial crack in the structure appears at the middle ring close to the longitudinal joint of the adjacent ring, and it develops into the main crack at final damage. The compression-flexure failure occurs in the middle of the structure and the compressive shear failure occurs at both ends of the structure. The failure mechanism is analysed and is found to be caused by cracking in the region where the stiffness is relatively larger. In addition, the cracking results in the redistribution of the overall stiffness of the structure, and subsequently the region with the greatest stiffness continues to crack, repeating the cycle until the ultimate bearing capacity is reached with continuous enlargement of the deformation. Based on the test results, a progressive N-M correlation curve is proposed to calculate the sectional ultimate bearing capacity. The contribution of the staggered assembly effect is included in the curve. The proposed calculation method is verified by the test results. Finally, the influence of the section size and material strength on the sectional ultimate bearing capacity are investigated using the proposed curve.

Assessment of the factors affecting the advance rate of the Tunnel Gerede, the longest and one of the most problematic water transmission tunnels of Turkey

The Gerede Tunnel, with approximately 31.6 km in length, is Turkey's longest water transmission tunnel as of 2018. The tunnel will transmit the water from the Gerede River to the Camlidere reservoir, providing drinking water to Ankara. The tunnel is divided into three sections as Umitkoy, Havullu and Camlidere, and excavations started in each section with separate tunnel boring machine (TBM-1, TBM-2 and TBM-3 respectively). The excavation, started in 2012, completed within 508 days without significant problem in the Umitkoy section having 9588 m length. In Havullu and Camlidere sections, TBMs were blocked due to high pressure water and also material ingression. This caused the progress in the tunnel to be delayed repeatedly. In addition, the harsh conditions forced to be drilled upwards after 6061th m in the Havullu section, and to be drive with another type of TBM after 7235 m in the Camlidere section. Finally, the last 8821 m was completed with the EPB machine.The daily average advance rates of TBM-1, TBM-2 and TBM-3 are respectively 18.77 m, 6.13 m and 9.37 m. For the modified EPB type TBM-4, which takes over the task of TBM-3 and TBM-2 in the last 8821 m, the advance rate is 9.56 m/day. According to the analysis, the tectonic structure, hydrogeology and TBM type are the most effective parameters on the advance rate of the Gerede Tunnel. Experiences obtained from the tunnel show that geological-tectonic-hydrogeological studies should be carried out in detail in project phase and TBM selection according to these conditions, particularly against collapse and high pressure water ingress, have vital importance.

A 3D numerical model to determine suitable reinforcement strategies for passing TBM through a fault zone, a case study: Safaroud water transmission tunnel, Iran

Mechanized tunneling, like other tunneling methods, is not an exception to dealing with complex geological structures in its direction. Therefore, the accurate perception of the geological structures and anomalous through the tunnel path and the challenges ahead of TBM can minimize the operational risk. The faults are complicated, loose, seismic, and saturated structures that present a great deal of danger when passing the tunnel from them, and each of these events, in turn, has the potential to stop the project and exert high economic costs. The instability of the tunnel environments and tunnel face due to the higher amount of stress concentration than the resistance of the host rock, pulpy material flowing from inside of the faults and water inrush are the most important events that TBM faced them through the fault zones. Hence, using the appropriate tool for realizing the operational model can be a considerable help in predicting problems. In this research, using precision numerical methods, accurate simulation of TBM motion was carried out to the excavation of Water Transmission Tunnel, Iran. The Safaroud water transmission tunnel is one of the longest Iranian water transmission tunnels that passes through numerous fault zones along its path. One of the main faults in this area is the Lalehzar fault with 40 m width which motivates us to utilize predicting procedure. The main purpose of this research is numerical modeling of mechanized tunneling in fault zone using FLAC3D and Phase2 software and selection of suitable reinforcement strategies for passing TBM from the fault zone. The results of numerical modeling illustrate the instability of the tunnel in the Lalehzar fault zone. Due to tunnel instability in this zone, reinforcement operations must be taken into account to stabilize the tunnel environment. The numerical modeling of the several reinforcement operations in the fault zone were simulated and we conclude that the combination of umbrella arch and radial grouting method are the most suitable strategies for passing TBM from the Lalehzar fault zone.

Water inflow into tunnels: assessment of the Gerede water transmission tunnel (Turkey) with complex hydrogeology

The Gerede is the longest and most problematic water transmission tunnel in Turkey, at 31.6 km long with an overburden of 600 m. The tunnel will transmit water from the Ulusu river to the Camlidere reservoir. High-pressure water ingress and collapses have resulted in many delays. Although construction began in 2012, and was intended to be completed in 2014, completion is now estimated to be in 2019. The tunnel passes through permeable Tertiary sedimentary and volcano-sedimentary rocks, and Jurassic–Cretaceous limestone. Water ingress has occurred on 45 occasions along the 26 km excavated. The initial total discharge was 1.7 m 3 s −1 and decreased to 0.5 m 3 s −1 over time. The recharge conditions, tectonic structure, progress of the excavation and sealing by grouting affect the quantity, locations and temporal changes of the inflow of water. The major faults and formation contacts are the most problematic sites to be considered. With the many delays in the tunnel, the driving plan and tunnel boring machine (TBM) were changed while the construction continued. The tunnel shows that hydrogeological conditions, in particular, should be taken into consideration when choosing the TBM and driving course. However, the problems we encountered provided valuable experience for future projects.

Spin-dependent transport properties of AA-stacked bilayer graphene nanoribbon

In this paper, the spin-dependent transport of a spin-valve, based on bilayer graphene in which the AA-stacked bilayer zigzag graphene nanoribbon (BLG) connected to two ferromagnetic (FM) semi-infinite single-layer zigzag graphene nanoribbons (FM/BLG/FM system), is numerically studied. Using the non-equilibrium Green's function method and tight-binding model in the framework of Landauer-Büttiker formalism, the spin-dependent transmission function, current and tunnel magnetoresistance of the system are calculated. Results show that the transmission function is always nonzero near the zero energy for the parallel alignment of electrode magnetizations, while it is zero for the antiparallel alignment due to the band-selective rule. Consequently, there is a region for the tunnel magnetoresistance with the value of 100%. The magnitude of this region depends on the strength of magnetization in ferromagnetic electrodes. Also, the effects of bilayer/single-layer coupling geometry,inter-layer coupling strength and width of BLG on the spin-dependent transport of the system are investigated. These results can be useful for designing graphene based spintronic devices.

Texture control and growth mechanism of WSe2 film prepared by rapid selenization of W film

The tungsten diselenide (WSe2) films with different orientation present unique properties suitable for specific applications, such as WSe2 with a C-axis⊥substrate for optoelectronics and WSe2 with a C-axis // substrate for electrocatalysts. Orientation control of WSe2 is essential for realizing the practical applications. In this letter, a WSe2 film has been prepared via rapid selenization of a magnetron-sputtered tungsten (W) film. The influence of the magnetron-sputtered W film on WSe2 film growth was studied systematically. Scanning electron microscopy, X-ray diffractometry and high-resolution transmission electron microscopy were used to evaluate the morphology, microstructure and phase composition of the W and WSe2 films. The substrate temperature has a significant effect on the W film phase composition, but little effect on the WSe2 film orientation. The WSe2 orientation can be controlled by changing the W film microstructure. A dense W film that is deposited at low pressure is conducive to the formation of WSe2 with a C-axis⊥substrate, whereas a porous W film deposited at high pressure favors the formation of WSe2 with a C-axis // substrate. A growth model for the WSe2 film with different texture has been proposed based on the experimental results. The direction of selenium (Se) vapor diffusion differs at the top and side surfaces. This is a key factor for the preparation of anisotropic WSe2 films. Highly oriented WSe2 films with a C-axis⊥substrate grow from the dense W film deposited at low pressure because Se vapor can only diffuse into the W film from the top surface where it is converted into selenide. Highly oriented WSe2 with a C-axis // substrate can be achieved for the porous W film that is deposited at high pressure because the nanopores provide a fast transmission tunnel for Se vapor diffusion. These findings will contribute to the controlled fabrication of WSe2 film and provide a theoretical basis for its application.

The Next Nearest Neighbor Effect on the Spin-Dependent Transport Properties of DNA Molecule Based Spin Valve

Based on tight-binding model and a generalized Green’s function method in Landauer-Buttiker formalism, the next nearest-neighbor (NNN) effects on the spin-dependent transport properties of a poly(G)-poly(C) DNA molecule sandwiched between ferromagnetic 3-dimensional electrodes are numerically investigated. Our results show that the spin-dependent transport characteristics, including the spin-dependent transmission probability, current-voltage characteristics, noise power, Fano factor (F), and tunnel magnetoresistance (TMR) are strongly influenced by NNN effect. Results show that the inclusion of NNN effect can broaden transmission spectra and leads to semiconductor-metal transition in the system. Therefore, the spin-dependent current and noise power amplitudes increase. The Poisson limit (F=1) region decreases due to the presence of NNN effect, where the inclusion of diagonal hopping integrals between the DNA sites increases electron correlations. Furthermore, with increasing diagonal hopping integrals strength between the DNA sites, the first sharp decrease of TMR happens in lower bias voltage and the region of the maximum value of TMR decreases.