Rectangular Tunnel Research Articles

Experimental Study on Fire Characteristics of Urban Rectangular Tunnels Based on Different Slopes

Experimental Study on Fire Characteristics of Urban Rectangular Tunnels Based on Different Slopes

Effectiveness analysis of a novel rectangular tunnel boring machine with planetary transmission for box jacking

Traditional rectangular tunnel boring machines have low tunneling efficiency, poor soil mixing effects, which has hindered the construction of long-distance and large-section box jacking projects. To overcome these limitations, a new type of full-face excavation boring machine was developed based on a planetary transmission mechanism. This machine achieves full-face excavation by utilizing three eccentric cutter heads that revolve around both the central axis of the cutter plate and their individual shafts. The design methodology, feasibility, and principles of this new mechanism were introduced. Furthermore, a successful construction project of an underground highway passage in Japan was presented as a case study to demonstrate the design and application of this tunnel boring machine. The case details include the excavation face support mechanism, optimal cutter-head layout, obstacle removal strategies, and methods for reducing jacking resistance. Monitoring data from the project verified the applicability, reliability, and overall engineering performance of the rectangular shield machine developed using the planetary mechanism. This research demonstrates that the planetary transmission mechanism-based boring machine offers superior performance in terms of ground settlement and tunneling speed, potentially providing a comprehensive solution to the challenges in the development of rectangular shield machines for box jacking projects.

Steady-State Temperature Prediction for Cluster-Laid Tunnel Cables Based on Self-Modeling in Natural Convection

Accurate temperature prediction of the operating tunnel cable is crucial for its safe and efficient function. To achieve a rapid and accurate prediction of the steady-state temperature of the tunnel cable, the self-modeling pattern in natural convection on the cable surface in the rectangular tunnel is investigated, and the self-modeling method for the convective heat transfer coefficient calculation is proposed. A thermal circuit model for single cables is further established to predict the cable core temperature, and the model is extended to predict the cluster-laid cable core temperature based on the combined method. The results show that when the tunnel size is neglected, the maximum relative deviation of the convective heat transfer coefficient between the self-modeling method and the finite element simulation is only 1.78% in the studied cases, indicating that the natural convection on the cable surface approximately satisfies the self-modeling method. Additionally, applying the self-modeling method to the thermal circuit can accurately predict the temperature of the single cable core. Furthermore, for the three-phase four-circuit cable, the maximum deviation between the temperature prediction results and the finite element results is within 2 K in the studied cases, which verifies the predictive accuracy of the combined method for the cluster-laid tunnel cable.

Shaking Table Test and Numerical Modeling of Seismic Behavior of Rectangular Tunnel Structures Embedded in Soft Clay

In this paper, a series of 1-g shaking table model tests were carried out to investigate the seismic behavior of a relatively stiff rectangular tunnel structure installed in soft clay bed, accounting for different ground motions with varying peak accelerations. Using a validated numerical analysis procedure, a suite of three-dimensional (3D) finite element (FE) analyses was performed to systematically study the factors of tunnel burial depth, seismic intensity, flexural rigidity of the middle column and tunnel wall thickness on the seismic response of rectangular tunnel structures installed in clayey ground. It was found that, with the increasing burial depth, the seismic response of rectangular tunnel structure became more intense due to the increased inertial force arising from the overlying clay; in terms of improving the seismic performance of tunnel structure, increasing tunnel wall thickness seemed more effective than increasing flexural rigidity of the middle column. Furthermore, it was found that the existing simplified approaches generally tended to overestimate the earthquake-induced racking distortions of rectangular tunnels installed in clayey ground. A new semi-empirical relationship was derived for better correlating the racking ratio with flexibility ratio for rectangular tunnels embedded in soft clays, which could provide a useful reference for the seismic design and risk assessment of similar clay-tunnel systems.

Rate Optimization of Intelligent Reflecting Surface-Assisted Coal Mine Wireless Communication Systems.

This paper proposes a three-step joint rate optimization method for intelligent reflecting surface (IRS)-assisted coal mine wireless communication systems. Different from terrestrial IRS-assisted communication scenarios, in coal mines, IRSs can be installed flexibly on the tops of rectangular tunnels to address the issues of signals being blocked and interfered with by mining equipment. Therefore, it is necessary to optimize the IRS deployment position, the transmit power and IRS phase shifts to achieve the maximum effective achievable rate at user stations equipped with the proposed system. However, due to the complex channel models of coal mines, the optimization problem of IRS deployment position is non-convex. To solve this problem, two auxiliary variables along with logarithmic operations and Taylor approximation are introduced. On this basis, a three-step joint rate optimization involving the transmit power, IRS phase shifts and IRS deployment position is proposed to maximize the effective achievable rates at the user station. The simulation results show that compared with other rate optimization schemes, the effective achievable rates at the user station using the proposed joint rate optimization scheme can be improved by approximately 12.32% to 54.17% for different parameter configurations. It is also pointed out that the deployment position of the IRS can converge to the same optimal position independent of the initial deployment position. Moreover, we investigate the effects of the roughness of the tunnel walls in a coal mine on the effective achievable rates at the user station, and the simulation results indicate that the proposed three-step joint rate optimization scheme performs better in the coal mine scenario regardless of the roughness.

Prediction of Jacking Force for Construction of Long-Distance Rectangular Utility Tunnel Using Differential Evolution–Bidirectional Gated Re-Current Unit–Attention Model

Most of the current machine learning algorithms are applied to predict the jacking force required in micro-tunneling; in contrast, few studies about long-distance, large-section jacking projects have been reported in the literature. In this study, an intelligent framework, consisting of a differential evolution (DE), a bidirectional gated re-current unit (BiGRU), and attention mechanisms was developed to automatically identify the optimal hyperparameters and assign weights to the information features, as well as capture the bidirectional temporal features of sequential data. Based on field data from a pipe jacking project crossing underneath a canal, the model’s performance was compared with those of four conventional models (RNN, GRU, BiGRU, and DE–BiGRU). The results indicated that the DE–BiGRU–attention model performed best among these models. Then, the generalization performance of the proposed model in predicting jacking forces was evaluated with the aid of a similar case at the site. It was found that fine-tuning parameters for specific projects is essential for improving the model’s generalization performance. More generally, the proposed prediction model was found to be practically useful to professionals and engineers in making real-time adjustments to jacking parameters, predicting jacking force, and carrying out performance evaluations.

On the possibility of long‐distance transmission of OAM beam in rectangular tunnels

AbstractThis letter explores the possibility of long‐distance transmission of an orbital angular momentum (OAM) beam through rectangular tunnels. Theoretical analysis reveals that the OAM beam propagating in the tunnel with square cross section fulfills the conditions for axial propagation and exhibits azimuth symmetry. In comparison with free‐space OAM generation, we draw the conclusion that long‐distance transmission of OAM beams is achievable in the tunnels with square cross section. The validity of our conclusion is further substantiated through numerical experiments. Simulation results demonstrate that the first‐order OAM beam radiated by a uniform circular antenna array exhibits favorable helical phase distribution and the circular symmetry of the amplitude distribution in the tunnel beyond the Rayleigh distance. However, these characteristics degrade with increasing mode order and propagation distance, because the increase of high‐order OAM beam divergence angle and propagation distance will exacerbate the impact of multipath effects in the tunnel environment.

Stability Design Charts and Equations for Rectangular Tunnels Using Terzaghi's Modified Stability Factors and Machine Learning

Stability Design Charts and Equations for Rectangular Tunnels Using Terzaghi's Modified Stability Factors and Machine Learning

Increasing the productivity and quality of cucumber crop by improving the performance of the evaporative cooling system

Evaporative cooling in the kingdom of Saudi Arabia is one of the most important cooling systems used inside greenhouses to obtain an acceptable temperature change in hot, dry climates. It is considered insufficient during very hot summer periods, when temperatures outside the greenhouse reach approximately 48 °C, which affects the efficiency of cooling, and thus, creates stress on the plants, leading to wilting and a decrease in the production rate. The cooling system is developed by making an insulated rectangular tunnel. The air comes out through vertical openings directly to the plants. The results of evaluating plant heat stress in the developed cooling system (DCS) showed an increase in the values of the photosynthesis rate, transpiration rate, carbon dioxide exchange, and stomatal conductance. The plants also appeared well in terms of the shape of the leaves, their freshness, the abundance of flowers, and the large size of the fruits, while in the traditional cooling system (TCS) the plants exhibited some wilting and some brown spots. The hectare yield reached 42.49 ton/ha for the DCS system, while it reached 37.53 ton/ha for the TCS with an increasing rate of 13.22 %. The total weight of fruits harvested within 60 days of cultivation was 4.25 kg/m2 for the DCS and 3.75 kg/m2 for the TCS. The dry and fresh weight of fruit, stem, and leaves, total dissolved solids, vitamin C, chlorophyll percentage in leaves, and total plant acidity, were higher in DCS compared to the TCS.

Mathematical modelling for strata deformation caused by rectangular pipe jacking construction in composite layered ground

In this study, analytical solutions of vertical deformation of ground surface and horizontal displacement of strata are derived combining the Mindlin solution and the mirror method due to rectangular pipe jacking tunneling in composite strata, which considers the combined effect of five factors of additional excavation pressure, friction of rectangular pipe jacking and soils, segment-soil friction, grouting filling and strata loss, respectively. The theoretical calculation results were verified against the measured data in two project cases. Moreover, effect factors of rectangular jacking pipe cross-sectional dimensions, embedment of tunnel axial depth, elasticity modulus on the interlayer and the Poisson's ratio of the interlayer on strata deformation is investigated. The results imply that the theoretical calculation values obtained using this method are more closely correlated with the observed values compared to those computed using the single stratum model. The primary cause of terrene upheaval in front of the working surface is the increased excavation pressure on the working face and the horizontal displacement of the deep soils and the surface subsidence behind the excavation face is resulting from the soil loss as the main influencing factor. The varying cross-section size of pipe jacking is able to impact on the vertical deformation of the soil, but it has a limited impact on the lateral displacement of the strata. The affection of the buried depth of the tunnel axis on strata deformation is more notable in the rectangular pipe jacking construction. As the axial tunnel depth growth, the ground surface maximum subsidence value gradually decreases, while the crest value of horizontal distortion mildly increases. When the rise of the interlayered modulus of elasticity, the maximum earth surface subsidence enlarged gradually while the subsidence trough slight diminution. Moreover, the greatest horizontal displacement exhibits a relatively minor fluctuation, but there is a trend of upward movement in the position. The influence of Poisson's ratio of the interlayer on the strata deformation is comparatively weak.

Seismic Stability Analysis of Square and Rectangular Tunnels in Cohesive-Frictional Soils

Seismic Stability Analysis of Square and Rectangular Tunnels in Cohesive-Frictional Soils

Stability Analyses of Shallow Rectangular Tunnels in Anisotropic and Nonhomogeneous Soils Using a Kinematic Approach

Stability Analyses of Shallow Rectangular Tunnels in Anisotropic and Nonhomogeneous Soils Using a Kinematic Approach

Innovative approaches for predicting seismic stability of circular and rectangular tunnels in cohesive-frictional soils using machine learning and finite element limit analysis

Innovative approaches for predicting seismic stability of circular and rectangular tunnels in cohesive-frictional soils using machine learning and finite element limit analysis

Effect of tunnel-building separation distance on the dynamic soil-structure interaction response

Understanding how buried structures respond to cyclic loading is crucial for designing earthquake-resistant underground infrastructure. The complexity of the dynamic response of these underground structures is accentuated when accounting for their interaction with adjacent buildings. This study focuses on the impact of the lateral distance between a shallow rectangular tunnel and an adjacent residential structure on dynamic soil-structure interaction, employing two dynamic centrifuge tests. Particle Image Velocimetry technique was adopted to observe the developed mechanisms of liquefied soil deformation, tunnel uplift, and foundation settlement. Results show the pronounced effects on soil deformation above the tunnel crown with a reduction in the tunnel-building separation distance. The distribution of excess pore pressure along the tunnel lining will be presented. Tunnel manifested additional lateral movement and reduced uplift when the adjacent building was in close proximity. A decrease in the tunnel-building distance contributed to a reduction of building rotation, primarily due to the significant mitigation of non-uniform settlement under the footing. Overall, the soil deformation mechanism around the tunnel and the building will be shown to change depending on the separation distance between them.

Numerical simulation and parametric analysis on a shallow tunnel in liquefiable ground subject to multiple shakings

In active earthquake zones, it is very likely that the structures would experience multiple shakings in major seismic events. For underground structures, the soil-structure interactions and the resultant dynamic responses could vary significantly according to the characteristics of the shakings. In this paper, the scenario of a shallow tunnel in liquefiable ground subject to multiple shakings is studied. The OpenSees platform and the PM4Sand constitutive model are employed to construct a plane-strain numerical model, where a rectangular tunnel is buried in saturated Hostun sand. Its validity is verified by the data from a centrifuge test of four consecutive shakings. The numerical soil-structure system is then configured for further investigation on the subject matter. Firstly, the liquefaction-induced uplift is identified as the main threat to the integrity of the tunnel in a seismic event of multiple shakings. Then, the pertinent soil-structure interactions are intensely discussed in a parametric analysis considering the influences of the permeability coefficient, the tunnel self-weight, and the shaking sequence.

Scaled Model for Studying the Propagation of Radio Waves Diffracted from Tunnels

One of the major challenges in designing a wireless indoor–outdoor communication network operating in tunnels and long corridors is to identify the optimal location of the outside station for attaining a proper coverage. It is required to formulate a combined model, describing the propagation along the tunnel and the resulting diffracted outdoor pattern from its exit. An integrated model enables estimations of the radiation patterns at the rectangular tunnel exit, as well as in the free space outside of the tunnel. The tunnel propagation model is based on a ray-tracing image model, while the free-space diffraction model is based on applying the far-field Fraunhofer diffraction equation. The model predictions of sensing the radiation intensity at the tunnel end and at a plane located at a distance ahead were compared with experimental data obtained using a down-scaled tunnel model and shorter radiation wavelength correspondingly. This down-scaling enabled detailed measurements of the radiation patterns at the tunnel exit and at the far field. The experimental measurements for the scaled tunnel case fit the theoretical model predictions. The presented model accurately described the multi-path effects emerging from inside the tunnel and the resulting outdoor diffracted pattern at a distance from the tunnel exit.

Study on the flame radiative heat transfer and near-field radiation heat flux predictive model of vehicle fires in a tunnel

As a major form of heat transfer, flame thermal radiation has an important effect on the ignition of adjacent energy, fire spread and environmental damage. Forecasting the flame radiation heat flux can provide theoretical basis for fire hazard assessment, fire extinguishing and salvation. Meanwhile, the distinctive structure of the arc tunnel can result in significant variations in the local heat and mass transfer processes during tunnel fires compared to those in rectangular tunnels, leading to different fire characteristics parameters. In this study, experiments and theoretical analyses were conducted to investigate the flame length scale and near-field radiation heat flux on the lower surface of an arc-shaped ceiling induced by vehicle fires in a tunnel. The findings reveal that the flame length scale in the transverse direction beneath the arc-shaped ceiling decreases with an increasing burner aspect ratio and increases with the increasing heat release rate. A dimensionless model of the flame length scale under the arced ceiling with various burner aspect ratios was proposed based on the amount of remaining unburned fuel after flame impingement and the buoyancy component along the arc-shaped ceiling. Simultaneously, radiative heat fluxes on the lower surface also increase with rising heat release rate. The flame geometry beneath the arc-shaped ceiling is assumed to be a combination of a cuboid and an arc plate model based on the actual flame length scale. Subsequently, the view factor, radiative fraction, and flame surface area are analyzed to predict the radiative heat fluxes on the lower surface. The predictions of the cuboid and arc plate flame model show good agreement with the current experimental data. This work presents a dimensionless correlation of the flame length scale and calculates the view factor between the target and the arc plate to predict the near-field radiative heat flux more accurately. This approach also facilitates the understanding of flame spreading behavior and thermal hazards impacted by arced ceiling.

Field research on supersized rectangle pipe-jacked tunnels beneath a navigable river in the urban area

With technological progress in recent years, supersized rectangular jacked pipe tunnels have been increasingly used for developing urban road-crossing nodes, owing to their convenient construction and economic benefits. However, owing to the weak waterproofing performance of the joint, jacked supersized rectangular pipes have been employed beneath a navigable river. This study used on-site monitoring data of an underground expressway with supersized rectangular jacked pipe tunnels in Shanghai. Additionally, we analyzed the deformation of the ground surface and embankment and the mutual influence of jacked adjacent pipes. The results revealed the following. 1) the over-excavation of the jacked pipe causes partial surface subsidence. The jacking parameters were adjusted through feedback to control the surface deformation. 2) The spatial deformation of the old embankment were stabilized, suggesting the successful realization of micro-disturbance jacking construction. 3) The secondary disturbance of the soil due to post-construction causes a slight sinking and tilting trend of the former jacked tunnel.

Experimental Study on the Distribution Law of Wind Speed in Rectangular Section Tunnels of Coal Mines

Ventilation is the cornerstone of coal mine safety production, and accurate monitoring of ventilation parameters is the fundamental guarantee for ventilation technology decision-making. A calculation model for the average wind speed line position in rectangular section tunnels of coal mines was established based on the Boussinesk theory and Prandtl turbulence theory to address the issue of difficulty in meeting decision-making needs in wind speed monitoring accuracy. The airflow field of rectangular section tunnels under different wind speed conditions was measured at the coal mine site, and the average position of the measured average wind speed line was obtained. The comparison and verification with the theoretical calculation results were carried out, with an absolute error of less than 5%.

A comparison of two numerical models for modeling a twin tunnel in a saturated half-space

In this work an analytical as well as a numerical model are established for computing vibrations induced by a twin tunnel buried in a saturated poroelastic half-space. In the analytical solution the mechanical response for the half-space ground is expressed as a superposition of planar waves from the ground surface and cylindrical waves from two tunnel-soil interfaces. While in the numerical solution, three-dimensional saturated poroelastic finite element and multi-transmitting formula are formulated. The comparisons are made between the two methodologies, and the advantages and disadvantages of the two models are highlighted. Using the analytical one, the influence of the fluid in the soils, the reflection effect of the ground surface and the existence of a neighboring tunnel with or without a source on the mechanical response is investigated. By using the three-dimensional numerical model, the influence of various irregular tunnels on the surface vibration is investigated. The results suggest that: for the displacement and pore pressure response, the difference between one source tunnel and twin source tunnel can be up to 20 dB; the rectangular tunnels lead to the largest response followed by horseshoes and circular ones.